Articles de revues : « Hydrothermal and continental sources »

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Li, Weiqiang, Brian L. Beard et Clark M. Johnson. « Biologically recycled continental iron is a major component in banded iron formations ». Proceedings of the National Academy of Sciences 112, n^o 27 (24 juin 2015) : 8193–98. http://dx.doi.org/10.1073/pnas.1505515112.

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Banded iron formations (BIFs) record a time of extensive Fe deposition in the Precambrian oceans, but the sources and pathways for metals in BIFs remain controversial. Here, we present Fe- and Nd-isotope data that indicate two sources of Fe for the large BIF units deposited 2.5 billion y ago. High-εNd and -δ56Fe signatures in some BIF samples record a hydrothermal component, but correlated decreases in εNd- and δ56Fe values reflect contributions from a continental component. The continental Fe source is best explained by Fe mobilization on the continental margin by microbial dissimilatory iron reduction (DIR) and confirms for the first time, to our knowledge, a microbially driven Fe shuttle for the largest BIFs on Earth. Detailed sampling at various scales shows that the proportions of hydrothermal and continental Fe sources were invariant over periods of 100–103 y, indicating that there was no seasonal control, although Fe sources varied on longer timescales of 105–106 y, suggesting a control by marine basin circulation. These results show that Fe sources and pathways for BIFs reflect the interplay between abiologic (hydrothermal) and biologic processes, where the latter reflects DIR that operated on a basin-wide scale in the Archean.

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Yuan, Jingying, Haigang Cao, Yuping Guo et Xuegang Chen. « Source and Evolution of Subduction–Related Hot Springs Discharged in Tengchong Geothermal Field, Southwest China : Constrained by Stable H, O, and Mg Isotopes ». Minerals 12, n^o 12 (23 novembre 2022) : 1490. http://dx.doi.org/10.3390/min12121490.

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The hydrothermal system plays a crucial role in material and energy cycling between the lithosphere and hydrosphere. In general, seafloor hydrothermal systems are one of important Mg sinks, but the situation may not be the same as it is in terrestrial hydrothermal systems. In addition, the behavior of Mg isotopes during hydrothermal circulation is still unclear. Thus, in this study, we determined the Mg isotopic compositions of the hydrothermal fluids discharged in the Tengchong region to understand better the fate of Mg in the continental hydrothermal system. The δ2H and δ18O values of the Tengchong hydrothermal fluids indicate that the recharge water sources are primary from meteoric water and influenced by the evaporation process. In contrast, the subduction–related volcanic water input is limited, except in for the Rehai area. The Mg in most of the samples is contributed by percolated meteoric water. The measured δ26Mg values range from –0.969 to 0.173‰, which are enriched in light Mg compared to the volcanic rocks of Tengchong. Combined with the precipitation dissolution of carbonate, we calculated the δ26Mg value for the endmember fluid before precipitation, which shows that the process of carbonate precipitation changes the Mg isotope of the fluid, substantially. The Shiqiang (SQ) vent is unique among all of the samples, characterized by an extremely a high δ26Mg value and Mg concentration, and it is estimated that it could have been mixed with an upper crustal material. This also reveals the diversity of the hydrothermal fluid material sources in the subduction zone.

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Coltat, Rémi, Philippe Boulvais, Yannick Branquet, Antonin Richard, Alexandre Tarantola et Gianreto Manatschal. « Moho carbonation at an ocean-continent transition ». Geology 50, n^o 3 (3 décembre 2021) : 278–83. http://dx.doi.org/10.1130/g49363.1.

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Abstract Carbonation of mantle rocks during mantle exhumation is reported in present-day oceanic settings, both at mid-ocean ridges and ocean-continent transitions (OCTs). However, the hydrothermal conditions of carbonation (i.e., fluid sources, thermal regimes) during mantle exhumation remain poorly constrained. We focus on an exceptionally well-preserved fossil OCT where mantle rocks have been exhumed and carbonated along a detachment fault from underneath the continent to the seafloor along a tectonic Moho. Stable isotope (oxygen and carbon) analyses on calcite indicate that carbonation resulted from the mixing between serpentinization-derived fluids at ~175°C and seawater. Strontium isotope compositions suggest interactions between seawater and the continental crust prior to carbonation. This shows that carbonation along the tectonic Moho occurs below the continental crust and prior to mantle exhumation at the seafloor during continental breakup.

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Zinchuk, N. N. « CRUSTS OF WEATHERING AS BASIC SUPPLIERS OF TERRIGENOUS MATERIAL DURING FORMATION OF ANCIENT DIAMONDIFEROUS PLACERS ». Proceedings of higher educational establishments. Geology and Exploration, n^o 2 (30 avril 2018) : 24–32. http://dx.doi.org/10.32454/0016-7762-2018-2-24-32.

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On the example of Mesozoic deposits of one of the main diamondiferous regions of the Siberian platform, basic suppliers of terrigenous material into the ancient diamondiferous placers under formation and their occurrences have been characterized. Special attention has been paid to characteristics of local sources of allothigenous material removal to sedimentation basins of the said period, the main of which were Middle-Late Triassic crusts of weathering on terrigenous-carbonate rocks, formations of trappean origin (dolerites, tuffs, tufogene thick layers) and kimberlites. Comparatively short transfer of weathering products and their accumulation mainly in freshwater continental basins determined weak hydrothermal effect of environment on allothigenous minerals. The received specific features of the mineral composition of various rocks' crusts of weathering have been recommended for application during paleogeographical reconstructions in diamondiferous regions, to determine source areas of terrigenous material, in particular. The stated recommendations have been implemented when assessing material from local sources of drift (including diamondiferous material as well) to continental (Irelyakh and Ukugut suites) and coastal (Pliensbachian and Toarcian stages) deposits of MaloBOtuobinsky region, where primary and placer diamond deposits are successfully mined.

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Chiaradia, Massimo, Lluís Fontboté et Agustín Paladines. « Metal Sources in Mineral Deposits and Crustal Rocks of Ecuador (1° N–4° S) : A Lead Isotope Synthesis ». Economic Geology 99, n^o 6 (1 septembre 2004) : 1085–106. http://dx.doi.org/10.2113/econgeo.99.6.1085.

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Abstract Ecuador consists of terranes having both continental (Chaucha, Tahuin, Loja terranes) and oceanic (Macuchi, Alao, Salado terranes) affinity, which were accreted to the Amazon craton from Late Jurassic to Eocene. Four main magmatic arcs were formed by the subduction of the Farallon/Nazca plate since the Jurassic: a Jurassic continental arc on the western margin of the Amazon craton, a Jurassic island arc (Alao terrane), an early Tertiary island arc (Macuchi terrane), and a middle-late Tertiary continental arc encompassing the terranes of Macuchi, Chaucha, Tahuin, Loja, and Alao after complete assembly of the Ecuadorian crust. Mineral deposits formed during these magmatic arc activities include porphyry-Cu and gold skarn deposits in association with the Jurassic continental arc, polymetallic volcanic-hosted massive sulfide deposits (VHMS) in association with the Jurassic island arc of Alao, Au-Cu-Zn VHMS deposits in association with the early Tertiary island arc of Macuchi, and porphyry-Cu and precious-metal epithermal deposits in association with the middle-late Tertiary continental-arc magmatism on the newly assembled crust of Ecuador (Macuchi, Chaucha, Tahuin, Loja, and Alao terranes). In this study, we have compiled 148 new and 125 previously published lead isotope analyses on Paleozoic to Miocene metamorphic, intrusive, volcanic, and volcanosedimentary rocks, as well as on Jurassic to Miocene magmatic-related ore deposits of Ecuador. Lead isotope compositions of the magmatic rocks of the four main arc events derive from mixing of various sources including mantle, variably enriched by pelagic sediments and/or by a high 238U/204Pb component, and heterogeneous continental crust rocks. Lead isotope compositions of the Ecuadorian ore deposits display a broad range of values (206Pb/204Pb = 18.3–19.3, 207Pb/204Pb = 15.54–15.74, 208Pb/204Pb = 38.2–39.2), which is as large as the range previously reported for all magmatic-related ore deposits of the Central Andean provinces I and II combined. Ore deposits formed before complete assembly of the Ecuadorian crust through complete accretion of the several terranes (i.e., pre-Eocene) have lead isotope compositions overlapping those of the associated magmatic rocks, suggesting a largely magmatic origin for their lead. In contrast, post-assembly ore deposits (i.e., post-Eocene) have lead isotope compositions that only partly overlap those of the coeval magmatic rocks of the continental arc. In fact, several ore deposits have lead isotope compositions shifted toward those of the basement rocks that host them, suggesting that lead derives from a mixture of magmatic lead and basement-rock lead leached by hydrothermal fluids. Most Ecuadorian ores have high 207Pb/204Pb values (>15.55), suggesting a dominant continental crust or pelagic sediment origin of the lead. However, we caution against concluding that chalcophile metals (for example, Cu and Au) also have a continental crust origin. Ore deposits of the different terranes of Ecuador, irrespective of their age, plot in distinct isotopic fields, which are internally homogeneous. This suggests that lithologic factors had an important control on the lead isotope compositions. Ultimately, lead isotope compositions of the ore deposits of Ecuador mirror the isotopic compositions of the rocks of the host terranes and are consistent with the multiterrane nature of the Ecuadorian crust.

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Ansari, Arif H., Veeru Kant Singh, Pankaj Kumar, Mukund Sharma, Anupam Sharma, Satyakam Patnaik, Gurumurthy P. Gundiga, Ishwar Chandra Rahi, Mohammad Arif Ansari et AL Ramanathan. « Hydrogeochemistry, Geothermometry, and Sourcing of High Dissolved Boron, Tungsten, and Chlorine Concentrations in the Trans-Himalayan Hotsprings of Ladakh, India ». Hydrology 10, n^o 6 (24 mai 2023) : 118. http://dx.doi.org/10.3390/hydrology10060118.

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Boron (B) and Tungsten (W) are often found enriched in high-temperature geothermal waters associated with the development of subduction-related mafic to felsic arc magma. However, knowledge about the sourcing and transportation of these elements from such hydrothermal systems is sparse and ambiguous. Being the only active continental collision site in the world, the Trans-Himalaya offers a unique chance to study how continental collision sources the high boron and tungsten concentrations in geothermal fluids. This study investigated the distribution of trace elements, major cations, and anions in three physicochemically distinct hotspring sites in the Ladakh region. The results were integrated with the existing geochemical and isotopic data to address the research problem more effectively. This study exhibits that the extreme concentrations of boron, sodium, chlorine, potassium, and tungsten in the hotspring waters were primarily governed by magmatic fluid inputs. In addition, this study recorded the highest-ever chlorine and boron concentrations for the Trans-Himalayan hotspring waters. The highest-ever boron and chlorine concentrations in the hotspring waters probably represented an increase in magmatic activity in the deeper source zone.

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Chugaev, A. V. « Orogenic Gold Deposits of Northern Transbaikalia, Russia : Geology, Age, Sources, and Genesis ». Geochemistry International 62, n^o 9 (septembre 2024) : 909–78. http://dx.doi.org/10.1134/s0016702924700484.

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Abstract The paper presents newly obtained and summarizes preexisting data of long-term geochronological and isotope studies of orogenic mesothermal gold deposits in the world’s largest Lena metallogenic province and reviews interpretations of their genesis. Geochronologic data indicate that the gold mineralization was formed during three ore-forming Paleozoic events. The early Late Ordovician–Early Silurian (450–430 Ma) event produced the abundant veinlet—disseminated gold–sulfide mineralization in Neoproterozoic carbonaceous terrigenous–carbonate rocks of the Baikal–Patom foldbelt (BPB). The mineralization was formed simultaneously with regional metamorphic processes. The rejuvenation of hydrothermal activity in the BPB resulted in gold-bearing quartz veins, which was produced in the Middle Carboniferous (340–330 Ma) in relation to postcollisional granitoid magmatism. The latest ore-forming event occurred in the Early Permian (290–280 Ma) and affected exclusively in Precambrian structures of the Baikal-Muya foldbelt (BMB). It was synchronous with the development of intraplate alkaline and subalkaline magmatism in the region. Newly obtained and preexisting isotopic-geochemical (87Sr/86Sr, 143Nd/144Nd, Pb–Pb, and δ34S) data indicate that the mesothermal ore-forming systems of northern Transbaikalia were heterogeneous in their isotopic characteristics, which distinguishes them from the ore–magmatic (intrusion-related type) systems. Comparison of the Sr, Nd, and Pb isotopic composition of the ores and rocks, including magmatic rocks coeval with the gold mineralization, indicates that the Precambrian continental crust was the dominant source of mineral-forming components for the hydrothermal systems of the gold deposits. The contribution of the magmatic source to the genesis of the orogenic gold mineralization was limited and is identifiable only for the Early Permian ore-forming systems of the BMB, for which the input of metals from alkaline mafic melts was suggested.

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Wang, Zhigao, Wenyan Cai, Shunda Li et Xuli Ma. « Magma Sources and Tectonic Settings of Concealed Intrusive Rocks in the Jinchang Ore District, Yanbian–Dongning Region, Northeast China : Zircon U–Pb Geochronological, Geochemical, and Hf Isotopic Evidence ». Minerals 12, n^o 6 (1 juin 2022) : 708. http://dx.doi.org/10.3390/min12060708.

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The Jinchang deposit is a large Au deposit in the Yanbian–Dongning region, in Northeast China, and is the product of magmatic–hydrothermal activities related to Early Cretaceous concealed igneous intrusions. However, these Early Cretaceous ore-causative igneous intrusions and the ore-hosting rocks in the Jinchang ore district have rarely been studied, with their magma sources and tectonic settings being ambiguous. Here, we integrate new geochemical, zircon U–Pb and Hf isotopic data from the concealed ore-hosting monzogranite and the ore-causative granodiorite to constrain their magma sources and tectonic settings. Zircon U–Pb dating indicates that the two monzogranites from the drill holes JIZKN01 and J18ZK0303 have similar crystallization ages of 202.0 ± 1.6 and 200.9 ± 1.2 Ma, respectively, whereas the granodiorite from the drill hole JXI-1ZK1001 was formed in the Early Cretaceous period (107.0 ± 3.0 Ma). They are all enriched in large-ion lithophile elements (e.g., Rb, Th, and K) and light rare-earth elements, depleted in high field strength elements (e.g., Nb, Ta, and Ti) and heavy rare-earth elements, and yield similar positive εHf(t) values of +4.4 to +11.5, with their two-stage model ages ranging from 799 to 389 Ma. These results indicate that the concealed Early Jurassic ore-hosting monzogranite was derived from the partial melting of the Neoproterozoic–Paleozoic continental crust in a continental arc setting related to the Paleo-Pacific subduction. The ore-causative granodiorite originated from the partial melting of both the mantle wedge and the overlying continental crust, most likely caused by the dehydration and metasomatism of the subducted Paleo-Pacific slab involved in the rollback in the Early Cretaceous period.

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Ma, Guoxiong, Xiaobo Zhao, Chunji Xue et Renke Wang. « Neoproterozoic Aksu Diabase Dyke, Chinese South Tianshan : Magma Sources and Implications for Regional Gold Metallogeny ». Minerals 13, n^o 3 (25 février 2023) : 326. http://dx.doi.org/10.3390/min13030326.

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Tianshan is one of the world’s largest gold provinces; however, the relationship between gold mineralization and metasomatized subcontinental lithospheric mantle (SCLM) remains poorly understood. To improve our understanding, we present new bulk-rock geochemistry and platinum group element (PGE) concentrations of the SCLM-sourced Aksu Neoproterozoic diabase dykes in Chinese South Tianshan. These data, combined with in situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of hydrothermal pyrite grains in the diabase dykes, are used to discuss the SCLM source characteristics in the region and their potential links to formation of gold deposits. The diabase dykes exhibit high Th/Yb (0.47–0.62) and low Nb/U (13.4–16.3) ratios, indicating that magma evolution involves subduction-related fluid metasomatism and limited contamination of the continental crust. This is consistent with little variation in whole-rock Pd/Zr, Cu/Zr, and Ni/MgO ratios, suggesting that no sulfide segregation was caused by crustal contamination and magma mixing. In addition, the diabase dykes show low PGE and Au contents, with high Cu/Pd (>105) and low Cu/Zr (<0.5) ratios, indicating that magmas were derived from low-degree partial melting of the SCLM under S-saturated conditions. Such source characteristics indicate residual sulfides and chalcophile elements (e.g., PGEs, Au, and Cu) were concentrated at the SCLM reservoir in South Tianshan. Hydrothermal pyrite in the studied dykes has similar Au/Ag ratios and trace element distribution patterns to gold-bearing pyrite of lode gold deposits in Chinese South Tianshan, indicating that metasomatized SCLM may have contributed ore metals during the formation of these gold deposits. Adding to the available data, our study highlights that the SCLM may be a potential metal source reservoir, and it may have contributed to formation of the lode gold deposits in Chinese South Tianshan.

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Peverelli, Veronica, Alfons Berger, Martin Wille, Thomas Pettke, Benita Putlitz, Andreas Mulch, Edwin Gnos et Marco Herwegh. « Multifaceted orogenic fluid dynamics unraveled by hydrothermal epidote ». European Journal of Mineralogy 36, n^o 5 (24 septembre 2024) : 879–98. http://dx.doi.org/10.5194/ejm-36-879-2024.

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Abstract. Characterizing fluid circulation in orogens is key to understanding orogenic processes because fluid–rock interaction modifies the physical properties of rocks, hence their response to deformation and, for example, their suitability for radioactive waste storage. Fluid circulation can be dated by applying geochronological methods to fluid-precipitated minerals. Fluid sources and associated pathways can be traced using isotope data measured in the same or in other cogenetic minerals. We applied this concept to the Aar Massif (central Swiss Alps), which was part of the former European passive continental margin that was deformed and exhumed during the (Cenozoic) Alpine orogeny. Newly collected epidote from veins and from one cleft at several localities in meta-granitoids in the Aar Massif yielded U–Pb ages ranging from 27.7 ± 3.4 to 12.4 ± 1.9 Ma, which complement previously published geochronological data revealing Permian (278 ± 29, 251 ± 50, and 275 ± 18 Ma) and Miocene (19.2 ± 4.3 and 16.9 ± 3.7 Ma) epidote veins. We used Pb–Sr–O–H isotope geochemistry of epidote to evaluate fluid sources and pathways during Permian rifting and the Miocene compressional phases of Alpine orogeny. Strontium isotope data of Permian epidote are consistent with previous work suggesting meteoric water infiltration along syn-rift faults and through syn-rift sediments. A more-complex structural framework existed in the Miocene, when a sedimentary lid covered the Aar Massif. Strontium, O, and H isotope data of Miocene epidote-forming fluids indicate (1) meteoric water, mixing with (2) fluids derived from sedimentary units being compacted during orogenesis and/or (3) metamorphic water. All three fluid endmembers may have been circulating and mixing in the Aar Massif during Miocene deformation. Strontium isotope data further indicate that Miocene fluids contributed to imprinting a highly radiogenic Sr isotope composition onto Alpine shear zones or that the fluids inherited a highly radiogenic Sr isotope component by dissolving the Rb-rich, high 87Sr / 86Sr biotite therein. Both possibilities can coexist, and they imply that external fluids could modify the chemical composition of the post-Variscan granitoids hosting the studied epidote veins by fluid–rock interaction processes during deformation. Lead, Sr, and H isotopic differences among Miocene samples further suggest complexity of large-scale fluid circulation. Our work supports the fact that the reconstruction of multifaceted and multi-stage fluid circulation in highly deformed rocks benefits from extracting geochronological and isotope data from the same mineral.

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Chi Fru, E. « Microbial evolution of sulphate reduction when lateral gene transfer is geographically restricted ». International Journal of Systematic and Evolutionary Microbiology 61, n^o 7 (1 juillet 2011) : 1725–35. http://dx.doi.org/10.1099/ijs.0.026914-0.

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Lateral gene transfer (LGT) is an important mechanism by which micro-organisms acquire new functions. This process has been suggested to be central to prokaryotic evolution in various environments. However, the influence of geographical constraints on the evolution of laterally acquired genes in microbial metabolic evolution is not yet well understood. In this study, the influence of geographical isolation on the evolution of laterally acquired dissimilatory sulphite reductase (dsr) gene sequences in the sulphate-reducing micro-organisms (SRM) was investigated. Sequences on four continental blocks related to SRM known to have received dsr by LGT were analysed using standard phylogenetic and multidimensional statistical methods. Sequences related to lineages with large genetic diversity correlated positively with habitat divergence. Those affiliated to Thermodesulfobacterium indicated strong biogeographical delineation; hydrothermal-vent sequences clustered independently from hot-spring sequences. Some of the hydrothermal-vent and hot-spring sequences suggested to have been acquired from a common ancestral source may have diverged upon isolation within distinct habitats. In contrast, analysis of some Desulfotomaculum sequences indicated they could have been transferred from different ancestral sources but converged upon isolation within the same niche. These results hint that, after lateral acquisition of dsr genes, barriers to gene flow probably play a strong role in their subsequent evolution.

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Dunseith, Regina F., Jay M. Gregg et G. Michael Grammer. « Fluid Histories of Middle Ordovician fault–fracture hydrothermal dolomite oil fields in the southern Michigan Basin, U.S.A. » Journal of Sedimentary Research 91, n^o 10 (8 octobre 2021) : 1067–92. http://dx.doi.org/10.2110/jsr.2020.170.

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ABSTRACT Dolomitized fault–fracture structures in the Trenton and Black River formations (TBR) are the type example for “hydrothermal” petroleum reservoirs world-wide. However, fluid histories of these structures are only partially understood. Trenton and Black River reservoirs in the southern Michigan Basin are composed of fault-associated, vertical dolomite bodies that are highly fractured and brecciated. Open spaces are partially to completely filled by saddle dolomite and less frequently by calcite cement. Cathodoluminescence microstratigraphies of void-filling carbonate cements are not correlatable between oil fields. Fluid inclusion homogenization temperatures (Th) measured in carbonate cements indicate two fluid endmembers: a warm fluid (∼ 80° to 180° C) and a hot fluid (180° to ∼ 260° C). Increasing Th proximal to the underlying Proterozoic Mid-Michigan Rift (MMR) suggest that the hot fluids emanated from the rift area. Included fluids are saline (16.1–49.4 wt. % NaCl equivalent), and salinity likely is sourced from overlying Silurian Salina Group evaporites. First melting temperatures (Tfm), interpreted as eutectic temperatures (Te), of fluids range from –112° C to –50° C, indicating a complex Na–Ca–KCl brine; the expected composition of dissolved Salina salts. Lower Te proximal to the MMR suggest the rift as a source of additional complexing ions. C and O isotope values for carbonate cements are depleted with respect to δ18O (–6.59 to –12.46‰ VPDB) relative to Ordovician seawaters, and somewhat depleted with respect to δ13C (–1.22 to +1.18‰ VPDB). Equilibrium calculations from δ18O and Th values indicate that cement precipitating waters were highly evolved (+1.3 to +14.4‰ δ18O‰ VSMOW) compared to Ordovician and Silurian seawaters (–5.5‰ δ18O‰ VSMOW). Strontium isotope values indicate two fluid sources: Proterozoic basement and Late Silurian evaporites. Values of 87Sr/86Sr for cements in the Freedom, Napoleon, Reading, and Scipio fields (0.7086–0.7088) are influenced by warm water sourced from Silurian strata, and values for cements in the Albion, Branch County, and Northville fields (0.7091–0.7110) record continental basement signatures. Cement precipitating fluids in TBR oil fields likely have similar sources and timing. However, water–rock interactions along fault pathways modified source waters, giving each oil field a unique petrographic and geochemical signature. Fluid movement in TBR oil fields likely were initiated by reactivation of basement faulting during Silurian–Devonian tectonism.

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Xia, Xinyu, et Yongli Gao. « Validity of geochemical signatures of abiotic hydrocarbon gases on Earth ». Journal of the Geological Society 179, n^o 3 (19 octobre 2021) : jgs2021–077. http://dx.doi.org/10.1144/jgs2021-077.

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Abiotic synthesis has been hypothesized as a mechanism for occurrences of hydrocarbon gases with atypical molecular and isotopic compositions. This paper provides biotic interpretations of these atypical compositions, as follows: (1) microbial CH4 oxidation and CO2-sourced methanogenesis may enrich 13C in hydrothermal CH4; (2) microbial hydrocarbon generation using serpentinization-derived H2 may deplete deuterium in hydrocarbons; (3) three processes may cause isotopic reversal with the carbon number in biotic hydrocarbons (the decrease of kinetic isotope effect (KIE) with the increase of carbon number during alkane biodegradation, inverse KIE during the thermal decomposition of higher alkanes and isotopic fractionation during gas diffusion in rock samples); (4) random scission of long alkyl chains may form the exponential distribution of alkane abundance with respect to carbon number (the ‘Schulz–Flory distribution’); (5) isotopic compositions are often not equilibrated; even if they are, the equilibrium temperatures are not necessarily the same as the temperature of hydrocarbon generation. Case studies demonstrate that previously proposed abiotic hydrocarbon gases in continental serpentinite-hosted seepages, continental or oceanic hydrothermal vents, volcanic emissions, gas fields in volcanic reservoirs and fluid inclusions in alkaline or granitic rocks were formed by various biotic processes. The occurrence of abiotic hydrocarbon gas with decisive evidence is limited to fluid inclusions in some mantle minerals.Supplementary material: Expressions for isotopic fractionation of CH4 and model details of the Xujiaweizi gas are available at https://doi.org/10.6084/m9.figshare.c.5660278

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Skuzovatov, S. Yu, et Yu I. Tarasova. « Sulfide mineralization in orogenic eclogites of the North Muya block (northeastern Transbaikalia) : genesis and the first data on the isotopic composition of sulfur ». Earth sciences and subsoil use 47, n^o 1 (28 avril 2024) : 35–43. http://dx.doi.org/10.21285/2686-9993-2024-47-1-35-43.

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Subduction processes are accompanied by the sites of hydrothermal activity including large deposits of gold and transitional metals of island-arc or back-arc origin, whereas volcanic arcs host most part of the worldwide resources of metallic minerals. However, the role of suprasubduction metal transfer and the associated role of redox processes in their formation are still ambiguous and require direct studies of sulfide mineralization in high-pressure rocks, as well as their formation stages and sulfide preservation during progressive and peak metamorphism. In order to describe the behavior of chalcophile elements in the paleozones of continental subduction we performed preliminary mineralogical (SEM-EDX) and isotope (S) studies of sulfides in the North Muya block eclogites (northeastern Transbaikalia). Sulfide mineralization of pyrite-chalcopyrite-pyrrhotite composition has a metasomatic origin associated with the retrograde fluid transformation of initially “dry” eclogite assemblages during exhumation to lower- or mid-crust levels after or synchronously to the decompression and formation of plagioclase-diopside±amphibole symplectites (below 10-12 kbar). Extremely heterogeneous isotopic composition of pyrite sulfur (δ34SVCDT) was caused by various sources of fluids of presumably metasedimentary origin (from -8.2 to -6 %) in the paragneiss segments of the North Muya block. But they also could be predominantly buffered by hydrothermally altered metabasites (from +0.7 to +7.1 %). An alternative mechanism could be the participation of a single predominantly oxidized (sulfate-containing) fluid with the significant isotopic fractionation (up to ~15–20 %).

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Tichomirowa, Marion, Axel Gerdes, Manuel Lapp, Dietmar Leonhardt et Martin Whitehouse. « The Chemical Evolution from Older (323–318 Ma) towards Younger Highly Evolved Tin Granites (315–314 Ma)—Sources and Metal Enrichment in Variscan Granites of the Western Erzgebirge (Central European Variscides, Germany) ». Minerals 9, n^o 12 (11 décembre 2019) : 769. http://dx.doi.org/10.3390/min9120769.

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The sources and critical enrichment processes for granite related tin ores are still not well understood. The Erzgebirge represents one of the classical regions for tin mineralization. We investigated the four largest plutons from the Western Erzgebirge (Germany) for the geochemistry of bulk rocks and autocrystic zircons and relate this information to their intrusion ages. The source rocks of the Variscan granites were identified as high-grade metamorphic rocks based on the comparison of Hf-O isotope data on zircons, the abundance of xenocrystic zircon ages as well as Nd and Hf model ages. Among these rocks, restite is the most likely candidate for later Variscan melts. Based on the evolution with time, we could reconstruct enrichment factors for tin and tungsten starting from the protoliths (575 Ma) that were later converted to high-grade metamorphic rocks (340 Ma) and served as sources for the older biotite granites (323–318 Ma) and the tin granites (315–314 Ma). This evolution involved a continuous enrichment of both tin and tungsten with an enrichment factor of ~15 for tin and ~7 for tungsten compared to the upper continental crust (UCC). Ore level concentrations (>10–100 times enrichment) were achieved only in the greisen bodies and dykes by subsequent hydrothermal processes.

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Kolpakova, E. S., et A. V. Velyamidova. « Organochlorine compounds in subarctic small lakes ». Arctic and Antarctic Research 66, n^o 2 (10 juillet 2020) : 180–97. http://dx.doi.org/10.30758/0555-2648-2020-66-2-180-197.

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The article presents the results of studies of the environmental properties of organochlorines which differ in properties and origin, in the lake ecosystems of the Bolshezemelskaya tundra (Nenets Autonomous Okrug, Russia). The purpose of this study was to evaluate and assess the levels, distribution characteristics and composition of organochlorines in the bottom sediments of small lakes located in the Adzva river basin in Pymvashor natural boundary (the northernmost location of the exit of thermal-mineral springs of the continental Europe) and in the adjacent area, outside this unique subarctic hydrothermal zone.In order to meet this goal, multi-method (hydrochemical, geochemical, etc.) research was carried out using standard generally approved laboratory practices with their adaptation to the study goals. The quantitative content and composition of the target individual organochlorines were determined by gas chromatographic method with electron-capture detection.The presence of chlorophenol compounds and polychlorinated benzenes (including persistent organic pollutants) was shown in the lakes sediments. The influence of specific microclimatic conditions of subarctic hydrothermal system on the composition and distribution of chlorophenol compounds in lake sediments was considered. In the small lake sediment core in Pymvashor natural boundary a reducing trend in the levels of organochlorines with depth has been recorded (conditioned among other things by the lithological features of bottom sediments). The chlorophenol compounds were found at highest concentrations (619.3–765.5 ng/g) in the sediment upper layers, rich in organic matter; chlorophenol composition was represented mainly by chlorinated phenols, most likely of biotic origin. A lower concentration (185.0 ng/g) of chlorophenol compounds of predominantly abiogenic origin was determined in the lake sediments outside hydrothermal system. The presence and levels of persistent organochlorine pollutants (pentachlorophenol 0.1–2.4 ng/g; hexa- and pentachlorobenzenes 0.4–3.6 ng/g) in the lake sediments were associated with long-range atmospheric transport from various origin sources in nearby regions and low-latitude territories.

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Eugster, Hans P. « Granites and hydrothermal ore deposits : a geochemical framework ». Mineralogical Magazine 49, n^o 350 (mars 1985) : 7–23. http://dx.doi.org/10.1180/minmag.1985.049.350.02.

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AbstractThe geochemical evolution of tin-tungsten deposits and their associated sulphides can be discussed in terms of four sequential processes: acquisition of the ore-forming elements (OFEs) by the granitic magma, emplacement of these elements in minerals and residual melt of the crystallizing granite, release of the OFEs to the circulating hydrothermal fluids and transport to the depositional sites, and finally, deposition of ore minerals through interaction of these fluids with the wall rock. Based on their crystallographic behaviour, it is useful to distinguish three principal classes of OFEs, here identified as BOC, LHC, and ALC elements. BOC (bivalent octahedral cation) elements are similar to ferrous iron and here are represented mainly by Zn, Mn, and perhaps Cu. Li also belongs to this class, although it is monovalent. LHC (large highly charged cations) elements encompass As, Nb, Mo, Sn, Sb, Ta, and W and they are similar to ferric iron or titanium in their crystallographic role. ALC (alkali-like cations) are capable of occupying alkali positions and are represented mainly by Pb, Ag, and Hg.LHCs are rejected from the polymerized silicate liquid network and become enriched in the roof of the acid magma chamber, where more non-bridging oxygens are available. Transport to the roof may be enhanced by the formation of hydrous complexes, as is the pronounced enrichment of Na and Li. BOCs, along with Cl, F, and B, fractionate strongly into the vapour phase during vesiculation. HCl in the ore fluid is crucial for the alteration process and can be produced during boiling by a hydrolysis reaction of the NaCl dissolved or immiscibly present in the silicate magma.Considerable laboratory information is available concerning release mechanisms of the OFEs to hydrothermal fluids. We can distinguish congruent and incongruent dissolution, both in response to acid buildup, as well as congruent and incongruent exchange not involving HCl. Melt-fluid fractionation is also thought to be important, though the physical mechanisms are not well understood. Any of these release mechanisms may be coupled with reduction or oxidation reactions. LHC, BOC, and ALC elements respond differently to each of these mechanisms, and these differences may in part be responsible for the observed separation of ore minerals in space and time. It is suggested that LHC elements are released preferentially during acid, non-oxidizing conditions typical of early stages, while BOC elements respond more readily to later acid-oxidizing environments, as well as exchange reactions with or without oxidation.Depositional reactions have been formulated with respect to two contrasting types of country rocks: carbonates and schists. Differences are related to the process of neutralization of the HCl produced by ore deposition: carbonate dissolution on one hand and feldspar-muscovite or biotite-muscovite conversion on the other. In carbonate rocks, evaporite-related sulphates may provide the H2S necessary for sulphide precipitation, while in schists disseminated sulphides and organic matter may be important sulphur reservoirs in addition to the sulphur liberated from the granite. A variety of situations can be envisaged with respect to the sources of the OFEs and the sulphur species required for ore deposition, including granite and wall rocks. Chloride is recognized as the crucial anion for OFE release, transport, and deposition, although F and B play a role yet to be evaluated. Final HCl neutralization is an essential step in the reactions responsible for the deposition of ore minerals.The ultimate sources of the OFEs must be related to the continental material involved in the process of melt production by partial melting. Oxidized sediments provide sources for LHC and ALC elements in the form of heavy minerals and clastic feldspars and micas. Organic-rich reduced sediments are hosts to BOC and LHC elements as sulphides and ALC elements in organic matter. Remelting of igneous and metamorphic rocks can enrich LHC, BOC, and ALC elements in the melt by extraction from opaques, Fe-Mg silicates, feldspars, and micas.

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Lein, A. Yu, O. M. Dara, O. Yu Bogdanova, G. V. Novikov, N. V. Ulyanova et A. P. Lisitsyn. « Sources of Minor and Rare-Earth Elements in Hydrothermal Edifices of Near-Continental Rifts with Sedimentary Cover : Evidence from the Guaymas Basin, Southern Trough ». Oceanology 58, n^o 2 (mars 2018) : 250–65. http://dx.doi.org/10.1134/s0001437018020078.

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Stern, Charles, Kwan-Nang Pang, Hao-Yang Lee, M. Skewes et Alejandra Arévalo. « Implications of Hf Isotopes for the Evolution of the Mantle Source of Magmas Associated with the Giant El Teniente Cu-Mo Megabreccia Deposit, Central Chile ». Minerals 9, n^o 9 (12 septembre 2019) : 550. http://dx.doi.org/10.3390/min9090550.

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We have determined the Hf isotopic compositions of 12 samples associated with the giant El Teniente Cu-Mo megabreccia deposit, central Chile. The samples range in age from ≥8.9 to 2.3 Ma and provide information about the temporal evolution of their magmatic sources from the Late Miocene to Pliocene. Together with previously published data, the new analysis indicates a temporal decrease of 10 εHf(t) units, from +11.6 down to +1.6, in the 12.7 m.y. from 15 to 2.3 Ma. These variations imply increasing incorporation of continental crust through time in the magmas that formed these rocks. The fact that the samples include mantle-derived olivine basalts and olivine lamprophyres suggests that these continental components were incorporated into their mantle source, and not by intra-crustal contamination (MASH). We attribute the increase, between the Middle Miocene and Pliocene, of crustal components in the subarc mantle source below El Teniente to be due to increased rates of subduction erosion and transport of crust into the mantle. The deposit formed above a large, long-lived, vertically zoned magma chamber that developed due to compressive deformation and persisted between ~7 to 4.6 Ma. Progressively more hydrous mantle-derived mafic magmas feed this chamber from below, providing heat, H2O, S and metals, but no unique “fertile” Cu-rich magma was involved in the formation of the deposit. As the volume of these mantle-derived magmas decreased from the Late Miocene into the Pliocene, the chamber crystallized and solidified, producing felsic plutons and large metal-rich magmatic-hydrothermal breccias that emplaced Cu and S into the older (≥8.9 Ma) mafic host rocks of this megabreccia deposit.

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Abd El-Naby, Hamdy H., et Yehia H. Dawood. « The Geochemistry, Petrogenesis, and Rare-Metal Mineralization of the Peralkaline Granites and Related Pegmatites in the Arabian Shield : A Case Study of the Jabal Sayid and Dayheen Ring Complexes, Central Saudi Arabia ». Applied Sciences 14, n^o 7 (27 mars 2024) : 2814. http://dx.doi.org/10.3390/app14072814.

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The Neoproterozoic period in the Jabal Sayid and Dayheen areas is characterized by three distinct magmatic phases: an early magmatic phase of granodiorite–diorite association, a transitional magmatic phase of monzogranites, and a highly evolved magmatic phase of peralkaline granites and associated pegmatites. The presence of various accessory minerals in the peralkaline granites and pegmatites, such as synchysite, bastnaesite, xenotime, monazite, allanite, pyrochlore, samarskite, and zircon, plays an important role as contributors of REEs, Zr, Y, Nb, Th, and U. The geochemical characteristics indicate that the concentration of these elements occurred primarily during the crystallization and differentiation of the parent magma, with no significant contributions from post-magmatic hydrothermal processes. The obtained geochemical data shed light on the changing nature of magmas during the orogenic cycle, transitioning from subduction-related granodiorite–diorite compositions to collision-related monzogranites and post-collisional peralkaline suites. The granodiorite–diorite association is thought to be derived from the partial melting of predominantly metabasaltic sources, whereas the monzogranites are derived from metatonalite and metagraywacke sources. The peralkaline granites and associated pegmatites are thought to originate from the continental crust. It is assumed that these rocks are formed by the partial melting of metapelitic rocks that are enriched with rare metals. The final peralkaline phase of magmatic evolution is characterized by the enrichment of the residual melt with alkalis (such as sodium and potassium), silica, water, and fluorine. The presence of liquid-saturated melt plays a decisive role in the formation of pegmatites.

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Markovic, Sava, Manuel Brunner, Lukas Müller, Irena Peytcheva, Marcel Guillong, Cyril Chelle-Michou, Kalin Kouzmanov, Daniela Gallhofer, Christoph A. Heinrich et Albrecht von Quadt. « Zircon Petrochronology of Au-Rich Porphyry and Epithermal Deposits in the Golden Quadrilateral (Apuseni Mountains, Romania) ». Economic Geology 119, n^o 4 (1 juin 2024) : 967–88. http://dx.doi.org/10.5382/econgeo.5073.

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Abstract The Golden Quadrilateral of the Apuseni Mountains (Romania) represents the richest Au(-Cu-Te) porphyry and epithermal district of Europe and the Western Tethyan metallogenic belt. The Au(-Cu-Te) mineralization is associated with Neogene calc-alkaline magmatism along graben structures growing during the late stages of the Alpine-Carpathian orogeny. We use zircon petrochronology to study the time-space distribution, sources, composition, and timescales of the Au(-Cu-Te)-mineralizing magmatism and explore its link to regional tectonics. Our own and published U-Pb zircon ages document ore-forming magmatic activity between ~13.61 and 7.24 Ma. In combination with available paleomagnetic data, the new zircon ages corroborate the hypothesis that the magmatism in the Golden Quadrilateral evolved in a tectonic environment dominated by major (up to 70°) crustal block rotation. Hafnium isotope composition of Neogene zircon (εHf between –2 and 10) supports the predominant origin of the magmas from a heterogeneous lithospheric mantle, which may have been fertilized during an earlier Cretaceous subduction event and possibly by concurrent Miocene subduction. Xenocrystic zircon shows involvement of crustal sources resembling European continental basement. Fertility indicators, including Eu/Eu* and oxygen fugacity based on zircon composition, show no systematic correlation with the mineralizing events and/or age. High-precision (isotope dilution-thermal ionization mass spectrometry) U-Pb zircon geochronology demonstrates that the magmatic systems exposed at district scale evolved over less than ~100 k.y. and that durations of hydrothermal mineralization pulses were even shorter.

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Wang, Zhen-Yu, Hong-Rui Fan, Lingli Zhou, Kui-Feng Yang et Hai-Dong She. « Carbonatite-Related REE Deposits : An Overview ». Minerals 10, n^o 11 (28 octobre 2020) : 965. http://dx.doi.org/10.3390/min10110965.

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The rare earth elements (REEs) have unique and diverse properties that make them function as an “industrial vitamin” and thus, many countries consider them as strategically important resources. China, responsible for more than 60% of the world’s REE production, is one of the REE-rich countries in the world. Most REE (especially light rare earth elements (LREE)) deposits are closely related to carbonatite in China. Such a type of deposit may also contain appreciable amounts of industrially critical metals, such as Nb, Th and Sc. According to the genesis, the carbonatite-related REE deposits can be divided into three types: primary magmatic type, hydrothermal type and carbonatite weathering-crust type. This paper provides an overview of the carbonatite-related endogenetic REE deposits, i.e., primary magmatic type and hydrothermal type. The carbonatite-related endogenetic REE deposits are mainly distributed in continental margin depression or rift belts, e.g., Bayan Obo REE-Nb-Fe deposit, and orogenic belts on the margin of craton such as the Miaoya Nb-REE deposit. The genesis of carbonatite-related endogenetic REE deposits is still debated. It is generally believed that the carbonatite magma is originated from the low-degree partial melting of the mantle. During the evolution process, the carbonatite rocks or dykes rich in REE were formed through the immiscibility of carbonate-silicate magma and fractional crystallization of carbonate minerals from carbonatite magma. The ore-forming elements are mainly sourced from primitive mantle, with possible contribution of crustal materials that carry a large amount of REE. In the magmatic-hydrothermal system, REEs migrate in the form of complexes, and precipitate corresponding to changes of temperature, pressure, pH and composition of the fluids. A simple magmatic evolution process cannot ensure massive enrichment of REE to economic values. Fractional crystallization of carbonate minerals and immiscibility of melts and hydrothermal fluids in the hydrothermal evolution stage play an important role in upgrading the REE mineralization. Future work of experimental petrology will be fundamental to understand the partitioning behaviors of REE in magmatic-hydrothermal system through simulation of the metallogenic geological environment. Applying “comparative metallogeny” methods to investigate both REE fertile and barren carbonatites will enhance the understanding of factors controlling the fertility.

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Kolawole, Folarin, et Rasheed Ajala. « Propagating rifts : the roles of crustal damage and ascending mantle fluids ». Solid Earth 15, n^o 7 (5 juillet 2024) : 747–62. http://dx.doi.org/10.5194/se-15-747-2024.

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Abstract. We investigate the upper-crustal structure of the Rukwa–Tanganyika rift zone in East Africa, where the Tanganyika rift interacts with the Rukwa and Mweru-Wantipa rift tips, evidenced by prominent fault scarps and seismicity across the rift interaction zones. We invert earthquake P-wave and S-wave travel times to produce 3D upper-crustal velocity models for the region and perform seismicity cluster analysis to understand strain accommodation in rift interaction zones and at the propagating rift tips. The resulting models reveal the occurrence of anomalously high Vp/Vs (primary-to-secondary wave velocity) ratios in the upper crust beneath the Rukwa and Mweru-Wantipa rift tips – regions with basement exposures and sparse rift sedimentation. We detect distinct earthquake families within the deeper clusters which exhibit a temporal evolution pattern characterized by an upward linear trend that suggests triggering caused by upward fluid migration and creep failure. A spatial transition from proximal tip zones dominated by a thinned crust and through-going crustal and upper-mantle seismicity to distal tip zones with a thick crust and dominantly upper-crustal seismicity indicates an along-axis variation in the controls on rift tip deformation. Overall, the collocation of basement faulting, crustal and upper-mantle seismicity, and high upper-crustal Vp/Vs ratios suggests a mechanically weakened crust at the rift tips, likely accommodated by brittle damage from crustal-bending strain and thermomechanical alteration via ascending fluids (mantle-sourced volatiles and hydrothermal fluids). These findings provide new insights into the physics of the propagation, linkage, and coalescence of continental rift tips – a necessary ingredient for initiating continental-breakup axes.

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Kepezhinskas, Pavel, Nikolai Berdnikov, Nikita Kepezhinskas et Natalia Konovalova. « Adakites, High-Nb Basalts and Copper–Gold Deposits in Magmatic Arcs and Collisional Orogens : An Overview ». Geosciences 12, n^o 1 (7 janvier 2022) : 29. http://dx.doi.org/10.3390/geosciences12010029.

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Adakites are Y- and Yb-depleted, SiO2- and Sr-enriched rocks with elevated Sr/Y and La/Yb ratios originally thought to represent partial melts of subducted metabasalt, based on their association with the subduction of young (<25 Ma) and hot oceanic crust. Later, adakites were found in arc segments associated with oblique, slow and flat subduction, arc–transform intersections, collision zones and post-collisional extensional environments. New models of adakite petrogenesis include the melting of thickened and delaminated mafic lower crust, basalt underplating of the continental crust and high-pressure fractionation (amphibole ± garnet) of mantle-derived, hydrous mafic melts. In some cases, adakites are associated with Nb-enriched (10 ppm < Nb < 20 ppm) and high-Nb (Nb > 20 ppm) arc basalts in ancient and modern subduction zones (HNBs). Two types of HNBs are recognized on the basis of their geochemistry. Type I HNBs (Kamchatka, Honduras) share N-MORB-like isotopic and OIB-like trace element characteristics and most probably originate from adakite-contaminated mantle sources. Type II HNBs (Sulu arc, Jamaica) display high-field strength element enrichments in respect to island-arc basalts coupled with enriched, OIB-like isotopic signatures, suggesting derivation from asthenospheric mantle sources in arcs. Adakites and, to a lesser extent, HNBs are associated with Cu–Au porphyry and epithermal deposits in Cenozoic magmatic arcs (Kamchatka, Phlippines, Indonesia, Andean margin) and Paleozoic-Mesozoic (Central Asian and Tethyan) collisional orogens. This association is believed to be not just temporal and structural but also genetic due to the hydrous (common presence of amphibole and biotite), highly oxidized (>ΔFMQ > +2) and S-rich (anhydrite in modern Pinatubo and El Chichon adakite eruptions) nature of adakite magmas. Cretaceous adakites from the Stanovoy Suture Zone in Far East Russia contain Cu–Ag–Au and Cu–Zn–Mo–Ag alloys, native Au and Pt, cupriferous Ag in association witn barite and Ag-chloride. Stanovoy adakites also have systematically higher Au contents in comparison with volcanic arc magmas, suggesting that ore-forming hydrothermal fluids responsible for Cu–Au(Mo–Ag) porphyry and epithermal mineralization in upper crustal environments could have been exsolved from metal-saturated, H2O–S–Cl-rich adakite magmas. The interaction between depleted mantle peridotites and metal-rich adakites appears to be capable of producing (under a certain set of conditions) fertile sources for HNB melts connected with some epithermal Au (Porgera) and porphyry Cu–Au–Mo (Tibet, Iran) mineralized systems in modern and ancient subduction zones.

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Zhang, Bang-Lu, Zhi-Cheng Lv, Zhi-Guo Dong, Xin Zhang, Xiao-Fei Yu, Yong-Sheng Li, Shi-Min Zhen et Chang-Le Wang. « Source Characteristics of the Carboniferous Ortokarnash Manganese Deposit in the Western Kunlun Mountains ». Minerals 12, n^o 7 (21 juin 2022) : 786. http://dx.doi.org/10.3390/min12070786.

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The specific source of ancient sedimentary manganese (Mn) deposits is commonly complex. Here we use systematic major and trace element data with strontium (Sr) and neodymium (Nd) isotopic analyses of the Ortokarnash Mn(II) carbonate ores and associated carbonate rocks from the Upper Carboniferous Kalaatehe Formation (ca. 320 Ma) in order to constrain the Mn source. This formation consists of three members: the first member is a volcanic breccia limestone, the second member is a sandy limestone, and the third member is a black marlstone with the Mn(II) carbonate interlayers. Petrographic observations in combination with low Al2O3 (<3.0 wt%) and Hf (<0.40 ppm) contents and the lack of correlations between the Al2O3 and 87Sr/86Sr ratios as well as εNd(t) values demonstrate a negligible influence of terrigenous detrital contamination on both Sr and Nd isotopic compositions of the Mn(II) carbonate ores. The Sr isotopes of Mn(II) carbonate ores are most likely affected by post-depositional alteration, while Nd isotopes remain unaltered. The initial 87Sr/86Sr ratios in the associated carbonate rocks are likely the result of a mixture of the chemical components (i.e., seawater) and the Al-rich components (e.g., volcanoclastic material), while the detrital effects on Nd isotopes are negligible. In addition, both Sr and Nd isotopes in these non-mineralized wall rocks remained unchanged during post-depositional processes. The relatively low Th/Sc ratios and positive εNd(t) values suggest that the aluminosilicate fraction in the calcarenite and sandy limestone was mainly derived from the weathering of a depleted mafic source, representing the riverine input into the seawater. Given that the Mn(II) carbonate ores are characterized by negative εNd(t) values, these suggest that seafloor-vented hydrothermal fluids derived from interaction with the underlying old continental crust mainly contribute to the source of the Mn(II) carbonates.

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Burisch, Mathias, Max Frenzel, Henning Seibel, Albert Gruber, Marcus Oelze, Jörg A. Pfänder, Cynthia Sanchez-Garrido et Jens Gutzmer. « Li-Co–Ni-Mn-(REE) veins of the Western Erzgebirge, Germany—a potential source of battery raw materials ». Mineralium Deposita 56, n^o 6 (25 juin 2021) : 1223–38. http://dx.doi.org/10.1007/s00126-021-01061-4.

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AbstractSituated in the western Erzgebirge metallogenetic province (Vogtland, Germany), the Eichigt prospect is associated with several quartz-Mn-Fe-oxyhydroxide veins that are exposed at surface. Bulk-rock geochemical assays of vein material yield high concentrations of Li (0.6–4.1 kg/t), Co (0.6–14.7 kg/t), and Ni (0.2–2.8 kg/t), as well as significant quantities of Mn, Cu, and light rare earth elements, a very unusual metal tenor closely resembling the mixture of raw materials needed for Li-ion battery production. This study reports on the results of a first detailed investigation of this rather unique polymetallic mineralization style, including detailed petrographic and mineralogical studies complemented by bulk rock geochemistry, electron microprobe analyses, and laser ablation inductively coupled mass spectrometry. The mineralized material comprises an oxide assemblage of goethite hematite, hollandite, and lithiophorite that together cement angular fragments of vein quartz. Lithiophorite is the predominant host of Li (3.6–11.1 kg/t), Co (2.5–54.5 kg/t), and Ni (0.2–8.9 kg/t); Cu is contained in similar amounts in hollandite and lithiophorite whereas light rare earth elements (LREE) are mainly hosted in microcrystalline rhabdophane and florencite, which are finely intergrown with the Mn-Fe-oxyhydroxides. 40Ar/39Ar ages (~ 40–34 Ma) of coronadite group minerals coincide with tectonic activity related to the Cenozoic Eger Graben rifting. A low-temperature hydrothermal overprint of pre-existing base metal sulfide-quartz mineralization on fault structures that were reactivated during continental rifting is proposed as the most likely origin of the polymetallic oxyhydroxide mineralization at Eichigt. However, tectonically enhanced deep-reaching fracture-controlled supergene weathering cannot be completely ruled out as the origin of the mineralization.

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Bell, K., A. N. Zaitsev, J. Spratt, S. Fröjdö et A. S. Rukhlov. « Elemental, lead and sulfur isotopic compositions of galena from Kola carbonatites, Russia – implications for melt and mantle evolution ». Mineralogical Magazine 79, n^o 2 (avril 2015) : 219–41. http://dx.doi.org/10.1180/minmag.2015.079.2.01.

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AbstractGalena from four REE-rich (Khibina, Sallanlatvi, Seblyavr, Vuoriyarvi) and REE-poor (Kovdor) carbonatites, as well as hydrothermal veins (Khibina) all from the Devonian Kola Alkaline Province of northwestern Russia was analysed for trace elements and Pb and S isotope compositions. Microprobe analyses show that the only detectable elements in galena are Bi and Ag and these vary from not detectable to 2.23 and not detectable to 0.43 wt.% respectively. Three distinct galena groups can be recognized using Bi and Ag contents, which differ from groupings based on Pb isotope data. The Pb isotope ratios show significant spread with 206Pb/204Pb ratios (16.79 to 18.99), 207Pb/204Pb (15.22 to 15.58) and 208Pb/204Pb ratios (36.75 to 38.62). A near-linear array in a 207Pb/204Pb vs.206Pb/204Pb ratio diagram is consistent with mixing between distinct mantle sources, one of which formed during a major differentiation event in the late Archaean or earlier. The S isotopic composition (δ34S) of galena from carbonatites is significantly lighter (–6.7 to –10.3% Canyon Diablo Troilite (CDT) from REE-rich Khibina, Seblyavr and Vuoriyarvi carbonatites, and – 3.2% CDT from REE-poor Kovdor carbonatites) than the mantle value of 0%. Although there is no correlation between S and any of the Pb isotope ratios, Bi and Ag abundances correlate negatively with δ34S values. The variations in the isotopic composition of Pb are attributed to partial melting of an isotopically heterogeneous mantle source, while those of δ34S (together with Bi and Ag abundances) are considered to be process driven. Although variation in Pb isotope values between complexes might reflect different degrees of interaction between carbonatitic melts and continental crust or metasomatized lithosphere, the published noble gas and C, O, Sr, Nd and Hf isotopic data suggest that the variable Pb isotope ratios are best attributed to isotopic differences preserved within a sub-lithospheric mantle source. Different Pb isotopic compositions of galena from the same complex are consistent with a model of magma replenishment by carbonatitic melts/fluids each marked by quite different Pb isotopic compositions.

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Goodfellow, Wayne D., et Jan M. Peter. « Sulphur isotope composition of the Brunswick No. 12 massive sulphide deposit, Bathurst Mining Camp, New Brunswick : implications for ambient environment, sulphur source, and ore genesis ». Canadian Journal of Earth Sciences 33, n^o 2 (1 février 1996) : 231–51. http://dx.doi.org/10.1139/e96-020.

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The Brunswick No. 12 massive sulphide deposit occurs within a Middle Ordovician bimodal volcanic and sedimentary sequence that is thought to have formed in a continental back-arc rift covered with a thick succession of carbonaceous hemipelagic and turbiditic sedimentary rocks. The deposit consists of three en echelon lenses that are zoned from Vent Complex to Bedded Ore and Bedded pyrite facies. The Bedded Ore facies has the lowest average δ34S values (14.2[Formula: see text]), but are only slightly less positive than laminated pyrite in footwall sedimentary rocks (δ34Smean = 15.1[Formula: see text]). δ34S values for the bedded sulphides show an upward increase from 14.2[Formula: see text] in Bedded Ore to 16.5[Formula: see text] in Bedded Pyrite. Average δ34S values for Vent Complex (15.8[Formula: see text]) and underlying stringer sulphides (16.1[Formula: see text]) are consistently more positive than those for Bedded Ore. In carbonaceous shales and siltstone of the Patrick Brook Formation that underlie the deposit, δ34S values that range between 13.8 and 25.6[Formula: see text], and the similarity of these values to those of the Brunswick No. 12 deposit indicate major bacterial reduction of sulphate to sulphide under closed or partly closed conditions, and that most of the S in the deposit originated from ambient sulphidic bottom waters. Furthermore, the average δ34S value for Brunswick No. 12 bedded ores lies on the Selwyn Basin pyrite evolutionary curve and indicates that anoxic conditions within the Tetagouche back-arc basin reflect a global anoxic episode. The Brunswick No. 12 deposit probably formed, therefore, by the mixing of hydrothermal metals with dissolved sulphide of seawater origin during periods of ocean anoxia. The increase of δ34S values towards the Vent Complex may reflect the addition of isotopically heavy S formed by the inorganic reduction of seawater sulphate.

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Galushko, N. A., et N. I. Sokolenko. « The most important selection criteria in winter wheat breeding for grain quality ». TAURIDA HERALD OF THE AGRARIAN SCIENCES 4 (28) (2021) : 50–57. http://dx.doi.org/10.33952/2542-0720-2021-4-28-50-57.

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The quality of wheat grain largely depends on the hereditary characteristics of the variety. In 2018-2020, in the North Caucasus Federal Agricultural Research Center, studies were carried out to search for source material among the diversity of genotypes of common winter wheat at the early stages of the breeding process to select the most promising in the context of grain quality. The soil of the experimental plot is ordinary medium-thick low-humus medium loamy chernozem. The climate of the zone is temperate continental. According to long-term data, the annual sum of effective temperatures is 3177.2 °C; average annual precipitation is 559.6 mm; Selyaninov's hydrothermal coefficient (HTC) is 1.06. Before sowing, complex mineral fertilizers were applied at a dose of N40P60K40; in spring, ammonium nitrate – 26 kg of active ingredient per ha. Fifteen lines of common winter wheat selected according to a complex of breeding valuable signs (yield, resistance to diseases, frost and winter hardiness, drought resistance) served as a material for the studies. Lines were compared with the standard variety ‘Aivina’ according to the most important criteria: gluten mass fraction and quality, protein mass fraction and sedimentation value. Four wheat lines (21663, 20029, 21728, 21944) characterized by gluten of I and II group (gluten content from 23 % to 25.7 %) were identified. They exceeded the standard by 2.0–4.7% and corresponded to the 3 class of grain quality. In line 21944, minor variability of the protein amount (10 %) in the grain by year was noted; in the lines 21226, 21924 and 20029 ‒ average (14.2‒18.7 %); in the rest genotypes, including standard, it was significant (20.1‒34.3 %). On average, over the years of studying, six lines (21420, 21663, 21683, 21118, 21944, 21924) were classified as strong wheat (sedimentation value was in the range of 51‒62 ml). The flour strength of the ‘Aivina’ wheat grain had an average sedimentation value – 49 ml. Lines 21944 and 21924, which exceeded the standard, can be used as sources of high-quality grain when creating new varieties of common winter wheat for regions with a dry period of grain formation.

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Yang, Mimi, Xingyuan Li, Guoxiang Chi, Hao Song, Zhengqi Xu et Fufeng Zhao. « Petrogenesis and Geodynamic Mechanisms of Porphyry Copper Deposits in a Collisional Setting : A Case from an Oligocene Porphyry Cu (Au) Deposit in Western Yangtze Craton, SW China ». Minerals 14, n^o 9 (27 août 2024) : 874. http://dx.doi.org/10.3390/min14090874.

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The Xifanping deposit is a distinct Cenozoic porphyry Cu (Au) deposit located in the Sanjing porphyry metallogenic belt 100–150 km east of the JinshajFiang fault in the western Yangtze craton. We present new zircon U–Pb–Lu–Hf isotopic studies and geochemical data of the ore-bearing quartz monzonite porphyry from the Xifanping deposit to determine their petrogenesis and geodynamic mechanisms. LA–ICP–MS zircon U–Pb dating yielded precise emplacement ages of 31.87 ± 0.41 Ma (MSWD = 0.86) and 32.24 ± 0.61 Ma (MSWD = 1.8) for quartz monzonite porphyry intrusions, and 254.9 ± 5.1 Ma (MSWD = 1.7) for inherited zircons of the monzonite porphyry. The ore-bearing monzonite porphyry is characterized by high-K calc–alkaline to shoshonite and peraluminous series, relatively enriched in light over heavy REEs, with no distinct Eu anomalies, as well as enrichment in LILEs and depletion of HFSEs, with adakitic affinities. The zircon Lu–Hf isotope data ranged from εHf(t) values of −2.94 to +3.68 (average −0.47) with crustal model (TDM2) ages ranging from 0.88 to 1.30 Ga, whereas the inherited zircons displayed positive εHf(t) values ranging from +1.83 to +7.98 (average +5.82), with crustal model (TDM2) ages ranging from 0.77 to 1.17 Ga. Results suggest that the Xifanping porphyry Cu (Au) deposit is related to two periods of magmatic activities. Early magmas were generated from the Paleo-Tethys oceanic subduction during the Late Permian. The subsequent porphyry magma was likely formed by the remelting of previously subduction-modified arc lithosphere, triggered by the continental collision between the Indian and Asian plates in the Cenozoic. The deep magmas and late hydrothermal fluids took advantage of the early magma transport channels along tectonically weak zones during the transition from an extrusive to an extensional–tensional tectonic environment. Early dikes from remelted and assimilated crust contributed to the two age ranges observed in the porphyry intrusions from the Xifanping deposit. The juvenile lower crust materials of the early magmatic arc were potential sources of the Cenozoic porphyry magmas, which has significant implications for mineral exploration and the geological understanding of porphyry Cu deposits in this region.

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Boye, M., B. D. Wake, P. Lopez Garcia, J. Bown, A. R. Baker et E. P. Achterberg. « Distributions of dissolved trace metals (Cd, Cu, Mn, Pb, Ag) in the southeastern Atlantic and the Southern Ocean ». Biogeosciences Discussions 9, n^o 3 (21 mars 2012) : 3579–613. http://dx.doi.org/10.5194/bgd-9-3579-2012.

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Abstract. Comprehensive synoptic datasets (surface water down to 4000 m) of dissolved cadmium (Cd), copper (Cu), manganese (Mn), lead (Pb) and silver (Ag) are presented along a section between 34° S and 57° S in the southeastern Atlantic Ocean and the Southern Ocean to the south off South Africa. The vertical distributions of Cu, Ag, and of Cd display nutrient-like profiles similar to silicic acid, and phosphate, respectively. The distribution of Mn shows a subsurface maximum in the oxygen minimum zone, whereas Pb concentrations are rather invariable with depth. Dry deposition of aerosols is thought to be an important source of Pb to surface waters close to South Africa, and dry deposition and snowfall may have been significant sources of Cu and Mn at the higher latitudes. Furthermore, the advection of water-masses enriched in trace metals following contact with continental margins appeared to be an important source of trace elements to the surface, intermediate and deep waters in the southeastern Atlantic Ocean and the Antarctic Circumpolar Current. Hydrothermal inputs appeared to have formed a source of trace metals to the deep waters over the Bouvet Triple Junction ridge crest, as suggested by relatively enhanced dissolved Mn concentrations. The biological utilization of Cu and Ag was proportional to that of silicic acid across the section, suggesting that diatoms formed an important control over the removal of Cu and Ag from surface waters. However uptake by dino- and nano-flagelattes may have influenced the distribution of Cu and Ag in the surface waters of the subtropical Atlantic domain. Cadmium correlated strongly with phosphate (P), yielding lower Cd/P ratios in the subtropical surface waters where phosphate concentrations were below 0.95 μM. The greater depletion of Cd relative to P observed in the Weddell Gyre compared to the Antarctic Circumpolar Current could be due to increase Cd-uptake induced by iron-limiting conditions in these High-Nutrient Low-Chlorophyll waters. Similarly, an increase of Mn uptake under Fe-depleted conditions may have caused the highest depletion of Mn relative to P in surface waters of the Weddell Gyre. In addition, a cellular Mn-transport channel of Cd was possibly activated in the Weddell Gyre, which in turn may have yielded depletion of both Mn and Cd in these surface waters.

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Boye, M., B. D. Wake, P. Lopez Garcia, J. Bown, A. R. Baker et E. P. Achterberg. « Distributions of dissolved trace metals (Cd, Cu, Mn, Pb, Ag) in the southeastern Atlantic and the Southern Ocean ». Biogeosciences 9, n^o 8 (23 août 2012) : 3231–46. http://dx.doi.org/10.5194/bg-9-3231-2012.

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Abstract. Comprehensive synoptic datasets (surface water down to 4000 m) of dissolved cadmium (Cd), copper (Cu), manganese (Mn), lead (Pb) and silver (Ag) are presented along a section between 34° S and 57° S in the southeastern Atlantic Ocean and the Southern Ocean to the south off South Africa. The vertical distributions of Cu and Ag display nutrient-like profiles similar to silicic acid, and of Cd similar to phosphate. The distribution of Mn shows a subsurface maximum in the oxygen minimum zone, whereas Pb concentrations are rather invariable with depth. Dry deposition of aerosols is thought to be an important source of Pb to surface waters close to South Africa, and dry deposition and snowfall may have been significant sources of Cu and Mn at the higher latitudes. Furthermore, the advection of water masses enriched in trace metals following contact with continental margins appeared to be an important source of trace elements to the surface, intermediate and deep waters in the southeastern Atlantic Ocean and the Antarctic Circumpolar Current. Hydrothermal inputs may have formed a source of trace metals to the deep waters over the Bouvet Triple Junction ridge crest, as suggested by relatively enhanced dissolved Mn concentrations. The biological utilization of Cu and Ag was proportional to that of silicic acid across the section, suggesting that diatoms formed an important control over the removal of Cu and Ag from surface waters. However, uptake by dino- and nano-flagellates may have influenced the distribution of Cu and Ag in the surface waters of the subtropical Atlantic domain. Cadmium correlated strongly with phosphate (P), yielding lower Cd / P ratios in the subtropical surface waters where phosphate concentrations were below 0.95 μM. The greater depletion of Cd relative to P observed in the Weddell Gyre compared to the Antarctic Circumpolar Current could be due to increase Cd uptake induced by iron-limiting conditions in these high-nutrient–low-chlorophyll waters. Similarly, an increase of Mn uptake under Fe-depleted conditions may have caused the highest depletion of Mn relative to P in the surface waters of the Weddell Gyre. In addition, a cellular Mn-transport channel of Cd was possibly activated in the Weddell Gyre, which in turn may have yielded depletion of both Mn and Cd in these surface waters.

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Ramirez-Llodra, E., A. Brandt, R. Danovaro, B. De Mol, E. Escobar, C. R. German, L. A. Levin et al. « Deep, diverse and definitely different : unique attributes of the world's largest ecosystem ». Biogeosciences 7, n^o 9 (22 septembre 2010) : 2851–99. http://dx.doi.org/10.5194/bg-7-2851-2010.

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Abstract. The deep sea, the largest biome on Earth, has a series of characteristics that make this environment both distinct from other marine and land ecosystems and unique for the entire planet. This review describes these patterns and processes, from geological settings to biological processes, biodiversity and biogeographical patterns. It concludes with a brief discussion of current threats from anthropogenic activities to deep-sea habitats and their fauna. Investigations of deep-sea habitats and their fauna began in the late 19th century. In the intervening years, technological developments and stimulating discoveries have promoted deep-sea research and changed our way of understanding life on the planet. Nevertheless, the deep sea is still mostly unknown and current discovery rates of both habitats and species remain high. The geological, physical and geochemical settings of the deep-sea floor and the water column form a series of different habitats with unique characteristics that support specific faunal communities. Since 1840, 28 new habitats/ecosystems have been discovered from the shelf break to the deep trenches and discoveries of new habitats are still happening in the early 21st century. However, for most of these habitats the global area covered is unknown or has been only very roughly estimated; an even smaller – indeed, minimal – proportion has actually been sampled and investigated. We currently perceive most of the deep-sea ecosystems as heterotrophic, depending ultimately on the flux on organic matter produced in the overlying surface ocean through photosynthesis. The resulting strong food limitation thus shapes deep-sea biota and communities, with exceptions only in reducing ecosystems such as inter alia hydrothermal vents or cold seeps. Here, chemoautolithotrophic bacteria play the role of primary producers fuelled by chemical energy sources rather than sunlight. Other ecosystems, such as seamounts, canyons or cold-water corals have an increased productivity through specific physical processes, such as topographic modification of currents and enhanced transport of particles and detrital matter. Because of its unique abiotic attributes, the deep sea hosts a specialized fauna. Although there are no phyla unique to deep waters, at lower taxonomic levels the composition of the fauna is distinct from that found in the upper ocean. Amongst other characteristic patterns, deep-sea species may exhibit either gigantism or dwarfism, related to the decrease in food availability with depth. Food limitation on the seafloor and water column is also reflected in the trophic structure of heterotrophic deep-sea communities, which are adapted to low energy availability. In most of these heterotrophic habitats, the dominant megafauna is composed of detritivores, while filter feeders are abundant in habitats with hard substrata (e.g. mid-ocean ridges, seamounts, canyon walls and coral reefs). Chemoautotrophy through symbiotic relationships is dominant in reducing habitats. Deep-sea biodiversity is among of the highest on the planet, mainly composed of macro and meiofauna, with high evenness. This is true for most of the continental margins and abyssal plains with hot spots of diversity such as seamounts or cold-water corals. However, in some ecosystems with particularly "extreme" physicochemical processes (e.g. hydrothermal vents), biodiversity is low but abundance and biomass are high and the communities are dominated by a few species. Two large-scale diversity patterns have been discussed for deep-sea benthic communities. First, a unimodal relationship between diversity and depth is observed, with a peak at intermediate depths (2000–3000 m), although this is not universal and particular abiotic processes can modify the trend. Secondly, a poleward trend of decreasing diversity has been discussed, but this remains controversial and studies with larger and more robust data sets are needed. Because of the paucity in our knowledge of habitat coverage and species composition, biogeographic studies are mostly based on regional data or on specific taxonomic groups. Recently, global biogeographic provinces for the pelagic and benthic deep ocean have been described, using environmental and, where data were available, taxonomic information. This classification described 30 pelagic provinces and 38 benthic provinces divided into 4 depth ranges, as well as 10 hydrothermal vent provinces. One of the major issues faced by deep-sea biodiversity and biogeographical studies is related to the high number of species new to science that are collected regularly, together with the slow description rates for these new species. Taxonomic coordination at the global scale is particularly difficult, but is essential if we are to analyse large diversity and biogeographic trends.

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Lowry, David, Adrian J. Boyce, Anthony E. Fallick et W. Edryd Stephens. « Genesis of porphyry and plutonic mineralisation systems in metaluminous granitoids of the Grampian Terrane, Scotland ». Transactions of the Royal Society of Edinburgh : Earth Sciences 85, n^o 3 (1994) : 221–37. http://dx.doi.org/10.1017/s0263593300003618.

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AbstractMineralisation associated with Late Caledonian metaluminous granitoids in the Grampian Terrane has been investigated using stable isotope, fluid inclusion and mineralogical techniques.A porphyry-stock-related style of mineralisation in the Grampian Terrane is characterised by a stockwork of veinlets and disseminations in dacite prophyries, consisting of quartz, dolomite, sulphides and late calcite, and well-developed wallrock alteration dominated by zones of phyllic, sericitic and propylitic alteration. On the basis of δ34S (+0·4±l·0‰), δ13C (−5·7‰ to + l·4‰) and δ18O (+10·8‰ to +19·9‰) it is likely that initial mineralising components were orthomagmatic with an input of external fluids during the later parageneses. Fluids were saline, boiling (up to 560°C), deficient in CO2, and ore deposition took place at depths of less than 3 km.Plutonic-hosted mineralisation in appinites, diorites, tonalites and monzogranites is commonly represented by sporadic disseminations and occasional veins consisting of quartz, calcite and sulphides. Wallrock alteration is generally propylitic with phyllic vein selvages. Deposition from a cooling magma sourced fluid is indicated by δ34S (+2·6±l·5‰), δ13C (−7·2‰ to −4·5‰) and δ18O (+9·5‰ to + ll·8‰) data. Fluids were CO2-rich and of low salinity; inclusions were trapped below ≈460°C, and formed at estimated depths of 3–5 km.Differences between these styles of mineralisation may due to multiple factors, the most important being the nature of the fluid: porphyry systems are dominated by greater volumes and much higher temperatures of hydrothermal fluids. Other controlling factors are likely to be the compositional characteristics of the melt source region, the mechanism of magma ascent, the level of emplacement, and the nature of the host metasediments. Variations in δ34S between the two groups are related, for the most part, to redox processes during magma and fluid genesis and not by crustal contamination.Nolarge porphyry-related mineral deposits have been found in the Grampian Terrane, unlike those in Mesozoic and Tertiary continental margin environments. This is largely due to a combination of detrimental factors which massively reducesthe probability of economic mineralisation. These include the already metamorphosed nature of the host Dalradian, the absence of seawater (which entered many subduction-related magmatic systems), a poorly-developed system of deep faults (most deposits too deep to be influenced by surface-derived fluids), and the absence of supergene enrichment. The main processes which aid the concentration of mineralisation involve encroachment of external fluids (formation, meteoric and seawaters) into the magmatic system, but these fluids were largely absent from the Grampian host block at the time of granitoid intrusion.The results of this study can be used in characterising the sources of fluids in sedimentary-hosted ore veins known (or considered) to be underlain by metaluminous granitoid batholiths, particularly in estimating the degree of magmatic fluid inputs into the vein systems: an example where this interaction has occurred (the Tyndrum Fault Zone) is discussed.

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Lowell, Robert P. « Modeling continental and submarine hydrothermal systems ». Reviews of Geophysics 29, n^o 3 (1991) : 457. http://dx.doi.org/10.1029/91rg01080.

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Brown, Sabrina R., et Sherilyn C. Fritz. « Eukaryotic organisms of continental hydrothermal systems ». Extremophiles 23, n^o 4 (22 mai 2019) : 367–76. http://dx.doi.org/10.1007/s00792-019-01101-y.

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Jones, Morgan T., Lawrence M. E. Percival, Ella W. Stokke, Joost Frieling, Tamsin A. Mather, Lars Riber, Brian A. Schubert et al. « Mercury anomalies across the Palaeocene–Eocene Thermal Maximum ». Climate of the Past 15, n^o 1 (6 février 2019) : 217–36. http://dx.doi.org/10.5194/cp-15-217-2019.

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Abstract. Large-scale magmatic events like the emplacement of the North Atlantic Igneous Province (NAIP) are often coincident with periods of extreme climate change such as the Palaeocene–Eocene Thermal Maximum (PETM). One proxy for volcanism in the geological record that is receiving increased attention is the use of mercury (Hg) anomalies. Volcanic eruptions are among the dominant natural sources of Hg to the environment; thus, elevated Hg∕TOC values in the sedimentary rock record may reflect an increase in volcanic activity at the time of deposition. Here we focus on five continental shelf sections located around the NAIP in the Palaeogene. We measured Hg concentrations, total organic carbon (TOC) contents, and δ13C values to assess how Hg deposition fluctuated across the PETM carbon isotope excursion (CIE). We find a huge variation in Hg anomalies between sites. The Grane field in the North Sea, the most proximal locality to the NAIP analysed, shows Hg concentrations up to 90 100 ppb (Hg∕TOC = 95 700 ppb wt %−1) in the early Eocene. Significant Hg∕TOC anomalies are also present in Danish (up to 324 ppb wt %−1) and Svalbard (up to 257 ppb wt %−1) sections prior to the onset of the PETM and during the recovery period, while the Svalbard section also shows a continuous Hg∕TOC anomaly during the body of the CIE. The combination with other tracers of volcanism, such as tephra layers and unradiogenic Os isotopes, at these localities suggests that the Hg∕TOC anomalies reflect pulses of magmatic activity. In contrast, we do not observe clear Hg anomalies on the New Jersey shelf (Bass River) or the Arctic Ocean (Lomonosov Ridge). This large spatial variance could be due to more regional Hg deposition. One possibility is that phreatomagmatic eruptions and hydrothermal vent complexes formed during the emplacement of sills led to submarine Hg release, which is observed to result in limited distribution in the modern era. The Hg∕TOC anomalies in strata deposited prior to the CIE may suggest that magmatism linked to the emplacement of the NAIP contributed to the initiation of the PETM. However, evidence for considerable volcanism in the form of numerous tephra layers and Hg∕TOC anomalies post-PETM indicates a complicated relationship between LIP volcanism and climate. Factors such as climate system feedbacks, changes to the NAIP emplacement style, and/or varying magma production rates may be key to both the onset and cessation of hyperthermal conditions during the PETM. However, processes such as diagenesis and organic matter sourcing can have a marked impact on Hg∕TOC ratios and need to be better constrained before the relationship between Hg anomalies and volcanic activity can be considered irrefutable.

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Dilles, John H., Greg B. Arehart, Peter I. Nabelek et Todd C. Feeley. « Mass Redistribution in Continental Magmatic-Hydrothermal Systems ». GSA Today 14, n^o 12 (2004) : 32. http://dx.doi.org/10.1130/1052-5173(2004)014<0032:mricms>2.0.co;2.

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Rihs, Sophie, Michel Condomines et Jean-Louis Poidevin. « Long-term behaviour of continental hydrothermal systems : ». Geochimica et Cosmochimica Acta 64, n^o 18 (septembre 2000) : 3189–99. http://dx.doi.org/10.1016/s0016-7037(00)00412-9.

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40

Cao, Wenrong, Cin-Ty A. Lee, Jiaming Yang et Andrew V. Zuza. « Hydrothermal circulation cools continental crust under exhumation ». Earth and Planetary Science Letters 515 (juin 2019) : 248–59. http://dx.doi.org/10.1016/j.epsl.2019.03.029.

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41

Silva, Bruna, Catarina Antunes, Filipa Andrade, Eduardo Ferreira da Silva, Jose Antonio Grande et Ana T. Luís. « Prokaryotic and eukaryotic diversity in hydrothermal continental systems ». Archives of Microbiology 203, n^o 7 (18 juin 2021) : 3751–66. http://dx.doi.org/10.1007/s00203-021-02416-1.

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42

Fiebig, Jens, Alan B. Woodland, Walter D'Alessandro et Wilhelm Püttmann. « Excess methane in continental hydrothermal emissions is abiogenic ». Geology 37, n^o 6 (juin 2009) : 495–98. http://dx.doi.org/10.1130/g25598a.1.

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Gimeno, Luis. « Oceanic sources of continental precipitation ». Water Resources Research 50, n^o 5 (mai 2014) : 3647–49. http://dx.doi.org/10.1002/2014wr015477.

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Ramirez-Llodra, E., A. Brandt, R. Danovaro, E. Escobar, C. R. German, L. A. Levin, P. Martinez Arbizu et al. « Deep, diverse and definitely different : unique attributes of the world's largest ecosystem ». Biogeosciences Discussions 7, n^o 2 (7 avril 2010) : 2361–485. http://dx.doi.org/10.5194/bgd-7-2361-2010.

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Abstract. The deep sea, the largest biome on Earth, has a series of characteristics that make this environment both distinct from other marine and land ecosystems and unique for the entire planet. This review describes these patterns and processes, from geological settings to biological processes, biodiversity and biogeographical patterns. It concludes with a brief discussion of current threats from anthropogenic activities to deep-sea habitats and their fauna. Investigations of deep-sea habitats and their fauna began in the late 19th Century. In the intervening years, technological developments and stimulating discoveries have promoted deep-sea research and changed our way of understanding life on the planet. Nevertheless, the deep sea is still mostly unknown and current discovery rates of both habitats and species remain high. The geological, physical and geochemical settings of the deep-sea floor and the water column form a series of different habitats with unique characteristics that support specific faunal communities. Since 1840, 27 new habitats/ecosystems have been discovered from the shelf break to the deep trenches and discoveries of new habitats are still happening in the early 21st Century. However, for most of these habitats, the global area covered is unknown or has been only very roughly estimated; an even smaller – indeed, minimal – proportion has actually been sampled and investigated. We currently perceive most of the deep-sea ecosystems as heterotrophic, depending ultimately on the flux on organic matter produced in the overlying surface ocean through photosynthesis. The resulting strong food limitation, thus, shapes deep-sea biota and communities, with exceptions only in reducing ecosystems such as inter alia hydrothermal vents or cold seeps, where chemoautolithotrophic bacteria play the role of primary producers fuelled by chemical energy sources rather than sunlight. Other ecosystems, such as seamounts, canyons or cold-water corals have an increased productivity through specific physical processes, such as topographic modification of currents and enhanced transport of particles and detrital matter. Because of its unique abiotic attributes, the deep sea hosts a specialized fauna. Although there are no phyla unique to deep waters, at lower taxonomic levels the composition of the fauna is distinct from that found in the upper ocean. Amongst other characteristic patterns, deep-sea species may exhibit either gigantism or dwarfism, related to the decrease in food availability with depth. Food limitation on the seafloor and water column is also reflected in the trophic structure of deep-sea communities, which are adapted to low energy availability. In most of the heterotrophic deep-sea settings, the dominant megafauna is composed of detritivores, while filter feeders are abundant in habitats with hard substrata (e.g. mid-ocean ridges, seamounts, canyon walls and coral reefs) and chemoautotrophy through symbiotic relationships is dominant in reducing habitats. Deep-sea biodiversity is among of the highest on the planet, mainly composed of macro and meiofauna, with high evenness. This is true for most of the continental margins and abyssal plains with hot spots of diversity such as seamounts or cold-water corals. However, in some ecosystems with particularly "extreme" physicochemical processes (e.g. hydrothermal vents), biodiversity is low but abundance and biomass are high and the communities are dominated by a few species. Two large-scale diversity patterns have been discussed for deep-sea benthic communities. First, a unimodal relationship between diversity and depth is observed, with a peak at intermediate depths (2000–3000 m), although this is not universal and particular abiotic processes can modify the trend. Secondly, a poleward trend of decreasing diversity has been discussed, but this remains controversial and studies with larger and more robust datasets are needed. Because of the paucity in our knowledge of habitat coverage and species composition, biogeographic studies are mostly based on regional data or on specific taxonomic groups. Recently, global biogeographic provinces for the pelagic and benthic deep ocean have been described, using environmental and, where data were available, taxonomic information. This classification described 30 pelagic provinces and 38 benthic provinces divided into 4 depth ranges, as well as 10 hydrothermal vent provinces. One of the major issues faced by deep-sea biodiversity and biogeographical studies is related to the high number of species new to science that are collected regularly, together with the slow description rates for these new species. Taxonomic coordination at the global scale is particularly difficult but is essential if we are to analyse large diversity and biogeographic trends. Because of their remoteness, anthropogenic impacts on deep-sea ecosystems have not been addressed very thoroughly until recently. The depletion of biological and mineral resources on land and in shallow waters, coupled with technological developments, is promoting the increased interest in services provided by deep-water resources. Although often largely unknown, evidence for the effects of human activities in deep-water ecosystems – such as deep-sea mining, hydrocarbon exploration and exploitation, fishing, dumping and littering – is already accumulating. Because of our limited knowledge of deep-sea biodiversity and ecosystem functioning and because of the specific life-history adaptations of many deep-sea species (e.g. slow growth and delayed maturity), it is essential that the scientific community works closely with industry, conservation organisations and policy makers to develop conservation and management options.

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Liu, Jintao, Shanshan Xu, Xiaole Han, Xi Chen et Ruimin He. « A Multi-Dimensional Hydro-Climatic Similarity and Classification Framework Based on Budyko Theory for Continental-Scale Applications in China ». Water 11, n^o 2 (14 février 2019) : 319. http://dx.doi.org/10.3390/w11020319.

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Our knowledge of the similarities and differences in ecological systems is vital to understanding the co-evolution of ecological factors. This study proposes a multi-dimensional hydro-climatic similarity and classification framework based on Budyko theory. The framework employs the dryness index (DI), evaporative index (EI), and an empirical parameter (ω) to further sub-divide four climatic zones (humid, semi-humid, semi-arid, and arid zones) in terms of DI. A criterion that define the similarities between stations is proposed to verify the classification to obtain optimal results. This method is applied to Mainland China, and 637 stations are adopted for continental-scale classification experiments. The point cloud of the Budyko curve for all the stations in Mainland China is plotted. We find that the hydrothermal conditions of the vertically distributed stations on the Budyko curve can be quite different in the same climatic zone when DI < 4.0. The higher the vertical locations of the stations on the Budyko curve are, the drier and colder the climates and corresponding natural landscapes. Under the proposed hydro-climatic classification framework, the four climatic zones are further divided into 17 sub-regions, and the hydrothermal conditions for each sub-region are discussed. The results suggest that regional differences of long-term water balance are resulted by not only mean annual hydrothermal factors and catchment forms but also annual distribution of hydrothermal factors. Our framework can provide hydrologically-based classification across continental scale and, thus, provide a profound understanding of hydrothermal conditions of continental-scale hydrological cycles.

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de Wit, Maarten J., et Roger A. Hart. « Earth's earliest continental lithosphere, hydrothermal flux and crustal recycling ». Lithos 30, n^o 3-4 (septembre 1993) : 309–35. http://dx.doi.org/10.1016/0024-4937(93)90043-c.

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Tsyhaniuk, Yu V. « SOURCES OF CONTINENTAL CRIMINAL PROCESS SYSTEM ». Uzhhorod National University Herald. Series : Law, n^o 60 (2020) : 191–94. http://dx.doi.org/10.32782/2307-3322/2020.60.42.

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Prather, Michael J. « Continental sources of halocarbons and nitrous oxide ». Nature 317, n^o 6034 (septembre 1985) : 221–25. http://dx.doi.org/10.1038/317221a0.

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Mahoney, J., C. Nicollet et C. Dupuy. « Madagascar basalts : tracking oceanic and continental sources ». Earth and Planetary Science Letters 104, n^o 2-4 (juin 1991) : 350–63. http://dx.doi.org/10.1016/0012-821x(91)90215-4.

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Nicklas, Robert W., James M. D. Day, Robert B. Trumbull, Haider Rangwalla et Savannah Kelly. « Continental flood basalts sample oxidized mantle sources ». Lithos 482-483 (octobre 2024) : 107697. http://dx.doi.org/10.1016/j.lithos.2024.107697.

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Articles de revues sur le sujet « Hydrothermal and continental sources »

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