Статті в журналах з теми "Thermobarometric analysis"
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1
Tamarit, J. Li, B. Legendre, and J. M. Buisine. "Thermodynamic Study of Some Neopentane Derivated by Thermobarometric Analysis." Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals 250, no. 1 (July 1994): 347–58. http://dx.doi.org/10.1080/10587259408028219.
Повний текст джерела
2
Hernández-Bernal, María del Sol, Pedro Corona-Chávez, Noemí Trujillo-Hernández, Consuelo Macías-Romo, Dante Jaime Morán-Zenteno, Adrián Jiménez-Haro, and Stefano Poli. "The Cuitzeo granitic xenolith: evidence of an Early Miocene magma plumbing system in central Mexico." Revista Mexicana de Ciencias Geológicas 38, no. 1 (March 24, 2021): 29–42. http://dx.doi.org/10.22201/cgeo.20072902e.2021.1.1591.
Повний текст джерелаАнотація:
Relevant data on the structure and composition of the crystalline basement in Central México can be found by means of plutonic, metamorphic, and sedimentary xenoliths transported by Neogene and Quaternary volcanic eruptions within the Trans-Mexican Volcanic Belt (TMVB). We present detailed major oxide and trace elements concentrations, isotopic analysis and thermobarometric estimations for a granitic xenolith found in an Early Miocene ignimbrite in Cuitzeo Lake, Michoacán. The xenolith is a calc-alkaline quartz-plagioclase-K-feldspar-biotite-amphibole granite-monzogranite with 73.7 wt.% SiO2. Trace element and isotopic signatures are compatible with a volcanic arc signature. According to amphibole-plagioclase pairs and Ti-in-zircon thermobarometry, the studied xenolith suggests that the granitic system crystallized between 655–737 °C and 1.3–1.9 kbar. U-Pb isotopic analyses of zircon grains from this rock have provided a concordia age of 20.76 ± 0.11 Ma. The presence of granitic xenoliths in Quaternary eruptions produced by the TMVB are not rare. However, this is the first zircon age of a Miocene granitic rock showing evidence of the shallow plutonic counterpart of the magma plumbing system of the Early Miocene (~23 to ~16 Ma) Mil Cumbres - Angangueo voluminous, andesitic-dacitic-rhyolitic episode. Implications for faulting, erosion, and Miocene-Pliocene ignimbrite emplacement in Cuitzeo region are also discussed.
3
Squali, A., L. Montagne, P. Vast, G. Palavit, and J. M. Buisine. "Thermobarometric analysis of physico-chemical transformations of coacervates and gels of polyphosphates." Journal of Thermal Analysis 37, no. 8 (August 1991): 1673–78. http://dx.doi.org/10.1007/bf01912196.
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4
Montel, Jean-Marc, Catherine Weber, and Michel Pichavant. "Biotite-sillimanite-spinel assemblages in high-grade metamorphic rocks : occurrences, chemographic analysis and thermobarometric interest." Bulletin de Minéralogie 109, no. 5 (1986): 555–73. http://dx.doi.org/10.3406/bulmi.1986.7958.
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5
Lucci, Federico, Gerardo Carrasco-Núñez, Federico Rossetti, Thomas Theye, John Charles White, Stefano Urbani, Hossein Azizi, Yoshihiro Asahara, and Guido Giordano. "Anatomy of the magmatic plumbing system of Los Humeros Caldera (Mexico): implications for geothermal systems." Solid Earth 11, no. 1 (January 23, 2020): 125–59. http://dx.doi.org/10.5194/se-11-125-2020.
Повний текст джерелаАнотація:
Abstract. Understanding the anatomy of magma plumbing systems of active volcanoes is essential not only for unraveling magma dynamics and eruptive behaviors but also to define the geometry, depth, and temperature of the heat sources for geothermal exploration. The Pleistocene–Holocene Los Humeros volcanic complex is part of the eastern Trans-Mexican Volcanic Belt (central Mexico), and it constitutes one of the most important exploited geothermal fields in Mexico with ca. 90 MW of produced electricity. With the aim to decipher the anatomy (geometry and structure) of the magmatic plumbing system feeding the geothermal field at Los Humeros, we carried out a field-based petrological and thermobarometric study of the exposed Holocene lavas. Textural analysis, whole-rock major-element data, and mineral chemistry are integrated with a suite of mineral-liquid thermobarometric models. Our results support a scenario characterized by a heterogeneous multilayered system, comprising a deep (depth of ca. 30 km) basaltic reservoir feeding progressively shallower and smaller discrete magma stagnation layers and batches, up to shallow-crust conditions (depth of ca. 3 km). The evolution of melts in the feeding system is mainly controlled by differentiation processes through fractional crystallization (plagioclase + clinopyroxene + olivine + spinel). We demonstrate the inadequacy of the existing conceptual models, where a single voluminous melt-controlled magma chamber (or “Standard Model”) at shallow depths was proposed for the magmatic plumbing system at Los Humeros. We instead propose a magmatic plumbing system made of multiple, more or less interconnected, magma transport and storage layers within the crust, feeding small (ephemeral) magma chambers at shallow-crustal conditions. This revised scenario provides a new configuration of the heat source feeding the geothermal reservoir at Los Humeros, and it should be taken into account to drive future exploration and exploitation strategies.
6
Ruiz-Cruz, M. D., and C. Sanz de Galdeano. "Diamond and coesite in ultrahigh-pressure–ultrahigh-temperature granulites from Ceuta, Northern Rif, northwest Africa." Mineralogical Magazine 76, no. 3 (June 2012): 683–704. http://dx.doi.org/10.1180/minmag.2012.076.3.17.
Повний текст джерелаАнотація:
AbstractDiamond and coesite occur in granulites of the Internal Zone of the Rif belt in northwest Africa. Diamond, identified by optical microscopy, electron microprobe analysis, Raman spectroscopy, cathodoluminescence and microstructural electron backscattered diffraction, is present as inclusions up to 20 μm across in garnet, K-feldspar, coesite relics and quartz. Thermobarometric estimates yield P >4.3 GPa and T >1100°C, which corresponds to a depth of formation >150 km. The estimates suggest that the diamond-bearing peridotites and adjacent crustal rocks experienced similar P–T conditions. If this is correct, there is an old (undated) core in the Betic–Rif cordillera and the current models of the tectonic evolution of the area, which are based on 'full Alpine' evolution, must be revised. This discovery provides further valuable information about the complex geotectonic environment of the southeast Spain and north Moroccan collisional orogen.
7
Zhdaneev, Oleg, Аlexader Zaytsev, and Тeodor Prodan. "Possibilities for creating Russian high-tech bottomhole assembly." Записки Горного института 252 (December 17, 2021): 872–84. http://dx.doi.org/10.31897/pmi.2021.6.9.
Повний текст джерелаАнотація:
Development of high-tech well electronic measuring systems is aimed at creating modern equipment: telemetry, well geophysical measurement equipment, the architecture of which is divided into basic (with measurement channels for gamma logging and inductive resistance) and advanced (with radioactive, acoustic, magnetic resonance and thermobarometric measurement channels, including azimuthal methods of investigation). Over-the-bit measurement modules, rotary steerable systems are being developed and channels for transmitting data to the surface are being improved. Vice versa, specialized surface equipment with highly integrated software is being created. Different measurement modules are manufactured by different companies, which creates uncertainties in the possibility of interfacing the manufacturers' measurement modules into a single well measurement system. The article presents an analysis of the readiness of Russian oil service companies to produce well and surface equipment for drilling Russian directional oil and gas wells, meeting modern requirements for accuracy, lifetime and operating conditions. The possibility of creating a fully Russian well high-tech equipment and the required resources, risks and measures to mitigate them when creating a modern well measurement system are considered.
8
Verdecchia, Sebastian O., Gilda Collo, and Edgardo G. Baldo. "Polyphase white mica growth in low-grade metapelites from La Cebila Metamorphic Complex (Famatinian Belt, Argentina): evidence from microstructural and XRD investigations." Andean Geology 38, no. 2 (August 9, 2011): 268. http://dx.doi.org/10.5027/andgeov38n2-a02.
Повний текст джерелаАнотація:
Two tectono-thermal metamorphic events, M1-D1 (S1, with associated white mica and chlorite: WM1-Chl1) and M2-D2 (S2, with development of WM2-Chl2), are established from polyphase white mica growth for low-grade units from the Ordovician metasedimentary successions of La Cebila Metamorphic Complex in the Famatinian belt (western-central Argentina). The thermobarometric characterization of the M1 main event was carried out by means of clay-mineral analysis and crystallo-chemical parameter measurements. Epizonal (temperatures between 300 and 400ºC) and low-pressure conditions are suggested for M1 event, based in Kübler index values ranging from 0.23 to 0.17 Δº2θ, white mica b parameter values between 9.004 and 9.022 Å (mean of 9.014 Å, n=16) and Si contents between 3.13-3.29 a.p.f.u. Temperatures of ~180-270ºC are estimated for the M2 event, with Kübler index values ranging from 0.31 to 0.46 Δº2θ. The M1-D1 event of La Cebila could be linked to highstrain heating tectono-metamorphic Ordovician regime recorded in others complexes from Famatinian foreland region of Sierras Pampeanas.
9
Goodwin-Bell, Jo-Anne S. "Delineation of isograds in siliceous dolomitic marbles along the Sharbot Lake – Frontenac terrane boundary of the Grenville Province, southeastern Ontario." Canadian Journal of Earth Sciences 45, no. 6 (June 2008): 669–91. http://dx.doi.org/10.1139/e08-017.
Повний текст джерелаАнотація:
This study presents details of the mineralogy and petrology of siliceous, dolomitic marbles of the Sharbot Lake domain along the Frontenac terrane boundary in the Grenville Province of southeastern Ontario. The location of four mineral isograds in the marble and the related univariant reactions were identified in the Almonte – Carleton Place area. Delineation of the isograds is based on detailed mapping, petrographic analysis of coexisting mineral assemblages, and a polybaric T–XCO2 diagram calculated using thermobarometric data from associated gneissic rocks, where T is temperature and X is fluid composition. The T–X section is based on a field gradient of 32 °C/km. The isograds correspond to the first appearance of tremolite (5 dolomite + 8 quartz + H2O = tremolite + 3 calcite + 7 CO2), diopside (tremolite + 3 calcite + 2 quartz = 5 diopside + 3 CO2 + H2O), diopside + dolomite (tremolite + 3 calcite = dolomite + 4 diopside + H2O + CO2), and forsterite (diopside + 3 dolomite = 2 forsterite + 4 calcite + 5 CO2). Mineral assemblages above and below each isograd are described and relevant examples are shown. Results of this study are consistent with a mixed volatile fluid of a uniform composition during mid- to upper amphibolite-facies metamorphism.
10
Himmelberg, Glen R., Peter J. Haeussler, and David A. Brew. "Emplacement, rapid burial, and exhumation of 90-Ma plutons in southeastern Alaska." Canadian Journal of Earth Sciences 41, no. 1 (January 1, 2004): 87–102. http://dx.doi.org/10.1139/e03-087.
Повний текст джерелаАнотація:
In southeastern Alaska, granodioritetonalite plutons of the AdmiraltyRevillagigedo belt intruded the JurassicCretaceous Gravina belt along the eastern side of the Alexander terrane around 90 Ma. These plutons postdate some deformation related to a major contractional event between the previously amalgamated Wrangellia and Alexander terranes and the previously accreted terranes of the North American margin. We studied the aureole mineral assemblages of these plutons near Petersburg, Alaska, determined pressure and temperature of equilibration, and examined structures that developed within and adjacent to these plutons. Parallelism of magmatic and submagmatic fabrics with fabrics in the country rock indicates synchroneity of pluton emplacement with regional deformation and suggests that magma transport to higher crustal levels was assisted by regional deformation. Replacement of andalusite by kyanite or sillimanite indicates crustal thickening soon after pluton emplacement. Regional structural analysis indicates the crustal thickening was accomplished by thrust burial. Thermobarometric analyses indicate the aureoles reached near-peak temperatures of 525 to 635 °C at pressures of 570 to 630 MPa. Consideration of the rate of thermal decay of the aureoles suggests that burial was rapid and occurred at rates around 5 to 8 mm/year. Structural observations indicate there was contractional deformation before, during, and after emplacement of the 90-Ma plutons. Initial exhumation of the AdmiraltyRevillagigedo belt in the Petersburg area may have occurred along a thrust west of the pluton belt within the Gravina belt.
11
Rottier, Bertrand, Andreas Audétat, Peter Koděra, and Jaroslav Lexa. "Origin and Evolution of Magmas in the Porphyry Au-mineralized Javorie Volcano (Central Slovakia): Evidence from Thermobarometry, Melt Inclusions and Sulfide Inclusions." Journal of Petrology 60, no. 12 (December 1, 2019): 2449–82. http://dx.doi.org/10.1093/petrology/egaa014.
Повний текст джерелаАнотація:
Abstract The effect of magmatic sulfide precipitation on the potential of magmatic systems to produce porphyry-type ore deposits is still a matter of debate. In particular, we need to know whether magmatic sulfide precipitation has an impact on the Cu and Au content of the exsolving magmatic volatile phases and, by this way, on the Cu/Au ratio of porphyry deposits. The Javorie volcano is a perfect place to explore these questions. First, it hosts several Au-only porphyry-type mineralized occurrences which have among the lowest Cu/Au ratios reported in the literature. Secondly, the geology of the Javorie volcano and the timing of porphyry Au mineralization are well established. The evolution of the Javorie magmatic system was reconstructed by detailed petrographic studies and laser ablation inductively coupled plasma mass spectrometry analysis of minerals, melt inclusions and sulfide inclusions. The Javorie volcano was formed during the post-subduction magmatic activity affecting the Western Carpathians. It is a typical stratovolcano, composed dominantly of basaltic andesites and andesites which were intruded by several small stocks of dacitic to dioritic composition. According to our thermobarometric data, the volcano was fed by a transcrustal magmatic system in which two levels of magma chambers could be identified. Part of the magma evolved in the lower crust as suggested by the occurrence of magmatic garnet antecrysts in some of the studied rocks. The occurrence of magmatic sulfide inclusions in garnet indicates that sulfide saturation was reached in this lower crustal magma chamber. Most of the rocks crystallized in an upper crustal magma chamber (∼2 ± 1 kbar) that was fed by a basaltic to basaltic andesite magmas. A large variation in temperatures, ranging between 820°C and 1025°C, recorded by the extrusive and intrusive rocks suggest either that the upper crustal magma chamber was thermally zoned, or that the temperature of the whole magma chamber varied dramatically during its lifetime. Magmatic sulfide inclusions are present in all minerals and rocks of the upper crustal magma chamber, independent of their timing relative to porphyry Au mineralization (pre-, syn-, post-ore). These observations suggest that the magmatic system was sulfide saturated during its entire evolution. With very few exceptions, the precipitating sulfides were composed of monosulfide solid solution containing 0·2–9·2 wt % Cu and 0·05–11 ppm Au. The presence of these magmatic sulfides, together with results of a numerical model, suggest that the primitive magma feeding the upper crustal magma chamber contained less than 2·75 wt % H2O and that only a minor part of the magmatic sulfides was fractionated out of the system. Finally, the Cu/Au ratios measured in the magmatic sulfide inclusions and the ones predicted for the exsolved aqueous fluids are 10 to 100 times higher than the Cu/Au ratios of the porphyry deposits. Therefore, the extremely low Cu/Au ratios of the porphyry deposits must have been acquired during the hydrothermal stage.
12
Naumko, I. M., M. I. Pavlyuk, A. A. Loktiev, Yu V. Khokha, В. E. Sakhno, Yu A. Belеts’ka, and N. H. Sava. "FEATURES OF THE FLUID REGIME OF POSTSEDIMENTOGENIC PROCESSES DURING THE FORMATION OF GAS CAPACITY OF THE TRANSCARPATHIAN BASIN (WITHIN THE LIMITS OF UKRAINE)." Mineralogical Journal 44, no. 3 (2022): 99–110. http://dx.doi.org/10.15407/mineraljournal.44.03.099.
Повний текст джерелаАнотація:
Gases in migrating paleofluids of the Transcarpathian Basin in Ukraine proper were investigated. Their properties were analyzed using fluid inclusions in minerals and fluids occurring in closed pores of promising gas-bearing rocks. Samples were taken from wells drilled within the Mukachevo (1-Borodivsk-Novosilsk) and Solotvyno (1-Bushtyno, 4-Hrushovo, 1-Danylovo, 28-Solotvyno) depressions. According to the data from mass-spectrometric chemical analysis, methane and its homologues and carbon dioxide were found in the composition of volatile compounds, which coincides with the identified advantage of methane and its homologues, on the one hand, and carbon dioxide, on the other hand, in the natural gases of fields of the Transcarpathian gas-bearing area. Methane (98.2 vol. %), ethane (1.2 vol. %) and propane (0.6 vol. %) are found in fluid inclusions in calcite of veinlet in the rock from the well 28 of the Solotvyno structure, which includes the Solotvyno natural gas field. Only methane is found in closed rock pores. Natural gases of the Solotvyno gas field contain methane (53.86%), ethane (2.65%) and propane + butane (1.34-0.32%). СО2 contents as high as 97.3 vol. % occur in fluid inclusions in calcite of veinlets in rocks of the well 1 at Ruski Komarivtsi of the Mukachevo depression and 100 % in fluid inclusions in zeolite (?) from impregnates in rocks of the well 1 at Bushtyno of the Solotvyno depression. This can be explained by the activity of two different composition paleofluids, namely reduced or oxidating types present in bowels of the Transcarpathian Basin. They are associated with significant amount of reduced compounds (methane and its homologues) or a high concentration of oxidized compounds for their (mainly СО2). This was determined by differences in the composition of the primary high-energy abiogenic deep fluid: hydrocarbon-containing or carbon dioxide-containing. The gas composition of paleofluids indicates that two types of natural gas deposits may exist, mainly hydrocarbon or mainly carbon dioxide rich and, accordingly, the discovery of natural gas fields such as Solotvyno and carbon dioxide – such as Martovo. Hydrocarbon formation over a wide range of conditions and primary material ("oil polygenesis") allows the assessment of oil and gas resources of the region. A polygenetic approach for understanding hydrocarbon formation processes requires a changes in exploration strategy. More geochemical and thermobarometric research as well thermodynamic study of mineral-forming fluids is needed in promising geologic structures of the Transcarpathian gas-bearing area. This necessary, in order to predict possible occurrence of high-energy gas deposits and to determine areas for exploration.
13
Sanità, Edoardo, Maria Di Rosa, Jean-Marc Lardeaux, Michele Marroni, and Luca Pandolfi. "The Moglio-Testico Unit (Ligurian Alps, Italy) as Subducted Metamorphic Oceanic Fragment: Stratigraphic, Structural and Metamorphic Constraints." Minerals 12, no. 11 (October 24, 2022): 1343. http://dx.doi.org/10.3390/min12111343.
Повний текст джерелаАнотація:
Along the Western Alps, the oceanic units showing blueschists to eclogite facies metamorphic imprint are classically regarded as fragments of the Ligurian-Piedmont Ocean. These units recorded a strongly deformation related to their subduction, accretion and subsequent exhumation into the Alpine wedge, developed during the convergence between the Europa and Adria Plates. However, some of these units, for example the Moglio-Testico Unit, are less pervasively deformed, providing evidence of their sedimentary evolution as well as the tectono-metamorphic history. Therefore, we present original stratigraphic, structural and thermo-barometric data to characterize the tectono-metamorphic history and the sedimentary evolution of the Moglio-Testico Unit, performing different techniques including fieldwork, structural analysis and chlorite-phengite multiequilibrium thermobarometry. Our dataset indicates that the Moglio-Testico Unit can be considered as a fragment of oceanic cover whose sedimentary evolution reflects that of a portion of oceanic lithosphere approaching to the subduction zone. Structural analysis combined with the thermobarometry indicate that this unit recorded a polyphase deformation history developed under High Pressure-Low Temperature metamorphic conditions (D1: 1.2–1.0 GPa and Tpeak: 330–260 °C; D2: 0.4–0.7 GPa and 230–170 °C) during its underthrusting, accretion into the Alpine wedge and subsequent exhumation up to the shallower crustal levels.
14
Sanità, Edoardo, Maria Di Rosa, Jean-Marc Lardeaux, Michele Marroni, and Luca Pandolfi. "The Moglio-Testico Unit (Ligurian Alps, Italy) as Subducted Metamorphic Oceanic Fragment: Stratigraphic, Structural and Metamorphic Constraints." Minerals 12, no. 11 (October 24, 2022): 1343. http://dx.doi.org/10.3390/min12111343.
Повний текст джерелаАнотація:
Along the Western Alps, the oceanic units showing blueschists to eclogite facies metamorphic imprint are classically regarded as fragments of the Ligurian-Piedmont Ocean. These units recorded a strongly deformation related to their subduction, accretion and subsequent exhumation into the Alpine wedge, developed during the convergence between the Europa and Adria Plates. However, some of these units, for example the Moglio-Testico Unit, are less pervasively deformed, providing evidence of their sedimentary evolution as well as the tectono-metamorphic history. Therefore, we present original stratigraphic, structural and thermo-barometric data to characterize the tectono-metamorphic history and the sedimentary evolution of the Moglio-Testico Unit, performing different techniques including fieldwork, structural analysis and chlorite-phengite multiequilibrium thermobarometry. Our dataset indicates that the Moglio-Testico Unit can be considered as a fragment of oceanic cover whose sedimentary evolution reflects that of a portion of oceanic lithosphere approaching to the subduction zone. Structural analysis combined with the thermobarometry indicate that this unit recorded a polyphase deformation history developed under High Pressure-Low Temperature metamorphic conditions (D1: 1.2–1.0 GPa and Tpeak: 330–260 °C; D2: 0.4–0.7 GPa and 230–170 °C) during its underthrusting, accretion into the Alpine wedge and subsequent exhumation up to the shallower crustal levels.
15
Sanità, Edoardo, Maria Di Rosa, Jean-Marc Lardeaux, Michele Marroni, and Luca Pandolfi. "The Moglio-Testico Unit (Ligurian Alps, Italy) as Subducted Metamorphic Oceanic Fragment: Stratigraphic, Structural and Metamorphic Constraints." Minerals 12, no. 11 (October 24, 2022): 1343. http://dx.doi.org/10.3390/min12111343.
Повний текст джерелаАнотація:
Along the Western Alps, the oceanic units showing blueschists to eclogite facies metamorphic imprint are classically regarded as fragments of the Ligurian-Piedmont Ocean. These units recorded a strongly deformation related to their subduction, accretion and subsequent exhumation into the Alpine wedge, developed during the convergence between the Europa and Adria Plates. However, some of these units, for example the Moglio-Testico Unit, are less pervasively deformed, providing evidence of their sedimentary evolution as well as the tectono-metamorphic history. Therefore, we present original stratigraphic, structural and thermo-barometric data to characterize the tectono-metamorphic history and the sedimentary evolution of the Moglio-Testico Unit, performing different techniques including fieldwork, structural analysis and chlorite-phengite multiequilibrium thermobarometry. Our dataset indicates that the Moglio-Testico Unit can be considered as a fragment of oceanic cover whose sedimentary evolution reflects that of a portion of oceanic lithosphere approaching to the subduction zone. Structural analysis combined with the thermobarometry indicate that this unit recorded a polyphase deformation history developed under High Pressure-Low Temperature metamorphic conditions (D1: 1.2–1.0 GPa and Tpeak: 330–260 °C; D2: 0.4–0.7 GPa and 230–170 °C) during its underthrusting, accretion into the Alpine wedge and subsequent exhumation up to the shallower crustal levels.
16
Sanità, Edoardo, Maria Di Rosa, Jean-Marc Lardeaux, Michele Marroni, and Luca Pandolfi. "The Moglio-Testico Unit (Ligurian Alps, Italy) as Subducted Metamorphic Oceanic Fragment: Stratigraphic, Structural and Metamorphic Constraints." Minerals 12, no. 11 (October 24, 2022): 1343. http://dx.doi.org/10.3390/min12111343.
Повний текст джерелаАнотація:
Along the Western Alps, the oceanic units showing blueschists to eclogite facies metamorphic imprint are classically regarded as fragments of the Ligurian-Piedmont Ocean. These units recorded a strongly deformation related to their subduction, accretion and subsequent exhumation into the Alpine wedge, developed during the convergence between the Europa and Adria Plates. However, some of these units, for example the Moglio-Testico Unit, are less pervasively deformed, providing evidence of their sedimentary evolution as well as the tectono-metamorphic history. Therefore, we present original stratigraphic, structural and thermo-barometric data to characterize the tectono-metamorphic history and the sedimentary evolution of the Moglio-Testico Unit, performing different techniques including fieldwork, structural analysis and chlorite-phengite multiequilibrium thermobarometry. Our dataset indicates that the Moglio-Testico Unit can be considered as a fragment of oceanic cover whose sedimentary evolution reflects that of a portion of oceanic lithosphere approaching to the subduction zone. Structural analysis combined with the thermobarometry indicate that this unit recorded a polyphase deformation history developed under High Pressure-Low Temperature metamorphic conditions (D1: 1.2–1.0 GPa and Tpeak: 330–260 °C; D2: 0.4–0.7 GPa and 230–170 °C) during its underthrusting, accretion into the Alpine wedge and subsequent exhumation up to the shallower crustal levels.
17
Sanità, Edoardo, Maria Di Rosa, Jean-Marc Lardeaux, Michele Marroni, and Luca Pandolfi. "The Moglio-Testico Unit (Ligurian Alps, Italy) as Subducted Metamorphic Oceanic Fragment: Stratigraphic, Structural and Metamorphic Constraints." Minerals 12, no. 11 (October 24, 2022): 1343. http://dx.doi.org/10.3390/min12111343.
Повний текст джерелаАнотація:
Along the Western Alps, the oceanic units showing blueschists to eclogite facies metamorphic imprint are classically regarded as fragments of the Ligurian-Piedmont Ocean. These units recorded a strongly deformation related to their subduction, accretion and subsequent exhumation into the Alpine wedge, developed during the convergence between the Europa and Adria Plates. However, some of these units, for example the Moglio-Testico Unit, are less pervasively deformed, providing evidence of their sedimentary evolution as well as the tectono-metamorphic history. Therefore, we present original stratigraphic, structural and thermo-barometric data to characterize the tectono-metamorphic history and the sedimentary evolution of the Moglio-Testico Unit, performing different techniques including fieldwork, structural analysis and chlorite-phengite multiequilibrium thermobarometry. Our dataset indicates that the Moglio-Testico Unit can be considered as a fragment of oceanic cover whose sedimentary evolution reflects that of a portion of oceanic lithosphere approaching to the subduction zone. Structural analysis combined with the thermobarometry indicate that this unit recorded a polyphase deformation history developed under High Pressure-Low Temperature metamorphic conditions (D1: 1.2–1.0 GPa and Tpeak: 330–260 °C; D2: 0.4–0.7 GPa and 230–170 °C) during its underthrusting, accretion into the Alpine wedge and subsequent exhumation up to the shallower crustal levels.
18
Sanità, Edoardo, Maria Di Rosa, Jean-Marc Lardeaux, Michele Marroni, and Luca Pandolfi. "The Moglio-Testico Unit (Ligurian Alps, Italy) as Subducted Metamorphic Oceanic Fragment: Stratigraphic, Structural and Metamorphic Constraints." Minerals 12, no. 11 (October 24, 2022): 1343. http://dx.doi.org/10.3390/min12111343.
Повний текст джерелаАнотація:
Along the Western Alps, the oceanic units showing blueschists to eclogite facies metamorphic imprint are classically regarded as fragments of the Ligurian-Piedmont Ocean. These units recorded a strongly deformation related to their subduction, accretion and subsequent exhumation into the Alpine wedge, developed during the convergence between the Europa and Adria Plates. However, some of these units, for example the Moglio-Testico Unit, are less pervasively deformed, providing evidence of their sedimentary evolution as well as the tectono-metamorphic history. Therefore, we present original stratigraphic, structural and thermo-barometric data to characterize the tectono-metamorphic history and the sedimentary evolution of the Moglio-Testico Unit, performing different techniques including fieldwork, structural analysis and chlorite-phengite multiequilibrium thermobarometry. Our dataset indicates that the Moglio-Testico Unit can be considered as a fragment of oceanic cover whose sedimentary evolution reflects that of a portion of oceanic lithosphere approaching to the subduction zone. Structural analysis combined with the thermobarometry indicate that this unit recorded a polyphase deformation history developed under High Pressure-Low Temperature metamorphic conditions (D1: 1.2–1.0 GPa and Tpeak: 330–260 °C; D2: 0.4–0.7 GPa and 230–170 °C) during its underthrusting, accretion into the Alpine wedge and subsequent exhumation up to the shallower crustal levels.
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Sanità, Edoardo, Maria Di Rosa, Jean-Marc Lardeaux, Michele Marroni, and Luca Pandolfi. "The Moglio-Testico Unit (Ligurian Alps, Italy) as Subducted Metamorphic Oceanic Fragment: Stratigraphic, Structural and Metamorphic Constraints." Minerals 12, no. 11 (October 24, 2022): 1343. http://dx.doi.org/10.3390/min12111343.
Повний текст джерелаАнотація:
Along the Western Alps, the oceanic units showing blueschists to eclogite facies metamorphic imprint are classically regarded as fragments of the Ligurian-Piedmont Ocean. These units recorded a strongly deformation related to their subduction, accretion and subsequent exhumation into the Alpine wedge, developed during the convergence between the Europa and Adria Plates. However, some of these units, for example the Moglio-Testico Unit, are less pervasively deformed, providing evidence of their sedimentary evolution as well as the tectono-metamorphic history. Therefore, we present original stratigraphic, structural and thermo-barometric data to characterize the tectono-metamorphic history and the sedimentary evolution of the Moglio-Testico Unit, performing different techniques including fieldwork, structural analysis and chlorite-phengite multiequilibrium thermobarometry. Our dataset indicates that the Moglio-Testico Unit can be considered as a fragment of oceanic cover whose sedimentary evolution reflects that of a portion of oceanic lithosphere approaching to the subduction zone. Structural analysis combined with the thermobarometry indicate that this unit recorded a polyphase deformation history developed under High Pressure-Low Temperature metamorphic conditions (D1: 1.2–1.0 GPa and Tpeak: 330–260 °C; D2: 0.4–0.7 GPa and 230–170 °C) during its underthrusting, accretion into the Alpine wedge and subsequent exhumation up to the shallower crustal levels.
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Zozulya, D. R., F. P. Mitrofanov, P. Peltonen, H. O’Brien, M. Lehtonen, and V. Yu Kalachev. "Lithosphere mantle structure and diamond prospects in the Kola region: Chemical and thermobarometric analyses of kimberlite pyrope." Doklady Earth Sciences 427, no. 1 (July 2009): 746–50. http://dx.doi.org/10.1134/s1028334x09050092.
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Cosca, Michael A., Eric J. Essene, and Johns R. Bowman. "Complete chemical analyses of metamorphic hornblendes: implications for normalizations, calculated H2O activities, and thermobarometry." Contributions to Mineralogy and Petrology 108, no. 4 (October 1991): 472–84. http://dx.doi.org/10.1007/bf00303451.
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Mäder, Urs K., John A. Percival, and Robert G. Berman. "Thermobarometry of garnet–clinopyroxene–hornblende granulites from the Kapuskasing structural zone." Canadian Journal of Earth Sciences 31, no. 7 (July 1, 1994): 1134–45. http://dx.doi.org/10.1139/e94-101.
Повний текст джерелаАнотація:
Amphibole mixing properties and standard state properties for the end members tremolite, tschermakite, pargasite, ferrotremolite, ferrotschermakite, and ferropargasite have been refined through analysis of relevant phase equilibrium experiments, coexisting cummingtonite–hornblende pairs, and natural mineral parageneses. When merged with the mineral properties given by R.G. Berman, these amphibole properties allow the calculation of numerous equilibria suitable for thermobarometry in a wide range of bulk compositions at amphibolite to granulite metamorphic grades. The method was applied to texturally equilibrated garnet–pyroxene–hornblende gneisses and compared both to results based on anhydrous assemblages and to those for garnet–biotite gneisses from the Kapuskasing structural zone. Thermometer resetting is apparent only in garnet–biotite gneisses, whereas touching garnet–pyroxene pairs in mafic gneiss show little evidence of retrograde Fe–Mg exchange. Computed metamorphic temperatures (garnet–clinopyroxene) for the 50 km wide garnet–clinopyroxene zone, in the range 750–790 °C, show no systematic variation with distance from the Ivanhoe Lake fault zone. Paleopressures computed from hydrous and anhydrous equilibria consistently indicate a north-trending high of 10–11 kbar (1 kbar = 100 MPa), decreasing to 3.3 kbar 60 km to the west in the Wawa gneiss domain. The pressure results define west-dipping Archean isobars with gentle (< 5°) attitudes through the Wawa gneiss domain and steeper dips (~ 17°) east of the amphibolite–granulite transition. The preserved record of high temperatures and pressures and moderate water activities (0.2–0.45) through a prolonged period of lower crustal residence and slow cooling indicated by zircon and titanite geochronology is difficult to reconcile at present.
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Llovet, Xavier, and Gumer Galan. "Correction of secondary X-ray fluorescence near grain boundaries in electron microprobe analysis: Application to thermobarometry of spinel lherzolites." American Mineralogist 88, no. 1 (January 2003): 121–30. http://dx.doi.org/10.2138/am-2003-0115.
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Lamont, Thomas N., Michael P. Searle, David J. Waters, Nick M. W. Roberts, Richard M. Palin, Andrew Smye, Brendan Dyck, Phillip Gopon, Owen M. Weller, and Marc R. St-Onge. "Compressional origin of the Naxos metamorphic core complex, Greece: Structure, petrography, and thermobarometry." GSA Bulletin 132, no. 1-2 (June 4, 2019): 149–97. http://dx.doi.org/10.1130/b31978.1.
Повний текст джерелаАнотація:
Abstract The island of Naxos, Greece, has been previously considered to represent a Cordilleran-style metamorphic core complex that formed during Cenozoic extension of the Aegean Sea. Although lithospheric extension has undoubtedly occurred in the region since 10 Ma, the geodynamic history of older, regional-scale, kyanite- and sillimanite-grade metamorphic rocks exposed within the core of the Naxos dome is controversial. Specifically, little is known about the pre-extensional prograde evolution and the relative timing of peak metamorphism in relation to the onset of extension. In this work, new structural mapping is presented and integrated with petrographic analyses and phase equilibrium modeling of blueschists, kyanite gneisses, and anatectic sillimanite migmatites. The kyanite-sillimanite–grade rocks within the core complex record a complex history of burial and compression and did not form under crustal extension. Deformation and metamorphism were diachronous and advanced down the structural section, resulting in the juxtaposition of several distinct tectono-stratigraphic nappes that experienced contrasting metamorphic histories. The Cycladic Blueschists attained ∼14.5 kbar and 470 °C during attempted northeast-directed subduction of the continental margin. These were subsequently thrusted onto the more proximal continental margin, resulting in crustal thickening and regional metamorphism associated with kyanite-grade conditions of ∼10 kbar and 600–670 °C. With continued shortening, the deepest structural levels underwent kyanite-grade hydrous melting at ∼8–10 kbar and 680–750 °C, followed by isothermal decompression through the muscovite dehydration melting reaction to sillimanite-grade conditions of ∼5–6 kbar and 730 °C. This decompression process was associated with top-to-the-NNE shearing along passive-roof faults that formed because of SW-directed extrusion. These shear zones predated crustal extension, because they are folded around the migmatite dome and are crosscut by leucogranites and low-angle normal faults. The migmatite dome formed at lower-pressure conditions under horizontal constriction that caused vertical boudinage and upright isoclinal folds. The switch from compression to extension occurred immediately following doming and was associated with NNE-SSW horizontal boudinage and top-to-the-NNE brittle-ductile normal faults that truncate the internal shear zones and earlier collisional features. The Naxos metamorphic core complex is interpreted to have formed via crustal thickening, regional metamorphism, and partial melting in a compressional setting, here termed the Aegean orogeny, and it was exhumed from the midcrust due to the switch from compression to extension at ca. 15 Ma.
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Benmammar, Anissa, Julien Berger, Antoine Triantafyllou, Stéphanie Duchene, Abderrahmane Bendaoud, Jean-Marc Baele, Olivier Bruguier, and Hervé Diot. "Pressure-temperature conditions and significance of Upper Devonian eclogite and amphibolite facies metamorphisms in southern French Massif central." BSGF - Earth Sciences Bulletin 191 (2020): 28. http://dx.doi.org/10.1051/bsgf/2020033.
Повний текст джерелаАнотація:
The southwestern French Massif central in western Rouergue displays an inverted metamorphic sequence with eclogite and amphibolite facies units forming the top of the nappe stack. They are often grouped into the leptyno-amphibolite complex included, in this area, at the base of the Upper Gneiss Unit. We sampled garnet micaschists and amphibolites to investigate their metamorphic history with isochemical phase diagrams, thermobarometry and U-Pb zircon dating. Our results demonstrate that two different tectono-metamorphic units can be distinguished. The Najac unit consists of biotite-poor phengite-garnet micaschists, a basic-ultrabasic intrusion containing retrogressed eclogites and phengite orthogneisses. Pressure and temperature estimates on micaschists with syn-kinematic garnets yield a prograde with garnet growth starting at 380 °C/6–7 kbar, peak pressure at 16 kbar for 570 °C, followed by retrogression in the greenschist facies. The age of high pressure metamorphism has been constrained in a recent publication between ca. 383 and 369 Ma. The Laguépie unit comprises garnet-free and garnet-bearing amphibolites with isolated lenses, veins or dykes of leucotonalitic gneiss. Thermobarometry and phase diagram calculation on a garnet amphibolite yield suprasolidus peak P-T conditions at 710 °C, 10 kbar followed by retrogression and deformation under greenschist and amphibolite facies conditions. New U-Pb analyses obtained on igneous zircon rims from a leucotonalitic gneiss yield an age of 363 ± 3 Ma, interpreted as the timing of zircon crystallization after incipient partial melting of the host amphibolite. The eclogitic Najac unit records the subduction of a continental margin during Upper Devonian. It is tentatively correlated to a Middle Allochthon, sandwiched between the Lower Gneiss Unit and the Upper Gneiss Unit. Such an intermediate unit is still poorly defined in the French Massif central but it can be a lateral equivalent of the Groix blueschists in the south Armorican massif. The Uppermost Devonian, amphibolite facies Laguépie unit correlates in terms of P-T-t evolution to the Upper Gneiss Unit in the Western French Massif central. This Late Devonian metamorphism is contemporaneous with active margin magmatism and confirms that the French Massif central belonged to the continental upper plate of an ocean-continent subduction system just before the stacking of Mississippian nappes.
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Kidder, Steven B., Virginia G. Toy, David J. Prior, Timothy A. Little, Ashfaq Khan, and Colin MacRae. "Constraints on Alpine Fault (New Zealand) mylonitization temperatures and the geothermal gradient from Ti-in-quartz thermobarometry." Solid Earth 9, no. 5 (September 25, 2018): 1123–39. http://dx.doi.org/10.5194/se-9-1123-2018.
Повний текст джерелаАнотація:
Abstract. We constrain the thermal state of the central Alpine Fault using approximately 750 Ti-in-quartz secondary ion mass spectrometer (SIMS) analyses from a suite of variably deformed mylonites. Ti-in-quartz concentrations span more than 1 order of magnitude from 0.24 to ∼ 5 ppm, suggesting recrystallization of quartz over a 300 °C range in temperature. Most Ti-in-quartz concentrations in mylonites, protomylonites, and the Alpine Schist protolith are between 2 and 4 ppm and do not vary as a function of grain size or bulk rock composition. Analyses of 30 large, inferred-remnant quartz grains ( > 250 µm) as well as late, crosscutting, chlorite-bearing quartz veins also reveal restricted Ti concentrations of 2–4 ppm. These results indicate that the vast majority of Alpine Fault mylonitization occurred within a restricted zone of pressure–temperature conditions where 2–4 ppm Ti-in-quartz concentrations are stable. This constrains the deep geothermal gradient from the Moho to about 8 km to a slope of 5 °C km−1. In contrast, the small grains (10–40 µm) in ultramylonites have lower Ti concentrations of 1–2 ppm, indicating a deviation from the deeper pressure–temperature trajectory during the latest phase of ductile deformation. These constraints suggest an abrupt, order of magnitude change in the geothermal gradient to an average of about 60 °C km−1 at depths shallower than about 8 km, i.e., within the seismogenic zone. Anomalously, the lowest-Ti quartz (0.24–0.7 ppm) occurs away from the fault in protomylonites, suggesting that the outer fault zone experienced minor plastic deformation late in the exhumation history when more fault-proximal parts of the fault were deforming exclusively by brittle processes.
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Ray, Srijita, Ashish Kumar Tiwari, and Tapabrato Sarkar. "Ultrahigh‐temperature mafic granulites from the Madurai Block, southern India: Constraints from conventional thermobarometry, pseudosection analysis, and rare earth element‐based thermometry." Geological Journal 56, no. 7 (March 28, 2021): 3720–44. http://dx.doi.org/10.1002/gj.4124.
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MANZOTTI, PAOLA, and MICHELE ZUCALI. "The pre-Alpine tectonic history of the Austroalpine continental basement in the Valpelline unit (Western Italian Alps)." Geological Magazine 150, no. 1 (August 20, 2012): 153–72. http://dx.doi.org/10.1017/s0016756812000441.
Повний текст джерелаАнотація:
AbstractThe Valpelline unit is a large slice of continental crust constituting the Austroalpine Dent Blanche nappe (NW Italy). The pre-Alpine evolution of this unit holds important clues about the Palaeozoic crustal structure at the northern margin of the Adria continent, about the history of rifting in the Alpine region, and thus about the thermomechanical conditions that preceded the Alpine convergent evolution. Several stages of the deformation history and of partial re-equilibration were identified, combining meso- and micro-structural analyses with thermobarometry. Reconstructed pre-Alpine P–T–t–d paths demonstrate that the Valpelline unit experienced an early stage at pressures between 4.5 and 6.5 kbar followed by migmatite formation. A subsequent stage reached amphibolite to granulite facies conditions. This stage was associated with the development of the most penetrative fabrics affecting all of the Valpelline lithotypes. The pre-Alpine evolution ended with a weak deformation associated with a local mineral-chemical re-equilibration under greenschist facies conditions at ≈ 4 kbar and T < 450°C. A Permo-Mesozoic lithospheric extension is thought to be responsible for asthenosphere upwelling, thereby causing high temperature metamorphism at medium pressure and widespread partial melting, which led to upper crustal magmatic activity.
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Bertauts, Maxime, Emilie Janots, Magali Rossi, Isabelle Duhamel-Achin, Marie-Christine Boiron, Laura Airaghi, Pierre Lanari, Philippe Lach, Chantal Peiffert, and Valérie Magnin. "A New Alpine Metallogenic Model for the Pb-Ag Orogenic Deposits of Macôt-la Plagne and Peisey-Nancroix (Western Alps, France)." Geosciences 12, no. 9 (August 31, 2022): 331. http://dx.doi.org/10.3390/geosciences12090331.
Повний текст джерелаАнотація:
Understanding mass transfer associated with fluids circultion and deformation in the Alpine orogeny is often complex due to common multistage crystallization. For example, in two emblematic and historic Pb-Ag deposits of the French Alps, Macôt-la Plagne (MP) and Peisey-Nancroix (PN), a sedimentary or orogenic origin is still debated. To discriminate between the metallogenic models of the two deposits, an integrative methodology combining field, microstructural, mineralogical, thermobarometrical, and geochronological data was here applied for establishing detailed Pressure–Temperature–Time–Deformation (P-T-t-d) mineralization conditions. Both deposits are located in Permo-Triassic quartzite of the External Briançonnais domain along the Internal Briançonnais Front (Internal Western Alps). The ore mainly occurs as veins and disseminated textures containing galena, pyrite, and variable content of tetrahedrite–tennantite and chalcopyrite. Quartz porphyroclasts and sulfide microstructures indicate a dynamic recrystallization of the quartzite during the main fluid mineralization episode. Chlorites and K-white micas (phengite) chemical analysis and thermodynamic modeling from compositional maps indicate an onset of the mineralization at 280 °C, with a main precipitation stage at 315 ± 35 °C and 6.25 ± 0.75 kbar. In situ U-Pb dating on monazite, cogenetic with sulfides, gives ages around 35 Ma for both deposits. The integrative dataset converges for a cogenetic MP-PN Alpine Pb-Ag mineralization during deformation in relation to the thrusting of the “Nappe des Gypses” and the Internal Briançonnais at the metamorphic peak.
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Tohver, E., D. K. Holm, B. A. van der Pluijm, E. J. Essene, and F. W. Cambray. "Late Paleoproterozoic (geon 18 and 17) reactivation of the Neoarchean Great Lakes Tectonic Zone, northern Michigan, USA: Evidence from kinematic analysis, thermobarometry and 40Ar/39Ar geochronology." Precambrian Research 157, no. 1-4 (August 1, 2007): 144–68. http://dx.doi.org/10.1016/j.precamres.2007.02.014.
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Baldwin, Suzanne L., Jan Schönig, Joseph P. Gonzalez, Hugh Davies, and Hilmar von Eynatten. "Garnet sand reveals rock recycling processes in the youngest exhumed high- and ultrahigh-pressure terrane on Earth." Proceedings of the National Academy of Sciences 118, no. 3 (January 11, 2021): e2017231118. http://dx.doi.org/10.1073/pnas.2017231118.
Повний текст джерелаАнотація:
Rock recycling within the forearcs of subduction zones involves subduction of sediments and hydrated lithosphere into the upper mantle, exhumation of rocks to the surface, and erosion to form new sediment. The compositions of, and inclusions within detrital minerals revealed by electron microprobe analysis and Raman spectroscopy preserve petrogenetic clues that can be related to transit through the rock cycle. We report the discovery of the ultrahigh-pressure (UHP) indicator mineral coesite as inclusions in detrital garnet from a modern placer deposit in the actively exhuming Late Miocene–Recent high- and ultrahigh-pressure ((U)HP) metamorphic terrane of eastern Papua New Guinea. Garnet compositions indicate the coesite-bearing detrital garnets are sourced from felsic protoliths. Carbonate, graphite, and CO2 inclusions also provide observational constraints for geochemical cycling of carbon and volatiles during subduction. Additional discoveries include polyphase inclusions of metastable polymorphs of SiO2 (cristobalite) and K-feldspar (kokchetavite) that we interpret as rapidly cooled former melt inclusions. Application of elastic thermobarometry on coexisting quartz and zircon inclusions in six detrital garnets indicates elastic equilibration during exhumation at granulite and amphibolite facies conditions. The garnet placer deposit preserves a record of the complete rock cycle, operative on <10-My geologic timescales, including subduction of sedimentary protoliths to UHP conditions, rapid exhumation, surface uplift, and erosion. Detrital garnet geochemistry and inclusion suites from both modern sediments and stratigraphic sections can be used to decipher the petrologic evolution of plate boundary zones and reveal recycling processes throughout Earth’s history.
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Nevitt, Johanna M., Jessica M. Warren, Steven Kidder, and David D. Pollard. "Comparison of thermal modeling, microstructural analysis, and Ti-in-quartz thermobarometry to constrain the thermal history of a cooling pluton during deformation in the Mount Abbot Quadrangle, CA." Geochemistry, Geophysics, Geosystems 18, no. 3 (March 2017): 1270–97. http://dx.doi.org/10.1002/2016gc006655.
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Cooper, Frances J., John P. Platt, and Whitney M. Behr. "Rheological transitions in the middle crust: insights from Cordilleran metamorphic core complexes." Solid Earth 8, no. 1 (February 21, 2017): 199–215. http://dx.doi.org/10.5194/se-8-199-2017.
Повний текст джерелаАнотація:
Abstract. High-strain mylonitic rocks in Cordilleran metamorphic core complexes reflect ductile deformation in the middle crust, but in many examples it is unclear how these mylonites relate to the brittle detachments that overlie them. Field observations, microstructural analyses, and thermobarometric data from the footwalls of three metamorphic core complexes in the Basin and Range Province, USA (the Whipple Mountains, California; the northern Snake Range, Nevada; and Ruby Mountains–East Humboldt Range, Nevada), suggest the presence of two distinct rheological transitions in the middle crust: (1) the brittle–ductile transition (BDT), which depends on thermal gradient and tectonic regime, and marks the switch from discrete brittle faulting and cataclasis to continuous, but still localized, ductile shear, and (2) the localized–distributed transition, or LDT, a deeper, dominantly temperature-dependent transition, which marks the switch from localized ductile shear to distributed ductile flow. In this model, brittle normal faults in the upper crust persist as ductile shear zones below the BDT in the middle crust, and sole into the subhorizontal LDT at greater depths.In metamorphic core complexes, the presence of these two distinct rheological transitions results in the development of two zones of ductile deformation: a relatively narrow zone of high-stress mylonite that is spatially and genetically related to the brittle detachment, underlain by a broader zone of high-strain, relatively low-stress rock that formed in the middle crust below the LDT, and in some cases before the detachment was initiated. The two zones show distinct microstructural assemblages, reflecting different conditions of temperature and stress during deformation, and contain superposed sequences of microstructures reflecting progressive exhumation, cooling, and strain localization. The LDT is not always exhumed, or it may be obscured by later deformation, but in the Whipple Mountains, it can be directly observed where high-strain mylonites captured from the middle crust depart from the brittle detachment along a mylonitic front.
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Ogilvie, Paula, and Roger L. Gibson. "Arrested development – a comparative analysis of multilayer corona textures in high-grade metamorphic rocks." Solid Earth 8, no. 1 (February 6, 2017): 93–135. http://dx.doi.org/10.5194/se-8-93-2017.
Повний текст джерелаАнотація:
Abstract. Coronas, including symplectites, provide vital clues to the presence of arrested reaction and preservation of partial equilibrium in metamorphic and igneous rocks. Compositional zonation across such coronas is common, indicating the persistence of chemical potential gradients and incomplete equilibration. Major controls on corona mineralogy include prevailing pressure (P), temperature (T) and water activity (aH2O) during formation, reaction duration (t) single-stage or sequential corona layer growth; reactant bulk compositions (X) and the extent of metasomatic exchange with the surrounding rock; relative diffusion rates for major components; and/or contemporaneous deformation and strain. High-variance local equilibria in a corona and disequilibrium across the corona as a whole preclude the application of conventional thermobarometry when determining P–T conditions of corona formation, and zonation in phase composition across a corona should not be interpreted as a record of discrete P–T conditions during successive layer growth along the P–T path. Rather, the local equilibria between mineral pairs in corona layers more likely reflect compositional partitioning of the corona domain during steady-state growth at constant P and T. Corona formation in pelitic and mafic rocks requires relatively dry, residual bulk rock compositions. Since most melt is lost along the high-T prograde to peak segment of the P–T path, only a small fraction of melt is generally retained in the residual post-peak assemblage. Reduced melt volumes with cooling limit length scales of diffusion to the extent that diffusion-controlled corona growth occurs. On the prograde path, the low melt (or melt-absent) volumes required for diffusion-controlled corona growth are only commonly realized in mafic igneous rocks, owing to their intrinsic anhydrous bulk composition, and in dry, residual pelitic compositions that have lost melt in an earlier metamorphic event. Experimental work characterizing rate-limiting reaction mechanisms and their petrogenetic signatures in increasingly complex, higher-variance systems has facilitated the refinement of chemical fractionation and partial equilibration diffusion models necessary to more fully understand corona development. Through the application of quantitative physical diffusion models of coronas coupled with phase equilibria modelling utilizing calculated chemical potential gradients, it is possible to model the evolution of a corona through P–T–X–t space by continuous, steady-state and/or sequential, episodic reaction mechanisms. Most coronas in granulites form through a combination of these endmember reaction mechanisms, each characterized by distinct textural and chemical potential signatures with very different petrogenetic implications. An understanding of the inherent petrogenetic limitations of a reaction mechanism model is critical if an appropriate interpretation of P–T evolution is to be inferred from a corona. Since corona modelling employing calculated chemical potential gradients assumes nothing about the sequence in which the layers form and is directly constrained by phase compositional variation within a layer, it allows far more nuanced and robust understanding of corona evolution and its implications for the path of a rock in P–T–X space.
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Rusin, A. I., A. A. Zvorygina, and P. M. Valizer. "Lawsonite eclogites and metasomatites of the Utarbaev Association of the Maksyutov complex." LITHOSPHERE (Russia) 21, no. 6 (December 29, 2021): 867–83. http://dx.doi.org/10.24930/1681-9004-2021-21-6-867-883.
Повний текст джерелаАнотація:
Research subject. This article presents mineralogical, petrological and geochemical studies of lawsonite eclogites and metasomatites of the Utarbayev Аssociation of the Maksyutov complex. The Utarbayev Association forms an independent unit in the Maksyutovsky complex accretion structure. This Association features a variety of lawsonite-bearing metasomatites that form zonal halos in the frame of block-like diopside-grossular bodies included in the antigorite-serpentinite melange. The Utarbayev Association differs from typical lawsonite-blue shale complexes of collisional oro genes by the absence of mineral parageneses of lawsonite-bearing rocks of blue amphibolites.Methods. A microprobe analysis of the mineral composition was performed using a Cameca SX-100 microanalyzer. The content of petrogenic, rare and rare-earth elements was determined by X-ray spectroscopy (CPM-18) and mass spectroscopy (ICP-MS, ELAN-90). Results. An indicator mine ral paragenesis (Grt + Omp + Lws + Di) ± (Coe-Qz + Ttn) that characterizes lawsonite eclogite was found. Omphacite (Jd38–44) and unchanged lawsonite (Н2O-OH – 11.8%, Ca/Al = 0.48–0.51 и Fe/Al = 0.01 0.02%) are represented as inclusions in grossular-almandine garnet (Alm39–46Grs41–51), coesite – as microinclusions in omphacite. Thermobarometry (Grt-Omp, Grt-Omp-Ph) showed the following formation conditions of lawsonite paragenesis: T = 495–622°C under P = 2.2–2.4 GPa. The age of crystallization of lawsonite eclogite was found to be Lower Paleozoic (471–444 Ma).Conclusions. The lawsonite eclogite of the Utarbayev Association is similar to the complexes of «cold» eclogites, which are formed under the conditions of a very low geothermal gradient and are rarely preserved when removed into the upper crust. The latest review published in the «Journal of Metamorphic Geology» (2014) mentions 19 sites, where lawsonite eclogites were discovered on the earth’s surface. Тhe HP-UHP lawsonitebearing Utarbayev Rock Association complements this list.
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Mahan, Kevin H., Michael L. Williams, and Julia A. Baldwin. "Contractional uplift of deep crustal rocks along the Legs Lake shear zone, western Churchill Province, Canadian Shield." Canadian Journal of Earth Sciences 40, no. 8 (August 1, 2003): 1085–110. http://dx.doi.org/10.1139/e03-039.
Повний текст джерелаАнотація:
The Legs Lake shear zone juxtaposes high-pressure (1.0+ GPa) granulite- and eclogite-facies rocks with low-pressure (~0.5 GPa) amphibolite- to granulite-facies rocks, and thus may represent an important crustal-scale, exhumation-related structure in the western Canadian Shield. Field mapping and structural and petrologic analysis document the deformation and metamorphic history of rocks within and adjacent to the shear zone. At least two important phases of deformation are recorded: (1) early oblique thrusting (D2) that placed high-grade rocks over lower grade rocks, and (2) more discrete and lower grade brittleductile normal faulting (D3) that may represent the later part of the exhumation history. The northwest-dipping shear zone consists of 58 km of mylonite in map view, which bounds the southeast margin of the East Athabasca mylonite triangle. High-pressure granulite-facies metamorphism (~750850 °C, 1.01.2 GPa) occurred in the East Athabasca mylonite triangle at ca. 1900 Ma, prior to D2 juxtaposition with the adjacent low-pressure Hearne domain. Thermobarometry from GrtCrdSilBtQtz metapelites in the Hearne domain suggests peak conditions reached 600700 °C and 0.450.5 GPa, which are interpreted to have occurred late during D2. Published and preliminary UPb isotope dilution - thermal ionization mass spectrometry (ID-TIMS) zircon geochronology and electron microprobe monazite geochronology suggest that deformation in the Legs Lake shear zone coincided with the ca. 18301810 Ma terminal collision in the Trans-Hudson orogeny. Extensional faulting during D3 most likely occurred after ca. 1780 Ma. A multi-stage process of exhumation involving both thrust and normal-sense shearing, may serve as a model for the exhumation of other regionally extensive deep-crustal exposures.
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Veikkolainen, Toni, Ilmo T. Kukkonen, and Timo Tiira. "Heat flow, seismic cut-off depth and thermal modeling of the Fennoscandian Shield." Geophysical Journal International 211, no. 3 (September 7, 2017): 1414–27. http://dx.doi.org/10.1093/gji/ggx373.
Повний текст джерелаАнотація:
Summary Being far from plate boundaries but covered with seismograph networks, the Fennoscandian Shield features an ideal test laboratory for studies of intraplate seismicity. For this purpose, this study applies 4190 earthquake events from years 2000–2015 with magnitudes ranging from 0.10 to 5.22 in Finnish and Swedish national catalogues. In addition, 223 heat flow determinations from both countries and their immediate vicinity were used to analyse the potential correlation of earthquake focal depths and the spatially interpolated heat flow field. Separate subset analyses were performed for five areas of notable seismic activity: the southern Gulf of Bothnia coast of Sweden (area 1), the northern Gulf of Bothnia coast of Sweden (area 2), the Swedish Norrbotten and western Finnish Lapland (area 3), the Kuusamo region of Finland (area 4) and the southernmost Sweden (area 5). In total, our subsets incorporated 3619 earthquake events. No obvious relation of heat flow and focal depth exists, implying that variations of heat flow are primarily caused by shallow lying heat producing units instead of deeper sources. This allows for construction of generic geotherms for the range of representative palaeoclimatically corrected (steady-state) surface heat flow values (40–60 mW m−2). The 1-D geotherms constructed for a three-layer crust and lithospheric upper mantle are based on mantle heat flow constrained with the aid of mantle xenolith thermobarometry (9–15 mW m−2), upper crustal heat production values (3.3–1.1 μWm−3) and the brittle-ductile transition temperature (350 °C) assigned to the cut-off depth of seismicity (28 ± 4 km). For the middle and lower crust heat production values of 0.6 and 0.2 μWm−3 were assigned, respectively. The models suggest a Moho temperature range of 460–500 °C.
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Zaccarini, Federica, Giorgio Garuti, Evgeny Pushkarev, and Oskar Thalhammer. "Origin of Platinum Group Minerals (PGM) Inclusions in Chromite Deposits of the Urals." Minerals 8, no. 9 (August 31, 2018): 379. http://dx.doi.org/10.3390/min8090379.
Повний текст джерелаАнотація:
This paper reviews a database of about 1500 published and 1000 unpublished microprobe analyses of platinum-group minerals (PGM) from chromite deposits associated with ophiolites and Alaskan-type complexes of the Urals. Composition, texture, and paragenesis of unaltered PGM enclosed in fresh chromitite of the ophiolites indicate that the PGM formed by a sequence of crystallization events before, during, and probably after primary chromite precipitation. The most important controlling factors are sulfur fugacity and temperature. Laurite and Os–Ir–Ru alloys are pristine liquidus phases crystallized at high temperature and low sulfur fugacity: they were trapped in the chromite as solid particles. Oxygen thermobarometry supports that several chromitites underwent compositional equilibration down to 700 °C involving increase of the Fe3/Fe2 ratio. These chromitites contain a great number of PGM including—besides laurite and alloys—erlichmanite, Ir–Ni–sulfides, and Ir–Ru sulfarsenides formed by increasing sulfur fugacity. Correlation with chromite composition suggests that the latest stage of PGM crystallization might have occurred in the subsolidus. If platinum-group elements (PGE) were still present in solid chromite as dispersed atomic clusters, they could easily convert into discrete PGM inclusions splitting off the chromite during its re-crystallization under slow cooling-rate. The presence of primary PGM inclusions in fresh chromitite of the Alaskan-type complexes is restricted to ore bodies crystallized in equilibrium with the host dunite. The predominance of Pt–Fe alloys over sulfides is a strong indication for low sulfur fugacity, thereby early crystallization of laurite is observed only in one deposit. In most cases, Pt–Fe alloys crystallized and were trapped in chromite between 1300 and 1050 °C. On-cooling equilibration to ~900 °C may produce lamellar unmixing of different Pt–Fe phases and osmium. Precipitation of the Pt–Fe alloys locally is followed by an increase of sulfur fugacity leading to crystallize erlichmanite and Ir–Rh–Ni–Cu sulfides, occurring as epitaxic overgrowth on the alloy. There is evidence that the system moved quickly into the stabilization field of Pt–Fe alloys by an increase of the oxygen fugacity marked by an increase of the magnetite component in the chromite. In summary, the data support that most of the primary PGM inclusions in the chromitites of the Urals formed in situ, as part of the chromite precipitation event. However, in certain ophiolitic chromitites undergoing annealing conditions, there is evidence for subsolidus crystallization of discrete PGM from PGE atomic-clusters occurring in the chromite. This mechanism of formation does not require a true solid solution of PGE in the chromite structure.
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Wolfe, Oliver M., and Frank S. Spear. "Regional Quartz Inclusion Barometry and Comparison with Conventional Thermobarometry and Intersecting Isopleths from the Connecticut Valley Trough, Vermont and Massachusetts, USA." Journal of Petrology 61, no. 8 (July 17, 2020). http://dx.doi.org/10.1093/petrology/egaa076.
Повний текст джерелаАнотація:
Abstract A comparative analysis of Raman shifts of quartz inclusions in garnet was made along two traverses across the Connecticut Valley Trough (CVT) in western New England, USA, to examine the regional trends of quartz inclusion in garnet (QuiG) Raman barometry pressure results and to compare this method with conventional thermobarometry and the method of intersecting garnet core isopleths. Overall, Raman shifts of quartz inclusions ranged from 1·2 to 3·5 cm–1 over all field areas and displayed a south to north decrease, matching the overall decrease in mapped metamorphic grade. Raman shifts of quartz inclusions typically did not show systematic variation with respect to their radial position within a garnet crystal, and indicate that garnet probably grew at nearly isothermal and isobaric pressure–temperature (P–T) conditions. The P–T conditions inferred from conventional thermobarometry were in the range of ∼500–575 °C and ∼7·4–10·3 kbar over the sample suite and are in good agreement with previous published thermobarometry throughout the CVT. These P–T results are broadly consistent with QuiG barometry and also suggest that garnet grew isothermally and isobarically at near peak P–T conditions. However, P–T conditions and P–T paths inferred using either garnet core thermobarometry or garnet core intersecting isopleths yield results that are internally inconsistent and generally disagree with the pressure results from QuiG barometry. Garnet core isopleth intersections consistently plotted between the nominal garnet-in curve on mineral assemblage diagrams and the P–T conditions constrained by QuiG isomekes for the majority of the sample suite. Additionally, most samples’ P–T results from QuiG barometry and rim thermobarometry show marked disagreement from those derived from garnet core thermobarometry, compared with the minority that showed agreement within uncertainty. Pressures calculated from QuiG barometry ranged from 8·5 to 9·5 kbar along the traverses in western Massachusetts (MA) and central Vermont (VT) and from 6·5 to 7·5 kbar in northern VT indicating an increase in peak burial of 3–6 km from north to south. Along the western end of the central VT traverse, there are differences in measured Raman shifts and inferred peak pressures of up to 1 kbar across the Richardson Memorial Contact (RMC), indicating a possible fault contact with minor post-peak metamorphic shortening of up to ∼3 km. In contrast, along an east–west traverse in the vicinity of the Goshen Dome, MA, there was little observed variation in Raman shifts across the contact. By contrast, QuiG barometry clearly indicates significant discontinuities in peak pressure east of the Strafford Dome in central VT. This supports the interpretation that post-peak metamorphic shortening was necessary to juxtapose upper staurolite–kyanite zone rocks next to lower garnet zone pelites. Overall, it is concluded that garnet core thermobarometry and garnet core isopleths may provide unreliable results for the P–T conditions of garnet nucleation and inferred P–T paths during garnet growth unless independently verified. The consistency of QuiG results with rim thermobarometry indicates that peak metamorphic conditions previously reported for the CVT using garnet rim thermobarometry are robust and that variation in QuiG barometry results is a valuable tool to analyze structural features within a metamorphic terrane.
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Wieser, Penny E., Adam J. R. Kent, Christy B. Till, John Donovan, David A. Neave, Dawnika L. Blatter, and Michael J. Krawczynski. "Barometers behaving badly: Assessing the influence of analytical and experimental uncertainty on clinopyroxene thermobarometry calculations at crustal conditions." Journal of Petrology, December 29, 2022. http://dx.doi.org/10.1093/petrology/egac126.
Повний текст джерелаАнотація:
Abstract The composition of clinopyroxene and Clinopyroxene-Liquid (Cpx-Liq) pairs are frequently used to calculate crystallization/equilibration pressures in igneous systems. While canonical uncertainties are often assigned to calculated pressures based on fits to calibration or test datasets, the sources of these uncertainties (and thus ways to reduce them) have not been rigorously assessed. We show that considerable uncertainties in calculated pressures arise from analytical error associated with Electron Probe Microanalyser (EPMA) measurements of Cpx. Specifically, low X-ray counts during analysis of elements with concentrations <1 wt% resulting from insufficient count times and/or low beam currents yield highly imprecise measurements (1σ errors of 10–40% for Na2O). Low analytical precision propagates into the calculation of pressure-sensitive mineral components such as jadeite. Using Monte Carlo approaches, we demonstrate that elemental variation resulting from analytical precision alone generates pressures spanning ~4 kbar (~15 km) for a single Cpx and ~6 kbar for a single Cpx-Liq pair using popular barometry expressions. In addition, analytical uncertainties in mineral compositions produce highly correlated arrays between pressure and temperature that have been previously attributed to transcrustal magma storage. Before invoking such geological interpretations, the more mundane origin from analytical imprecision must be ruled out. Most importantly, low analytical precision does not just affect the application of barometers to natural systems; it has also affected characterization of Cpx in experimental products used to calibrate and test barometers. The impact of poor precision on each individual measurement is also often magnified by the small number of measurements made within experimental charges, meaning that low analytical precision and true variability in mineral compositions have not been sufficiently mediated by averaging multiple EPMA analyses. We compile the number of Cpx measurements performed in N=295 experiments used to calibrate existing barometers, and N=459 new experiments, finding ~40% of experiment charges were characterized by ≤5 individual Cpx analyses. Insufficient characterization of the true composition of experimental phases likely accounts for the fact that all Cpx-based barometers exhibit large errors (± 3 kbar) when tested using global experimental datasets. We suggest specific changes to analytical and experimental protocols, such as increased count times and/or higher beam currents when measuring low concentration elements in relatively beam resistant Cpx in experiments and natural samples. We also advocate for increasing the number of analyses per experimental charge, resolving interlaboratory analytical offsets and improving data reporting. Implementing these changes is essential to produce a more robust dataset to calibrate and test the next generation of more precise and accurate Cpx-based barometers. In turn, this will enable more rigorous investigation of magma storage geometries in a variety of tectonic settings (e.g., distinguishing true transcrustal storage vs. storage in discrete reservoirs).
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Yang, Yang, Yi-Can Liu, Yang Li, C. Groppo, and F. Rolfo. "Magmatism and related metamorphism as a response to mountain-root collapse of the Dabie orogen: Constraints from geochronology and petrogeochemistry of metadiorites." GSA Bulletin, November 16, 2021. http://dx.doi.org/10.1130/b36194.1.
Повний текст джерелаАнотація:
Post-collisional mountain-root collapse and subsequent massive partial melting occurred in the high-temperature (HT) ultrahigh-pressure (UHP) metamorphic terrane of the North Dabie complex zone (NDZ), central China. The NDZ was deeply subducted in the Triassic, producing widespread migmatites and various magmatic intrusions in the Cretaceous. Post-collisional metadiorites with distinctive large K-feldspar augen porphyroblasts, locally reported but rarely exposed in the NDZ, underwent a complex evolutional history. In this contribution, integrated studies including field investigation, petrographic observation and mineral analysis, zircon U-Pb geochronological and Hf isotopic analyses, and whole-rock elemental and Sr-Nd-Pb isotopic analyses of the metadiorites were carried out. Our results provide new constraints on the mountain-root collapse in the Dabie orogen. The metadiorites are enriched in large ion lithophile elements and light rare earth elements, whereas they are depleted in high field strength elements and heavy rare earth elements with significant Ba positive anomalies, a composition consistent with the lower continental crust. All the studied samples have moderately enriched initial 87Sr/86Sr ratios (0.707582−0.708099), low εNd(t) values (−15.3 to −20.4), and low initial Pb isotopic ratios (16.0978−16.8452, 15.3167−15.4544, and 37.1778−37.8397 for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb, respectively). However, they have highly negative εHf(t) values and Paleoproterozoic two-stage Hf model ages, which are only partially consistent with data from the associated UHP metamorphic rocks. Such features suggest the metadiorites resulted from a magma produced by mixing of Triassic UHP mafic lithologies and minor amounts of mantle-derived materials. Zircon morphological analysis and U-Pb sensitive high-resolution ion microprobe dating combined with conventional thermobarometry indicate that these upwelling melts crystallized at pressure-temperature (P-T) conditions of 5.4−5.7 kbar and 750−768 °C at ca. 130 Ma and subsequently suffered HT metamorphism at ca. 125 Ma. We conclude that the metadiorites’ precursors were derived from partial melting of the Triassic subducted Neoproterozoic mafic lower-crustal rocks, with addition of minor amounts of mantle-derived materials in the Early Cretaceous, in response to mountain-root collapse of the orogen. Based on petrographic textures and mineral compositions, it is moreover inferred that formation of the distinctive K-feldspar porphyroblasts is likely related to a two-stage process, i.e., crystallization derived from biotite breakdown after the formation of the metadiorite at T = 640−703 °C and P < 4.5 kbar and coarsening related to shear deformation.
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Tedonkenfack, Sylvin S. T., Jacek Puziewicz, Sonja Aulbach, Theodoros Ntaflos, Mary-Alix Kaczmarek, Magdalena Matusiak-Małek, Anna Kukuła, and Małgorzata Ziobro. "Lithospheric mantle refertilization by DMM-derived melts beneath the Cameroon Volcanic Line—a case study of the Befang xenolith suite (Oku Volcanic Group, Cameroon)." Contributions to Mineralogy and Petrology 176, no. 5 (April 24, 2021). http://dx.doi.org/10.1007/s00410-021-01796-3.
Повний текст джерелаАнотація:
AbstractThe origin and evolution of subcontinental lithospheric mantle (SCLM) are important issues of Earth’s chemical and physical evolution. Here, we report detailed textural and chemical analyses on a mantle xenolith suite from Befang (Oku Volcanic Group, Cameroon Volcanic Line), which represents a major tectono-magmatic structure of the African plate. The samples are sourced from spinel-facies mantle and are dominated by lherzolites. Their texture is cataclastic to porphyroclastic, and foliation defined by grain-size variation and alignment of spinel occurs in part of peridotites. Spinel is interstitial and has amoeboidal shape. Clinopyroxene REE patterns are similar to those of Depleted MORB Mantle (DMM) except LREEs, which vary from depleted to enriched. The A-type olivine fabric occurs in the subset of one harzburgite and 7 lherzolites studied by EBSD. Orthopyroxene shows deformation consistent with olivine. The fabric of LREE-enriched clinopyroxene is equivalent to those of orthopyroxene and olivine, whereas spinel and LREE-depleted clinopyroxene are oriented independently of host rock fabric. The textural, chemical and thermobarometric constraints indicate that the Befang mantle section was refertilised by MORB-like melt at pressures of 1.0–1.4 GPa and temperatures slightly above 1200–1275 °C. The olivine-orthopyroxene framework and LREE-enriched clinopyroxene preserve the protolith fabric. In contrast, the LREE-depleted clinopyroxene, showing discordant deformation relative to the olivine-orthopyroxene protolith framework, and amoeboidal spinel crystallized from the infiltrating melt. The major element and REEs composition of minerals forming the Befang peridotites indicate subsequent reequilibration at temperatures 930–1000 °C. This was followed by the formation of websterite veins in the lithospheric mantle, which can be linked to Cenozoic volcanism in the Cameroon Volcanic Line that also brought the xenoliths to the surface. This study therefore supports the origin of fertile SCLM via refertilization rather than by extraction of small melt fractions, and further emphasizes the involvement of depleted melts in this process.
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He, Lingchao, Jian Zhang, Guochun Zhao, Changqing Yin, Jiahui Qian, Jin Liu, Xiaoguang Liu, and Chen Zhao. "Macro- and microstructural analysis of the Zhujiafang ductile shear zone, Hengshan Complex: Tectonic nature and geodynamic implications of the evolution of Trans−North China orogen." GSA Bulletin, October 29, 2020. http://dx.doi.org/10.1130/b35672.1.
Повний текст джерелаАнотація:
In worldwide orogenic belts, crustal-scale ductile shear zones are important tectonic channels along which the orogenic root (i.e., high-grade metamorphic lower-crustal rocks) commonly experienced a relatively quick exhumation or uplift process. However, their tectonic nature and geodynamic processes are poorly constrained. In the Trans−North China orogen, the crustal-scale Zhujiafang ductile shear zone represents a major tectonic boundary separating the upper and lower crusts of the orogen. Its tectonic nature, structural features, and timing provide vital information into understanding this issue. Detailed field observations showed that the Zhujiafang ductile shear zone experienced polyphase deformation. Variable macro- and microscopic kinematic indicators are extensively preserved in the highly sheared tonalite-trondhjemite-granodiorite (TTG) and supracrustal rock assemblages and indicate an obvious dextral strike-slip and dip-slip sense of shear. Electron backscattered diffraction (EBSD) was utilized to further determine the crystallographic preferred orientation (CPO) of typical rock-forming minerals, including hornblende, quartz, and feldspar. EBSD results indicate that the hornblendes are characterized by (100) <001> and (110) <001> slip systems, whereas quartz grains are dominated by prism <a> and prism <c> slip systems, suggesting an approximate shear condition of 650−700 °C. This result is consistent with traditional thermobarometry pressure-temperature calculations implemented on the same mineral assemblages. Combined with previously reported metamorphic data in the Trans−North China orogen, we suggest that the Zhujiafang supracrustal rocks were initially buried down to ∼30 km depth, where high differential stress triggered the large-scale ductile shear between the upper and lower crusts. The high-grade lower-crustal rocks were consequently exhumed upwards along the shear zone, synchronous with extensive isothermal decompression metamorphism. The timing of peak collision-related crustal thickening was further constrained by the ca. 1930 Ma metamorphic zircon ages, whereas a subsequent exhumation event was manifested by ca. 1860 Ma syntectonic granitic veins and the available Ar-Ar ages of the region. The Zhujiafang ductile shear zone thus essentially record an integrated geodynamic process of initial collision, crustal thickening, and exhumation involved in formation of the Trans−North China orogen at 1.9−1.8 Ga.
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Zaitsev, Anatoly N., Andrei A. Arzamastsev, Michael A. W. Marks, Simon Braunger, Thomas Wenzel, John Spratt, Tobias Salge, and Gregor Markl. "Hybridisation of alkali basaltic magmas: a case study of the Ogol lavas from the Laetoli area, Crater Highlands (Tanzania)." Journal of Petrology, April 28, 2021. http://dx.doi.org/10.1093/petrology/egab035.
Повний текст джерелаАнотація:
Abstract The southern part of the eastern branch of the East African Rift is characterized by extensive volcanic activity since the late Miocene. In the Crater Highlands, part of the North Tanzanian Divergence zone, effusive and pyroclastic rocks reflect nephelinitic and basaltic compositions that formed between 4.6 and 0.8 Ma. The former are best represented by the Sadiman volcano (4.6–4.0 Ma) and the latter occur in the giant Ngorongoro crater (2.3–2.0 Ma), the Lemagarut volcano (2.4–2.2 Ma) and as a small volcanic field in the Laetoli area (2.3 Ma), where basaltic rocks known as Ogol lavas were erupted through fissures and several cinder cones. Compositionally, they are alkaline basalts with 46.0–47.9 wt % SiO2, 3.0–4.3 wt % of Na2O+K2O, Mg# of 61 to 55, and high Cr and Ni content (450–975 and 165–222 ppm respectively). Detailed textural and compositional analysis of the major minerals (olivine, clinopyroxene, plagioclase and spinel-group minerals) reveals the heterogeneity of the rocks. The primary mineral assemblage that crystallized from the Ogol magmas comprises macro- and microcrysts of olivine (Fo89.5–84.2), Cr-bearing diopside to augite, magnesiochromite-chromitess, magnetite-ulvöspinelss, andesine-oligoclasess and fluorapatite, with glass of phonolitic composition in the groundmass. All samples contain appreciable proportions of xenocrystic minerals of macro- and microcrysts sizes, with large variations in both concentration and mineral populations between samples. Xenocrysts include olivine with reverse zonation (Fo84.1–72.5), rounded and embayed clinopyroxene cores of variable composition, anhedral Cr-free magnetite-ulvöspinelss and embayed oligoclase. These xenocrysts as well as variations in major and trace element contents, 87Sr/86Sr(i) (0.70377–0.70470) and 143Nd/144Nd(i) (0.51246–0.51261) ratios provide evidence of multi-stage magma mixing and mingling between Ogol and adjacent Lemagarut volcano basaltic melts with only very minor contamination by Precambrian granite-gneisses. Elevated alkalinity of Ogol lavas, which positively correlates with isotope ratios and the presence of xenocrystic green core clinopyroxene, perovskite, schorlomite and titanite indicate additional mixing and mingling with evolved nephelinitic magmas and/or assimilation of nephelinitic Laetolil tuffs or foidolitic rocks related to the Sadiman volcano. Due to their heterogeneity, estimates on the crystallization conditions for the Ogol rocks are difficult. Nevertheless, clinopyroxene-liquid thermobarometry indicates crystallization temperatures of around 1150–1220 °C and records upper-crustal depths of 3–12 km (1–4 kbar). Despite the fact that Ogol basalts are hybrid rocks that formed under open-system conditions with well documented mixing and mingling processes, they seem to be the examples closest to primary basaltic melts within the Crater Highlands.
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Cooper, Lauren, Terry Plank, Richard Arculus, Erik Hauri, and Katherine A. Kelley. "Arc–Backarc Exchange Along the Tonga-Lau System: Constraints from Volatile Elements." Journal of Petrology, August 2, 2022. http://dx.doi.org/10.1093/petrology/egac072.
Повний текст джерелаАнотація:
Abstract Analyses of olivine-, pyroxene- and plagioclase-hosted melt (now preserved as glass) inclusions (MI) in submarine glasses and subaerial scoria from seven volcanoes along the volcanic front of the Tonga arc provide the first comprehensive dataset including volatile contents (H2O, CO2, S, Cl and F) for this arc. Maximum water contents at each volcano are typical (3-5 wt%) of other arc volcanoes worldwide, and within each volcano, water generally correlates with sulfur, consistent with degassing but not diffusive re-equilibration. The Tonga arc is notable for the eruption of magmas sourced from strongly depleted upper mantle, including boninites in the northern half of the active arc. A key question has been whether such boninites are derived from high degrees of melting actively occurring under the arc, driven by high mantle temperatures and water contents, or from high integrated degrees of melting including melting of depleted mantle in the backarc. This study supports the latter view, based on sub-arc mantle melt fractions of 17-23%, calculated from primary melt water contents and mantle-melt thermobarometry. Such fractions are not high enough to generate boninites from a typical, fertile mantle source in a single melting stage, and melt fractions do not increase north of 22°S, where the boninitic magmas appear. Instead, the northern Tonga arc boninites reflect high cumulative degrees of melting (> 30%, with respect to fertile mantle) and occur along the volcanic front where adjacent backarc spreading is fast, proximal and mature. Slab tracers such as the Ba/La ratio peak at around 20-21°S, in the central part of the Tonga arc. A Ba/La peak also appears at about the same latitude in the Lau backarc basin. This peak is consistent with the coolest slab temperatures beneath the arc and backarc at this latitude, as the slab warms to the north due to an increase in mantle potential temperature, and to the south due to less heat extraction from melting. A new concept developed here is cooling of the mantle wedge by melting, due to the supply of the heat of fusion and melt removal. Such a process can cool the mantle by more than 100 degrees, and thus affect slab heating as well. We find a critical distance of slab influence in the Lau spreading centers; back-arc magmas erupted > 70 km from the arc are > 210 km above the slab, beyond the point of slab dehydration, and show no enrichment in Ba/La. The coupled dynamics of the Tonga arc-Lau basin are rich in their connections, and demonstrate how melting processes beneath the back-arc and arc can affect slab processes, which in turn can affect the composition of fluids that feed the arc and backarc.
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Pan, Ronghao, Tong Hou, Xudong Wang, John Encarnación, and Roman Botcharnikov. "Multiple magma storage regions and open system processes revealed by chemistry and textures of the Datong tholeiitic lavas, North China Craton." Journal of Petrology, April 5, 2022. http://dx.doi.org/10.1093/petrology/egac034.
Повний текст джерелаАнотація:
Abstract The geochemistry of lavas combined with textural constraints can provide important information on magmatic processes occurring at inaccessible depths. Here we carry out a detailed textural and geochemical study on 0.23 Ma contemporaneous and adjacent Qiulin, Longbao and Dayukou volcanoes in the intraplate Quaternary Datong Volcanic Field (DVF) in the North China Craton. Lavas from the three tholeiitic volcanoes have similar major and trace element compositions with their trace element patterns resembling enriched Mid-Ocean Ridge Basalts (E-MORB). However, distinct textures are observed between the samples from the three volcanoes. Samples from Qiulin are generally poorly-phyric (<10 vol.%) containing orthopyroxene, plagioclase, and olivine phenocrysts and monomineralic orthopyroxene glomerocrysts set in a groundmass of plagioclase, clinopyroxene, orthopyroxene and Fe-Ti oxides. In contrast, samples from both Longbao and Dayukou are highly-phyric (up to ~50 vol.%), and consist mainly of plagioclase, orthopyroxene, clinopyroxene, and olivine phenocrysts with mm- to cm-sized polymineralic glomerocrysts enclosed in a groundmass comprising plagioclase, clinopyroxene, olivine and Fe-Ti oxides. Crystal types and proportions vary significantly between the glomerocrysts of Longbao and Dayukou even on a thin section scale. The phenocrysts and glomerocrysts at the two volcanoes commonly show resorbed and embayed margins and sieve textures. Moreover, pyroxenes present as phenocrysts and glomerocrysts are always characterised by corona textures containing orthopyroxene cores mantled by clinopyroxene. Notably, orthopyroxene is never observed in contact with groundmass. The relatively low Mg# (75-85) and Ca content in the cores indicate that the orthopyroxenes from all three volcanoes are crystallised early from the magma rather than being mantle xenocrysts. Thermobarometry and kernel density estimation indicate that orthopyroxenes in all three volcanoes initially crystallised at ~7 kbar (23 km depth), whereas clinopyroxenes crystallised at ~4 kbar (13 km) and the final crystallisation pressure is ~3 kbar (10 km). Thermodynamic modelling by COMAGMAT suggests early near-liquidus crystallisation of the orthopyroxene at high pressures, followed by partial dissolution likely associated with decompression. The relatively larger proportions of phenocrysts compared with glomerocrysts in Qiulin samples implies that the magma reservoir was only partially turned into mushes at the periphery. Magma ascending via the melt-rich interior of the magma reservoir formed the crystal-poor Qiulin lava. In contrast, those ascending through the mushes at the peripheries of the deeper reservoir and discrete shallower storage regions formed the highly-phyric Longbao and Dayukou lavas. The pervasive occurrence of sieve textures and complex mineral composition profiles in both phenocrysts and glomerocrysts in Longbao and Dayukou samples belie complicated open system crystallisation histories of these magmas. We conclude that open system processes involving mush disaggregation and magma recharge in multi-level plumbing systems played an important role in the petrogenesis of these intracontinental tholeiites. Moreover, the important role of orthopyroxene in the petrogenesis of these tholeiites distinguishes them from many other tholeiite suites like MORB, as well as those erupted through thickened oceanic crust like in Iceland and the Shatsky Rise. This study highlights the importance of combining textural constraints with geochemical analyses.
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Zhang, Daohan, Junhao Wei, Olivier Nadeau, Wenjie Shi, and Kaibo Dan. "Magmatic and Hydrothermal Evolution at Qian’echong, Central-Eastern China: Insights into Dabie-Type Porphyry Mo Mineralization." Journal of Petrology 63, no. 3 (February 21, 2022). http://dx.doi.org/10.1093/petrology/egac013.
Повний текст джерелаАнотація:
Abstract Dabie-type porphyry Mo deposits have recently been identified as a new subtype of porphyry Mo deposits, but several questions remain about the role of ore-related magmas in the formation of this type of deposit, as well as distinctions in genetic processes with the well-studied Climax-type porphyry Mo deposits. Here, mineral and melt inclusions from the giant Qian’echong deposit, Dabie orogen, central-eastern China, were studied in order to improve our understanding of the nature and the role of ore-related magmas in the genesis of Dabie-type porphyry Mo deposits. The magmatic and hydrothermal evolution of the system was reconstructed based primarily on the analysis of quartz-hosted silicate melt and mineral inclusions, in concert with field and petrographic relations as well as previously published U–Pb and Re-Os geochronology. Ore-related magmas at Qian’echong include, from early to late, quartz porphyry dikes, rhyolite porphyry dikes, granite porphyries (stock and dikes) and a newly discovered, deep-seated monzogranite porphyry stock. Based on TitaniQ thermobarometry, these lithologies were sourced from a ~16–19-km deep (500–600 MPa) magma chamber and underwent nearly isothermal decompression to ~7 km (200 MPa), at temperatures ranging from 720°C to 690°C. According to the trace element composition of melt inclusions, in combination with published whole-rock Nd isotopic compositions, the early magma evolved from quartz porphyry to rhyolite porphyry through fractionation crystallization and thus became a crystal mush. This viscous crystal mush was subsequently re-melted to produce the granite porphyries and was injected with melts from a different source to generate the monzogranite porphyry. At Qian’echong, all melt inclusions have low concentrations of Mo (2–8 ppm), >5 wt. % H2O, and little to no F (≤0.26 wt. %), arguing against the requirement for ore-related magmas to be enriched in Mo to form large porphyry Mo deposits. Rayleigh fractionation modeling shows that the concentration of Mo in the quartz and granite porphyries increased through fractionation of quartz, feldspars, biotite, magnetite, and ilmenite and that Mo was subsequently depleted in the melt through fluid exsolution, exclusively in the rhyolite and monzogranite porphyries, as a result of magma ascent and decompression. This suggests that, in addition to ore-related granite porphyry, both the rhyolite and the monzogranite porphyries also contributed to the hydrothermal mineralization. This study confirms that the formation of porphyry Mo deposits does not rely on abnormally high concentrations of Mo in ore-related magmas but instead requires efficient extraction of Mo from large volumes of magmas, with normal concentrations of Mo. Unlike the Climax-type deposits where multiple pulses of ore-forming fluids are delivered from convecting shallow magma chambers, Mo mineralization in Dabie-type deposits was achieved by the assembling of ore-forming fluids from successively emplaced, relatively deep intrusions. Although the Dabie- and Climax-type Mo deposits are respectively associated with I-type and A-type granitoids in the Dabie orogen, it is suggested that both types of magmas are derived from the partial melting of subducted Yangtze continental crust and that it is the tectonic transition from compressional to extensional settings that controlled the different styles of porphyry Mo mineralization in this orogen.