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Li, Jiahao, Xing Ding, and Junfeng Liu. "The Role of Fluids in Melting the Continental Crust and Generating Granitoids: An Overview." Geosciences 12, no. 8 (July 22, 2022): 285. http://dx.doi.org/10.3390/geosciences12080285.
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Granite is a distinctive constituent part of the continental crust on Earth, the formation and evolution of which have long been hot research topics. In this paper, we reviewed the partial melting processes of crustal rocks without or with fluid assistance and summarized the role of fluids and volatiles involved in the formation of granitic melts. As a conventional model, granitoids were thought to be derived from the dehydration melting of hydrous minerals in crustal basement metamorphic rocks in the absence of external fluids. However, the external-fluid-assisted melting of crustal metamorphic rocks has recently been proposed to produce granitoids as extensive fluids could be active in the deep continental crust, especially in the subduction zones. It has been demonstrated experimentally that H2O plays a crucial role in the partial melting of crustal rocks, in which H2O can (1) significantly lower the solidus temperature of the melted rocks to facilitate partial melting; (2) affect the melting reaction process, mineral stability, and the composition of melt; and (3) help the melt to separate more easily from the source area and aggregate to form a large-scale magma chamber. More importantly, dissolved volatiles and salts in the crustal fluids could also lower the solidus temperature of rocks, affect the partitioning behaviors of trace elements between minerals and melts, and facilitate the formation of some distinctive granitoids (e.g., B-rich, F-rich, and high-K granitoids). Furthermore, various volatiles dissolved in fluids could result in elemental or isotopic fractionation as well as the diversity of mineralization during fluid-assisted melting. In-depth studies regarding the fluid-assisted partial melting of crustal rocks will facilitate a more comprehensive understanding of melting of the Earth’s crust, thus providing strong theoretical constraints on the genesis and mineralization of granitoids as well as the formation and evolution of the continental crust.
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Cheng, Yuanzhi, Yanlong Kong, Zhongxing Wang, Yonghui Huang, and Xiangyun Hu. "Crustal Electrical Structure of the Ganzi Fault on the Eastern Tibetan Plateau: Implications for the Role of Fluids in Earthquakes." Remote Sensing 14, no. 13 (June 22, 2022): 2990. http://dx.doi.org/10.3390/rs14132990.
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The initiation and evolution of seismic activity in intraplate regions are controlled by heterogeneous stress and highly fractured rocks within the rock mass triggered by fluid migration. In this study, we imaged the electrical structure of the crust beneath the Ganzi fault using a three-dimensional magnetotelluric inversion technique, which is host to an assemblage of resistive and conductive features extending into the lower crust. It presents a near-vertical low-resistance zone that cuts through the brittle ductile transition zone, extends to the lower crust, and acts as a pathway for fluid migration from the crustal flow to the upper crustal depths. Conductors in the upper and lower crust are associated with saline fluids and 7% to 16% partial melting, respectively. The relationship between the earthquake epicenter and the surrounding electrical structure suggests that the intraplate seismicity is triggered by overpressure fluids, which are dependent on fluid volume changes generated by the decompression dehydration of partially molten material during upwelling and native fluid within the crustal flow.
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Gudelius, Dominik, Sonja Aulbach, Hans-Michael Seitz, and Roberto Braga. "Crustal fluids cause strong Lu-Hf fractionation and Hf-Nd-Li isotopic provinciality in the mantle of continental subduction zones." Geology 50, no. 2 (November 2, 2021): 163–68. http://dx.doi.org/10.1130/g49317.1.
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Abstract Metasomatized mantle wedge peridotites exhumed within high-pressure terranes of continental collision zones provide unique insights into crust-mantle interaction and attendant mass transfer, which are critical to our understanding of terrestrial element cycles. Such peridotites occur in high-grade gneisses of the Ulten Zone in the European Alps and record metasomatism by crustal fluids at 330 Ma and high-pressure conditions (2.0 GPa, 850 °C) that caused a transition from coarse-grained, garnet-bearing to fine-grained, amphibole-rich rocks. We explored the effects of crustal fluids on canonically robust Lu-Hf peridotite isotope signatures in comparison with fluid-sensitive trace elements and Nd-Li isotopes. Notably, we found that a Lu-Hf pseudo-isochron is created by a decrease in bulk-rock 176Lu/177Hf from coarse- to fine-grained peridotite that is demonstrably caused by heavy rare earth element (HREE) loss during fluid-assisted, garnet-consuming, amphibole-forming reactions accompanied by enrichment in fluid-mobile elements and the addition of unradiogenic Nd. Despite close spatial relationships, some peridotite lenses record more intense fluid activity that causes complete garnet breakdown and high field strength element (HFSE) addition along with the addition of crust-derived unradiogenic Hf, as well as distinct chromatographic light REE (LREE) fractionation. We suggest that the observed geochemical and isotopic provinciality between peridotite lenses reflects different positions relative to the crustal fluid source at depth. This interpretation is supported by Li isotopes: inferred proximal peridotites show light δ7Li due to strong kinetic Li isotope fractionation (−4.7–2.0‰) that accompanies Li enrichment, whereas distal peridotites show Li contents and δ7Li similar to those of the depleted mantle (1.0–7.2‰). Thus, Earth's mantle can acquire significant Hf-Nd-Li-isotopic heterogeneity during locally variable ingress of crustal fluids in continental subduction zones.
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Erslev, Eric A., Lindsay L. Worthington, Megan L. Anderson, and Kate C. Miller. "Laramide crustal detachment in the Rockies: Cordilleran shortening of fluid-weakened foreland crust." Rocky Mountain Geology 57, no. 2 (December 1, 2022): 65–97. http://dx.doi.org/10.24872/rmgjournal.57.2.65.
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ABSTRACT What causes previously stable continental crust in the forelands of Cordilleran orogenic systems to shorten during low-angle subduction? The National Science Foundation/EarthScope Bighorn Project combined seismic imaging of the crust and Moho with kinematic modeling of Laramide (Late Cretaceous–Paleogene) basement-involved deformation to address this question. In north-central Wyoming, asymmetrical ENE-verging upper-crustal folds are highly discordant with broader, N-trending warps in the Moho, indicating crustal detachment. Restorable cross sections of ENE-directed detachment at a depth of ~30 km, combined a smaller component of NNW–SSE shortening due to the east-narrowing shape of the crustal allochthon, can explain the anastomosing network of Laramide basement-cored arches without major deformation of the underlying mantle lithosphere. Thrust-related fold geometries and west-to-east initiation of deformation in the Laramide and Sevier thrust belts point to Cordilleran end-loading from the west. Differences between Laramide (~N65E) and plate (~N25E) convergence directions, along with the fanning of Laramide shortening directions from nearly E–W to the south to NE–SW to the north, indicate slip partitioning during end-loading west of the Rockies. Sub-horizontal detachment with a near-zero critical taper within cratonic crust suggests an extremely weak Laramide detachment zone during deformation. Analogous lower-crustal deformation in subduction forearcs is associated with slow earthquakes and slab dehydration. We hypothesize that low-angle subduction of the Farallon Plate suppressed fluid-consuming melting and corner-flow processes that characterize higher-angle subduction. This allowed subduction-generated fluids to escape upward into the overlying continental lithosphere, causing retrograde metamorphism and increased fluid pressure that facilitated crustal detachment. This hydration-based hypothesis predicts that crustal detachment will accompany major earthquakes in active analog orogens.
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Beaudoin, Georges, D. F. Sangster, and C. I. Godwin. "Isotopic evidence for complex Pb sources in the Ag–Pb–Zn–Au veins of the Kokanee Range, southeastern British Columbia." Canadian Journal of Earth Sciences 29, no. 3 (March 1, 1992): 418–31. http://dx.doi.org/10.1139/e92-037.
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In the Kokanee Range, more than 370 Ag–Pb–Zn–Au vein and replacement deposits are hosted by the Middle Jurassic Nelson batholith and surrounding Cambrian to Triassic metasedimentary rocks. The Kokanee Range forms the hanging wall of the Slocan Lake Fault, an Eocene, east-dipping, low-angle normal fault. The Pb isotopic compositions of galenas permit the deposits to be divided into four groups that form linear arrays in tridimensional Pb isotopic space, each group having a distinct geographic distribution that crosses geological boundaries. The Kokanee group Pb is derived from a mixture of local upper crustal country rocks. Ainsworth group Pb and Sandon group Pb plot along a mixing line between a lower crustal Pb reservoir and the upper crustal Pb reservoir. The Ainsworth group Pb isotopic signature is markedly lower crustal, whereas the Sandon group Pb is slightly lower crustal. The Bluebell group Pb plots along a mixing line between a depleted upper mantle Pb reservoir and the lower crustal Pb reservoir.The geographic distribution and the Pb isotopic composition of each group probably reflect deep structures that permitted mixing of lower crustal, upper crustal, and mantle Pb by hydrothermal fluids. Segments of, or fluids derived from, the lower crust and the upper mantle were leached by, or mixed with, evolved meteoric water convecting in the upper crust. Fracture permeability, hydrothermal fluid flow, and mineralization resulted from Eocene crustal extension in southeastern British Columbia.
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Zhang, Mingjie, Pengyu Feng, Tong Li, Liwu Li, Juerong Fu, Peng Wang, Yuekun Wang, Zhongping Li, and Xiaodong Wang. "The Petrogenesis of the Permian Podong Ultramafic Intrusion in the Tarim Craton, Western China: Constraints from C-He-Ne-Ar Isotopes." Geofluids 2019 (August 22, 2019): 1–14. http://dx.doi.org/10.1155/2019/6402571.
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The Podong Permian ultramafic intrusion is only one ultramafic intrusion with massif Ni-Cu sulfide mineralization in the Pobei layered mafic-ultramafic complex, western China. It is obviously different in sulfide mineralization from the nearby coeval Poyi ultramafic intrusion with the largest disseminated Ni-Cu sulfide mineralization and mantle plume contribution (Zhang et al., 2017). The type and addition mechanism of the confirmed crustal contaminations and possible mantle plume involved in the intrusion formation require evidences from carbon and noble gas isotopic compositions. In the present study, we have measured C, He, Ne, and Ar isotopic compositions of volatiles from magmatic minerals in the Podong ultramafic intrusion. The results show that olivine, pyroxene, and plagioclase minerals in the Podong intrusion have variable δ13C of CO2 (-24.5‰ to -3.2‰). The CH4, C2H6, C3H8, and C4H10 hydrocarbon gases show normal or partial reversal distribution patterns of carbon isotope with carbon number and light δ13C1 value of CH4, indicating the hydrocarbon gases of biogenic origin. The δ13C of CO2 and CH4 suggested the magmatic volatile of the mantle mixed with the volatiles of thermogenic and crustal origins. Carbon and noble gas isotopes indicated that the Podong intrusion could have a different petrogenesis from the Poyi ultramafic intrusion. Two types of contaminated crustal materials can be identified as crustal fluids from subducted altered oceanic crust (AOC) in the lithospheric mantle source and a part of the siliceous crust. The carbon isotopes for different minerals show that magma spent some time crystallizing in a magma chamber during which assimilation of crustal material occurred. Subduction-devolatilization of altered oceanic crust could be the best mechanism that transported large proportion of ASF (air-saturated fluid) and crustal components into the mantle source. The mantle plume existing beneath the Poyi intrusion could provide less contribution of real materials of silicate and fluid components.
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Comeau, Matthew J., Michael Becken, Alexey V. Kuvshinov, Sodnomsambuu Demberel, Erdenechimeg Batmagnai, and Shoovdor Tserendug. "The Bayankhongor Metal Belt (Mongolia): Constraints on Crustal Architecture and Implications for Mineral Emplacement from 3-D Electrical Resistivity Models." Environmental Sciences Proceedings 6, no. 1 (February 25, 2021): 32. http://dx.doi.org/10.3390/iecms2021-09360.
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The Bayankhongor Metal Belt, a metallogenic belt that extends for more than 100 km in central Mongolia, is an economically significant zone that includes sources of gold and copper. Unfortunately, the crustal architecture is poorly understood throughout this region. However, it is known that the crustal structure strongly influences the development and emplacement of mineral zones. Electrical resistivity is a key physical parameter for mineral exploration that can help to locate mineral zones and determine the regional crustal structure. We use natural-source magnetotelluric data to generate three-dimensional electrical resistivity models of the crust. The results show that anomalous, low-resistivity zones in the upper crust are spatially associated with the surface expressions of known mineral occurrences, deposits, and mining projects. We thus infer that the development of the mineralization is closely linked to the low-resistivity signatures and, therefore, to crustal structures, due primarily to their influence on fluid flow. The low-resistivity signatures are possibly related to associated sulfide mineralogy within the host complex and to structures and weaknesses that facilitated fluid movement and contain traces of past hydrothermal alteration. Thus, the crustal architecture, including major crustal boundaries that influence fluid distribution, exerts a first-order control on the location of the metallogenic belt. By combining our electrical resistivity results with other geological and petrological data, we attempt to gain insights into the emplacement and origin of mineral resources.
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Manning, Craig E. "Fluids of the Lower Crust: Deep Is Different." Annual Review of Earth and Planetary Sciences 46, no. 1 (May 30, 2018): 67–97. http://dx.doi.org/10.1146/annurev-earth-060614-105224.
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Deep fluids are important for the evolution and properties of the lower continental and arc crust in tectonically active settings. They comprise four components: H2O, nonpolar gases, salts, and rock-derived solutes. Contrasting behavior of H2O-gas and H2O-salt mixtures yields immiscibility and potential separation of phases with different chemical properties. Equilibrium thermodynamic modeling of fluid-rock interaction using simple ionic species known from shallow-crustal systems yields solutions too dilute to be consistent with experiments and resistivity surveys, especially if CO2 is added. Therefore, additional species must be present, and H2O-salt solutions likely explain much of the evidence for fluid action in high-pressure settings. At low salinity, H2O-rich fluids are powerful solvents for aluminosilicate rock components that are dissolved as polymerized clusters. Addition of salts changes solubility patterns, but aluminosilicate contents may remain high. Fluids with Xsalt = 0.05 to 0.4 in equilibrium with model crustal rocks have bulk conductivities of 10−1.5 to 100 S/m at porosity of 0.001. Such fluids are consistent with observed conductivity anomalies and are capable of the mass transfer seen in metamorphic rocks exhumed from the lower crust.
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Lacombe, Olivier, and Yann Rolland. "Fluids in crustal deformation: Fluid flow, fluid-rock interactions, rheology, melting and resources." Journal of Geodynamics 101 (November 2016): 1–4. http://dx.doi.org/10.1016/j.jog.2016.08.004.
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Leary, Peter, Peter Malin, and Rami Niemi. "Fluid Flow and Heat Transport Computation for Power-Law Scaling Poroperm Media." Geofluids 2017 (2017): 1–12. http://dx.doi.org/10.1155/2017/9687325.
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In applying Darcy’s law to fluid flow in geologic formations, it is generally assumed that flow variations average to an effectively constant formation flow property. This assumption is, however, fundamentally inaccurate for the ambient crust. Well-log, well-core, and well-flow empirics show that crustal flow spatial variations are systematically correlated from mm to km. Translating crustal flow spatial correlation empirics into numerical form for fluid flow/transport simulation requires computations to be performed on a single global mesh that supports long-range spatial correlation flow structures. Global meshes populated by spatially correlated stochastic poroperm distributions can be processed by 3D finite-element solvers. We model wellbore-logged Dm-scale temperature data due to heat advective flow into a well transecting small faults in a Hm-scale sandstone volume. Wellbore-centric thermal transport is described by Peclet number Pe ≡ a0φv0/D (a0 = wellbore radius, v0 = fluid velocity at a0, φ = mean crustal porosity, and D = rock-water thermal diffusivity). The modelling schema is (i) 3D global mesh for spatially correlated stochastic poropermeability; (ii) ambient percolation flow calibrated by well-core porosity-controlled permeability; (iii) advection via fault-like structures calibrated by well-log neutron porosity; (iv) flow Pe ~ 0.5 in ambient crust and Pe ~ 5 for fault-borne advection.
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Sibson, Richard H. "Crustal stress, faulting and fluid flow." Geological Society, London, Special Publications 78, no. 1 (1994): 69–84. http://dx.doi.org/10.1144/gsl.sp.1994.078.01.07.
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Torgersen, T. "Crustal fluid flow: Continuous or episodic?" Eos, Transactions American Geophysical Union 72, no. 3 (1991): 18. http://dx.doi.org/10.1029/90eo00019.
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Yuasa, Y., S. Matsumoto, S. Nakao, T. Matsushima, and T. Ohkura. "Inelastic strain rate and stress fields in and around an aseismic zone of Kyushu Island, Japan, inferred from seismic and GNSS data." Geophysical Journal International 221, no. 1 (January 9, 2020): 289–304. http://dx.doi.org/10.1093/gji/ggaa008.
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SUMMARY Understanding earthquake processes and crustal deformation requires knowledge of the stress concentration process in the crust. With the enhancement of observation networks, it has become possible to consider in detail the relationships between localized deformation and seismic activity in island arcs and the process of stress concentration. According to previous studies, inelastic deformation in localized weak zones in the crust is considered to play an important role in the stress concentration process. Kyushu, located in southwest Japan, has a 20–30 km band-like active seismic activity and an enclosed aseismic zone. In particular, a part of the seismic active region called the Beppu-Simahara Graben, which is dominated by north–south extensional deformation, is characterized by high seismic activity and a remarkable aseismic zone. We identified the relationship between inelastic deformation and stress concentration processes in this area by using analyses of geodetic and seismic data. The results inverted from both the strain rate field obtained by the geodetic observations and the deviatoric stress field estimated from focal mechanism data reveal a large inelastic deformation zone ($\sim {10^{ - 7}} \,\mathrm{ yr}^{-1}$) beneath the area of active seismicity. From comparison with previous works, the inelastic deformation zone in the lower crust may correspond to an area with high temperature and/or fluid. This may suggest that inelastic deformation is in progress in the area where the strength of lower crustal rocks has reduced due to the presence of geothermics and/or fluids. Furthermore, we confirmed that this inelastic deformation causes stress concentrations of up to $10\,\,{\rm{kPa}}\,\,{\rm{yr}}^{-1}$ in the upper crust. These results show that stress concentration occurs locally in the upper crust, above the inelastic deformation zone in the weakened lower crust, owing to the presence of geothermal and/or fluid; this stress concentration induces seismic activity and crustal deformation.
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Jin, Xiao-Ye, Albert H. Hofstra, Andrew G. Hunt, Jian-Zhong Liu, Wu Yang, and Jian-Wei Li. "NOBLE GASES FINGERPRINT THE SOURCE AND EVOLUTION OF ORE-FORMING FLUIDS OF CARLIN-TYPE GOLD DEPOSITS IN THE GOLDEN TRIANGLE, SOUTH CHINA." Economic Geology 115, no. 2 (March 1, 2020): 455–69. http://dx.doi.org/10.5382/econgeo.4703.
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Abstract Precise constraints on the source and evolution of ore-forming fluids of Carlin-type gold deposits in the Golden Triangle (south China) are of critical importance for a better understanding of the ore genesis and a refined genetic model for gold mineralization. However, constraints on the source of ore fluid components have long been a challenge due to the very fine grained nature of the ore and gangue minerals in the deposits. Here we present He, Ne, and Ar isotope data of fluid inclusion extracts from a variety of ore and gangue minerals (arsenian pyrite, realgar, quartz, calcite, and fluorite) representing the main and late ore stages of three well-characterized major gold deposits (Shuiyindong, Nibao, and Yata) to provide significant new insights into the source and evolution of ore-forming fluids of this important gold province. Measured He isotopes have R/RA ratios ranging from 0.01 to 0.4 that suggest a maximum of 5% mantle helium with an R/RA of 8. The Ne and Ar isotope compositions are broadly comparable to air-saturated water, with a few analyses indicating the presence of an external fluid containing nucleogenic 38Ar and radiogenic 40Ar. Plotted on the 20Ne/4He vs. helium R/RA and 3He/20Ne vs. 4He/20Ne diagrams, the results define two distinct arrays that emanate from a common sedimentary pore fluid or deeply sourced metamorphic fluid end-member containing crustal He. The main ore-stage fluids are interpreted as a mixture of magmatic fluid containing mantle He and sedimentary pore fluid or deeply sourced metamorphic fluid with predominantly crustal He, whereas the late ore-stage fluids are a mixture of sedimentary pore fluid or deeply sourced metamorphic fluid bearing crustal He and shallow meteoric groundwater containing atmospheric He. Results presented here, when combined with independent evidence, support a magmatic origin for the ore-forming fluids. The ascending magmatic fluid mixed with sedimentary pore fluid or deeply sourced metamorphic fluid in the ore stage and subsequently mixed with the meteoric groundwater in the late ore stage, eventually producing the Carlin-type gold deposits in the Golden Triangle.
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Ingebritsen, Steven E., and Craig E. Manning. "Implications of crustal permeability for fluid movementbetween terrestrial fluid reservoirs." Journal of Geochemical Exploration 78-79 (May 2003): 1–6. http://dx.doi.org/10.1016/s0375-6742(03)00037-2.
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Koger, Jace M., and Dennis L. Newell. "Spatiotemporal history of fault–fluid interaction in the Hurricane fault, western USA." Solid Earth 11, no. 6 (November 5, 2020): 1969–85. http://dx.doi.org/10.5194/se-11-1969-2020.
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Abstract. The Hurricane fault is a ∼250 km long, west-dipping, segmented normal fault zone located along the transition between the Colorado Plateau and the Basin and Range tectonic provinces in the western USA. Extensive evidence of fault–fluid interaction includes calcite mineralization and veining. Calcite vein carbon (δ13CVPDB) and oxygen (δ18OVPDB) stable isotope ratios range from −4.5 ‰ to 3.8 ‰ and from −22.1 ‰ to −1.1 ‰, respectively. Fluid inclusion microthermometry constrains paleofluid temperatures and salinities from 45 to 160 ∘C and from 1.4 wt % to 11.0 wt % as NaCl, respectively. These data suggest mixing between two primary fluid sources, including infiltrating meteoric water (70±10 ∘C, ∼1.5 wt % NaCl, δ18OVSMOW ∼-10 ‰) and sedimentary brine (100±25 ∘C, ∼11 wt % NaCl, δ18OVSMOW ∼ 5 ‰). Interpreted carbon sources include crustal- or magmatic-derived CO2, carbonate bedrock, and hydrocarbons. Uranium–thorium (U–Th) dates from five calcite vein samples indicate punctuated fluid flow and fracture healing at 539±10.8 (1σ), 287.9±5.8, 86.2±1.7, and 86.0±0.2 ka in the upper 500 m of the crust. Collectively, data predominantly from the footwall damage zone imply that the Hurricane fault imparts a strong influence on the regional flow of crustal fluids and that the formation of veins in the shallow parts of the fault damage zone has important implications for the evolution of fault strength and permeability.
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Evans, Katy A., and Andrew G. Tomkins. "Metamorphic Fluids in Orogenic Settings." Elements 16, no. 6 (December 1, 2020): 381–87. http://dx.doi.org/10.2138/gselements.16.6.381.
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Metamorphic reactions within the Earth’s crust produce fluids of variable composition that play a major role in the evolution of continents. Metamorphic fluids facilitate reactions that alter crustal rheology, reduce melting temperature, cycle elements between geological reservoirs and form ore deposits. These fluids are relatively inaccessible, other than by study of fluid inclusions, so most studies rely on a combination of indirect evidence and predictive thermodynamic models to determine the characteristics and roles of the fluids. In this article, the origins, compositions, controlling phase equilibria, and roles of metamorphic fluids are reviewed, followed by a discussion of selected areas of current and future research.
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Torgersen, Thomas. "Crustal-scale fluid transport: Magnitude and mechanisms." Geophysical Research Letters 18, no. 5 (May 1991): 917–18. http://dx.doi.org/10.1029/91gl00948.
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Torgersen, Thomas. "Crustal-scale fluid transport: Magnitude and mechanisms." Eos, Transactions American Geophysical Union 71, no. 1 (1990): 1. http://dx.doi.org/10.1029/90eo00001.
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Gupta, Sandeep, P. Mahesh, Nagaraju Kanna, K. Sivaram, and Ajay Paul. "3-D seismic velocity structure of the Kumaun–Garhwal (Central) Himalaya: insight into the Main Himalayan Thrust and earthquake occurrence." Geophysical Journal International 229, no. 1 (October 30, 2021): 138–49. http://dx.doi.org/10.1093/gji/ggab449.
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SUMMARY Objective assessment of seismic hazard and understanding of the Himalayan arc's tectonics requires detailed information on the crustal structure and geometry of the underthrusting Indian Plate beneath the Himalaya. Here, we present high-resolution 3-D P-wave velocity (Vp) and P-to-S-wave velocity ratio (Vp/Vs) images of the Kumaun–Garhwal Himalaya, a proposed potential region for the future great earthquake. We generate these images by inverting arrival times of 515 local earthquakes recorded by 41 broad-band stations during November 2006–June 2008. The tomographic images show a heterogeneous structure in the upper-mid crust. These images, along with available geophysical and geological information, indicate the presence of quartz-rich felsic rocks in the uppermost crust and the occurrence of saline-rich aqueous fluid/partial melt in the upper-mid crust. We propose that the Main Himalayan Thrust (MHT), having a flat-ramp-flat geometry, lies at the base of these fluid zones. The small- and moderate-to-strong-magnitude earthquakes are mainly confined to the fluid-rich zones along the MHT and quartz-rich rocks in the upper crust. Such an interpretation implies that the earthquake occurrence in the Kumaun–Garhwal Himalaya is largely controlled by the geometry of the MHT and crustal lithology.
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Neil Phillips, G. "Metamorphic fluids and gold." Mineralogical Magazine 57, no. 388 (September 1993): 365–74. http://dx.doi.org/10.1180/minmag.1993.057.388.02.
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AbstractLow-salinity fluids (T > 200°C reduced S, modest CO2) and high geothermal gradients are common to many gold deposits and provinces. In contrast, host rocks, hosting structures, depth of formation (in the crust during deposition), subsequent metamorphic overprint, alteration mineralogy and isotopic signatures can vary dramatically within single deposits or provinces. Gold deposits with co-product base metals are an exception to the above comments, and probably relate to saline fluids.The low salinity fluids inferred for major gold-only deposits are not easily explained by seawater, basinal brines, meteoric fluid or common magmatic processes. In contrast, metamorphic devolatilisation of mafic/greywacke rocks is one effective way to produce low-salinity metamorphic fluids with characteristics matching the gold fluids. Such an origin also explains the link to geothermal gradients.The transition from chlorite—albite—carbonate assemblages to amphibole-plagioclase assemblages (commonly greenschist—amphibolite facies boundary) involves considerable loss of metamorphic fluid whose composition is buffered by the mineral assemblage, and is a function of P and T. This low salinity, H2O-CO2 fluid is evolved at T > 400°C commonly carries reduced sulphur, and may contain Au complexed with this sulphur. This auriferous fluid is likely to mix with other fluid types during times of elevated temperature, especially magmatic fluids at depth, and upper crustal fluids at higher levels.Gold deposits in Archaean greenstone belts exhibit good evidence of low salinity, H2O-CO2 fluids of T > 300°C these include examples from Canada, Australia, Brazil, Zimbabwe, India, and South Africa. Turbidite-hosted (slate-belt) deposits exhibit similar evidence for such fluids but commonly with appreciable CH4; the Victoria and Juneau (Alaska) goldfields are examples. The Witwatersrand goldfields also show evidence of low salinity, H2O-CO2 fluids carrying reduced sulphur and gold, but their distribution and timing are not well established. Epithermal (sensu lato) gold deposits have evidence for low salinity fluids carrying Au and S, but are much more diverse in character than those from the previously mentioned gold provinces: this probably arises from mixing of several fluid types at high crustal levels. Together these four types of gold provinces account for over 80% of the primary gold mined to date.
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Gao, Yun, Bailin Chen, Liyan Wu, Jianfeng Gao, Guangqian Zeng, and Jinghui Shen. "Mantle-Derived Noble Gas Isotopes in the Ore-Forming Fluid of Xingluokeng W-Mo Deposit, Fujian Province." Minerals 12, no. 5 (May 7, 2022): 595. http://dx.doi.org/10.3390/min12050595.
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China has the largest W reserves in the world, which are mainly concentrated in south China. Although previous studies have been carried out on whether mantle material is incorporated in granites associated with W deposits, the conclusions have been inconsistent. However, rare gas isotopes can be used to study the contribution of mantle-to-W mineralization. In this paper, we investigated the He and Ar isotope compositions of fluid inclusions in pyrite and wolframite from the Xingluokeng ultra-large W-Mo deposit to evaluate the origin of ore-forming fluids and discuss the contribution of the mantle-to-tungsten mineralization. The He-Ar isotopic compositions showed that the 3He/4He ratios of the ore-forming fluid of the Xingluokeng deposit ranged from 0.14 to 1.01 Ra (Ra is the 3He/4He ratio of air, 1 Ra = 1.39 × 10−6), with an average of 0.58 Ra, which is between the 3He/4He ratios of mantle fluids and crustal fluids, suggesting that the mantle-derived He was added to the mineralizing fluid, with a mean of 8.7%. The 40Ar/36Ar ratios of these samples ranged from 361 to 817, with an average of 578, between the atmospheric 40Ar/36Ar and the crustal and/or mantle 40Ar/36Ar. The results of the He-Ar isotopes from Xingluokeng W-Mo deposit showed that the ore-forming fluid of the deposit was not the product of the evolution of pure crustal melt. The upwelling mantle plays an important role in the formation of tungsten deposits.
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Brown, Larry D., and Doyeon Kim. "Extensive Sills in the Continental Basement from Deep Seismic Reflection Profiling." Geosciences 10, no. 11 (November 10, 2020): 449. http://dx.doi.org/10.3390/geosciences10110449.
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Crustal seismic reflection profiling has revealed the presence of extensive, coherent reflections with anomalously high amplitudes in the crystalline crust at a number of locations around the world. In areas of active tectonic activity, these seismic “bright spots” have often been interpreted as fluid magma at depth. The focus in this report is high-amplitude reflections that have been identified or inferred to mark interfaces between solid mafic intrusions and felsic to intermediate country rock. These “frozen sills” most commonly appear as thin, subhorizontal sheets at middle to upper crustal depths, several of which can be traced for tens to hundreds of kilometers. Their frequency among seismic profiles suggest that they may be more common than widely realized. These intrusions constrain crustal rheology at the time of their emplacement, represent a significant mode of transfer of mantle material and heat into the crust, and some may constitute fingerprints of distant mantle plumes. These sills may have played important roles in overlying basin evolution and ore deposition.
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de Riese, Tamara, Paul D. Bons, Enrique Gomez-Rivas, and Till Sachau. "Interaction between Crustal-Scale Darcy and Hydrofracture Fluid Transport: A Numerical Study." Geofluids 2020 (November 5, 2020): 1–14. http://dx.doi.org/10.1155/2020/8891801.
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Crustal-scale fluid flow can be regarded as a bimodal transport mechanism. At low hydraulic head gradients, fluid flow through rock porosity is slow and can be described as diffusional. Structures such as hydraulic breccias and hydrothermal veins both form when fluid velocities and pressures are high, which can be achieved by localized fluid transport in space and time, via hydrofractures. Hydrofracture propagation and simultaneous fluid flow can be regarded as a “ballistic” transport mechanism, which is activated when transport by diffusion alone is insufficient to release the local fluid overpressure. The activation of a ballistic system locally reduces the driving force, through allowing the escape of fluid. We use a numerical model to investigate the properties of the two transport modes in general and the transition between them in particular. We developed a numerical model in order to study patterns that result from bimodal transport. When hydrofractures are activated due to low permeability relative to fluid flux, many hydrofractures form that do not extend through the whole system. These abundant hydrofractures follow a power-law size distribution. A Hurst factor of ~0.9 indicates that the system self-organizes. The abundant small-scale hydrofractures organize the formation of large-scale hydrofractures that ascend through the whole system and drain fluids in large bursts. As the relative contribution of porous flow increases, escaping fluid bursts become less frequent, but more regular in time and larger in volume. We propose that metamorphic rocks with abundant veins, such as in the Kodiak accretionary prism (Alaska) and Otago schists (New Zealand), represent regions with abundant hydrofractures near the fluid source, while hydrothermal breccias are formed by the large fluid bursts that can ascend the crust to shallower levels.
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Channer, D. M. DeR, and E. T. C. Spooner. "Geochemistry of late (~ 1.1 Ga) fluid inclusions in rocks of the Kapuskasing Archean crustal section." Canadian Journal of Earth Sciences 31, no. 7 (July 1, 1994): 1235–55. http://dx.doi.org/10.1139/e94-109.
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Three outcrops, well constrained by geochronological and structural studies, and representing a traverse running from tonalite-dominated outcrops in the eastern Wawa gneiss terrane to high-grade granulites of the Kapuskasing structural zone, were mapped and sampled in detail in order to study the trapped fluids. All fluid inclusions in quartz are secondary and consist mostly of CO2-dominated (type II) and saline aqueous (type IIIa) fluids usually occurring on separate healed fractures but also coexisting on some fractures. Healed fractures in quartz contain fluid inclusions but are associated with carbonate–sericite alteration where they pass into adjacent mineral grains. Homogeneous H2O–CO2–salt fluid inclusions (type Ia) in carbonate-rich veins of probable Keweenawan (~ 1.1 Ga) age were trapped at 400–550 °C and ambient pressures of 1.5–2 kbar (1 kbar = 100 MPa). As these fluids cooled on penetration into cool (~ 200 °C) country rocks along fractures they underwent open-system H2O-CO2 phase separation from ~ 350 °C down to ~ 190 °C, producing a range of fluid compositions, including physically segregated CO2-rich (type II) and H2O–salt–rich (type IIIa). Combined gas and ion chromatographic bulk fluid inclusion analyses show that fluid types II and IIIa are not related to shield brines. Br−/Cl− ratios of samples containing phase-separated fluids are similar to the Br−/Cl− ratio of fluids in the carbonate-rich vein. The results of this study show that Keweenawan alkalic magmatism caused widespread carbonate alteration throughout the Kapuskasing structural zone and Wawa gneiss domain. The CO2 component of the fluids is probably magmatic in origin, whereas the aqueous part could also be magmatic or, alternatively, formation waters activated by Keweenawan magmatism.
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Al-Shukri, Haydar J., and Brian J. Mitchell. "Reduced seismic velocities in the source zone of New Madrid earthquakes." Bulletin of the Seismological Society of America 78, no. 4 (August 1, 1988): 1491–509. http://dx.doi.org/10.1785/bssa0780041491.
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Abstract A three-dimensional inversion of P-wave travel-time residuals from local earthquakes reveals a remarkable pattern of low seismic velocities in crustal rocks immediately adjacent to the active portions of the New Madrid fault system. Seismic velocities are lowest in regions of greatest concentration of earthquake activity near two intersections of linear trends in seismicity. The maximum reduction in compressional wave velocity is at least 7 per cent in the upper 5 km of the crust and at least 4 per cent in the depth range of 5 to 14 km. The reductions are consistent with a velocity decrease which would be expected if crustal rocks in the source zone contain fluid-filled cracks in which pore pressure is a substantial fraction of external pressure. The presence or absence of such fluids may explain why some portions of the faults in and surrounding the upper Mississippi Embayment are active while others are not.
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Louis-Napoléon, Aurélie, Muriel Gerbault, Thomas Bonometti, Cédric Thieulot, Roland Martin, and Olivier Vanderhaeghe. "3-D numerical modelling of crustal polydiapirs with volume-of-fluid methods." Geophysical Journal International 222, no. 1 (March 20, 2020): 474–506. http://dx.doi.org/10.1093/gji/ggaa141.
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SUMMARY Gravitational instabilities exert a crucial role on the Earth dynamics and in particular on its differentiation. The Earth’s crust can be considered as a multilayered fluid with different densities and viscosities, which may become unstable in particular with variations in temperature. With the specific aim to quantify crustal scale polydiapiric instabilities, we test here two codes, JADIM and OpenFOAM, which use a volume-of-fluid (VOF) method without interface reconstruction, and compare them with the geodynamics community code ASPECT, which uses a tracking algorithm based on compositional fields. The VOF method is well-known to preserve strongly deforming interfaces. Both JADIM and OpenFOAM are first tested against documented two and three-layer Rayleigh–Taylor instability configurations in 2-D and 3-D. 2-D and 3-D results show diapiric growth rates that fit the analytical theory and are found to be slightly more accurate than those obtained with ASPECT. We subsequently compare the results from VOF simulations with previously published Rayleigh–Bénard analogue and numerical experiments. We show that the VOF method is a robust method adapted to the study of diapirism and convection in the Earth’s crust, although it is not computationally as fast as ASPECT. OpenFOAM is found to run faster than, and conserve mass as well as JADIM. Finally, we provide a preliminary application to the polydiapiric dynamics of the orogenic crust of Naxos Island (Greece) at about 16 Myr, and propose a two-stages scenario of convection and diapirism. The timing and dimensions of the modelled gravitational instabilities not only corroborate previous estimates of timing and dimensions associated to the dynamics of this hot crustal domain, but also bring preliminary insight on its rheological and tectonic contexts.
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Halliday, Alex N., Matthias Ohr, Klaus Mezger, John T. Chesley, Shun'ichi Nakai, and Charles P. DeWolf. "Recent developments in dating ancient crustal fluid flow." Reviews of Geophysics 29, no. 4 (1991): 577. http://dx.doi.org/10.1029/91rg01813.
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Cathles, Lawrence M. "Changes in crustal fluid flow over geologic time." Journal of Geochemical Exploration 89, no. 1-3 (April 2006): 45–46. http://dx.doi.org/10.1016/j.gexplo.2006.01.002.
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Zhang, Shiyu, and Min Zhong. "Vertical crustal displacements due to surface fluid changes." Geo-spatial Information Science 10, no. 4 (January 2007): 260–64. http://dx.doi.org/10.1007/s11806-007-0137-6.
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Rivers, Toby, and Walfried Schwerdtner. "Post-peak Evolution of the Muskoka Domain, Western Grenville Province: Ductile Detachment Zone in a Crustal-scale Metamorphic Core Complex." Geoscience Canada 42, no. 4 (December 7, 2015): 403. http://dx.doi.org/10.12789/geocanj.2015.42.080.
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The Ottawa River Gneiss Complex (ORGC) in the western Grenville Province of Ontario and Quebec is interpreted as the exhumed mid-crustal core of a large metamorphic core complex. This paper concerns the post-peak evolution of the Muskoka domain, the highest structural level in the southern ORGC that is largely composed of amphibolite-facies straight gneiss derived from retrogressed granulite-facies precursors. It is argued that retrogression and high strain occurred during orogenic collapse and that the Muskoka domain acted as the ductile detachment zone between two stronger crustal units, the underlying granulite-facies core known as the Algonquin domain and the overlying lower grade cover comprising the Composite Arc Belt. Formation of the metamorphic core complex followed Ottawan crustal thickening, peak metamorphism and possible channel flow, and took place in a regime of crustal thinning and gravitational collapse in which the cool brittle–ductile upper crust underwent megaboudinage and the underlying hot ductile mid crust flowed into the intervening megaboudin neck regions. Post-peak crustal thinning in the Muskoka domain began under suprasolidus conditions, was facilitated by widespread retrogression, and was heterogeneous, perhaps attaining ~90% locally. It was associated with a range of ductile, high-temperature extensional structures including multi-order boudinage and associated extensional bending folds, and a regional system of extension-dominated transtensional cross-folds. These ductile structures were followed by brittle–ductile fault propagation folding at higher crustal level after the gneiss complex was substantially exhumed and cooled. Collectively the data record ~60 m.y. of post-peak extension on the margin of an exceptionally large metamorphic core complex in which the ductile detachment zone has a true thickness of ~7 km. The large scale of the core complex is consistent with the deep level of erosion, and the long duration of extensional collapse is compatible with double thickness crust at the metamorphic peak, the presence of abundant leucosome in the mid crust and widespread fluid-fluxed retrogression, collectively pointing to the important role of core complexes in crustal cooling after the peak of the Grenvillian Orogeny.RÉSUMÉLe complexe gneissique de la rivière des Outaouais (ORGC) dans la portion ouest de la Province de Grenville au Québec et en Ontario est interprété comme le cœur d’un grand complexe métamorphique à coeur de noyau. Le présent article porte sur l’évolution post-pic du domaine de Muskoka, soit le niveau structural le plus élevé de l’ORGC composé en grande partie d’orthogneiss au faciès amphibolite dérivés de précurseurs au faciès granulite. Nous soutenons que la rétromorphose et les grandes déformations se sont produites durant l’effondrement orogénique et que le domaine de Muskoka en a été une zone de détachement ductile entre deux unités crustales plus résistantes, le cœur au faciès granulite sous-jacent étant le domaine Algonquin, et la chapeau sus-jacent à plus faible grade de métamorphisme comprenant le Ceinture d’Arc Composite. La formation du complexe métamorphique à coeur de noyau est survenue après l’épaississement crustale ottavien, le pic métamorphique et le possible flux en chenal, et s’est produit en régime d’amincissement crustal et d’effondrement gravitationnel au cours duquel la croûte supérieure refroidie a subit un mégaboudinage et où la croûte moyenne chaude et ductile sous-jacente a flué dans les régions entre les mégaboudins. L’amincissement crustale post-pic dans le domaine de Muskoka, qui a débuté en conditions suprasolidus, a été facilité par une rétromorphose généralisée, hétérogène, atteignant à peu près 90 % par endroits. Celle-ci a été associée avec une gamme de structures d’extension ductiles de haute température, incluant du boudinage de plusieurs ordres de grandeur et de plis de flexure d’extension, ainsi qu’un système régional de plis croisés d’origine transtensionnelle. À ces structures ductiles a succédé une phase de plissement de propagation de failles cassantes à ductiles à un plus haut niveau crustal, après que le complexe gneissique ait été exhumé et se soit refroidi. Prises ensemble, les données indiquent une extension post-pic sur la marge d’un complexe métamorphique à coeur de noyau exceptionnellement grand aux environs de 60 m.y. et dans laquelle la zone de détachement montre une épaisseur véritable d’environ 7 km. La grandeur de l’échelle du complexe métamorphique à coeur de noyau concorde avec le fort niveau d’érosion, et la grande durée de l’effondrement d’extension est compatible avec une croûte de double épaisseur au pic de métamorphisme, la présence de leucosomes abondants dans la croûte moyenne et d’une rétromorphose à flux fluidique généralisée, l’ensemble indiquant l’importance du rôle des complexes métamorphiques à coeur de noyau dans le refroidissement de la croûte après le pic de l’orogenèse grenvillienne.
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Nesbitt, Bruce E., and Karlis Muehlenbachs. "Geochemistry of syntectonic, crustal fluid regimes along the Lithoprobe Southern Canadian Cordillera Transect." Canadian Journal of Earth Sciences 32, no. 10 (October 1, 1995): 1699–719. http://dx.doi.org/10.1139/e95-134.
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In conjunction with the Lithoprobe southern Canadian Cordillera program, an extensive examination of geochemical indicators of origins, movement, chemical evolution, and economic significance of paleocrustal fluids was conducted. The study area covers approximately 360 000 km2from the Canadian Rockies to Vancouver Island. Research incorporated petrological, mineralogical, fluid-inclusion, δ18O, δD, δ13C, and Rb/Sr studies of samples of quartz ± carbonate veins and other rock types. The results of the study document a variety of pre-, syn-, and postorogenic, crustal fluid events. In the Rockies, a major pre-Laramide hydrothermal event was identified, which was comprised of a west to east migration of warm, saline brines. This was followed by a major circulation of meteoric water in the Rockies during Laramide uplift. In the southern Omineca extensional zone, convecting surface fluids penetrated to the brittle–ductile transition at 350–450 °C and locally into the underlying more ductile rocks. A principal conclusion of the study is that most quartz ± carbonate veins in metamorphic rocks in the southern Canadian Cordillera precipitated from deeply converted surface fluids. This conclusion supports a surface fluid convection model for the genesis of mesothermal Au–quartz veins, common in greenschist-facies rocks worldwide. The combination of our geochemical results with the results of other Lithoprobe studies indicates that widespread and deep convection of surface fluids in rocks undergoing active metamorphism is a commonplace phenomena in extensional settings, while in compressional-thrust settings the depth of penetration of surface fluids is more limited.
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Boerner, David E., Ron D. Kurtz, and James A. Craven. "A summary of electromagnetic studies on the Abitibi-Grenville transect." Canadian Journal of Earth Sciences 37, no. 2-3 (April 2, 2000): 427–37. http://dx.doi.org/10.1139/e99-063.
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Electromagnetic surveys on the Abitibi-Grenville Lithoprobe transect have elucidated a number of conductivity signatures that can be genetically linked to Precambrian tectonic processes. Some major fault zones are moderately conductive, possibly signalling graphite deposition from a mantle CO2 flux along crust-penetrating fault systems. However, conductive (graphitic) metasedimentary rocks characteristic of foreland basins are apparently absent from the transect area. A weak inverse correlation between metamorphic grade and electrical conductivity was observed by following rock units across the Grenville Front into high-grade equivalents within the parautochthonous belt. A uniformly conductive mid-crustal layer extends across the Grenville Front, apparently without change in character. The existence of this ubiquitous mid-crustal conductor has been interpreted to mean that electrical conductivity is controlled by the present-day pressure, temperature, and fluid saturation of the lower crust, independent of ancient structure, mineralogy, or metamorphic grade. Lower crustal (upper mantle?) electrical anisotropy is pervasive across the transect area. An apparent spatial correlation of conductivity anisotropy with Archean tectonic deformation patterns has been interpreted to indicate that the lithosphere has remained intact since the Neoarchean.
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Dvorkin, Jack, and Amos Nur. "Filtration fronts in pressure compliant reservoirs." GEOPHYSICS 57, no. 8 (August 1992): 1089–92. http://dx.doi.org/10.1190/1.1443320.
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Hydrofracturing is believed to be the major mechanism responsible for the migration of crust fluids and for the transport of hydrocarbons from overpressured fluid compartments. In their analysis of the process of porosity reduction in the earth’s crust and crustal pore pressure generation, Walder and Nur (1984) point out that elevated pore pressure generated as a result of local porosity reduction may lead to brittle failure with partial relief of high pore pressure. Such episodic fracturing accompanied by crack healing, may be a common process throughout most of the crust. Hunt (1990) also speculates that the generation of oil and gas within the compartments plus the thermal expansion of pore fluids eventually causes fracturing of the top compartment seal during periods of basin sinking. Seal fracturing causes a pressure drop with compartment fluids rushing to the breakout point. Episodic cycles of resealing and breakout may occur in intervals of thousands of years in rapidly sinking basins such as the United States Gulf coast.
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Antipin, V. S., L. V. Kushch, D. Odgerel, and O. Yu Belozerova. "Early Mesozoic Rare-Metal Granites and Metasomatites of Mongolia: Mineral and Geochemical Features and Hosted Ore Mineralization (Baga Gazriin Chuluu Pluton)." Russian Geology and Geophysics 62, no. 9 (September 1, 2021): 1061–73. http://dx.doi.org/10.2113/rgg20194162.
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Abstract —We present results of petrographic, mineralogical, and geochemical study of all types of rocks of a multiphase pluton and consider the chemical evolution of igneous and metasomatic rocks of the Baga Gazriin Chuluu pluton, based on new precise analytical data. At the early stage of their formation, the pluton granites were already enriched in many trace elements (Li, Rb, Cs, Be, Nb, Ta, Th, and U), F, and HREE relative to the upper continental crust. They show strong negative Ba, Sr, La, and Eu anomalies, which is typical of rare-metal Li–F granites. The geochemical evolution of the Baga Gazriin Chuluu multiphase pluton at the postmagmatic stage was marked by the most intense enrichment of greisens and microclinites with lithophile and ore elements (Sn, W, and Zn) and the formation of ore mineralization. In the permeable rift zone where the Baga Gazriin Chuluu pluton is located, the fluid–magma interaction took place under the impact of a mantle plume. High-temperature mantle fluids caused melting of the crustal substratum, which determined the geochemical specifics of Li–F granite intrusions. Genesis of granitic magma enriched in Li, F, Rb, Sn, and Ta is possible at the low degrees of melting of the lower crustal substratum. The Baga Gazriin Chuluu pluton formed in the upper horizons of the Earth’s crust, where magma undergoes strong differentiation and the saturation of fluids with volatiles can lead to the postmagmatic formation of metasomatites of varying alkalinity (zwitters (greisens), microclinites, and albitites) producing rare-metal mineralization. By the example of the early Mesozoic magmatism area of Mongolia, it is shown that the formation of granites and associated rare-metal minerals is due to the interaction of mantle fluids with the crustal material and the subsequent evolution of granitic magmas.
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Huppert, Herbert E., R. Stephen, and J. Sparks. "The fluid dynamics of crustal melting by injection of basaltic sills." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 79, no. 2-3 (1988): 237–43. http://dx.doi.org/10.1017/s0263593300014243.
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ABSTRACTWhen basaltic magma is emplaced into continental crust, melting and generation of granitic magma can occur. We present experimental and theoretical investigations of the fluid dynamical and heat transfer processes at the roof and floor of a basaltic sill in which the wall rocks melt. At the floor, relatively low density crustal melt rises and mixes into the overlying magma, which would form hybrid andesitic magma. Below the roof the low-density melt forms a stable layer with negligible mixing between it and the underlying hotter, denser magma. Our calculations applied to basaltic sills in hot crust predict that sills from 10-1500 m thick require only 2-200 years to solidify, during which time large volumes of overlying layers of convecting silicic magma are formed. These time scales are very short compared with the lifetimes of large silicic magma systems of around 106 years, and also with the time scale of 107 years for thermal relaxation of the continental crust. An important feature of the process is that crystallisation and melting occur simultaneously, though in different spots of the source region. The granitic magmas formed are thus a mixture of igneous phenocrysts and lesser amounts of restite crystals. Several features of either plutonic or volcanic silicic systems can be explained without requiring large, high-level, long-lived magma chambers.
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Tary, Jean Baptiste, Richard W. Hobbs, Christine Peirce, Catalina Lesmes Lesmes, and Matthew J. Funnell. "Local rift and intraplate seismicity reveal shallow crustal fluid-related activity and sub-crustal faulting." Earth and Planetary Science Letters 562 (May 2021): 116857. http://dx.doi.org/10.1016/j.epsl.2021.116857.
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Malin, Peter E., Peter C. Leary, Lawrence M. Cathles, and Christopher C. Barton. "Observational and Critical State Physics Descriptions of Long-Range Flow Structures." Geosciences 10, no. 2 (January 28, 2020): 50. http://dx.doi.org/10.3390/geosciences10020050.
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Using Fracture Seismic methods to map fluid-conducting fracture zones makes it important to understand fracture connectivity over distances greater 10–20 m in the Earth’s upper crust. The principles required for this understanding are developed here from the observations that (1) the spatial variations in crustal porosity are commonly associated with spatial variations in the magnitude of the natural logarithm of crustal permeability, and (2) many parameters, including permeability have a scale-invariant power law distribution in the crust. The first observation means that crustal permeability has a lognormal distribution that can be described as κ ≈ κ 0 exp ( α ( φ − φ 0 ) ) , where α is the ratio of the standard deviation of ln permeability from its mean to the standard deviation of porosity from its mean. The scale invariance of permeability indicates that αϕο = 3 to 4 and that the natural log of permeability has a 1/k pink noise spatial distribution. Combined, these conclusions mean that channelized flow in the upper crust is expected as the distance traversed by flow increases. Locating the most permeable channels using Seismic Fracture methods, while filling in the less permeable parts of the modeled volume with the correct pink noise spatial distribution of permeability, will produce much more realistic models of subsurface flow.
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Safonov, O. G., V. G. Butvina, E. V. Limanov, and S. A. Kosova. "Mineral indicators of reactions involving fluid salt components in the deep lithosphere." Петрология 27, no. 5 (August 18, 2019): 525–56. http://dx.doi.org/10.31857/s0869-5903275525-556.
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The salt components of H2O and H2O–CO2 fluids are very important agents of metasomatism and partial melting of crustal and mantle rocks. The paper presents examples and synthesized data on mineral associations in granulite- and amphibolite-facies rocks of various composition in the middle and lower crust and in upper-mantle eclogites and peridotites that provide evidence of reactions involving salt components of fluids. These data are analyzed together with results of model experiments that reproduce some of these associations and make it possible to more accurately determine their crystallization parameters.
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Sibson, Richard H. "Dual-Driven Fault Failure in the Lower Seismogenic Zone." Bulletin of the Seismological Society of America 110, no. 2 (January 28, 2020): 850–62. http://dx.doi.org/10.1785/0120190190.
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ABSTRACT Frictional instability leading to fault rupture may be driven by increasing differential stress or by increases in pore-fluid pressure within the rock mass. Geological evidence (from hydrothermal vein systems in exhumed faults) together with geophysical information around active faults support the localized invasion of near lithostatically overpressured hydrothermal fluids, derived from prograde metamorphism at greater depths, into lower portions of the crustal seismogenic zone at depths of about 10–15 km (250°C<T<350°C). This is especially true of compressional–transpressional tectonic regimes that lead to crustal thickening and dewatering and are better at containing overpressure. Extreme examples are associated with areas undergoing active compressional inversion where existing faults, originally formed as normal faults during crustal extension, undergo reverse-slip reactivation during subsequent shortening though poorly oriented for reactivation. Extreme fault-valve action is likely widespread in such settings with failure driven by a combination of rising fluid pressure in the lower seismogenic zone lowering fault frictional strength, as well as by rising tectonic shear stress—dual-driven fault failure. Localized overpressure affects rupture nucleation sites, but dynamic rupturing may extend well beyond the regions of intense overpressuring. Postfailure, enhanced fracture permeability along fault rupture zones promotes fault-valve discharge throughout the aftershock period, increasing fault frictional strength before hydrothermal sealing occurs and overpressures begin to reaccumulate. The association of rupture nucleation sites with concentrated fluid overpressure is consistent with selective invasion of overpressured fluid into the roots of major fault zones and with nonuniform spacing of major vein systems along exhumed brittle–ductile shear zones.
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Richard, Antonin, David A. Banks, Nina Hendriksson, and Yann Lahaye. "Lithium isotopes in fluid inclusions as tracers of crustal fluids: An exploratory study." Journal of Geochemical Exploration 184 (January 2018): 158–66. http://dx.doi.org/10.1016/j.gexplo.2017.10.017.
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Zhong, Xin, Arianne J. Petley-Ragan, Sarah H. M. Incel, Marcin Dabrowski, Niels H. Andersen, and Bjørn Jamtveit. "Lower crustal earthquake associated with highly pressurized frictional melts." Nature Geoscience 14, no. 7 (June 17, 2021): 519–25. http://dx.doi.org/10.1038/s41561-021-00760-x.
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AbstractEarthquakes at lower crustal depths are common during continental collision. However, the coseismic weakening mechanisms required to propagate an earthquake at high pressures are poorly understood. Transient high-pressure fluids or melts have been proposed as a viable mechanism, but verifying this requires direct in situ measurement of fluid or melt overpressure along fault planes that have hosted dynamic ruptures. Here, we report direct measurement of highly overpressurized frictional melts along a seismic fault surface. Using Raman spectroscopy, we identified high-pressure quartz inclusions sealed in dendritic garnets that grew from frictional melts formed by lower crustal earthquakes in the Bergen Arcs, Western Norway. Melt pressure was estimated to be 1.8–2.3 GPa on the basis of an elastic model for the quartz-in-garnet system. This is ~0.5 GPa higher than the pressure recorded by the surrounding pseudotachylyte matrix and wall rocks. The recorded melt pressure could not arise solely from the volume expansion of melting, and we propose that it was generated when melt pressure approached the maximum principal stress in a system subject to high differential stress. The associated palaeostress field demonstrates that a strong lower crust accommodated up to 1 GPa differential stress during the compressive stage of the Caledonian orogeny.
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Walter, Bastien, Yves Géraud, Yann Hautevelle, Marc Diraison, and François Raisson. "Fluid Circulations at Structural Intersections through the Toro-Bunyoro Fault System (Albertine Rift, Uganda): A Multidisciplinary Study of a Composite Hydrogeological System." Geofluids 2019 (February 27, 2019): 1–20. http://dx.doi.org/10.1155/2019/8161469.
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Regional fault structures along rift basins play a crucial role in focusing fluid circulation in the upper crust. The major Toro-Bunyoro fault system, bounding to the east of the Albertine Rift in western Uganda, hosts local fluid outflow zones within the faulted basement rocks, one of which is the Kibiro geothermal prospect. This major fault system represents a reliable example to investigate the hydrogeological properties of such regional faults, including the local structural setting of the fluid outflow zones. This study investigated five sites, where current (i.e., geothermal springs, hydrocarbon seeps) and fossil (i.e., carbonate veins) fluid circulation is recognized. This work used a multidisciplinary approach (structural interpretation of remote sensing images, field work, and geochemistry) to determine the role of the different macroscale structural features that may control each studied fluid outflow zones, as well as the nature and the source of the different fluids. The local macroscale structural setting of each of these sites systematically corresponds to the intersection between the main Toro-Bunyoro fault system and subsidiary oblique structures. Inputs from three types of fluid reservoirs are recognized within this fault-hosted hydrogeological system, with “external basin fluids” (i.e., meteoric waters), “internal basin fluids” (i.e., hydrocarbons and sediment formation waters), and deep-seated crustal fluids. This study therefore documents the complexity of a composite hydrogeological system hosted by a major rift-bounding fault system. Structural intersections act as local relative permeable areas, in which significant economic amounts of fluids preferentially converge and show surface manifestations. The rift-bounding Toro-Bunyoro fault system represents a discontinuous barrier for fluids where intersections with subsidiary oblique structures control preferential outflow zones and channel fluid transfers from the rift shoulder to the basin, and vice versa. Finally, this work contributes to the recognition of structural intersections as prime targets for exploration of fault-controlled geothermal systems.
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Vartanyan, G. S. "Global Endodrainage System: Fluid Geodynamics of Strong Crustal Earthquakes." Izvestiya, Atmospheric and Oceanic Physics 57, no. 11 (December 2021): 1436–60. http://dx.doi.org/10.1134/s0001433821110098.
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Walther, John V. "Fluid-Rock Reactions during Metamorphism at Mid-Crustal Conditions." Journal of Geology 102, no. 5 (September 1994): 559–70. http://dx.doi.org/10.1086/629698.
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Yokochi, Reika, Neil C. Sturchio, and Roland Purtschert. "Determination of crustal fluid residence times using nucleogenic 39Ar." Geochimica et Cosmochimica Acta 88 (July 2012): 19–26. http://dx.doi.org/10.1016/j.gca.2012.04.034.
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Nicoli, Gautier. "Water budget and partial melting in an Archean crustal column: example from the Dharwar Craton, India." Geological Society, London, Special Publications 489, no. 1 (February 19, 2019): 115–33. http://dx.doi.org/10.1144/sp489-2018-88.
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AbstractThe fluid budget of a composite crustal column is a critical parameter that influences many lithospheric processes. The amount of water introduced into the middle and lower crust can be quantified using phase equilibrium modelling. The Dharwar Craton, India, displays a now-exposed continuous crustal section from near-surface conditions to c. 30 km depth. This section records the different steps of a c. 15 myr-long high-temperature metamorphic event (60°C kbar−1) responsible for the formation of syn- to post-tectonic anatectic intrusions. The global water budget is assessed using thermodynamic modelling on bulk-rock compositions of an average early Proterozoic supracrustal unit and c. 3.0 Ga felsic basement, the Peninsular gneisses. Results show the fast burial of a water-saturated supracrustal package (1.6 wt%) will release c. 50% of its mineral-bound water, triggering water-fluxed partial melting of the basement. Modelled anatectic magma compositions match the observed granitoid chemistries, and distinction can be made between water-fluxed melting and water-absent melting in the origin of syn- to post-tectonic anatectic granites. Findings from this study show the importance of crustal pile heterogeneity in controlling the nature of partial melting reactions, the composition of the magmas and the rheology of the crust.
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Shaw, D. M., M. G. Truscott, E. A. Gray, and T. A. Middleton. "Boron and lithium in high-grade rocks and minerals from the Wawa–Kapuskasing region, Ontario." Canadian Journal of Earth Sciences 25, no. 9 (September 1, 1988): 1485–502. http://dx.doi.org/10.1139/e88-141.
Full textAbstract:
There is no preferential partitioning of boron among the principal rock-forming minerals in high-grade rocks of the Kapuskasing Structural Zone (KSZ) and the Wawa Domal Gneiss region (WDG). Lithium is strongly concentrated in biotite and other ferromagnesian minerals but does not show consistent partitioning between these and the sialic minerals.The distribution of B and Li within a rock may be studied using an alpha-track image, which shows that the inconsistencies in partitioning may be largely attributed to disturbance of mineral equilibria by postmetamorphic low-grade alteration that deposited B and Li.Boron has similar concentrations in all the rock types studied, although it is an incompatible element that elsewhere accumulates in pegmatites. Lithium concentrations are low in the anorthositic rocks but are otherwise very variable. In some but not all rocks higher than usual B and Li can be attributed to introduction during alteration.Boron occurs at low concentrations (2–3 ppm) throughout both the KSZ and the WDG areas and has an abundance similar to that in other granulite terranes. It is significantly lower than in average upper crustal rocks (9–15 ppm), and this is attributed to loss by fluid transport during formation of lower crustal material. Lithium occurs at similar concentrations in upper crustal rocks (20–22 ppm) as in the WDG area (27 ppm) but is lower in the KSZ (13 ppm), suggesting again a loss by fluid transport in the deep crust. Both estimates of loss are minima because of the evidence of reintroduction of the elements during later alteration.Although there is field and petrological evidence of anatectic melting in the KSZ–WDG region the distribution patterns of B and Li show no evidence of this: this is not unexpected for elements that readily partition into a fluid phase.
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Zhu, Jiao, Shan, Zhang, and Li. "Land Surface Temperature Variation Following the 2017 Mw 7.3 Iran Earthquake." Remote Sensing 11, no. 20 (October 17, 2019): 2411. http://dx.doi.org/10.3390/rs11202411.
Full textAbstract:
During an earthquake, crustal deformation, fluid flow, and temperature variation are coupled; however, earthquake-related land surface temperature (LST) variations remain unclear. To determine whether post-seismic fluid migration can cause changes in LST, and taking the Mw 7.3 2017 Iran earthquake as an example, we modeled surface cooling (CA) and warming (WA) areas induced by co-seismic slip and fluid migration using a thermo-hydro-mechanical (THM) coupled numerical simulation. Moreover, using nighttime LST data with 15-min resolution, the daily attenuation coefficient k of nighttime LST was extracted by attenuation function fitting, and the trend of the k time series was analyzed using the Mann–Kendall and Sen’s methods. Based on the comparison of k trends between the post-seismic and 2010–2016 periods, we obtained cooling and warming trends for the modeled CA and WA. The numerical simulation and observational data show good consistency, and both indicate that fluid migration caused by crustal deformation can lead to changes in LST. The numerical simulations show that after the Iran earthquake, the surface projection area of co-seismic slip correlated with a cooling area (CA), while the surrounding area correlated with a warming area (WA). For the LST observational data, the post-seismic k trends of the calculated CA and WA are positive and negative, indicating sustained cooling and warming processes, respectively. This study provides evidence that LST variation is caused by co-seismic crustal deformation and fluid migration and reveals the coupled evolution of deformation, fluid, and temperature fields. The results provide new insights into the mechanisms of seismic thermal anomalies.
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Robinson, A. H., L. Zhang, R. W. Hobbs, C. Peirce, and V. C. H. Tong. "Magmatic and tectonic segmentation of the intermediate-spreading Costa Rica Rift—a fine balance between magma supply rate, faulting and hydrothermal circulation." Geophysical Journal International 222, no. 1 (March 28, 2020): 132–52. http://dx.doi.org/10.1093/gji/ggaa152.
Full textAbstract:
SUMMARY 3-D tomographic modelling of wide-angle seismic data, recorded at the intermediate-spreading Costa Rica Rift, has revealed a P-wave seismic velocity anomaly low located beneath a small overlapping spreading centre that forms a non-transform discontinuity at the ridge axis. This low velocity zone displays a maximum velocity anomaly relative to the ‘background’ ridge axis crustal structure of ∼0.5 km s−1, has lateral dimensions of ∼10 × 5 km, and extends to depths ≥2.5 km below the seabed, placing it within layer 2 of the oceanic crust. We interpret these observations as representing increased fracturing under enhanced tectonic stress associated with the opening of the overlapping spreading centre, that results in higher upper crustal bulk porosity and permeability. Evidence for ongoing magmatic accretion at the Costa Rica Rift ridge axis takes the form of an axial magma lens beneath the western ridge segment, and observations of hydrothermal plume activity and microearthquakes support the presence of an active fluid circulation system. We propose that fracture pathways associated with the low velocity zone may provide the system through which hydrothermal fluids circulate. These fluids cause rapid cooling of the adjacent ridge axis and any magma accumulations which may be present. The Costa Rica Rift exists at a tipping point between episodic phases of magmatic and tectonically enhanced spreading. The characteristics inherited from each spreading mode have been preserved in the crustal morphology off-axis for the past 7 Myr. Using potential field data, we contextualize our seismic observations of the axial ridge structure at the whole segment scale, and find that the proposed balance between magmatic and tectonically dominated spreading processes observed off-axis may also be apparent along-axis, and that the current larger-scale magma supply system at the Costa Rica Rift may be relatively weak. Based on all available geophysical observations, we suggest a model for the inter-relationships between magmatism, faulting and fluid circulation at the Costa Rica Rift across a range of scales, which may also be influenced by large lithosphere scale structural and/or thermal heterogeneity.