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Journal articles on the topic 'Fluides crustaux'

Author: Grafiati

Published: 18 May 2024

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1

HADLICH, Ingrid Weber, Fernando Jacques ALTHOFF, Luiz Henrique RONCHI, and Michel DUBOIS. "Estudo de inclusões fluidas do Granito Parapente, Gaspar (SC): implicações para a evolução tectônica da Zona de Cisalhamento Itajaí-Perimbó." Pesquisas em Geociências 44, no. 3 (May 28, 2017): 401. http://dx.doi.org/10.22456/1807-9806.83264.

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Ao colocar rochas do Complexo Metamórfico Brusque em contato com rochas da Bacia do Itajaí, a Zona de Cisalhamento Itajaí-Perimbó assinala o limite entre os domínios central e externo do Cinturão Dom Feliciano no Escudo Catarinense. A evolução desta estrutura de escala crustal pode ser investigada por meio do estudo do Granito Parapente, que aflora no Município de Gaspar em meio à zona de cisalhamento. Com idade de cristalização de 843 Ma, este granito tipo A é um excelente marcador de deformação relacionada ao funcionamento da zona de cisalhamento. Para estimar condições de temperatura, pressão e profundidade relacionadas à deformação foram analisadas inclusões fluidas em três tipos de quartzo do Granito Parapente. As temperaturas mínimas de aprisionamento e as pressões e profundidades médias obtidas pelas inclusões fluidas são as seguintes: 220-190ºC, 6 kbar e ~23 km, para o quartzo I, da fácies menos deformada do granito, considerado mais antigo; 160-130ºC, 4 kbar e 14 km, para o quartzo II, de filonito, formado em etapa mais recente da evolução da zona de cisalhamento; e 260-220ºC, 190-170ºC, <12 km e <3 kbar para o quartzo III, de veio que corta a foliação da zona de cisalhamento. A variação de profundidade evidenciada para a formação dos quartzos I e II atesta que a zona de cisalhamento funcionou inicialmente como cavalgamento, alçando o Granito Parapente em cerca de 10 km em níveis crustais intermediários. Nos três tipos de quartzo foram observadas inclusões com fluidos aquosos com salinidades baixas, o que evidencia que a Zona de Cisalhamento Itajaí-Perimbó foi conduto para fluidos durante um longo período.

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2

Nesbitt, Bruce E. "Electrical resistivities of crustal fluids." Journal of Geophysical Research: Solid Earth 98, B3 (March 10, 1993): 4301–10. http://dx.doi.org/10.1029/92jb02576.

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3

Fyfe, W. S. "Fluids, tectonics and crustal deformation." Tectonophysics 119, no. 1-4 (October 1985): 29–36. http://dx.doi.org/10.1016/0040-1951(85)90031-9.

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4

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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5

Yardley, B. W. D. "The Ligand Chemistry of Crustal Fluids." Mineralogical Magazine 58A, no. 2 (1994): 994–95. http://dx.doi.org/10.1180/minmag.1994.58a.2.252.

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6

Tagirov, Boris, and Jacques Schott. "Aluminum speciation in crustal fluids revisited." Geochimica et Cosmochimica Acta 65, no. 21 (November 2001): 3965–92. http://dx.doi.org/10.1016/s0016-7037(01)00705-0.

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7

Saxena, S. K., and Y. Fei. "Fluids at crustal pressures and temperatures." Contributions to Mineralogy and Petrology 95, no. 3 (March 1987): 370–75. http://dx.doi.org/10.1007/bf00371850.

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8

Chen, Chien-Chih, Chow-Son Chen, and Chiou-Fen Shieh. "Crustal Electrical Conductors, Crustal Fluids and 1999 Chi-Chi, Taiwan, Earthquake." Terrestrial, Atmospheric and Oceanic Sciences 13, no. 3 (2002): 367. http://dx.doi.org/10.3319/tao.2002.13.3.367(cce).

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9

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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10

Kim, Heejung. "Need for Seismic Hydrology Research with a Geomicrobiological Focus." Sustainability 13, no. 16 (August 4, 2021): 8704. http://dx.doi.org/10.3390/su13168704.

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Earthquakes cause deformation in previously stable groundwater environments, resulting in changes to the hydrogeological characteristics. The changes to hydrological processes following large-scale earthquakes have been investigated through many physicochemical studies, but understanding of the associated geomicrobiological responses remains limited. To complement the understanding of earthquakes gathered using hydrogeochemical approaches, studies on the effects of the Earth’s deep crustal fluids on microbial community structures can be applied. These studies could help establish the degree of resilience and sustainability of the underground ecosystem following an earthquake. Furthermore, investigations on changes in the microbial community structure of the Earth’s deep crustal fluids before and after an earthquake can be used to predict an earthquake. The results derived from studies that merge hydrogeochemical and geomicrobiological changes in the deep crustal fluids due to the effect of stress on rock characteristics within a fault zone can be used to correlate these factors with earthquake occurrences. In addition, an earthquake risk evaluation method may be developed based on the observable characteristics of fault-zone aquifers.

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11

Cornet, F. H. "L’étude in situ du rôle des fluides en mécanique crustale." Revue Française de Géotechnique, no. 102 (2003): 53–70. http://dx.doi.org/10.1051/geotech/2003102053.

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12

Newton, R. C., L. Ya Aranovich, E. C. Hansen, and B. A. Vandenheuvel. "Hypersaline fluids in Precambrian deep-crustal metamorphism." Precambrian Research 91, no. 1-2 (August 1998): 41–63. http://dx.doi.org/10.1016/s0301-9268(98)00038-2.

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13

Gı́slason, Sigurdur R., Eric H. Oelkers, and Jordi Bruno. "Geochemistry of crustal fluids: an Andalusian perspective." Chemical Geology 190, no. 1-4 (October 2002): 1–11. http://dx.doi.org/10.1016/s0009-2541(02)00242-5.

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14

Manning, Craig E. "Mobilizing aluminum in crustal and mantle fluids." Journal of Geochemical Exploration 89, no. 1-3 (April 2006): 251–53. http://dx.doi.org/10.1016/j.gexplo.2005.12.019.

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15

Fehn, Udo. "Tracing Crustal Fluids: Applications of Natural129I and36Cl." Annual Review of Earth and Planetary Sciences 40, no. 1 (May 30, 2012): 45–67. http://dx.doi.org/10.1146/annurev-earth-042711-105528.

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16

Ragnarsdottir, K. Vala, and Eric H. Oelkers. "Geochemistry of crustal fluids: a Tyrolean perspective." Chemical Geology 151, no. 1-4 (October 1998): 1–9. http://dx.doi.org/10.1016/s0009-2541(98)00108-9.

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17

Huber, Julie A., H. Paul Johnson, David A. Butterfield, and John A. Baross. "Microbial life in ridge flank crustal fluids." Environmental Microbiology 8, no. 1 (January 2006): 88–99. http://dx.doi.org/10.1111/j.1462-2920.2005.00872.x.

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18

Knapp, R. B. "The role of fluids in crustal processes." Tectonophysics 202, no. 1 (February 1992): 95–96. http://dx.doi.org/10.1016/0040-1951(92)90457-h.

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19

Martin, R. J., and E. G. Bombolakis. "The role of fluids in crustal processes." Geochimica et Cosmochimica Acta 56, no. 9 (September 1992): 3607. http://dx.doi.org/10.1016/0016-7037(92)90407-a.

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20

Stel, H. "The role of fluids in crustal processes." Journal of Structural Geology 15, no. 6 (June 1993): 812. http://dx.doi.org/10.1016/0191-8141(93)90069-m.

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21

Li, Yuan, and Hans Keppler. "Nitrogen speciation in mantle and crustal fluids." Geochimica et Cosmochimica Acta 129 (March 2014): 13–32. http://dx.doi.org/10.1016/j.gca.2013.12.031.

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22

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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23

Kanna, Nagaraju, and Sandeep Gupta. "Crustal seismic structure beneath the Garhwal Himalaya using regional and teleseismic waveform modelling." Geophysical Journal International 222, no. 3 (June 22, 2020): 2040–52. http://dx.doi.org/10.1093/gji/ggaa282.

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SUMMARY We investigate the crustal seismic structure of the Garhwal Himalayan region using regional and teleseismic earthquake waveforms, recorded over 19 closely spaced broad-band seismic stations along a linear profile that traverses from the Sub Himalayas to Higher Himalayas. The regional earthquake traveltime analysis provides uppermost mantle P- and S-wave velocities as 8.2 and 4.5 km s−1, respectively. The calculated receiver functions from the teleseismic P waveforms show apparent P-to-S conversions from the Moho as well as from intracrustal depths, at most of the seismic stations. These conversions also show significant azimuthal variations across the Himalayas, indicating complex crustal structure across the Garhwal Himalaya. We constrain the receiver function modelling using the calculated uppermost mantle (Pn and Sn) velocities. Common conversion point stacking image of P-to-S conversions as well as receiver function modelling results show a prominent intracrustal low shear velocity layer with a flat–ramp–flat geometry beneath the Main Central Thrust zone. This low velocity indicates the possible presence of partial melts/fluids in the intracrustal depths beneath the Garhwal Himalaya. We correlate the inferred intracrustal partial melts/fluids with the local seismicity and suggest that the intracrustal fluids are one of the possible reasons for the occurrence of upper-to-mid-crustal earthquakes in this area. The results further show that the Moho depth varies from ∼45 km beneath the Sub Himalayas to ∼58 km to the south of the Tethys Himalayas. The calculated lower crustal shear wave velocities of ∼3.9 and 4.3 km s−1 beneath the Lesser and Higher Himalayas suggest the presence of granulite and partially eclogite rocks in the lower crust below the Lesser and Higher Himalayas, respectively. We also suggest that the inferred lower crustal rocks are the possible reasons for the presence and absence of the lower crustal seismicity beneath the Lesser and Higher Himalayas, respectively.

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24

Anonymous. "New center for study of crustal fluids opens." Eos, Transactions American Geophysical Union 75, no. 20 (1994): 228. http://dx.doi.org/10.1029/94eo00907.

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25

Dandurand, Jean Louis, and Jacques Schott. "Prediction of ion association in mixed-crustal fluids." Journal of Physical Chemistry 96, no. 19 (September 1992): 7770–77. http://dx.doi.org/10.1021/j100198a050.

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26

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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27

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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28

Brenguier, F., M. Campillo, T. Takeda, Y. Aoki, N. M. Shapiro, X. Briand, K. Emoto, and H. Miyake. "Mapping pressurized volcanic fluids from induced crustal seismic velocity drops." Science 345, no. 6192 (July 3, 2014): 80–82. http://dx.doi.org/10.1126/science.1254073.

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Volcanic eruptions are caused by the release of pressure that has accumulated due to hot volcanic fluids at depth. Here, we show that the extent of the regions affected by pressurized fluids can be imaged through the measurement of their response to transient stress perturbations. We used records of seismic noise from the Japanese Hi-net seismic network to measure the crustal seismic velocity changes below volcanic regions caused by the 2011 moment magnitude (Mw) 9.0 Tohoku-Oki earthquake. We interpret coseismic crustal seismic velocity reductions as related to the mechanical weakening of the pressurized crust by the dynamic stress associated with the seismic waves. We suggest, therefore, that mapping seismic velocity susceptibility to dynamic stress perturbations can be used for the imaging and characterization of volcanic systems.

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29

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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30

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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31

Shaparenko, Elena, Nadezhda Gibsher, Anatoly Tomilenko, Anatoly Sazonov, Taras Bul’bak, Maria Ryabukha, Margarita Khomenko, Sergey Silyanov, Natalya Nekrasova, and Marina Petrova. "Ore–Bearing Fluids of the Blagodatnoye Gold Deposit (Yenisei Ridge, Russia): Results of Fluid Inclusion and Isotopic Analyses." Minerals 11, no. 10 (October 3, 2021): 1090. http://dx.doi.org/10.3390/min11101090.

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The Blagodatnoye deposit with 340 t gold reserves is one of the most productive mines in Russia. Modern methods of studying fluid inclusions were used to determine the properties of fluids that formed this deposit. A comprehensive study revealed that the Blagodatnoye gold deposit was formed between 120 and 350 °C and at 0.2–2.6 kbar, and from fluids with salinities ranging from 0.5 to 30 wt.% (NaCl–eq.). These fluids are: 1—water–carbon dioxide; 2—carbon dioxide–hydrocarbon; 3—highly saline aqueous. According to Raman spectroscopy and gas chromatography–mass spectrometry, ore–forming fluids contained H2O, CO2, hydrocarbons and oxygenated organic compounds, sulfonated, nitrogenated and halogenated compounds. Early oxidized water–carbon dioxide fluids formed barren associations of the deposit. Later reduced carbon dioxide–hydrocarbon fluids had a key role in the formation of gold-bearing quartz veins. The stable isotope data (δ34S = 0.8 to 21.3‰, δ13C = −2.8 to −20.9‰, 3He/4He = 0.14 ± 0.3 × 10–6) suggest the ore-forming fluids have a crustal source.

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32

SANTOSH, M., Toshiaki TSUNOGAE, and Shin-ichi YOSHIKURA. ""Ultrahigh density" carbonic fluids in ultrahigh-temperature crustal metamorphism." Journal of Mineralogical and Petrological Sciences 99, no. 4 (2004): 164–79. http://dx.doi.org/10.2465/jmps.99.164.

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33

Walther, J. V. "Determining the thermodynamic properties of solutes in crustal fluids." American Journal of Science 291, no. 5 (May 1, 1991): 453–72. http://dx.doi.org/10.2475/ajs.291.5.453.

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34

Pokrovski, Gleb S., Sami Kara, and Jacques Roux. "Stability and solubility of arsenopyrite, FeAsS, in crustal fluids." Geochimica et Cosmochimica Acta 66, no. 13 (July 2002): 2361–78. http://dx.doi.org/10.1016/s0016-7037(02)00836-0.

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35

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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36

Long, Leland Timothy. "A Model for Major Intraplate Continental Earthquakes." Seismological Research Letters 59, no. 4 (October 1, 1988): 273–78. http://dx.doi.org/10.1785/gssrl.59.4.273.

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Abstract Traditional paradigms of continental seismicity assert the stationarity of the earthquake process and a causal association of earthquakes with active faults, increasing levels of stress, and crustal structures, in a framework of Plate Tectonics. I propose, instead, that the seismicity associated with a magnitude six or greater intraplate continental earthquake is a transient phenomenon responding to a perturbation in crustal strength independent of existing faults and crustal structures. Regional plate stress may still provide the driving energy, but the causative stress is released by a perturbation in crustal strength in the vicinity of a major earthquake. The timing of a major earthquake and the characteristics of the associated seismicity may then be described by a sequence of five phases which are as follows: (1) Initiation. A major intraplate continental earthquake is initiated with a disturbance in the hydraulic or thermal properties of the crust below the epicenter. Such disturbances could be induced by the intrusion of a sill or by partial melting. (2) Strength corrosion. A corrosion in crustal strength follows the upward migration of fluids or heat from the area of recent disturbance. (3) Stress concentration. As a weakened central zone deforms in response to tectonic plate stress, stresses are concentrated in the surrounding rigid crust. (4) Failure. A major earthquake occurs when the stress surrounding the weakened core exceeds the crustal strength, either because the concentrated stresses are anomalously high or because the dispersing fluids have spread beyond the core. (5) Crustal healing. The final phase in the occurrence of a major intraplate continental earthquake is an extended aftershock sequence which is concentrated along the rupture zone of the main event. The occurrence of a major intraplate earthquake as described above releases the strain energy in a perturbed area. Additional major events would be unlikely until the strength has recovered sufficiently to equalize intraplate stress and permit a repeat of the cycle.

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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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Trembath-Reichert, Elizabeth, Sunita R. Shah Walter, Marc Alec Fontánez Ortiz, Patrick D. Carter, Peter R. Girguis, and Julie A. Huber. "Multiple carbon incorporation strategies support microbial survival in cold subseafloor crustal fluids." Science Advances 7, no. 18 (April 2021): eabg0153. http://dx.doi.org/10.1126/sciadv.abg0153.

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Biogeochemical processes occurring in fluids that permeate oceanic crust make measurable contributions to the marine carbon cycle, but quantitative assessments of microbial impacts on this vast, subsurface carbon pool are lacking. We provide bulk and single-cell estimates of microbial biomass production from carbon and nitrogen substrates in cool, oxic basement fluids from the western flank of the Mid-Atlantic Ridge. The wide range in carbon and nitrogen incorporation rates indicates a microbial community well poised for dynamic conditions, potentially anabolizing carbon and nitrogen at rates ranging from those observed in subsurface sediments to those found in on-axis hydrothermal vent environments. Bicarbonate incorporation rates were highest where fluids are most isolated from recharging bottom seawater, suggesting that anabolism of inorganic carbon may be a potential strategy for supplementing the ancient and recalcitrant dissolved organic carbon that is prevalent in the globally distributed subseafloor crustal environment.

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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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Yaxley, Gregory M., Bruce A. Kjarsgaard, and A. Lynton Jaques. "Evolution of Carbonatite Magmas in the Upper Mantle and Crust." Elements 17, no. 5 (October 1, 2021): 315–20. http://dx.doi.org/10.2138/gselements.17.5.315.

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Carbonatites are the most silica-poor magmas known and are amongst Earth’s most enigmatic igneous rocks. They crystallise to rocks dominated by the carbonate minerals calcite and dolomite. We review models for carbonatite petrogenesis, including direct partial melting of mantle lithologies, exsolution from silica-undersaturated alkali silicate melts, or direct fractionation of carbonated silicate melts to carbonate-rich residual melts. We also briefly discuss carbonatite–mantle wall-rock reactions and other processes at mid-to upper crustal depths, including fenitisation, overprinting by carbohydrothermal fluids, and reaction between carbonatite melt and crustal lithologies.

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Barberio, Marino Domenico, Francesca Gori, Maurizio Barbieri, Tiziano Boschetti, Antonio Caracausi, Giovanni Luca Cardello, and Marco Petitta. "Understanding the Origin and Mixing of Deep Fluids in Shallow Aquifers and Possible Implications for Crustal Deformation Studies: San Vittorino Plain, Central Apennines." Applied Sciences 11, no. 4 (February 3, 2021): 1353. http://dx.doi.org/10.3390/app11041353.

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Expanding knowledge about the origin and mixing of deep fluids and the water–rock–gas interactions in aquifer systems can represent an improvement in the comprehension of crustal deformation processes. An analysis of the deep and meteoric fluid contributions to a regional groundwater circulation model in an active seismic area has been carried out. We performed two hydrogeochemical screenings of 15 springs in the San Vittorino Plain (central Italy). Furthermore, we updated the San Vittorino Plain structural setting with a new geological map and cross-sections, highlighting how and where the aquifers are intersected by faults. The application of Na-Li geothermometers, coupled with trace element and gas analyses, agrees in attributing the highest temperatures (>150 °C), the greatest enrichments in Li (124.3 ppb) and Cs (>5 ppb), and traces of mantle-derived He (1–2%) to springs located in correspondence with high-angle faults (i.e., S5, S11, S13, and S15). This evidence points out the role of faults acting as vehicles for deep fluids into regional carbonate aquifers. These results highlight the criteria for identifying the most suitable sites for monitoring variations in groundwater geochemistry due to the uprising of deep fluids modulated by fault activity to be further correlated with crustal deformation and possibly with seismicity.

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Meyer, Franz Michael. "Case Histories of Orogenic Gold Deposits." Minerals 13, no. 3 (March 6, 2023): 369. http://dx.doi.org/10.3390/min13030369.

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This review compares genetic parameters of 12 orogenic gold deposits. The set of examples is considered to represent largely the variability of orogenic gold deposit (OGD) characteristics. The data are presented in tables and include following definitive parameters: regional geologic settings, nature of hosts rocks and mineralization, ore controlling structures, ages of host rocks and mineralization and timing of mineralization relative to metamorphism, hydrothermal alteration mineralogy and ore mineral assemblages, isotopic signatures, physical conditions of ore formation and proposed origin of ore fluids aa well as gold reserves, production, and grades. This allows comparison of deposits from different geologic terrains having different ages and formed under different P-T conditions. The data are further discussed before the background of the orogenic gold system and the crustal metamorphic models that provide different scenarios to explain the source of ore fluids. The orogenic gold system model advocates a metal and fluid source external to the terrain in which mineralization occurred, but the model applies only for 3 of the 12 deposits studied. All other deposits formed most likely from a crustal source, which would favor the crustal metamorphic model. However, the formation of hypozonal OGDs cannot be accounted for by the crustal metamorphic model or by the metamorphic devolatilization model. The data identify a set of coherent signatures in OGDs, but there seem to be no unified model for all possible environmental conditions and facets of ore formation and fluid sources, tectonic and lithologic setting, and scale of gold endowment.

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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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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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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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Thompson, Alan Bruce, and James A. D. Connolly. "Generation and migration of deep crustal fluids during regional metamorphism." Chemical Geology 70, no. 1-2 (August 1988): 165. http://dx.doi.org/10.1016/0009-2541(88)90685-7.

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47

Ayers, J. C., L. Zhang, Y. Luo, and T. J. Peters. "Zircon solubility in alkaline aqueous fluids at upper crustal conditions." Geochimica et Cosmochimica Acta 96 (November 2012): 18–28. http://dx.doi.org/10.1016/j.gca.2012.08.027.

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48

Weber, Ulrich Wolfgang, Niko Kampman, and Anja Sundal. "Techno-Economic Aspects of Noble Gases as Monitoring Tracers." Energies 14, no. 12 (June 10, 2021): 3433. http://dx.doi.org/10.3390/en14123433.

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A comprehensive monitoring program is an integral part of the safe operation of geological CO2 storage projects. Noble gases can be used as geochemical tracers to detect a CO2 anomaly and identify its origin, since they display unique signatures in the injected CO2 and naturally occurring geological fluids and gases of the storage site complex. In this study, we assess and demonstrate the suitability of noble gases in source identification of CO2 anomalies even when natural variability and analytical uncertainties are considered. Explicitly, injected CO2 becomes distinguishable from shallow fluids (e.g., subsea gas seeps) due to its inheritance of the radiogenic signature (e.g., high He) of deep crustal fluids by equilibration with the formation water. This equilibration also results in the CO2 inheriting a distinct Xe concentration and Xe/noble gas elemental ratios, which enable the CO2 to be differentiated from deep crustal hydrocarbon gases that may be in the vicinity of a storage reservoir. However, the derivation has uncertainties that may make the latter distinction less reliable. These uncertainties would be best and most economically addressed by coinjection of Xe with a distinct isotope ratio into the CO2 stream. However, such a tracer addition would add significant cost to monitoring programs of currently operating storage projects by up to 70% (i.e., from 1 $US/t to 1.7 $US/t).

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49

Nakagawa, Satoshi, Fumio Inagaki, Yohey Suzuki, Bjørn Olav Steinsbu, Mark Alexander Lever, Ken Takai, Bert Engelen, Yoshihiko Sako, Charles Geoffrey Wheat, and Koki Horikoshi. "Microbial Community in Black Rust Exposed to Hot Ridge Flank Crustal Fluids." Applied and Environmental Microbiology 72, no. 10 (August 21, 2006): 6789–99. http://dx.doi.org/10.1128/aem.01238-06.

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ABSTRACT During Integrated Ocean Drilling Program Expedition 301, we obtained a sample of black rust from a circulation obviation retrofit kit (CORK) observatory at a borehole on the eastern flank of Juan de Fuca Ridge. Due to overpressure, the CORK had failed to seal the borehole. Hot fluids from oceanic crust had discharged to the overlying bottom seawater and resulted in the formation of black rust analogous to a hydrothermal chimney deposit. Both culture-dependent and culture-independent analyses indicated that the black-rust-associated community differed from communities reported from other microbial habitats, including hydrothermal vents at seafloor spreading centers, while it shared phylotypes with communities previously detected in crustal fluids from the same borehole. The most frequently retrieved sequences of bacterial and archaeal 16S rRNA genes were related to the genera Ammonifex and Methanothermococcus, respectively. Most phylotypes, including phylotypes previously detected in crustal fluids, were isolated in pure culture, and their metabolic traits were determined. Quantification of the dissimilatory sulfite reductase (dsrAB) genes, together with stable sulfur isotopic and electron microscopic analyses, strongly suggested the prevalence of sulfate reduction, potentially by the Ammonifex group of bacteria. Stable carbon isotopic analyses suggested that the bulk of the microbial community was trophically reliant upon photosynthesis-derived organic matter. This report provides important insights into the phylogenetic, physiological, and trophic characteristics of subseafloor microbial ecosystems in warm ridge flank crusts.

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LaFlamme, Crystal, Christopher R. M. McFarlane, and David Corrigan. "Neoarchean Mantle-derived Magmatism within the Repulse Bay Block, Melville Peninsula, Nunavut: Implications for Archean Crustal Extraction and Cratonization." Geoscience Canada 42, no. 3 (July 29, 2015): 305. http://dx.doi.org/10.12789/geocanj.2015.42.065.

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SUMMARYThe Repulse Bay block (RBb) of the southern Melville Peninsula, Nunavut, lies within the Rae craton and exposes a large (50,000 km2) area of middle to lower crust. The block is composed of ca. 2.86 Ga and 2.73–2.71 Ga tonalite-trondhjemite-granodiorite (TTG) and granitic gneiss that was derived from an older 3.25 and 3.10 Ga crustal substrate. This period of crustal generation was followed by the emplacement of ca. 2.69–2.66 Ga enderbite, charnockite, and granitoid intrusions with entrained websterite xenoliths. These voluminous batholith-scale bodies (dehydrated and hydrated intrusions), and the associated websterite xenoliths, have similar whole rock geochemical properties, including fractionated light rare earth element (LREE)–heavy (H)REE whole rock patterns and negative Nb, Ti, and Ta anomalies. Dehydrated intrusions and websterite xenoliths also contain similar mineralogy (two pyroxene, biotite, interstitial amphibole) and similar pyroxene trace element compositions. Based on geochemical and mineralogical properties, the two lithologies are interpreted to be related by fractional crystallization, and to be the product of a magmatic cumulate processes. Reworking of the crust in a ca. 2.72 Ga subduction zone setting was followed by ca. 2.69 Ga upwelling of the asthenospheric mantle and the intrusion of massif-type granitoid plutons. Based on a dramatic increase in FeO, Zr, Hf, and LREE content of the most evolved granitoid components from the 2.69–2.66 Ga cumulate intrusion, we propose that those granitoid plutons were in part derived from a metasomatized mantle source enriched by fluids from the subducting oceanic slab that underwent further hybridization (via assimilation) with the crust. Large-scale, mantle-derived Neoarchean sanukitoid-type magmatism played a role in the development of a depleted lower crust and residual sub-continental lithospheric mantle, a crucial element in the preservation of the RBb.RÉSUMÉLe bloc de Repulse Bay (RBb) dans le sud de la péninsule de Melville, au Nunavut, est situé dans le craton de Rae et expose une large zone (50 000 km2) de croûte moyenne à inférieur. Ce bloc est composé de tonalite-trondhjémite-granodiorite (TTG) daté à ca. 2,86 Ga et 2,73–2,71 Ga, et de gneiss granitique dérivé d’un substrat crustal plus ancien daté à 3,25 Ga et 3,10 Ga. Cette période de croissance crustale a été suivie par la mise en place entre ca. 2,69 et 2,66 Ga d’intrusions d’enderbite, charnockite et de granitoïde incluant des xénolites d’entraînement de websterite. Ces intrusions de taille batholitique (intrusions déshydratées et hydratées) ainsi que les xénolites d’entraînement de websterite associés, ont des propriétés géochimiques sur roche totale semblables notamment leurs profils de fractionnement des terres rares légers (LREE) et des terres rares lourds (HREE) ainsi que leurs anomalies négatives en Nb, Ti et Ta. Les intrusions déshydratées et les xénolites de websterite ont aussi des minéralogies similaires (deux pyroxènes, biotite, amphibole interstitielle) ainsi que des compositions semblables en éléments traces de leurs pyroxènes. Étant donné leurs propriétés géochimiques et minéralogiques, ces deux lithologies sont interprétées comme provenant d’une cristallisation fractionnée, et comme étant le produit de processus d'accumulations magmatiques. Le remaniement de la croûte dans un contexte de subduction vers ca. 2,72 Ga, a été suivi vers ca. 2,69 Ga d’une remontée du manteau asthénosphérique et de l’intrusion de granitoïdes de type massif. D'après l’importante augmentation en FeO, Zr, Hf et LREE dans les granitoïdes les plus évolués du magmatisme ayant pris place entre ca. 2,69 Ga et 2,66 Ga, nous proposons que ces plutons aient été en partie dérivés d’une source mantélique métasomatisée enrichies par des fluides d’une plaque océanique en subduction et qui a subi une hybridation supplémentaire (par assimilation) avec la croûte. Le magmatisme néo-archéen de type sanukitoïde, dérivé du manteau et de grande échelle, a joué un rôle dans le développement d’une croûte inférieure et d’un manteau lithosphérique continental résiduel appauvri, un élément déterminant pour la préservation du RBb.

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