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David Phillips - One of the best experts on this subject based on the ideXlab platform.
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mid Crustal Fluid mixing in a proterozoic fe oxide cu au deposit ernest henry australia evidence from ar kr xe cl br and i
Earth and Planetary Science Letters, 2007Co-Authors: Mark A. Kendrick, Geordie Mark, David PhillipsAbstract:Fluid inclusions in six quartz veins associated with Cu–Au mineralisation at the giant Ernest Henry iron oxide–copper–gold deposit (167 Mt 1.1% Cu, 0.54 ppm Au) in northwest Queensland, have been analysed for naturally occurring and neutron produced noble gas isotopes of Ar, Kr and Xe. A combination of thermal and mechanical decrepitation methods enables distinction between four types of Fluid inclusion. Ultra-high-salinity (∼30 to 70 wt. % NaCl eq.) Fluid inclusions have compositions that define two end-members that are variably mixed in different samples. The first end-member has a 40 Ar/ 36 Ar value of ∼29,000, a 40 ArE/Cl value of ∼3×10 −3 and mantle-like Br/Cl and I/Cl values of 1–2×10 −3 and ∼11×10 −6 , respectively. The second end-member has a much lower 40 Ar/ 36 Ar value of less than 2500, a 40 ArE/Cl value of ∼10 −6 , low Br/Cl values of ∼0.4×10 −3 and I/Cl values of 1–2×10 −6 (all ratios are molar). Carbon dioxide and later, lower salinity liquid-vapour Fluid inclusions have similar 40 Ar/ 36 Ar values of less than ∼2500 in all samples. These data are compatible with genetic models in which Cu–Au mineralisation formed at a depth of 6-10 km, from circulation of magmatic Fluids derived from regionally abundant ‘A-type’ granites and a high salinity halite dissolution brine generated from sedimentary formation waters in the upper crust. The largest source of CO2 was probably carbonate-rich lithologies in the midcrust. Later, lower salinity Fluids with a surficial origin diluted the mineralising brines and are preserved in the latest, secondary Fluid inclusions. These data provide insight on the composition of Crustal Fluids during the Proterozoic. Furthermore, the magmatic Fluid endmember, derived from melts generated by re-melting lower-Crustal Paleoproterozoic igneous rocks with a mantle source, preserves mantle-like Br/Cl and I/Cl. These geochemical characteristics are interpreted to provide insight on I-recycling at subduction zones and the composition of seawater in the Paleoproterozoic. © 2007 Elsevier B.V. All rights reserved.
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Mid-Crustal Fluid mixing in a Proterozoic Fe oxide–Cu–Au deposit, Ernest Henry, Australia: Evidence from Ar, Kr, Xe, Cl, Br, and I
Earth and Planetary Science Letters, 2007Co-Authors: Mark A. Kendrick, Geordie Mark, David PhillipsAbstract:Fluid inclusions in six quartz veins associated with Cu–Au mineralisation at the giant Ernest Henry iron oxide–copper–gold deposit (167 Mt 1.1% Cu, 0.54 ppm Au) in northwest Queensland, have been analysed for naturally occurring and neutron produced noble gas isotopes of Ar, Kr and Xe. A combination of thermal and mechanical decrepitation methods enables distinction between four types of Fluid inclusion. Ultra-high-salinity (∼30 to 70 wt. % NaCl eq.) Fluid inclusions have compositions that define two end-members that are variably mixed in different samples. The first end-member has a 40 Ar/ 36 Ar value of ∼29,000, a 40 ArE/Cl value of ∼3×10 −3 and mantle-like Br/Cl and I/Cl values of 1–2×10 −3 and ∼11×10 −6 , respectively. The second end-member has a much lower 40 Ar/ 36 Ar value of less than 2500, a 40 ArE/Cl value of ∼10 −6 , low Br/Cl values of ∼0.4×10 −3 and I/Cl values of 1–2×10 −6 (all ratios are molar). Carbon dioxide and later, lower salinity liquid-vapour Fluid inclusions have similar 40 Ar/ 36 Ar values of less than ∼2500 in all samples. These data are compatible with genetic models in which Cu–Au mineralisation formed at a depth of 6-10 km, from circulation of magmatic Fluids derived from regionally abundant ‘A-type’ granites and a high salinity halite dissolution brine generated from sedimentary formation waters in the upper crust. The largest source of CO2 was probably carbonate-rich lithologies in the midcrust. Later, lower salinity Fluids with a surficial origin diluted the mineralising brines and are preserved in the latest, secondary Fluid inclusions. These data provide insight on the composition of Crustal Fluids during the Proterozoic. Furthermore, the magmatic Fluid endmember, derived from melts generated by re-melting lower-Crustal Paleoproterozoic igneous rocks with a mantle source, preserves mantle-like Br/Cl and I/Cl. These geochemical characteristics are interpreted to provide insight on I-recycling at subduction zones and the composition of seawater in the Paleoproterozoic. © 2007 Elsevier B.V. All rights reserved.
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Mid-Crustal Fluid mixing in a Proterozoic Fe oxide–Cu–Au deposit, Ernest Henry, Australia: Evidence from Ar, Kr, Xe, Cl, Br, and I
Earth and Planetary Science Letters, 2007Co-Authors: Mark A. Kendrick, G. Mark, David PhillipsAbstract:Fluid inclusions in six quartz veins associated with Cu-Au mineralisation at the giant Ernest Henry iron oxide-copper-gold deposit (167\ua0Mt 1.1% Cu, 0.54\ua0ppm Au) in northwest Queensland, have been analysed for naturally occurring and neutron produced noble gas isotopes of Ar, Kr and Xe. A combination of thermal and mechanical decrepitation methods enables distinction between four types of Fluid inclusion. Ultra-high-salinity (∼ 30 to 70\ua0wt. % NaCl eq.) Fluid inclusions have compositions that define two end-members that are variably mixed in different samples. The first end-member has a Ar/Ar value of ∼ 29,000, a Ar/Cl value of ∼ 3 × 10 and mantle-like Br/Cl and I/Cl values of 1-2 × 10 and ∼ 11 × 10, respectively. The second end-member has a much lower Ar/Ar value of less than 2500, a Ar/Cl value of ∼ 10, low Br/Cl values of ∼ 0.4 × 10 and I/Cl values of 1-2 × 10 (all ratios are molar). Carbon dioxide and later, lower salinity liquid-vapour Fluid inclusions have similar Ar/Ar values of less than ∼ 2500 in all samples. These data are compatible with genetic models in which Cu-Au mineralisation formed at a depth of 6-10\ua0km, from circulation of magmatic Fluids derived from regionally abundant 'A-type' granites and a high salinity halite dissolution brine generated from sedimentary formation waters in the upper crust. The largest source of CO was probably carbonate-rich lithologies in the mid-crust. Later, lower salinity Fluids with a surficial origin diluted the mineralising brines and are preserved in the latest, secondary Fluid inclusions. These data provide insight on the composition of Crustal Fluids during the Proterozoic. Furthermore, the magmatic Fluid end-member, derived from melts generated by re-melting lower-Crustal Paleoproterozoic igneous rocks with a mantle source, preserves mantle-like Br/Cl and I/Cl. These geochemical characteristics are interpreted to provide insight on I-recycling at subduction zones and the composition of seawater in the Paleoproterozoic
J.-l. Devidal - One of the best experts on this subject based on the ideXlab platform.
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Disturbance versus preservation of U–Th–Pb ages in monazite during Fluid–rock interaction: textural, chemical and isotopic in situ study in microgranites (Velay Dome, France)
Contributions to Mineralogy and Petrology, 2013Co-Authors: A. Didier, V. Bosse, P. Boulvais, J. Bouloton, J.-l. Paquette, J.-m. Montel, J.-l. DevidalAbstract:Monazite is extensively used to date Crustal processes and is usually considered to be resistant to diffusive Pb loss. Nevertheless, Fluid-assisted recrystallisation is known to be capable of resetting the monazite chronometer. This study focuses on chemical and isotopic disturbances in monazite grains from two microgranite intrusions in the French Central Massif (Charron and Montasset). Petrologic data and oxygen isotopes suggest that both intrusions have interacted with alkali-bearing hydrothermal-magmatic Fluids. In the Charron intrusion, regardless of their textural location, monazite grains are sub-euhedral and cover a large domain of compositions. U–Pb chronometers yield a lower intercept age of 297 ± 4 Ma. An inherited component at 320 Ma is responsible for the scattering of the U–Th–Pb ages. The Montasset intrusion was later affected by an additional F-rich Crustal Fluid with crystallisation of Ca-REE-fluorocarbonates, fluorite, calcite and chloritisation. Pristine monazite is chemically homogeneous and displays ^208Pb/^232Th and ^206Pb/^238U concordant ages at 307 ± 2 Ma. By contrast, groundmass monazite shows dissolution-recrystallisation features associated with apatite and thorite precipitation (Th-silicate) and strong chemical reequilibration. ^208Pb/^232Th ages are disturbed and range between 270 and 690 Ma showing that the Th/Pb ratio is highly fractionated during the interaction with Fluids. Apparent U–Pb ages are older due to common Pb incorporation yielding a lower intercept age at 312 ± 10 Ma, the age of the pristine monazite. These results show that F-rich Fluids are responsible for Th mobility and incorporation of excess Pb, which thus strongly disturbed the U–Th–Pb chronometers in the monazite.
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Disturbance versus preservation of U-Th-Pb ages in monazite during Fluid-rock interaction: textural, chemical and isotopic in situ study in microgranites (Velay Dome, France)
Contributions to Mineralogy and Petrology, 2013Co-Authors: A. Didier, V. Bosse, P. Boulvais, J. Bouloton, J.-l. Paquette, J.-m. Montel, J.-l. DevidalAbstract:Monazite is extensively used to date Crustal processes and is usually considered to be resistant to diffusive Pb loss. Nevertheless, Fluid-assisted recrystallisation is known to be capable of resetting the monazite chronometer. This study focuses on chemical and isotopic disturbances in monazite grains from two microgranite intrusions in the French Central Massif (Charron and Montasset). Petrologic data and oxygen isotopes suggest that both intrusions have interacted with alkali-bearing hydrothermal-magmatic Fluids. In the Charron intrusion, regardless of their textural location, monazite grains are sub-euhedral and cover a large domain of compositions. U-Pb chronometers yield a lower intercept age of 297 ± 4 Ma. An inherited component at 320 Ma is responsible for the scattering of the U-Th-Pb ages. The Montasset intrusion was later affected by an additional F-rich Crustal Fluid with crystallisation of Ca-REE-fluorocarbonates, fluorite, calcite and chloritisation. Pristine monazite is chemically homogeneous and displays 208Pb/232Th and 206Pb/238U concordant ages at 307 ± 2 Ma. By contrast, groundmass monazite shows dissolution- recrystallisation features associated with apatite and thorite precipitation (Th-silicate) and strong chemical reequilibration. 208Pb/232Th ages are disturbed and range between 270 and 690 Ma showing that the Th/Pb ratio is highly fractionated during the interaction with Fluids. Apparent U-Pb ages are older due to common Pb incorporation yielding a lower intercept age at 312 ± 10 Ma, the age of the pristine monazite. These results show that F-rich Fluids are responsible for Th mobility and incorporation of excess Pb, which thus strongly disturbed the U-Th-Pb chronometers in the monazite.
Mark A. Kendrick - One of the best experts on this subject based on the ideXlab platform.
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mid Crustal Fluid mixing in a proterozoic fe oxide cu au deposit ernest henry australia evidence from ar kr xe cl br and i
Earth and Planetary Science Letters, 2007Co-Authors: Mark A. Kendrick, Geordie Mark, David PhillipsAbstract:Fluid inclusions in six quartz veins associated with Cu–Au mineralisation at the giant Ernest Henry iron oxide–copper–gold deposit (167 Mt 1.1% Cu, 0.54 ppm Au) in northwest Queensland, have been analysed for naturally occurring and neutron produced noble gas isotopes of Ar, Kr and Xe. A combination of thermal and mechanical decrepitation methods enables distinction between four types of Fluid inclusion. Ultra-high-salinity (∼30 to 70 wt. % NaCl eq.) Fluid inclusions have compositions that define two end-members that are variably mixed in different samples. The first end-member has a 40 Ar/ 36 Ar value of ∼29,000, a 40 ArE/Cl value of ∼3×10 −3 and mantle-like Br/Cl and I/Cl values of 1–2×10 −3 and ∼11×10 −6 , respectively. The second end-member has a much lower 40 Ar/ 36 Ar value of less than 2500, a 40 ArE/Cl value of ∼10 −6 , low Br/Cl values of ∼0.4×10 −3 and I/Cl values of 1–2×10 −6 (all ratios are molar). Carbon dioxide and later, lower salinity liquid-vapour Fluid inclusions have similar 40 Ar/ 36 Ar values of less than ∼2500 in all samples. These data are compatible with genetic models in which Cu–Au mineralisation formed at a depth of 6-10 km, from circulation of magmatic Fluids derived from regionally abundant ‘A-type’ granites and a high salinity halite dissolution brine generated from sedimentary formation waters in the upper crust. The largest source of CO2 was probably carbonate-rich lithologies in the midcrust. Later, lower salinity Fluids with a surficial origin diluted the mineralising brines and are preserved in the latest, secondary Fluid inclusions. These data provide insight on the composition of Crustal Fluids during the Proterozoic. Furthermore, the magmatic Fluid endmember, derived from melts generated by re-melting lower-Crustal Paleoproterozoic igneous rocks with a mantle source, preserves mantle-like Br/Cl and I/Cl. These geochemical characteristics are interpreted to provide insight on I-recycling at subduction zones and the composition of seawater in the Paleoproterozoic. © 2007 Elsevier B.V. All rights reserved.
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Mid-Crustal Fluid mixing in a Proterozoic Fe oxide–Cu–Au deposit, Ernest Henry, Australia: Evidence from Ar, Kr, Xe, Cl, Br, and I
Earth and Planetary Science Letters, 2007Co-Authors: Mark A. Kendrick, Geordie Mark, David PhillipsAbstract:Fluid inclusions in six quartz veins associated with Cu–Au mineralisation at the giant Ernest Henry iron oxide–copper–gold deposit (167 Mt 1.1% Cu, 0.54 ppm Au) in northwest Queensland, have been analysed for naturally occurring and neutron produced noble gas isotopes of Ar, Kr and Xe. A combination of thermal and mechanical decrepitation methods enables distinction between four types of Fluid inclusion. Ultra-high-salinity (∼30 to 70 wt. % NaCl eq.) Fluid inclusions have compositions that define two end-members that are variably mixed in different samples. The first end-member has a 40 Ar/ 36 Ar value of ∼29,000, a 40 ArE/Cl value of ∼3×10 −3 and mantle-like Br/Cl and I/Cl values of 1–2×10 −3 and ∼11×10 −6 , respectively. The second end-member has a much lower 40 Ar/ 36 Ar value of less than 2500, a 40 ArE/Cl value of ∼10 −6 , low Br/Cl values of ∼0.4×10 −3 and I/Cl values of 1–2×10 −6 (all ratios are molar). Carbon dioxide and later, lower salinity liquid-vapour Fluid inclusions have similar 40 Ar/ 36 Ar values of less than ∼2500 in all samples. These data are compatible with genetic models in which Cu–Au mineralisation formed at a depth of 6-10 km, from circulation of magmatic Fluids derived from regionally abundant ‘A-type’ granites and a high salinity halite dissolution brine generated from sedimentary formation waters in the upper crust. The largest source of CO2 was probably carbonate-rich lithologies in the midcrust. Later, lower salinity Fluids with a surficial origin diluted the mineralising brines and are preserved in the latest, secondary Fluid inclusions. These data provide insight on the composition of Crustal Fluids during the Proterozoic. Furthermore, the magmatic Fluid endmember, derived from melts generated by re-melting lower-Crustal Paleoproterozoic igneous rocks with a mantle source, preserves mantle-like Br/Cl and I/Cl. These geochemical characteristics are interpreted to provide insight on I-recycling at subduction zones and the composition of seawater in the Paleoproterozoic. © 2007 Elsevier B.V. All rights reserved.
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Mid-Crustal Fluid mixing in a Proterozoic Fe oxide–Cu–Au deposit, Ernest Henry, Australia: Evidence from Ar, Kr, Xe, Cl, Br, and I
Earth and Planetary Science Letters, 2007Co-Authors: Mark A. Kendrick, G. Mark, David PhillipsAbstract:Fluid inclusions in six quartz veins associated with Cu-Au mineralisation at the giant Ernest Henry iron oxide-copper-gold deposit (167\ua0Mt 1.1% Cu, 0.54\ua0ppm Au) in northwest Queensland, have been analysed for naturally occurring and neutron produced noble gas isotopes of Ar, Kr and Xe. A combination of thermal and mechanical decrepitation methods enables distinction between four types of Fluid inclusion. Ultra-high-salinity (∼ 30 to 70\ua0wt. % NaCl eq.) Fluid inclusions have compositions that define two end-members that are variably mixed in different samples. The first end-member has a Ar/Ar value of ∼ 29,000, a Ar/Cl value of ∼ 3 × 10 and mantle-like Br/Cl and I/Cl values of 1-2 × 10 and ∼ 11 × 10, respectively. The second end-member has a much lower Ar/Ar value of less than 2500, a Ar/Cl value of ∼ 10, low Br/Cl values of ∼ 0.4 × 10 and I/Cl values of 1-2 × 10 (all ratios are molar). Carbon dioxide and later, lower salinity liquid-vapour Fluid inclusions have similar Ar/Ar values of less than ∼ 2500 in all samples. These data are compatible with genetic models in which Cu-Au mineralisation formed at a depth of 6-10\ua0km, from circulation of magmatic Fluids derived from regionally abundant 'A-type' granites and a high salinity halite dissolution brine generated from sedimentary formation waters in the upper crust. The largest source of CO was probably carbonate-rich lithologies in the mid-crust. Later, lower salinity Fluids with a surficial origin diluted the mineralising brines and are preserved in the latest, secondary Fluid inclusions. These data provide insight on the composition of Crustal Fluids during the Proterozoic. Furthermore, the magmatic Fluid end-member, derived from melts generated by re-melting lower-Crustal Paleoproterozoic igneous rocks with a mantle source, preserves mantle-like Br/Cl and I/Cl. These geochemical characteristics are interpreted to provide insight on I-recycling at subduction zones and the composition of seawater in the Paleoproterozoic
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Fluid inclusion noble gas and halogen evidence on the origin of cu porphyry mineralising Fluids
Geochimica et Cosmochimica Acta, 2001Co-Authors: Mark A. Kendrick, R Burgess, R A D Pattrick, G TurnerAbstract:The naturally occurring noble gas isotopes (40Ar, 36Ar, 84Kr and 129Xe) and halogens (Cl, Br, I) have been determined simultaneously in irradiated quartz vein samples by noble gas mass spectrometry. Quartz vein samples were collected from the potassic and propylitic alteration zones of six porphyry copper deposits (PCD): Bingham Canyon, Utah; and Silverbell, Ray, Mission, Pinto Valley and Globe-Miami in Arizona. In addition, analyses of 3He/4He have been obtained from sulphide minerals hosted by the quartz veins at Silverbell, Ray, Pinto Valley and Globe-Miami. The majority of PCD Fluids studied have Br/Cl and I/Cl ratios that overlap those of Fluids included in mantle diamond, suggesting that the salinity had a juvenile origin. The high I/Cl (121 × 10−6 mole, M) in samples from the propylitic zone of Silverbell is attributed to the presence of sedimentary formation water. 3He/4He ratios have R/Ra values in the range 0.3 to 1.72, and provide evidence for the involvement of a Crustal component in addition to mantle volatiles. 40Ar/36Ar ratios vary from meteoric values of ∼317 in the propylitic zone of Bingham Canyon, and 323 in the skarn alteration of Mission up to 3225 in the potassic zone of Pinto Valley. Fluids in both the potassic and propylitic alteration zones of every deposit are a mixture of a low salinity end-member comprising meteoric water and air, and a high salinity end-member consisting of a mixed mantle and Crustal Fluid. The 40Ar/Cl ratio of Fluid inclusions at Pinto Valley (∼10−4 M) is similar to values obtained previously for mantle Fluids. The 40Ar/Cl value is two orders of magnitude lower at Bingham Canyon, where a depleted 36Ar concentration (0.2 × 10−6 cm3/g) below that of air saturated water (ASW), and a range of highly fractionated noble gas compositions (F84Kr = 13 and F129Xe = 160) indicate that boiling and pulsed Fluid flow have occurred.
Phaedra Upton - One of the best experts on this subject based on the ideXlab platform.
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Young orogenic gold mineralisation in active collisional mountains, Taiwan
Mineralium Deposita, 2010Co-Authors: Dave Craw, Phaedra Upton, Travis Horton, Yue-gau ChenAbstract:Gold-bearing vein systems in the high mountains of Taiwan are part of the youngest tectonic-hydrothermal system on Earth. Tectonic collision initiated in the Pliocene has stacked Eocene–Miocene marine sedimentary rocks to form steep mountains nearly 4 km high. Thinner portions of the sedimentary pile (∼5 km) are currently producing hydrocarbons in a fold and thrust belt, and orogenic gold occurs in quartz veins in thicker parts of the pile (∼10 km) in the Slate Belt that underlies the mountains. Metamorphic Fluids (2–5 wt.% NaCl equivalent) are rising from the active greenschist facies metamorphic zone and transporting gold released during rock recrystallisation. Metamorphic Fluid flow at the Pingfengshan historic gold mine was focussed in well-defined (4 km^3) fracture zones with networks of quartz veins, whereas large surrounding volumes of rock are largely unveined. Gold and arsenopyrite occur in several superimposed vein generations, with ankeritic alteration of host rocks superimposed on chlorite–calcite alteration zones as Fluids cooled and became out of equilibrium with the host rocks. Mineralising Fluids had δ^18O near +10‰, δ^13C was between −1‰ and −6‰ and these Fluids were in isotopic equilibrium with host rocks at ∼350°C. Ankeritic veins were emplaced in extensional sites in kink fold axial surfaces, formed as the rock mass was transported laterally from compressional to extensional regimes in the orogen. Rapid exhumation (>2 mm/year) of the Slate Belt is causing a widespread shallow conductive thermal anomaly without igneous intrusions. Meteoric water is penetrating into the conductive thermal anomaly to contribute to Crustal Fluid flow and generate shallow boiling Fluids (∼250°C) with Fluid temperature greater than rock temperature. The meteoric-hydrothermal system impinges on, but causes only minor dilution of, the gold mineralisation system at depth.
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Upper Crustal Fluid flow in the outboard region of the Southern Alps, New Zealand
Geofluids, 2003Co-Authors: Phaedra Upton, D. Craw, T. G. Caldwell, Peter O. Koons, Z. James, Philip E. Wannamaker, G. J. Jiracek, C. P. ChamberlainAbstract:The currently active Fluid regime within the outboard region of the Southern Alps, New Zealand was investigated using a combination of field observations, carbon- and oxygen-stable isotopes from fault-hosted calcites and interpretation of magnetotelluric (MT) data. Active faulting in the region is dominated by NE striking and N striking, oppositely dipping thrust fault pairs. Stable isotopic analyses of calcites hosted within these fault zones range from 10 to 25‰δ18O and from −33 to 0‰δ13C. These values reflect mixing of three parent Fluids: meteoric water, carbon-exchanged groundwater and minor deeper rock-exchanged Fluids, at temperatures of 10–90°C in the upper 3–4 km of the crust. A broad, ‘U-shaped’ zone of high electrical conductivity (maximum depth c. 28 km) underlies the central Southern Alps. In the ductile region of the crust, the high-conductivity zone is subhorizontal. Near-vertical zones of high conductivity extend upward to the surface on both sides of the conductive zone. On the outboard side of the orogen, the conductive zone reaches the surface coincident with the trace of the active Forest Creek Faults. Near-surface flow is shown to dominate the outboard region. Topographically driven meteoric water interacts, on a kilometre scale, with either carbon-exchanged groundwater or directly with organic material within Pliocene gravels, resulting in a distinctive low 13C signal within fault-hosted calcites of the outboard region. The high-strain zone in the lower crust focuses the migration of deeply sourced Fluids upward to the base of the brittle–ductile transition. Interconnected Fluid is imaged as a narrow vertical zone of high conductivity in the upper crust, implying continuous permeability and possibly buoyancy-driven flow of deeply sourced Fluids to higher levels of the crust where they are detected by the isotopic analysis of the fault-hosted calcites.
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Fluids in a backthrust regime (Southern Alps, New Zealand)
Journal of Geochemical Exploration, 2000Co-Authors: Phaedra Upton, D. Craw, T. G. Caldwell, Peter O. Koons, Z. James, G. J. Jiracek, C. P. Chamberlain, Philip E. WannamakerAbstract:Abstract New Zealand's Southern Alps are the surface expression of recent (c. 5 Ma) oblique convergence between the Australian and Pacific plates. A broad, ‘U shaped’, zone of high electrical conductivity (maximum depth c. 25 km) underlies this orogen. In the ductile region of the crust, the high conductivity zone is sub-horizontal and is interpreted to be a zone of interconnected Fluid marking a decollement zone above the root of the orogen. Near vertical zones of high conductivity extend upwards to the surface on both sides of the conductive zone. On the outboard side of the orogen, which is a broad zone of thrust faulting and folding, the conductive zone reaches the surface at the trace of an active fault. Carbon and oxygen isotopic analysis of material from the faults suggests that mid-Crustal Fluids have been present. Mid-Crustal Fluid appears to have been transported upwards in both the ductile and brittle parts of the crust within the ‘backthrust’ region of the orogen.
Michel Dubois - One of the best experts on this subject based on the ideXlab platform.
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Syntectonic Fluid-flow along thrust faults: Example of the South-Pyrenean fold-and-thrust belt
Marine and Petroleum Geology, 2014Co-Authors: Brice Lacroix, Anna Trave, Martine Buatier, Pierre Labaume, Torsten Vennemann, Michel DuboisAbstract:During compressive events, deformation in sedimentary basins is mainly accommodated by thrust faulting and related fold growth. Thrust faults are generally rooted in the basement and may act as conduits or barriers for Crustal Fluid flow. Most of recent studies suggest that Fluid flow through such discontinuities is not apparent and depends on the structural levels of the thrust within the fold-and-thrust belt. In order to constrain the paleoFluid flow through the Jaca thrust-sheet-top basin (Paleogene southwest-Pyrenean fold-and-thrust belt) this study compares on different thrust faults located at different structural levels. The microstructures in the different fault zones studied are similar and consist of pervasive cleavage, calcite shear veins (SV1), extension veins (EV1) and late dilatation veins (EV3). In order to constrain the nature and the source of Fluids involved in Fluid-rock interactions within fault zones, a geochemical approach, based on oxygen and carbon stable isotope and trace element compositions of calcite from different vein generations and host rocks was adopted. The results suggest a high complexity in the paleohydrological behaviors of thrust faults providing evidence for a Fluid-flow compartmentalization within the basin. Previous studies in the southern part of the Axial Zone (North of the Jaca basin) indicates a circulation of deep metamorphic water, probably derived from the Paleozoic basement, along fault zones related to the major basement Gavarnie thrust. In contrast, in northern part of the Jaca basin, the Monte Perdido thrust fault is affected by a closed hydrological Fluid system involving formation water during its activity. The Jaca and Cotiella thrust faults, in turn, both located more to the south in the basin, are characterized by a composite Fluid flow system. Indeed, stable isotope and trace element compositions of the first generations of calcite veins suggest a relatively closed paleohydrological system, whereas the late calcite vein generations, which are probably associated with the late tectonic activity of the basin, support a contribution of both meteoric and marine waters. Based on these results, a schematic Fluid-flow model is presented. This model allows visualization of three main Fluid flow compartments along a N-S transect.