Fluids and thrusting

Fyfe, W. S.; Kerrich, Robert

doi:10.1016/0009-2541(85)90167-6

Cited by 128 publications

(24 citation statements)

References 25 publications

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“…Prograde metamorphism occured over the entire thickness of the underplate. Water and metals were lost from the underplate and such fluids would penetrate upwards to the thrust plate (Fyfe and Kerrich 1985). Fluids were then focussed along thrust planes and connected fractures that acted as high permeability conduits for the release, by hydraulic fracturing, of overpressured, probably supralithostatic, fluids (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…In deep regions, after thrusting and before thermal equilibration, relatively high pressure, low temperature assemblages formed and been occasionally preserved as observed south of Luzi~nia (Hagemann 1988;. On a larger time scale the P-T-t path depended on thermal equilibration and temperature distributions in the thrust slice that are constrained by erosion rates at the top and possible melting at the base (Fyfe and Kerrich 1985).…”

Section: Discussionmentioning

confidence: 99%

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Thin-skinned thrust mineralization in the Bras�lia fold belt: the example of the old Luzi�nia gold deposit

1992

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The Luzigmia gold deposits in southern Goi/ts lie within the Late Proterozoic Brasilia fold belt. The rocks that host the gold mineralization are a monotonous series of hydrothermally altered phyllites that have been subject to low grade regional metamorphism. The major controls on the gold mineralization are northeast trending and gently northwest dipping ductile-brittle, dextralreverse shear zones associated with regional thin-skinned thrusting of the Canastra Group. From a preliminary fluid inclusion study it is deduced that low salinity, < 7 eq. wt% NaC1, moderately dense, H20-CO 2 + C H 4 o r e fluids deposited gold at temperatures of 300 + 75 ~ and pressures of 1.5 to 3 kb in the filling stage of the vein formation. Post-filling stage gold deposition probably occured by mixing of fluids at higher crustal levels (1.5-2 kb). During thrusting, prograde metamorphism released pore water which penetrated along thrust planes that acted as high permeability zones for the ponding and release, by hydraulic fracturing, of overpressured fluids. Later in the tectonic evolution and at shallower crustal levels, there was likely an incursion of near suface water into the fault zone.Although thin-skinned thrust related gold deposits in Proterozoic metasedimentary rocks have recently become important exploration targets, their structural setting, mode of emplacement and geochemical signatures are poorly understood and widely accepted genetic models are generally lacking. For this reason, an integrated and continuing study of a Proterozoic thin-skinned thrust related gold deposit in the central part of the Brasilia fold belt has been undertaken. The goals of the study are to: (1) identify structural processes that may have controlled and influenced the development of the mineralized veins, (2) determine the timing of gold deposition, (3) reconstruct the P-T conditions during the rain-* Present address:

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Thin-skinned thrust mineralization in the Bras�lia fold belt: the example of the old Luzi�nia gold deposit

1992

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“…The total mass of the hydrosphere is about 1.4 Â 10 21 kg (~1.36 Â 10 24 g). Thus, without mechanical fluid expulsion, the Earth's oceans would be subducted in~1 billion (10 9 ) years (see Fyfe and Kerrich 1985). As a consequence, future research should evaluate whether, for some chemical components, the cycling of seawater through active sediment-dominated forearcs could contribute significantly to ocean water chemical evolution.…”

Section: Outer Rise Metasomatism Of Sub-crustal Mantle Rocks In Slabsmentioning

confidence: 98%

Metasomatism in Subduction Zones of Subducted Oceanic Slabs, Mantle Wedges, and the Slab-Mantle Interface

Bebout

2012

Lecture Notes in Earth System Sciences

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Physical juxtaposition of chemically disparate rocks, and the mobility of "fluids" at up to tens of kilometer scales, lead to myriad metasomatic effects in subduction zones, with larger scale manifestations including the metasomatism related to mass flux leading to arc magmatism and convergent margin volatiles cycling. Subduction-zone metasomatism is initiated at very shallow levels, as oceanic slabs entering trenches bend and are potentially infiltrated by seawater and as sedimentary sections begin their journey into forearcs resulting in extensive physical compaction, fluid expulsion, and diagenetic alteration. Studies of forearc fluid geochemistry (e.g., in accretionary complexes and, for the Marianas margin, in serpentinite seamounts) track this shallow-level metasomatic alteration, whereas high-and ultrahigh-pressure metamorphic suites provide records of fluid generation and flow, and related metasomatism to depths approaching those beneath volcanic fronts (and, in a smaller number of cases, depths beyond those beneath arcs). Uncertainty remains regarding the geochemical influence of strongly mechanically mixed zones along the slab-mantle interface (i.e., in the "subduction channel"), represented by mélange zones in many metamorphic suites. Experimental studies predict dramatic change in the physicochemical properties, and metasomatic capabilities, of subduction-zone "fluids," as a function of depth. However, the studies of metamorphic suites have yet to document results of this change and, toward this goal, further work is warranted on UHP suites representing subduction-zone depths of 100 km or greater. Work on higher-P suites is also necessary in order to test the generally accepted hypothesis that subduction-zone metamorphism serves as a geochemical "filter" altering the

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“…Another important development was establishing that the banded veins characteristic of many lode gold deposits formed syn-kinematically in the seismogenic zone, during pulsed discharge of ore solutions in a suprahydrostatic to supralithostatic fluid pressure cycle -the fault valve model (Robert and Brown 1986;Sibson et al 1988). The next step in developing an integrated model for lode gold deposits was the recognition that they occurred in a specific geodynamic environment -convergent margin tectonics (Fyfe and Kerrich 1985).…”

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confidence: 99%

Perspectives on genetic models for lode gold deposits

Kerrich

1993

Mineral. Deposita

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Structurally hosted lode gold vein systems in metamorphic terranes constitute a single, coherent group of epigenetic precious metal deposits. Their origin, however, has been contentious for over a century, and there remain polarized views on both the timing and mode of their formation. The status of thinking on lode gold deposits contrasts with that on several other deposit classes. For volcanic-hosted massive base-metal sulphide (VMS) deposits, copper-, and molybdenum -porphyry deposits, and epithermal precious metal deposits, amongst other classes, the results of research over the last two decades has led to a broad concensus on genetic origins. Results from diverse lines of investigation have been integrated into conceptual models that have proven effective in formulating exploration strategies for these classes of deposit. In this Preface I trace the historical development of ideas on the origin of lode gold deposits as a context for the papers in this Thematic Issue, and as a framework for evaluating the current crustal continuum model, as described in several papers in this Thematic Issue.Examples of this class of epigenetic precious metal vein deposit have variously been called Archaean gold, mesothermal gold, gold only or lode gold. The term Archaean gold deposit arose because of the relative abundance of lode gold deposits in late Archaean greenstone belts. Moreover, within such belts the mineralization may show a spatial association with komatiites or Algoman banded iron formations (BIF) -lithological types for the most part restricted to the Archaean Era. However, it is now recognized that lode gold deposits in metamorphic belts of Proterozoic to Cenozoic age share numerous characteristics with Archaean counterparts, and all likely formed by a single, common process (Kerrich and Wyman 1990). Gold only (Hodgson and MacGeehan 1982) is a misnomer, inasmuch as the deposits invariably contain significant silver, with Au/Ag ratios averaging 5, and sporadically have enrichments of W and Te. The term mesothermal is appropriate, given that the vast majority of deposits occur in greenschist facies metamorphic terranes:here, mesothermal has the connotation of mid-crustal environment, rather than referring to a process. Recently it has been recognized that lode gold deposits in subgreenschist, amphibolite and granulite facies rocks, share numerous characteristics, such as structural hosting, metal inventory, and element association of Au, Ag, W, As, Sb, Se, Te, Bi, and ore fluid source, in common with greenschist hosted mesothermal counterparts. Accordingly the term lode gold is preferable for this single class of structurally hosted Au, Ag vein deposits, which now may be viewed as forming over a crustal depth range, or crustal continuum, extending from granulite to subgreenschist facies environments hence the term crustal continuum model for these lode gold deposits Groves 1993 this issue).This class of structurally hosted lode gold deposits differ from "Carlin" type deposits, or epithermal and bonaza gold depo...

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Fluids and thrusting

Cited by 128 publications

References 25 publications

Thin-skinned thrust mineralization in the Bras�lia fold belt: the example of the old Luzi�nia gold deposit

Thin-skinned thrust mineralization in the Bras�lia fold belt: the example of the old Luzi�nia gold deposit

Metasomatism in Subduction Zones of Subducted Oceanic Slabs, Mantle Wedges, and the Slab-Mantle Interface

Perspectives on genetic models for lode gold deposits

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