Oxygen isotope fractionations in muscovite, phlogopite, and rutile

Chacko, Thomas; Hu, Xiangsheng; Mayeda, T. K.; Clayton, Robert N.; Goldsmith, Julian R.

doi:10.1016/0016-7037(96)00112-3

Cited by 90 publications

(49 citation statements)

References 54 publications

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“…Quartz and muscovite from VM show δ 18 O values of 10.9 and 9.3 ‰, respectively. Assuming equilibrium, this quartz-muscovite pair yields a formation temperature of 673°C (Chacko et al 1996), whereas the fluid in equilibrium with the minerals has a δ 18 O value of 10.5 ‰ (Matsuhisa et al 1979). This value most likely reflects magmatic origin (Sheppard 1986).…”

Section: Oxygen Isotopesmentioning

confidence: 99%

The Paleoproterozoic metaconglomerate-hosted Castelo de Sonhos gold deposit, Tapajós Gold Province, Amazonian Craton: a modified paleoplacer origin

Queiroz¹,

Klein

2018

JGSB

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The Castelo de Sonhos gold deposit (~1.5 Moz Au) is located in the southeastern Tapajós Gold Province and is hosted in variably deformed metaconglomerates and metasandstones of the Castelo dos Sonhos Formation, which was deposited between 2011 and 2050 Ma and considered to be a relic of a major foreland system. Gold is found mainly in the matrix of metaconglomerates and subordinately in fractures of metasandstones. The host rocks are strongly silicified, which was demonstrated to be the result of silica overgrowth during diagenesis, without relationship to hydrothermal alteration. The rocks are also impregnated with secondary iron oxides, which are interpreted to be consequence of weathering of the metasedimentary sequence and total or partial dissolution of iron-bearing minerals and re-precipitation of iron during circulation of oxidized (meteoric and/or magmatic) fluids. The morphology of matrix gold particles indicates that they are not pristine, but only slightly modified and reshaped, which suggests detrital provenance and relatively proximal distance of transport from the original sources. The chemical composition of the particles, with Au grading 94-97%, very high Au/ Ag and lack of other significant metals, suggest single source, or sourcing from a single class (orogenic?) of gold deposits. The gold particles from fractures are platy and show even higher Au/Ag ratios, given by very low Ag contents (<<1%), which are interpreted as epigenetic remobilization of the matrix gold. Oxygen isotope compositions of hydrothermal quartz-sulfide-muscovite veins cutting across the host metasedimentary sequence indicate magmatic origin for the fluids, which might have been produced by granites that intruded the metasedimentary rocks and helped gold remobilization to fractures. As a consequence, Castelo de Sonhos is interpreted as a modified paleoplacer gold deposit.

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Section: Oxygen Isotopesmentioning

confidence: 99%

The Paleoproterozoic metaconglomerate-hosted Castelo de Sonhos gold deposit, Tapajós Gold Province, Amazonian Craton: a modified paleoplacer origin

Queiroz¹,

Klein

2018

JGSB

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“…In this study we calculate the fractionation of d 18 O on coeval pairs of quartz and white mica in three calcite-quartz-white mica rich veins (samples MC494, MC497 and MC498) using the following coefficients: A = −0.0086, B = 0.042, C = 0.000, D = 1.350, E = 0.00 and F = 0.00 [Chacko et al, 1996]. Further details of the method are given in Appendix D.…”

Section: Oxygen Isotope Thermometrymentioning

confidence: 99%

Geochronological evidence for continuous exhumation through the ductile‐brittle transition along a crustal‐scale low‐angle normal fault: Simplon Fault Zone, central Alps

et al. 2010

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[1] Major low-angle normal faults juxtapose different structural levels of the crust that record both brittle and ductile deformation. Field relationships alone cannot establish whether these different responses to deformation represent (1) parts of a single process of exhumation along the detachment or (2) two separate events, with the later, more discrete brittle detachment exhuming a fossil ductile shear zone from depth. These two general models are critically assessed for the lowangle normal Simplon Fault Zone (SFZ) in the central Alps. The SFZ shows a spatial transition from a broad ductile mylonitic shear zone to a discrete brittle detachment with identical kinematics. The age of the ductile shear zone and ductile-brittle transition is controversial. We present a detailed geochronological study based on fission track, 40 Ar/ 39 Ar, and Rb/Sr microsampling dating, coupled with structural, petrological, and chemical analyses that provides tight constraints on SFZ timing. Discontinuous mineral cooling ages over a broad range of temperatures across the fault zone argue for fault activity between 20 and 3 Ma. On the basis of synkinematic white mica in low-temperature shear zones and necks of foliation boudinage, the brittle-ductile transition in the footwall could be dated at ∼14.5-10 Ma. Overall, the data presented here are consistent with a continuous transition from ductile shearing to a more localized zone of brittle deformation within the same geological framework, over a period of ∼15 Ma. The SFZ is therefore an example of a telescoped crustal section within a single major lowangle fault, involving a continuous period of exhumation rather than a two-stage structure.

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“…Finally, fractionation factors from Zheng [1993aZheng [ , 1993b were replaced with those of Clayton and Keiffer [1991] (quartzalbite), Wenner and Taylor [1971] (quartz-chlorite), and Chacko et al [1996] (quartz-muscovite) and substituted into the Á quartz À i term of (A2). The predicted uncertainties, which arise from changing one of conditions 1 -3 while holding the other two constant, are presented in Table A3.…”

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confidence: 99%

New evidence for syntectonic fluid migration across the hinterland‐foreland transition of the Canadian Cordillera

2002

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[1] Oxygen isotope data from syntectonic veins, thrust faults, and wall rocks suggest that fluids infiltrated the Western Ranges of the Rocky Mountain foreland from deeper rocks of the Dogtooth Range during Mesozoic contraction. This signifies the first such evidence for kilometerscale fluid migration at the hinterland-foreland transition of the Canadian Cordillera. Fluid infiltration resulted in isotopic depletion in wall rocks and isotopic disequilibrium between veins (fluid) and their host rocks downstream of a lithologic, structural, and isotopic shift between predominantly siliciclastic (Dogtooth Range) and calcareous (Western Ranges) sequences. The shift corresponds with an average d 18 O that is 3.0% higher in the Western Ranges. In the Dogtooth Range, atypically low carbonate values (15.6% ± 0.8% (VSMOW)), and the consistency with which vein signatures approach the average bulk rock d18 O of individual outcrops indicate fluid buffering by a siliciclastic reservoir and outcrop-scale (10 -100 m) fluid circulation. In contrast, rocks and veins in the Western Ranges exhibit a gradational increase in d18 O that extends !14 km eastward and up section from the isotopic shift and possess values that are below or at the low end of typical carbonate compositions (16.2 -20.9% (VSMOW)). Furthermore, veins systematically exhibit lower oxygen values than their host rocks; this implies that the fluids that entered the Western Ranges were in modest disequilibrium with the rocks through which they flowed. We use a one-dimensional reactive transport model to infer that rocks in the Western Ranges experienced a time-integrated fluid flux of 1.1 Â 10 5 mol H 2 O cm À2 (%2.4 Â 10 6 cm 3 cm À2 ) and sluggish reaction kinetics during the flow event.

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Oxygen isotope fractionations in muscovite, phlogopite, and rutile

Cited by 90 publications

References 54 publications

The Paleoproterozoic metaconglomerate-hosted Castelo de Sonhos gold deposit, Tapajós Gold Province, Amazonian Craton: a modified paleoplacer origin

The Paleoproterozoic metaconglomerate-hosted Castelo de Sonhos gold deposit, Tapajós Gold Province, Amazonian Craton: a modified paleoplacer origin

Geochronological evidence for continuous exhumation through the ductile‐brittle transition along a crustal‐scale low‐angle normal fault: Simplon Fault Zone, central Alps

New evidence for syntectonic fluid migration across the hinterland‐foreland transition of the Canadian Cordillera

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