Strontium and oxygen isotope profiles across marble-silicate contacts, Lizzies Basin, East Humboldt Range, Nevada; constraints on metamorphic permeability contrasts and fluid flow

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doi: 10.1007/s004100050105
Authors:Bickle, M. J.; Chapman, H. J.; Wickham, S. M.; Peters, M. T.
Author Affiliations:Primary:
University of Cambridge, Cambridge, United Kingdom
University of Chicago, United States
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 121(4), p.400-413. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999
Publication Date:1995
Note:In English. 26 refs.; illus., incl. 3 tables, geol. sketch map
Summary:Sr isotope profiles across marble-silicate rock contacts are used in conjunction with published oxygen isotope profiles to constrain fluid movements, porosity and permeability contrasts in migmatitic rocks from this basin. The 18O/16O systematics in the high-grade sequence are interpreted to reflect infiltration of ∼ 2 × 102 m3/m2 of a relatively low 18O hydrous fluid through the sequence, but with preservation of Δ^>18O anomalies in thin marble bands due to a 30-fold lower porosity in the marble compared with silicate rocks. The Sr isotope profiles confirm that tracer exchange between marble and silicate rock was primarily by diffusion, and in one case, indicate that porosities differed by less than a factor of 4 in the ∼ 10 cm boundary layer which exhibits diffusive modification of 87Sr/86Sr ratios. This contrasts with modelling of the oxygen isotope profiles which imply porosity contrasts >><[dollar]I> 10 for one marble band and >><[dollar]I> 50 for another. Either Sr and oxygen isotope diffusion reflect different events (possible if fluid Sr contents varied with time) or porosity varied substantially with the silicate rocks. Oxygen isotope profiles in the deeper part of the metamorphic section in which Δ^>18O values of silicate rocks have been homogenized and lowered, indicate similar diffusion distances (and thus porosity-time evolution) to oxygen isotope profiles higher in the section. Comparison of Sr and O isotope diffusion distances constrains fluid Sr contents to between ∼ 50 and ∼ 550 deep in the section, but less than ∼ 10 ppm higher in the section. The difference is related to release of relatively saline, Sr-rich fluids, by the abundant leucogranites and associated skarns deep in the section. [P.Br.]
Subjects:Alkaline earth metals; Aureoles; Boundary conditions; Cenozoic; Controls; Diffusivity; Fluid phase; Isotopes; Marbles; Metals; Metamorphic rocks; Metamorphism; O-18/O-16; Oxygen; Permeability; Silicates; Solute transport; Sr-87/Sr-86; Stable isotopes; Strontium; Tertiary; East Humboldt Range; Elko County Nevada; Nevada; Ruby Mountains; United States; Lizzies Basin; Rb-87/Rb-86
Coordinates:N400000 N405700 W1172000 W1192000
Abstract Numbers:96M/1946
Record ID:1996014570
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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