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Geochemical studies of the origins and effects of synorogenic crustal fluids in the southern Omineca Belt of British Columbia, Canada

Bruce E. Nesbitt and Karlis Muehlenbachs
Geochemical studies of the origins and effects of synorogenic crustal fluids in the southern Omineca Belt of British Columbia, Canada
Geological Society of America Bulletin (September 1995) 107 (9): 1033-1050

Abstract

Fluid inclusion and stable isotope investigations of 400+ samples of quartz + or - carbonate veins and their zeolite to amphibolite grade host rocks from the southern Omineca Belt of the Canadian Cordillera have been used to determine origins, evolution, and effects of crustal fluids during and after orogenic activity. Correlations between fluid inclusion characteristics and tectonic and lithologic features indicate that salinities and gas compositions (CO (sub 2) /CH (sub 4) ratios) are controlled by host rock lithology. High total gas contents are linked to high inclusion homogenization temperatures, which parallel increasing metamorphic grades. The delta D values of the vast majority of vein-forming fluids range from -100 per mil to -150 per mil (Standard Mean Ocean Water [SMOW]), indicating meteoric water as the source of the fluids. The delta (super 18) O (sub Water) values of the fluids were homogeneous over large sections of the crust, with a typical range of delta (super 18) O values of 6 per mil to 11 per mil (SMOW). Homogenization of delta (super 18) O values of vein-forming fluids is believed to reflect interaction of the meteoric water with a variety of rock types at temperatures in excess of 350 degrees C. This process resulted in resetting of delta (super 18) O values of both fluids and rock units. The absence of vein formation from low delta (super 18) O water requires that mixing of ascending and descending fluids does not occur. Carbon and strontium isotope analyses indicate a strong degree of host rock control on these isotopic ratios. Synthesis of the results yields a model for the hydrogeology of the brittle crust consisting of moderately high permeabilities in fractured brittle rocks with deep convection of surface, meteoric water. The maximum depth of penetration of the fluids is limited by the rheological brittle/ductile transition at temperatures of 350 to 450 degrees C and depths of 10 km or greater. The vast majority of veins found in greenschist and lower grades of metamorphic rocks are formed on the upflow limbs of the meteoric water convection cells.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 107
Serial Issue: 9
Title: Geochemical studies of the origins and effects of synorogenic crustal fluids in the southern Omineca Belt of British Columbia, Canada
Affiliation: University of Alberta, Department of Geology, Edmonton, AB, Canada
Pages: 1033-1050
Published: 199509
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 59
Accession Number: 1995-059757
Categories: General geochemistryIgneous and metamorphic petrologyStructural geology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 9540; Lithoprobe Publ. No. 666
Illustration Description: illus. incl. 500 anals., 3 tables, geol. sketch map
N48°25'00" - N60°00'00", W139°00'00" - W114°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 199521
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