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Fluid-rock interaction in orogenic crust tracked by zircon depth profiling

S. M. Gordon, M. Grove, D. L. Whitney, A. K. Schmitt and C. Teyssier
Fluid-rock interaction in orogenic crust tracked by zircon depth profiling
Geology (Boulder) (August 2009) 37 (8): 735-738

Abstract

Ion microprobe U-Pb, delta (super 18) O, and Ti depth profiling analyses of natural zircon rims permit unprecedented assessment of the relationship between timing, temperature, and geochemical environment during crystallization and cooling of deep orogenic crust. Zircon from migmatite in a deeply exhumed gneiss dome in the Valhalla metamorphic core complex, southeast British Columbia, Canada, records the timing of melt crystallization and subsequent fluid-rock interaction before the final stages of extension and exhumation. Zircon interiors reveal a weighted mean age of 58+ or -2 Ma, interpreted as the timing of melt crystallization. Depth profiling U-Pb measurements of unpolished zircon rims yield an age of 51+ or -2 Ma over 4 mu m. Ti-in-zircon thermometry indicates 650 degrees C for both rim and interior, confirming that the complex remained at high temperature during zircon crystallization. Previous delta (super 18) O measurements suggest that high-temperature fluids with delta (super 18) O of approximately 10 per mil pervasively infiltrated the complex. The oxygen zircon results clearly resolve a delta (super 18) O contrast between zircon interiors (7.2+ or -0.2 per mil) and rims (8.4+ or -0.2 per mil). The lighter interior delta (super 18) O values indicate the timing of melt crystallization and equilibration of the rims with melt at 58 Ma ago. Alternatively, delta (super 18) O values from the 51 Ma rims match the composition predicted (8.4 per mil) from fluid interaction based upon previous work. Integrating the age and delta (super 18) O results reveals that amphibolite facies fluid-rock interaction persisted until final rapid exhumation of the Valhalla complex. The results further indicate the power of using the ion microprobe to track the timing of fluid infiltration in the crust as well as the effect of fluid infiltration on the subgrain scale.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 37
Serial Issue: 8
Title: Fluid-rock interaction in orogenic crust tracked by zircon depth profiling
Affiliation: University of Minnesota, Department of Geology and Geophysics, Minneapolis, MN, United States
Pages: 735-738
Published: 200908
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 45
Accession Number: 2009-072368
Categories: GeochronologyIsotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2009177
Illustration Description: illus. incl. sect., geol. sketch map
N49°00'00" - N50°00'00", W120°00'00" - W118°00'00"
Secondary Affiliation: Stanford University, USA, United StatesUniversity of California, Los Angeles,
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200939
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