Computer Science
Scientific paper
Jun 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993gecoa..57.2613p&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 57, Issue 11, pp.2613-2629
Computer Science
3
Scientific paper
This study examines oxygen-isotope zoning in garnets from a Barrovian metamorphic terrane in eastern Vermont using a CO 2 laser extraction system. Previous strontium isotopic and structural studies of these garnets have shown that they grew over an approximately 10 Ma interval during thrusting and nappe emplacement ( , 1970; et al., 1989). Our studies show that the garnets are strongly zoned in 18 O . This zoning is the result of equilibration of garnet with water derived from dehydration of subjacent pelites during nappe stage deformation. The magnitude and nature of 18 O zoning depends upon the garnet's location in the outcrop studied. The garnets examined in this study come from an isotopically low 18 O paragonitic schist ( 18 O whole rock ~ 9 ) that is adjacent to a relatively high 18 O schist ( 18 O whole rock ~12.5 ). Garnets from the paragonitic schists within 10 m of the contact with the isotopically heavier schists have relatively homogenous 18 O values varying from 9.5 in the core to 10.5 at the rim. Garnet in the paragonitic schists 85 m from the contact are more strongly zoned, with 18 O ranging from a low of ~6.0 in the cores to a high of ~9.0 at the rims of the garnet. These zoning patterns were produced by continuous infiltration of relatively high 18 O waters derived from the subjacent schists into the paragonitic schists during garnet-grade metamorphism. It is possible to determine the time-integrated fluid fluxes by comparison of observed 18 O zoning profiles in garnet with those calculated from the equation describing combined advection-diffusion of a tracer. Using this method, we calculate time-integrated fluid fluxes of ~ 1.5 × 10 4 cm 3 /cm 2 . Fluxes of this magnitude could have been produced by dewatering of ~ 1.5 km of schist during garnet-grade metamorphism.
Chamberlain Page C.
Conrad Mark E.
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