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Mineralogy and Geochemistry of Metamorphosed Ultramafic Rocks in the Paleigh Terrane, Piedmont Province, Virginia
Zerolis, John
Zerolis, John
Abstract
The Raleigh Terrane in the southeast Piedmont Province of Virginia contains numerous, scattered small occurrences of rocks rich in talc. This study focuses on the mineralogy and geochemistry of these rocks with the goal of understanding their origin. Four different rock types were identified: 13 samples were designated talc schists and the three remaining samples were characterized as a chlorite amphibole schist, talc amphibole schist and chlorite-rich “blackwall” rock. Whole rock major element compositions shows a wide range of SiOz (30.46 — 62.57 wt. %) and Al,O3 compositions (0.65 — 25.73 wt. %), but relatively consistent MgO (22.48 — 29.13 wt. %), with high Mg# (80.02 — 96.52). Almost all the rocks of the study have considerably high Ni (up to 2672.5 ppm) and Cr (up to 4846.9 ppm) and, with the exception of a chlorite-rich “blackwall.” Normative mineralogy suggests probable harzburgite protoliths for most samples, but the current bulk compositions clearly reflect substantial metasomatism. Given the harzburgitic protliths, a plausible interpretation is that these rocks represent basal portions of ophiolites.
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2010-01-01
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Geology