FIG 12 - uploaded by Driouch Youssef
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The low-P/high-T Variscan metamorphic dome of Gavarnie-Gèdre-Héas, Central Pyrenees, harbors a small (1 m3) but special cordierite and orthoamphibole-bearing enclave embedded within an anatectic granite. Compared to other cordieriteorthoamphibole occurrences described in the literature, the enclave shows singular characteristics: (1) its mineral co...
Citations
... The assemblage cordierite-garnet-anthophyllite-chlorite may form by processes like metamorphism of paleosols (Young, 1973) and partial melting of metasediments (Grant, 1968;Hoffer and Grant, 1980). However, the most common process involves metasomatism of basic rocks by hydrothermal fluid (Schumacher, 1988;Smith et al., 1992;Araujo et al., 1996;Elliott-Meadows et al., 2000;O'Neil et al., 2011;Driouch et al., 2017). Such rocks are often termed as Ca-poor amphibolites (Spear, 1993). ...
The tectonic evolution of the Rengali Province and its eventual juxtaposition to the Eastern Ghats Province has important bearings on the geological evolution of the Eastern Indian terrane. New zircon and monazite age data from the Rengali Province and the northern-northwestern part of the Eastern Ghats are presented in this study to trace this evolutionary history. Monazite U-Th-total Pb data from the paragneissic rocks of the eastern Ren-gali Province show a metamorphic age of 2775 ± 18 Ma while an older age of 2943 ± 35 Ma from the same rock probably suggests an older metamorphic/magmatic event. Zircon U-Pb (LA-ICPMS) data from the northern part of the Eastern Ghats show 1230 ± 21 Ma and 1220 ± 9 Ma ages that we interpret as a major phase of high-grade metamorphism of the basement. Paragneissic rocks from the northwestern margin of the Eastern Ghats yields monazite ages of 966 ± 21 Ma and 555 ± 12 Ma respectively from the core and rim parts of monazite grains. Similar ages of 966 ± 25 Ma and 540 ± 12 Ma are reported from paragneissic rock occurring at the contact of Rengali Province and the Eastern Ghats. This younger (~555-540 Ma) age likely correlates to the amphibolite facies reworking of the granulitic lower crust which coincides with the emplacement of nepheline syenite at 556 ± 28 Ma (zircon U-Pb data) and the contact metamorphism of the ultramafic gra-nofels at 553 ± 18 Ma (monazite data). Nepheline monzosyenite veins intruded the gneissic nepheline syenite at 506 ± 9 Ma (zircon U-Pb data). Emplacement of the monzosyenite veins within the felsic gneiss country at the northwestern margin of the Eastern Ghats at 490 ± 3 Ma (zircon U-Pb data) marks the last thermal imprint in response to large-scale shear-induced deformation at the northern/northwestern contacts of the Eastern Ghats. We infer that the Neoarchean (ca. 2943-2775 Ma) events possibly resulted from the ensuing convergent tectonics driven by lithospheric peeling (peel-back convergent tectonics). The Eastern Ghats and its Antarctic counterpart juxtaposed with the Rengali Province during ca. 1000-900 Ma and become a part of the Eastern Indian terrane. The Ediacaran-Cambrian (ca. 556-490 Ma) events imply the reactivation of the deep crustal Tonian-age shear systems in a transpressional tectonic setting.
