Anticlockwise P-T evolution at ∼280 Ma recorded from ultrahigh-temperature metapelitic granulite in the Chinese Altai orogenic belt, a possible link with the Tarim mantle plume?
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An ultrahigh-temperature (UHT) metapelitic granulite assemblage consisting of garnet(g)–spinel(sp)–orthopyroxene(opx)-sillimanite(sil)–cordierite(cd)–ilmenite(ilm)–biotite(bi)–plagioclase(pl)–quartz(q) occurs within migmatitic paragneiss near Kalasu in the Chinese Altai, NW China. Textural relations, mineral compositions and P-T estimates, indicate three stages of mineral assemblages: (1) pre-peak prograde stage (M1) consisting of a sp–sil-bearing or sp–opx-bearing inclusion assemblage, with low-Al2O3 contents (4–5 wt.%) in orthopyroxene and P-T conditions of ∼7 kbar and ∼890 °C, (2) peak UHT stage (M2) comprising a g–opx–cd-bearing coarse-grained assemblage, with high-Al2O3 contents (8–9 wt.%) in orthopyroxene and peak conditions of ∼8 kbar and ∼970 °C, and (3) post-peak HT stage (M3) containing an oriented opx–bi–sil-bearing assemblage in matrix, with moderate amounts of Al2O3 (6–7 wt.%) in orthopyroxene and P-T conditions of 8–9 kbar and ∼870 °C. The three discrete stages define an anticlockwise P-T path involving initial prograde heating and post-peak near isobaric cooling. Such a near isobaric cooling anticlockwise P-T path suggests that UHT metamorphism likely occurred in an overall extensional tectonic setting with associated underplating of mantle-derived mafic magma. A SHRIMP zircon U–Pb age of 278 ± 2 Ma obtained from the metapelitic granulite indicates UHT metamorphism in the Altai orogen occurred during the Permian, coeval with spacially associated mantle-derived mafic intrusions (∼280 Ma) and the Tarim mantle plume (∼275 Ma). Thus, the Permian UHT metamorphism of the Chinese Altai is likely associated with underplating and heating of mantle-derived mafic magma as a result of the Tarim mantle plume.
Tong , L , Xu , Y-G , Cawood , P A , Zhou , X , Chen , Y & Liu , Z 2014 , ' Anticlockwise P-T evolution at ∼280 Ma recorded from ultrahigh-temperature metapelitic granulite in the Chinese Altai orogenic belt, a possible link with the Tarim mantle plume? ' Journal of Asian Earth Sciences , vol 94 , pp. 1-11 . DOI: 10.1016/j.jseaes.2014.07.043
Journal of Asian Earth Sciences
Copyright © 2014 Elsevier Ltd. All rights reserved.. This work is made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at http://dx.doi.org/10.1016/j.jseaes.2014.07.043