Building of the Deep Gangdese Arc, South Tibet: Paleocene Plutonism and Granulite-Facies Metamorphism

Os–Nd–Sr isotopes in Miocene ultrapotassic rocks of southern Tibet: Partial melting of a pyroxenite-bearing lithospheric mantle?

“…65 Ma (Yin and Harrison, 2000;Mo et al, 2007). The southern part of the Lhasa Terrane is typified by the Andean-type calc-alkaline Linzizong volcanics and the Gangdese batholith (Early Jurassic to Eocene, Zhou et al, 2004;Mo et al, 2007Mo et al, , 2008Ji et al, 2009;Lee et al, 2009Lee et al, , 2012Zhu et al, 2011;Zhang et al, 2013). All this magmatism was caused by the northwards subduction of the Neo-Tethyan lithosphere and the subsequent India-Eurasia collision.…”

Metamorphic P–T–water conditions of the Yushugou granulites from the southeastern Tianshan orogen: Implications for Paleozoic accretionary orogeny

“…The common occurrence of weakly retrogressed granulite facies assemblages is consistent with substantial melt loss from the majority of granulite facies rocks (White & Powell, 2002). Phase equilibria modeling indicate that the degree of partial melting of normal pelitic granulites with H 2 O content of~1.8% will be more than 25-30 vol.% of the whole rock volume when the metamorphic temperature reaches 900°C between 10 and 14 kbar (White et al, 2001Guilmette et al, 2011;Zhang et al, 2013). For the Yushugou pelitic granulites, the estimated melt mode is ca.…”

“…Typical island arcs contain an upper mantle section of ultramafic rocks (harzburgite, dunite and pyroxenite) and a lower crust section of HP mafic granulites (meta-gabbros and gabbronorite) (e.g., DeBari & Coleman, 1989;Yamamoto & Nakamura, 1996;Burg et al, 1998;Garrido et al, 2006;Greene et al, 2006;Farris, 2009;Jagoutz et al, 2009;Bosch et al, 2011;Jagoutz et al, 2011). By contrast, continental magmatic arcs contain an upper mantle section of metaultramafic rocks (spinel peridotite and garnet pyroxenite) and a lower crust section of mafic granulites (meta-gabbros) as well as schist, marble and calc-silicate rocks (meta-supracrustal rocks) (Saleeby et al, 2003;Zandt et al, 2004;Miller & Snoke, 2009;Zhang et al, 2010aZhang et al, , 2013Palin et al, 2014). Therefore, the Yushugou massif is likely to represent a continental arc root.…”

“…(5) HP/UHP metamorphic rocks in subduction and collision zones are characterized by low geothermal gradient (4-15°C/km; Chopin, 2003;Zhang et al, 2003;Liou et al, 2009;Gilotti, 2013). By contrast, granulites in magmatic arc roots commonly witnessed a high geothermal gradient of N 20°C/km (Bohlen, 1987;Ellis, 1987;Harley, 1989;Bohlen, 1991;Ringuette et al, 1999;Müntener et al, 2000;Bhowmik et al, 2005;Brandt et al, 2006;Zhang et al, 2013;Zhao & Zhai, 2013). In general, plate convergence and magma accretion resulting in crustal thickening and growth, and associated HT/UHT granulite-facies metamorphism and anatexis may be one of the most important processes in subduction-related magmatic arcs (e.g., Gibson et al, 1988;Brown, 1996;Clarke et al, 2000;Collins, 2002aCollins, , 2002bHollis et al, 2003; Hyndman et al, 2005;Currie & Hyndman, 2006;Klepeis et al, 2007;Scott et al, 2009;Stowell et al, 2010;Yin et al, 2014).…”

“…The accretionary orogenic system is a plausible tectonic setting for generating large-scale UHT metamorphism (Kelsey, 2008). Voluminous mantle-derived magmatic accretion and loading, convective removal of lithospheric mantle following crustal thickening, upwelling of asthenosphere induced by rollback and breakoff of deeply subducted oceanic slab, and mid-oceanic ridge subduction are potential tectonothermal processes that can induce regional scale HT/UHT metamorphism of the lower crust of accretionary orogens (Baba, 1999;Sengupta et al, 1999;Underwood et al, 1999;Iwamori, 2000;Collins, 2002aCollins, ,b, 2011Bradley et al, 2003;Brandt et al, 2003;Saleeby et al, 2003;Zandt et al, 2004;Yin et al, 2009;Santosh & Kusky, 2010;Zhang et al, 2010aZhang et al, ,b, 2011Yin et al, 2011;Guo et al, 2012;Santosh et al, 2012;Zhang et al, 2013;Yin et al, 2014). This study provides the first documentation of Paleozoic UHT metamorphism in the Tianshan orogenic collage and new insights into the accretionary orogeny of the STAC although detailed tectonic mechanism remains to be revealed in future studies.…”