Reworking of the Gangdese magmatic arc, southeastern Tibet: post‐collisional metamorphism and anatexis

Abstract

The Gangdese magmatic arc, southeastern Tibet, was built by mantle-derived magma accretion and juvenile crustal growth during the Mesozoic to Early Cenozoic northward subduction of the Neo-Tethyan oceanic slab beneath the Eurasian continent. The petrological and geochronological data reveal that the lower crust of the southeastern Gangdese arc experienced Oligocene reworking by metamorphism, anatexis and magmatism after the India and Asia collision. The post-collisional metamorphic and migmatitic rocks formed at 34-26 Ma and 28-26 Ma respectively. Meta-granitoids have protolith ages of 65-38 Ma. Inherited detrital zircon from metasedimentary rocks has highly variable ages ranging from 2708 to 37 Ma. These rocks underwent post-collisional amphibolite facies metamorphism and coeval anatexis under P-T conditions of~710-760°C and~12 kbar with geothermal gradients of 18-20°C km À1 , indicating a distinct crustal thickening process. Crustal shortening, thickening and possible subduction erosion due to the continental collision and ongoing convergence resulted in high-P metamorphic and anatectic reworking of the magmatic and sedimentary rocks of the deep Gangdese arc. This study provides a typical example of the reworking of juvenile and ancient continental crust during active collisional orogeny.

Geochronology and geochemistry of a suite of mafic rocks in Chencai area, South China: Implications for petrogenesis and tectonic setting

“…Since zircons crystallized earlier than garnet (which formed during the granulite facies stage), this also explains why the zircons do not show garneteffect in chondrite-normalized REE patterns. Similar cases have been described in previous studies from different terranes (Berger et al, 2008;Zandt et al, 2004;Zhang et al, 2013Zhang et al, , 2014b2015aand, 2015bZhao et al, 2014a). We thus favor thee second possibility and the age of 440 Ma is interpreted to represent the time of granulite facies metamorphism while the age of magmatism would be slightly older than this.…”

“…2) (Kong et al, 1995;Zhejiang, 1989;Lan et al, 1995a and1995b). These rock associations are typical of a continental shelf suite (Wang et al, 2013c;Zhao, 2014;Lan et al, 1995aLan et al, , 1995b and are similar to those reported from accretionary continental margins (Rao and Santosh, 2011;Zhang et al, 2013Zhang et al, , 2014b2015a and2015b). Kong et al (1995) divided the Chencai Group metasedimentary rocks into four formations which are (from the base upwards): the Daojiuwan Formation, Xiahetu Formation, Xiawuzhai Formation and Xu'an Formation (Fig.…”

“…This field relationship implies that the long-lived mafic magmatism (from~450 Ma tõ 420 Ma) might have provided the heat source for this episode of highgrade metamorphism. Such contemporaneous and long-lived magmatism and high-grade metamorphism have been reported from many subduction-influenced regions, especially in the arc root area (Berger et al, 2008;Zandt et al, 2004;Zhang et al, 2013Zhang et al, , 2014b2015aand, 2015b. The high-heat flow in the middle and lower part of the arc can readily cause amphibolite to granulite facies metamorphism.…”

“…12) and it is thus clear that all the zircons crystallized within a short period of time (perhaps within 20-50 million years). Such a time-gap is typical for metamorphism and magmatism in arc regions, especially continental arcs (Berger et al, 2008;Zandt et al, 2004;Zhang et al, 2013Zhang et al, , 2014b2015aand, 2015bZhao et al, 2014a).…”

Late Devonian-Early Carboniferous magmatism in the Lhasa terrane and its tectonic implications: Evidences from detrital zircons in the Nyingchi Complex

“…The South Lhasa terrane consists of the high-grade metamorphic sequence (Nyingchi Complex), Carboniferous−Triassic strata and 165-22 Ma granitoids and mafic rocks (Booth et al, 2009;Burg et al, 1997;Dong et al, 2010a;Geng et al, 2006; A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT 2011Zhang et al, 2010aZhang et al, , 2013. The Nyingchi Complex is a tectonic mélange and mainly consists of schists, migmatite, orthogneisses, paragneisses and metasandstone, with minor quartzite, calc-silicate rocks, marble and granulite (Dong et al, 2010a;Guo et al, 2011Guo et al, , 2012Guo et al, , 2013Lin et al, 2013a;Zhang et al, 2008Zhang et al, , 2010bZhang et al, , 2013Zhang et al, , 2015. Due to the lack of detailed geological and geochemical investigation, the age and origin of the protoliths of the metamorphic rocks from the Nyingchi Complex have not yet been well documented.…”