Long-lived high-temperature granulite-facies metamorphism in the Eastern Himalayan orogen, south Tibet

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).…”

“…Although the sections of deep magmatic arc roots are much less exposed and studied, some arc roots, like the Gangdese arc in Tibetan Plateau (Zhang et al, 2013;Zhang et al, 2013Zhang et al, , 2014b2015aand, 2015b, and the Talkeetna arc in southern Alaska (Debari and Coleman, 1989;Greene et al, 2006), have been well described. Thus in a typical section of deep continental arc root, from base upward, the following assemblages can be seen: (1) ultramafic cumulates; (2) gabbros, gabbronorite, norite; (3) intermediate plutonic rocks; and (4) amphibolite to granulite facies meta-sedimentary rocks such as metapelites.…”