Late Paleozoic subduction system in the northern margin of the Alxa block, Altaids: Geochronological and geochemical evidences from ophiolites

An Early Permian (ca. 280Ma) silicic igneous province in the Alxa Block, NW China: A magmatic flare-up triggered by a mantle-plume?

“…The main requirement for the generation of these large volume felsic melts is that their protoliths are hydrous (e.g., Bryan et al, 2002), which is consistent with the fact that reported Phanerozoic SLIPs are all restricted to continental margins that acquire fertile, hydrous lower-crustal materials by long-lived subduction (e.g., Bryan and Ferrari, 2013;Bryan et al, 2002). Although there is no contemporaneous subduction around the Alxa silicic igneous province, the hydrous lowercrust would have been created by Paleo-subduction in the southern (e.g., Song et al, 2013), eastern (Dan et al, 2013) and northern (Zheng et al, 2013) part of the Alxa Block.…”

Linking the Alxa Terrane to the eastern Gondwana during the Early Paleozoic: Constraints from detrital zircon U–Pb ages and Cambrian sedimentary records

“…The Alxa Terrane is located to the south of the Central Asian Orogenic Belt (Windley et al, 2007;Xiao et al, 2010;Safonova et al, 2011;Yarmolyuk et al, 2012;Feng et al, 2013;Kröner et al, 2014;Zheng et al, 2014). The Ordos Terrane (North China Terrane) lies to the east, separated from the Alxa Terrane by the Mesozoic Helan Shan thrust belt which was caused by the eastward compression of the Alxa Terrane (Liu, 1998;Darby and Ritts, 2002).…”

“…To the west of the Alxa Terrane is the Beishan Orogenic Belt with the Engeerwusu ophiolites as the boundary between them ; recent studies indicated that the Paleo-Asian Ocean closed along the north Alxa Terrane to form the Engeerwusu ophiolites at ca. 275 Ma (Feng et al, 2013;Zheng et al, 2014). There is no consistent view on the southern boundary of the Alxa Terrane; some authors argued that the Longshoushan-Western Ordos fault is the boundary (Zhang et al, 2009 and references therein), however, different geophysical observations showed that the crustal structures of the Hexi Corridor (i.e.…”

Tracking deep crust by zircon xenocrysts within igneous rocks from the northern Alxa, China: Constraints on the southern boundary of the Central Asian Orogenic Belt

“…Numerous zircon xenocrysts from several tectonic units were identified in many of these studies Zhou, 2010, 2012;Li et al, 2010;Wu, 2011;Shi et al, 2012;Wang, 2012;Gong, 2013;Feng et al, 2013;Zhang et al, 2013c;Dan et al, 2014b;Wu et al, 2014;Zheng et al, 2014). These zircon xenocrysts may provide a good opportunity to trace information on the deep continental crust and to constrain the boundary between the CAOB and the Alxa Block.…”

“…The boundary of the Alxa Block modified after (Lamb et al, 1999;Zhang et al, 2013a,b;Zhao and Zhai, 2013;Dan et al, 2014a,b). was previously regarded as a major paleo-plate boundary between the Alxa Block and the Southern CAOB (Wu andHe, 1992, 1993;Wang et al, 1998;Dan et al, 2012Dan et al, , 2014aGong et al, 2012;Feng et al, 2013;Song et al, 2013;Zheng et al, 2014). However, this assumed suture/tectonic boundary has not been confirmed by robust evidence, due to (1) the difficulty of defining tectonic units due to poor exposure of ophiolites and the allochthonous ophiolites, mélanges; (2) the limited knowledge of the deep crust in this region.…”