Diverse Permian magmatism in the Tarim Block, NW China: Genetically linked to the Permian Tarim mantle plume?

Abstract

24 25 Zircon U-Pb ages and geochemical data are reported for the Piqiang oxide-bearing 26 ultramfic-mafic complex, the Bachu mafic dyke swarm, the Yingan and Kaipaizileike basalts 27 and the Halajun A-type granites in the Tarim Block, Northwest China. The Piqiang complex 28 and the Halajun A-type granites were emplaced at ca. 276 Ma and ca. 278 Ma, respectively. 29 Together with previously reported geochronological data, the diverse intrusive and extrusive 30 rocks in Tarim show a peak age at ca. 275 Ma. Elemental and Nd isotope geochemistry 31 suggests that the spatially and temporally related Piqiang complex (including some dolerite 32 dykes or stocks) and the Halajun A-type granites were formed via crystal 33 fractionation/accumulation of a common plume-derived parental mafic magma (melting 34 degree > 10%), coupled with variable extents of crustal contamination. Crystal 35 fractionation/accumulation in one or several magma chambers resulted in the diversity of 36 rocks types. The Bachu mafic dyke swarm shares a similar mantle source with the intrusive 37 rocks in the Piqiang-Halajun area but with a relatively lower degree of partial melting (~5%). 38 In contrast, the basalts were derived from a time-integrated, enriched lithospheric mantle 39 source as suggested by their high-Ti, LREE-and LILE-enriched trace element signature and 40 negative ε Nd (T) values (-2.0 ~ -2.6). The synchronous yet diverse range of Permian igneous 41 rocks in Tarim can best be accounted for by a Permian mantle plume, which is about 15 Ma 42 earlier than the Emeishan plume in southwestern China. 43

The Early Permian Tarim Large Igneous Province: Main characteristics and a plume incubation model

“…So far only one high-Nb-Ta rhyolite sample has been dated ( Fig. 6), but it has the essentially same age as equivalent plutons (i.e., A-type granites; Zhang et al, 2010b). Moreover, the age range of the high-Nb-Ta rhyolites and Atype granites is similar to those of the syenite plutons, layered intrusion and mafic dykes (Wei and Xu, 2011;Yang et al, 1996Yang et al, , 2007.…”

“…The dykes also intrude the Xiaohaizi syenite complex although some of the dykes intermingle with the syenite (Zhang et al, 2008b). At several outcrops, ultramafic-mafic-felsic intrusions and bimodal dykes consisting of dolerite and quartz syenite porphyry are observed Yang et al, 2007;Zhang et al, 2008bZhang et al, , 2010b. Due to disturbed Ar systematics caused by severe alteration, most of the 40 Ar/ 39 Ar results published are not reliable because the plateau ages often contain less than 40% of the total 39 Ar released and are mostly discrepant with the inverse isochron ages (Zhang et al, 2010c).…”

“…In addition to extrusive rocks, the Tarim LIP also comprises a great diversity of intrusive rocks, which mainly occur in Bachu, Wajilitag and Piqiang in the western part of the Tarim Basin (e.g., Jiang et al, 2004a,b,c;Yang et al, 2006a,b;Zhang et al, 2008aZhang et al, , 2010bZhang et al, , 2013Li et al, 2011Li et al, , 2012aCao et al, 2013). These intrusions cut Silurian and Devonian strata and host economic Fe-Ti oxide mineralization Zhang et al, 2008a), consistent with strong aeromagnetic anomalies in the Piqiang, Bachu and Akesu regions (Rui et al, 2002).…”

“…Elemental modeling further suggests that the parental magma of Xiaohaizi syenites were residual melt after olivine and clinopyroxene fractional crystallization from mantle-derived alkaline basaltic magma. U-Pb zircon dating of the Xiaohaizi syenite complex yields ages varying from 277 Ma to 282 Ma Wei and Xu, 2011;Yang et al, 2006b;Zhang et al, 2008aZhang et al, , 2010b.…”

“…Recent gas and petroleum exploration in the Tarim Basin has provided drill boreholes and seismic profiles of variable scale, offering an ideal opportunity to better understand this LIP (e.g., Li et al, 2011;Liu et al, 2014;Tian et al, 2010). In addition, there are sufficiently large amounts of data available from exposed lava sections, intrusions and numerous dykes, and kimberlite pipes in the NW and W Tarim (Bachu, Keping, Piqiang) for an integrated analysis to be undertaken (Chen et al, 1997;Jiang et al, 2006;Wei et al, 2014;Yang et al, 2005;Yu et al, 2011b;Zhang et al, 2008aZhang et al, , 2010bZhang et al, , 2013Zhou et al, 2009). This review paper starts with a summary of the main characteristics of the Tarim LIP including its rock type, composition and emplacement ages.…”