1.3 Research History on the Early Permian Tarim Large Igneous Province (Tarim LIP)

One notable feature of the Tarim Block is the wide occurrence of the Early Permian intraplate magmatism (Fig. 1.7 and Fig. 1.8), and the magmatic rocks were constituted mainly of basaltic rocks including basalts, diabase, basaltic andesite, ultramafic rocks, etc. The residual distribution area of the magmatic rocks can reach about 2.5×105 km2 (Fig. 1.9), and the residual thickness is from dozens of meters to several hundred meters (Yang et al., 1996, 2005, 2006a, 2007a, b; Chen et al., 1997a, 1998; Jia, 1997; Jia et al., 2004). With the scale as large as the Emeishan basalt, we regard the Tarim Early Permian intraplate magmatism as a new Large Igneous Province (Tarim LIP).

Fig. 1.7 The remote sensing images showing the distribution of basalts in the Yingan and Sishichang area (A) and basalts profile of the Kupukuziman Formation in Sishichang area (B)

Fig. 1.8 Early Permian basalt (A) and Permian intrusion (B) in the Seismic profile, and borehole histogram of Tz-47 (C)

Fig. 1.9 The distribution of the Tarim Large Igneous Province (Tarim LIP)

Tarim Permian intraplate basalts were first reported by Wang and Liu (1991), who studied the Permian basalts in Kaipaizileike section outcropped in Keping County, northwest of the Tarim Block. Wang and Liu (1991) believed that the basalts were formed in the continental rift environment during the Late Carboniferous to Early Permian, and that they belong to subalkaline basalts at the lower part and to alkali basalt at the upper part. However, it is hard to know about their distribution and geodynamic importance because most of the basaltic rocks in the basin are buried by the upper strata. Large-scale, systematic studies of the Tarim Permian intraplate basalts were carried out by a group from the School of Earth Sciences, Zhejiang University in 1992 (Yang et al., 1994, 1996, 2005, 2006a, b, 2007a, b; Chen et al., 1997a, b, 1998; Li et al., 2008). They investigated basalts from both outcrops in the marginal area and boreholes in the interior area of the Tarim Block. The results show that the Tarim Permian magmatism was mainly made up of basalts with synchronous diabase, alkali granite, and ultra-basic rocks. The basalts are mainly in an alkali and subalkaline series with minor tholeiites. The results of whole rock K—Ar and Ar—Ar isotopic ages show that the magmatism occurred mainly in the Early Permian period with ages ranging from 290 to 277 Ma. The SHRIMP (sensitive high resolution ion microprobe) zircon U—Pb data of the basalts from the Keping area indicated that it first erupted at about 290 Ma and lasted until about 288 Ma (Yu et al., 2011; Li et al., 2011). From the study of the Yingan section in the Keping area, the chemical composition of basalts has a richer upward trend of K, Fe, and P. Together with the results of trace-element and rare-earth element, the group refers to the basalts as continental flood basalts (CFBs) which should have a close relation with mantle plume activities. In the meantime, the basalts, diabase, and ultrabasic rocks from outcrops in the Keping and Bachu areas were also investigated by many other authors (Jiang et al., 2004a, b, c). Jiang et al. (2004a, b, c) noted that the ultramafic rocks may have sourced from the D＂ layer above the core-mantle boundary. Systematic studies of different units on the Tarim LIP with different perspectives have been carried out since 2006. There are representative studies of Tarim LIP that focus on the systematic studies of the geochronology and geochemistry for the Permian basalts (Li Y. et al., 2007; Li Z.-L. et al., 2008; Zhang et al., 2009; Zhou et al., 2009; Chen et al., 2010; Tian et al., 2010; Yu et al., 2010, 2011; Zhang et al., 2010a, b; Li Y.-Q. et al., 2012a; Li H.-Y. et al., 2013; Wei et al., 2014; Xu et al., 2014), intermediate-acid rocks (Chen H.-L. et al., 1998; Chen M.-M. et al., 2010; Yang et al., 2006b; Li Y. et al., 2007; Tian et al., 2010; Shangguan et al., 2011), basic and ultrabasic dikes and ultramafic rocks (Jia et al., 2001; Li Y. et al., 2007; Sun et al., 2007; Zhang C.-L. et al., 2008; Zhang H.-A. et al., 2009; Li Y.-Q. et al., 2010, 2012b; Zhou et al., 2009); the time sequence of different units in the Tarim LIP (Chen et al., 2009; Li Z.-L. et al., 2011); the comparative studies on the Tarim LIP with the Permian magmatism in adjacent areas (Yu et al., 2009; Zhang et al., 2010a, b; Qin et al., 2011; Xia et al., 2012); the relationship between the Tarim LIP and the formation of mineral resources and environmental change (Zhu et al., 2005; Chen et al., 2006; Yang et al., 2006a; Kang, 2008; Cao et al., 2013; Li et al., 2014). After about twenty years of systematic studies, we found that the Tarim LIP has the following features:

(1) The Tarim LIP is characterized by various types of magmatic rocks and a wide area of distribution, and the area of residual distribution of the magmatic rocks is over 2.5×105 km2 with that of basalts reaching about 2.0×105 km2 (Yang et al., 2005, 2006a).

(2) The timing of the Tarim LIP igneous suites is between 290 and 275 Ma (Chen et al., 2009; Li Z.-L. et al., 2011), with the large scale of basaltic magma that erupted between ca. 290 and 288 Ma (Yu et al., 2011).

(3) The basalts from the Keping area have an OIB-like (OIB means oceanic island basalt) trace element pattern with enrichments in LILE (large ion lithophile elements) and HFSE (high field strength elements), a relatively high 87Sr/86Sriand negative εNd(t) value suggesting that they were derived from an enriched mantle (Zhou et al., 2009; Zhang et al., 2010a), and should have a close relationship with the interaction of the mantle plume and the lithosphere (Yu et al., 2009, 2011; Zhang Y.-T. et al., 2010; Wei and Xu, 2013).

(4) The generation of the intermediate-felsic volcanic rocks in the northern Tarim Block, Bachu syenites (A-type granite) and syenitic porphyry and Piqiang A-type granite were correlated to mantle plume and the appearances of A-type granite means the end of Tarim LIP magmatism (Chen et al., 1998; Yang et al., 2006b; Sun et al., 2007; Zhang et al., 2010a).

(5) All of the geological characteristics, such as the large scale of crustal uplift (Chen et al., 2006; Li et al., 2014), the similar geochemical features of the ultrabasic rocks to the picrite (Yang et al., 2007b; Tian et al., 2010), and the large scale of dike swarms and V—Ti magnetite deposit give support to the theory that the Tarim LIP is related to the mantle plume.

(6) The Early Permian basic and ultrabasic rocks distributed in the Tarim, Junggar and Tuha Basins and in the Altay orogen may be the different parts of one tremendous LIP over 6×105 km2 (Zhang et al., 2010a, b; Qin et al., 2011; Zhang C.-L. et al., 2013a, b; Zhang D.-Y. et al., 2013; Xu et al., 2014).

(7) The Tarim LIP magmatism had led to the formation of large V—Ti magnetite deposits and the change in the Permian depositional environment (Zhu et al., 2005; Yang et al., 2005; Chen et al., 2006; Kang, 2008; Cao et al., 2013).

(8) The early-stage magmatism of the Tarim LIP mainly derives from the melting of the Tarim sub-continental lithospheric mantle (SCLM) caused by the heating of the mantle plume, and the late-stage magmatism of the Tarim LIP mainly derives from the decompression melting of the Tarim mantle plume (Yu, 2009; Xu et al., 2014).