Geochemistry of Permian bimodal volcanic rocks from central Inner Mongolia, North China: Implication for tectonic setting and Phanerozoic continental growth in Central Asian Orogenic Belt

Evolution of the Early Permian volcanic-plutonic complex in the western part of the Permian Gobi-Altay Rift (Khar Argalant Mts., SW Mongolia)

“…High La/Nb and low La/Ba (Fig. 11b) are comparable with compositions of basic volcanites given by Zhang et al (2008Zhang et al ( , 2011, which were interpreted as a product of partial melting of metasomatized asthenospheric mantle in a post-collisional extensional regime (Zhang et al 2011). studied mafic rocks indicate high degrees of partial melting of an asthenospheric mantle (e. g. Zhou et al 2004).…”

“…f -ε i (Pearce 1996). A post-collisional volcanic complex with comparable age, chemical and isotopic compositions was described by Zhang et al (2008Zhang et al ( , 2011 from the Xilinhot area in central Inner Mongolia (North China). The Shar Oroy granites plot near the low-pressure thermal minimum on the normative Qtz-Ab-Or diagram of Johannes and Holtz (1996), which indicates a shallow level of intrusion (Fig.…”

“…Permian post-collisional bimodal magmatism was commonly ascribed to continental rift settings (Mazzarini et al 2004) and its products are frequently encountered in the Mongolian segment of the CAOB (Kovalenko et al 2006;Yarmolyuk et al 2008;Zhang et al 2008;Jahn et al 2009). The crustal extension most likely caused a thermal and mechanical instability of the thickened lithosphere (Marotta et al 1998) during the early stages of post-collisional evolution in this part of the CAOB, accompanied by extensive crustal anatexis.…”

“…The CAOB is a large mosaic of various geological terranes amalgamated between the Siberian Block in the north, the Tarim Block in the southwest and the Sino-Korean Block in the south (Hendrix et al 1992;Sengör et al 1993;Jahn et al 2000;Dergunov 2001). Suturing in the southern part of the CAOB proceeded eastwards from the latest Palaeozoic in the Tien Shan to the Triassic in Inner Mongolia (Xixi et al 1990;Xiao et al 2004Xiao et al , 2008 and was accompanied by intracontinental magmatic activity in the terranes accreted to the southern margin of the Siberia craton (Zhu et al 2001;Zhang et al 2008;Jahn et al 2009). Yarmolyuk andKovalenko (1991, 2001) assumed the existence of five linear systems controlled by large E-W oriented faults and related to Upper Palaeozoic igneous bimodal associations.…”

A new interpretation of the tectonic setting and age of meta-basic volcanics in the Ondor Sum Group, Inner Mongolia

“…Many scholars believed that the Ondor Sum Group represent slices of Early-Paleozoic Oceanic crust and had experienced a blueschist facies metamorphism [3][4][5]8,[15][16][17]32]. This idea was supported by a few 40 Ar/ 39 Ar plateau age dating results, which, for instance, are 446±15 Ma for glaucophane from blueschist [33] and 453.2±1.8 Ma and 449.4±1.8 Ma for phengite from quartzite mylonites [32] in the southern zone of the Ondor Sum group, and 383 Ma for glaucophane from blueschist in the northern zone of the Ondor Sum group [4]. It was noted that Chen et al [19] dated the same blueschist in the northern zone using zircon U-Pb method and the results suggest that the protolith of the blueschist should be younger than 280-318 Ma, completely different from the Ar-Ar ages.…”