Abstract
Extensive Early Permian mafic-ultramafic intrusions, doleritic dykes, and basalts crop out within the Beishan area, southern Central Asian Orogenic Belt (CAOB). We present new geochronological and geochemical data for Gubaoquan dolerite dyke swarms in the Beishan orogenic belt. Zircon U-Pb Dating of the Gubaoquan dykes indicates that they were emplaced during the Early Permian (280.7 ± 4 Ma), that was coeval with Yinaoxia and Podong mafic dykes in Beishan area. The dykes are characterized by low Mg# (47–84) in the clinopyroxene crystals, and the content of whole-rock Fe2O3 (t), MgO, and alkali (Na2O + K2O) range from 12.5–17.4, 4.06–5.51, and 2.8–4.4 wt.%, respectively. The samples from the Gubaoquan dykes have high and variable Ba/La (5.93–14.2) and Ba/Nb (15.0–37.3) ratios but low Th/Yb (0.17–0.24) ratios. The rocks show slightly enrichments in LREE, HFSE, Th, and Hf, and depletion in Nb and Ta. The εNd (t = 280 Ma) values and initial 87Sr/86Sr ratios of the Gubaoquan dykes show variations ranging from 6.4 to 6.8 and 0.706240 to 0.707546, respectively. These data suggest that the parental magmas for the Gubaoquan dykes were probably derived from partially decompressed melting of upwelling depleted asthenosphere mantle that was metasomatized previously by subducted fluids.
Highlights
The Central Asian Orogenic Belt (CAOB) is the important Phanerozoic accretionary orogenic belt in the world (Figure 1A; Sengör et al, 1993; Jahn et al, 2000)
We present new geochronological and geochemical data for Gubaoquan mafic dyke swarms in the Beishan area (Figure 1B), and investigate their petrogenesis and the dynamic background This study aims to provide a basis for further understanding the geotectonic background in Beishan area during Early Permian
Zircon U-Pb dating indicates that the Gubaoquan doleritic dykes in the Beishan orogenic belt were emplaced at ca. 280 Ma, that was the same time as the formation of the dolerite dyke swarms extensively distribution in Beishan and the Tarim Large Igneous Province (LIP)
Summary
The Central Asian Orogenic Belt (CAOB) is the important Phanerozoic accretionary orogenic belt in the world (Figure 1A; Sengör et al, 1993; Jahn et al, 2000) It was formed by the amalgamation of accretionary complexes, magmatic arcs, arc-related basins, ophiolites, seamounts, and microcontinents during the long-lived subduction of the Paleo-Asian Ocean (Kröner et al, 2007; Windley et al, 2007; Xiao et al, 2008, 2011, 2019). The Early Permian was a crucial period in the evolutionary history of the CAOB, marked by the closure of the Paleo-Asian Ocean, the transition from subductionaccretion to post-collisional tectonism and the occurrence of extensive mantle-derived magmatism. The petrogenesis of the Early Permian mafic-ultramafic complexes, doleritic dykes, and basalts in the Beishan orogenic belt, and is still in controversial. Zhou et al (2004) believe that the Permian magmatic rocks in the Tarim area and the adjacent Beishan area together constitute a Large Igneous Province (LIP), which is a product of mantle plume activities (Zhou et al, 2004; Qin et al, 2011; Su et al, 2011, 2012). Zhang et al (2011) suggest that the Permian mantle-derived coeval in the Beishan area are both products of the post-subduction extension (Zhang et al, 2011; Li et al, 2013, 2020; Zheng et al, 2014). Ao et al (2010) believe that Permian mafic-ultramafic complexes, such as Pobei and Hongshishan, were formed by subduction process of the PaleoAsian Ocean, representing the Late Paleozoic island arc settings in the Beishan area (Ao et al, 2010)
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