Petrogenesis and geochemical characteristics of Early Carboniferous sanukitic high‐Mg andesite from Atengtao Mountain, Yili Block: Implications for the tectonic setting during Late Palaeozoic in Chinese West Tianshan

Abstract

Tianshan contains voluminous Late Palaeozoic volcanic rocks. Here, we present geochronological, geochemical, and in situ Lu-Hf isotopic data from the Atengtao sanukitic high-Mg andesites (HMAs) of the western Yili Block. LA-ICP-MS zircon U-Pb analyses indicate that the Atengtao high-Mg andesites were generated in the Early Carboniferous (346 ± 2 Ma). All the studied rock samples are characterized by high MgO (3.30-5.45 wt.%), SiO 2 (53.25-60.10 wt.%), Cr (90.3-157 ppm), and Ni (31.0-46.7 ppm) contents, with geochemical characteristics analogous to those of sanukitoids of the Setouchi Volcanic Belt (SVB), SW Japan, and Bieluagaxi area, West Junggar. The Atengtao sanukitic HMAs are enriched in LILE and LREE but depleted in HFSE, similar to those of typical arc-related magmatic rocks. They are also characterized by high Nb (11.4-15.8 ppm) concentrations, high Th/La (0.3) and Th/Yb (2.6-4.0) ratios, and varying zircon εHf(t) values (−2.3 to +4.3). These features are suggested to result from the partial melting of a relatively enriched mantle wedge metasomatized by subducting oceanic slab-derived sediments. Considering the occurrence of sanukitic HMAs, combined with the contemporaneous special rock assemblages (such as slab-derived adakite, Nb-enrich basalt, A-type granite/rhyolite, and bimodal volcanic rocks) found in the western part of Yili Block, we propose that the generation of the Carboniferous sanukitic HMAs in Atengtao Mountain were most likely related to the slab break-off following the southern Tianshan Ocean slab northward subduction beneath the Yili-Central Tianshan Block. This mechanism not only produces intense magmatism with compositional diversity but also gives rise to a local extension in the western part of Yili Block. The slab break-off model may play an important role in the crustal growth of the CAOB in Phanerozoic time.

Early Carboniferous mafic dike–syenitic granite association in the Atengtao Mountain, Yili Block (NW China): Geochronology, petrogenesis, and tectonic significance

“…Li et al, ), calc‐alkaline volcanic suites, bimodal volcanic suites (Z.P. Wang, Li, et al, ), sanukitic high‐Mg andesite (Wang et al, ), and mafic dike–syenitic granite association (this study), coupled with minor Late Devonian granites. Numerous zircon U–Pb dating results indicate that these rocks in Atengtao Mountain mainly formed during the middle Early Carboniferous (338–347 Ma), consistent with coeval adakitic granitoids and Nb‐enriched basalt from Wusun Range (See Table S2; Y.J.…”

“…Moreover, as discussed in Section , mafic rock–granitoid associations are commonly generated in extensional tectonic settings (Tang et al, ). Thus, such characteristics involving a high‐temperature regime, lithosphere extension, and magmatic flare‐up events in the Atengtao and Wusun Range from the western Yili Block during the ages of 338 Ma to 347 Ma (Table S2) could have been attributed to the following models as a possible geodynamic mechanism: (a) postcollisional extensional setting (Han et al, ; Sun, Wang, Fan, & Zi, ), (b) mantle plume ascent (Xia et al, ), or (c) slab break‐off or slab rollback (Tang et al, ; Wang et al, ; Yin et al, ).…”

“…Li et al, ; Z.P. Wang, Li, et al, ), which can be attributed to the upwelling of the asthenosphere induced by a slab rollback (Tang et al, ; Yin et al, ; Yin et al, ) or slab break‐off (Wang et al, ).…”

Geochronology, geochemistry, and petrogenesis of the Kezijiaer gabbros, southern Chinese Altai: Evidence for ridge subduction

“…The ridge subduction model has been widely reported worldwide, such as in the Chinese Altai, western Junggar, Tibet, southern Alaska, and western California and refers to an active oceanic spreading ridge travelling across the ocean to a subduction zone where the ridge–trench interaction may take place (Cai et al, ; Cole & Stewart, ; Fan et al, ; Geng et al, ), leading to a unique geodynamic and geochemical environment (Windley & Xiao, ). A slab window generally forms along the edges of the diverging plate when a ridge continues to subduct beneath a continental margin or when slab tearing/breakoff occurs (Cai et al, ; Tang et al, ; Wang et al, ; Yin et al, ) and then triggers massive asthenospheric mantle upwelling (Sun et al, ; Thorkelson, Madsen, & Sluggett, ). The upwelling of asthenospheric materials through the slab window can not only provide sufficient high heat flux inducing partial melting of the overriding slab, lithospheric mantle wedge, and crust rocks, but also lead to a local extension above the window (Yogodzinski et al, ).…”

“…subduct beneath a continental margin or when slab tearing/breakoff occurs (Cai et al, 2011;Tang et al, 2012;Wang et al, 2019;Yin et al, 2013) and then triggers massive asthenospheric mantle upwelling Thorkelson, Madsen, & Sluggett, 2011). The upwelling of asthenospheric materials through the slab window can not only provide sufficient high heat flux inducing partial melting of the overriding slab, lithospheric mantle wedge, and crust rocks, but also lead to a local extension above the window (Yogodzinski et al, 2001).…”