Initial opening of the southern Paleo-Asian Ocean: evidence from Neoproterozoic magmatism in the Beishan area, southern central Asia orogenic belt, NW China

Geology, geochronology, mineral chemistry and geochemistry of the Hongnieshan mafic–ultramafic complex in the Beishan area, southern Central Asian orogenic Belt, NW China: Implications for petrogenesis and regional Ni mineralization

Permian doleritic dikes in the Beishan Orogenic Belt, NW China: Asthenosphere–lithosphere interaction in response to slab break-off

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.

Early Permian mafic-ultramafic complexes in eastern Xinjiang (新疆) are mainly distributed in the Beishan (北山) area, Mid-Tianshan (天山) massif and Jueluotage (觉罗塔格) belt. Systematic compositional mapping of olivines from these Early Permian mafic-ultramafic complexes demonstrates that an apparently spatial distribution and heterogeneous partial melting in the mantle source exists from the Beishan area, across the Mid-Tianshan massif, to the Jueluotage belt from the south to the north. This is probably consistent with the spatial evolutional differences and tectonic features of these three belts. The decreasing degree of partial melting, as revealed by decreasing Fo contents of olivines, from south to north and from east to west reflects the southward subduction of the Paleo-Asian Ocean and the south location of the indistinct mantle plume in the Permian. Simultaneously, NiO and Fo-mapping in olivine also indicates that sulfide segregation before olivine crystallization played an important role in Ni-Cu mineralization in the mafic-ultramafic complexes. Olivines with the compositional range of Fo (77–86) and NiO (less than 0.22 wt.%) are more favorable for Ni-Cu sulfide mineralization.

The Early Permian mafic–ultramafic complexes in the Beishan Terrane, NW China: Alaskan-type intrusives or rift cumulates?

Geochronology and geochemistry of Early Permian mafic–ultramafic complexes in the Beishan area, Xinjiang, NW China: Implications for late Paleozoic tectonic evolution of the southern Altaids

Early Paleozoic (ca. 465 Ma) eclogites from Beishan (NW China) and their bearing on the tectonic evolution of the southern Central Asian Orogenic Belt

The tectonic attributes of different blocks within orogenic belts are of great significance for the study of accretionary processes and the evolution of Earth. The Hongliuhe‐Niujianzi‐Baiyunshan‐Xichangjing ophiolitic mélange belt (HXOMB) is distributed in the heart of the Beishan Orogen, the Shuangyingshan and Minshui‐Hanshan blocks being distributed in the south and north of the HXOMB respectively, and a large number of Early Paleozoic geological units are exposed on the blocks. According to the zircon age populations of the metasandstones in the Baiyunshan area recovered in this paper, when compared with the zircon age populations of the Paleozoic metasandstones reported in the Niujuanzi and Hanshan areas, we found that the metasandstones of the Shuangyingshan Block have age peaks at c. 598 Ma, 742 Ma, 828 Ma, 941 Ma, 990 Ma, 1168Ma, 1636 Ma, 2497 Ma with non‐significant age populations of 1500–1300 Ma, showing a possible affinity with the Tarim Craton; the metasandstones of the Minshui‐Hanshan Block have age peaks at c. 606 Ma, 758 Ma, 914 Ma, 1102 Ma, 1194 Ma, 1304 Ma, 1672 Ma with significant age populations of 1500‐1300 Ma, showing a possible affinity with the Chinese Central Tianshan Block. Therefore, the HXOMB of the Beishan Orogen is of great significance in plate segmentation, which separates the Tarim Craton in the south and the Chinese Central Tianshan Block in the north. Based on the evolutionary process of the Hongliuhe‐Xichangjing ocean in the Beishan Orogen, we believe that break‐up and convergence can be recognized as having occurred twice between the Chinese Central Tianshan Block and the Tarim Craton since the Mesoproterozoic in the Beishan area. This was related firstly to the break‐up of the Columbia Supercontinent and the convergence of the Rodinia Supercontinent, mainly during the Middle Mesoproterozoic to Early Neoproterozoic, and secondly to the opening and closing of the Hongliuhe‐Xichangjing ocean, mainly during the Early Paleozoic.

Constraints on the tectonic evolution of the southern central Asian orogenic belt from early Permian–middle Triassic granitoids from the central Dunhuang orogenic belt, NW China

Recognition of a Permian to Triassic foreland basin in the central Beishan Orogen, NW China: Provenance variations and their constraints on latest Palaeozoic orogeny

The Beishan area, located in the southernmost part of the Central Asia Orogenic Belt, is crucial for understanding the tectonic evolution associated with the closure of the Paleo‐Asian Ocean. One intermediate and two granitic plutons from the eastern Beishan area between Mingshui–Shibanjing–Xiaohuangshan (MSX) and Niujuanzi–Xichangjing (NX) ophiolitic belts, including Tongchangkou gabbroic diorite, Northern Tongchangkou and Sandaomingshui plutons, are dated at 426 ± 3, 408 ± 2, and 365 ± 2 Ma by SIMS U–Pb zircon analyses. The Middle Silurian Tongchangkou gabbroic diorites with medium‐K calc‐alkaline metaluminous characteristics represent volcanic arc rocks. The Early Devonian Northern Tongchangkou pluton, a highly evolved calc‐alkaline mylonitic monzogranite with low εNd(t), −3.5 and −2.4, and relatively low initial 87Sr/86Sr (0.707095 and 0.707249), was mainly derived from Mesoproterozoic mafic to intermediate igneous protolith and shows both volcanic arc and postcollisional characteristics. The Late Devonian Sandaomingshui pluton, a calc‐alkaline granite with slightly positive εNd(t), 0.6 and 0.9, and low (87Sr/86Sr)t, 0.705543 and 0.705851, is likely from a more depleted source and represents a volcanic arc granite. Combined with previous studies of Late Paleozoic granites, we find that the widely distributed Permian granites in Central Asia Orogenic Belt are absent between MSX and NX ophiolitic belts. Given the regional geology, we conclude that the back‐arc basin represented by the NX ophiolitic belt closed during Early Devonian and afterward, flat subduction of the oceanic basin represented by the MSX ophiolitic belt occurred. It also indicates that the oceanic crust was still being produced in the Paleo‐Asian Ocean during the early Carboniferous.

The Cihai diabase in the Beishan region, NW China: Isotope geochronology, geochemistry and implications for Cornwall-style iron mineralization

Intracontinental strike-slip faults, associated magmatism, mineral systems and mantle dynamics: examples from NW China and Altay-Sayan (Siberia)

Episodic Neoproterozoic magmatic suites in the Altyn Tagh, NW China, are thought to be related break-up of the Rodinia supercontinent. These suites resulted from long-term extension of the lithosphere during orogenic collapse and subsequent rifting. New geochemical and U-Pb-Hf zircon data indicate that the 825 Ma Hongliugou granite displays the characteristics of A-type granites derived from a juvenile source. Gneissic granites (780–760 Ma) are characterized by high Rb (>200 × 10−6), low Zr/Hf (23.28–29.28) and low Nb/Ta (4.20–12.99) typical of highly fractionated granites. A diabase exhibits trace element patterns between OIB and E-MORB which we infer as derivation from an enriched asthenosphere mantle. Combined with previous reported ca. 850 Ma and 620 Ma extension-related magmatism in this region, we interpreted the Altyn Tagh sequences as part of a lengthy supercontinental break-up process. Neoproterozoic magmatism in the Altyn Tagh is broadly correlative with magmatism in East Kunlun and North Qaidam orogenic belts around the Qaidam basin. Collectively, the Qaidam block, exposed mainly in the Altyn Tagh, East Kunlun and North Qaidam, represents a succession of accretionary orogenic, postorogenic, and within plate magmatism between 1200 and 620 Ma. The similarity in age of magmatism and metamorphism in the Altyn Tagh-North Qaidam-East Kunlun regions indicate that these Precambrian sequences collectively represent the basement of Qaidam block.

The Sidingheishan mafic–ultramafic intrusion is located in the eastern part of the Northern Tianshan Mountain, along the southern margin of the Central Asian Orogenic Belt in northern Xinjiang autonomous region of China. The Sidingheishan intrusion is mainly composed of wehrlite, olivine websterite, olivine gabbro, gabbro and hornblende gabbro. At least two pulses of magma were involved in the formation of the intrusion. The first pulse of magma produced an olivine‐free unit and the second pulse produced an olivine–bearing unit. The magmas intruded the Devonian granites and granodiorites. An age of 351.4±5.8 Ma (Early Carboniferous) for the Sidingheishan intrusion has been determined by U‐Pb SHRIMP analysis of zircon grains separated from the olivine gabbro unit. A U‐Pb age of 359.2±6.4 Ma from the gabbro unit has been obtained by LA‐ICP‐MS. Olivine of the Sidingheishan intrusion reaches 82.52 mole% Fo and 1414 ppm Ni. On the basis of olivine‐liquid equilibria, it has been calculated that the MgO and FeO included in the parental magma of a wehrlite sample were approximately 10.43wt% and 13.14wt%, respectively. The Sidingheishan intrusive rocks are characterized by moderate enrichments in Th and Sm, slight enrichments in light REE, and depletions in Nb, Ta, Zr and Hf. The εNd (t) values in the rock units vary from +6.70 to +9.64, and initial 87Sr/86Sr ratios range between 0.7035 and 0.7042. Initial 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values fall in the ranges of 17.23–17.91, 15.45–15.54 and 37.54–38.09 respectively. These characteristics are collectively similar to the Heishan intrusion and the Early Carboniferous subduction related volcanic rocks in the Santanghu Basin, North Tianshan and Beishan area. The low (La/Gd)PM values between 0.26 and 1.77 indicate that the magma of the Sidingheishan intrusion was most likely derived from a depleted spinel–peridotite mantle. (Th/Nb)PM ratios from 0.59 to 20.25 indicate contamination of the parental magma in the upper crust. Crystallization modeling methods suggest that the parental magma of the Sidingheishan intrusion was generated by flush melting of the asthenosphere and subsequently there was about 10vol% contamination from a granitic melt. This was followed by about 5vol% assimilation of upper crustal rocks. Thus, the high‐Mg basaltic parental magma of Sidingheishan intrusion is interpreted to have formed from partial melting of the asthenosphere during the break‐off of a subducted slab.