Geochronology, geochemistry, and Hf isotopes of mafic rocks from Dalabute ophiolitic mélange in West Junggar, Xinjiang (NW China): Implications for the magmatic source and tectonic setting

Abstract

Several Palaeozoic ophiolitic mélanges distributed in the West Junggar, Xinjiang, are remnants of the Paleo‐Asian Ocean evolution. They are important keys for studying the component, tectonic evolution, and crust–mantle interaction of the Central Asian Orogenic Belt (CAOB). This paper presents petrology, zircon U‐Pb chronology, geochemistry, and Hf isotope data of mafic rocks from the Dalabute ophiolitic mélange, West Junggar. The zircon U‐Pb chronology data of gabbro in the Dalabute ophiolitic mélange can be divided into two groups. The first group magmatic zircons yield a weighted mean age of 389.7 ± 7.7 Ma. It suggests that gabbros of the Dalabute ophiolitic mélange were formed during the period of Early‐middle Devonian, which represents the main period that the Dalabute back‐arc ocean basin expanded. The second group inherited zircons with ages ranging from 910 to 975 Ma were interpreted as Neoproterozoic materials of basement entered its magmatic source. Geochemical characteristics show that the mafic rocks from the Dalabute ophiolitic mélange can be subdivided into alkaline and tholeiite series. Whole‐rock and Hf isotopic data indicate that alkaline basalts have the signatures of typical OIB and formed in the oceanic island or seamount settings related to mantle plume, which were most likely derived from an enriched mantle source. Besides, tholeiitic rocks exhibit the features of MORB and generated in an immature back‐arc basin in the supra‐subduction zone. Their magmas originated from a depleted mantle that had been metasomatized by subduction‐related fluids and contaminated by materials with crustal nature. Therefore, Dalabute ophiolites are supposed to be generated from a back‐arc oceanic basin, which is relate to intra‐subduction and with mantle plumes developed within it. These results jointly provide convincing evidence for the evolution and property of the Dalabute ophiolite in the West Junggar and further supply reference and base for reconstruct the evolutionary history of the CAOB.

Geochronology, geochemistry, and Sr-Nd isotopes of Early Carboniferous magmatism in southern West Junggar, northwestern China: Implications for Junggar oceanic plate subduction

“…For example, Zircon U-Pb dating of volcanic rocks in Baogutu and Miaoergou regions of southern West Junggar has shown that northwestward intra-oceanic subduction of Junggar oceanic plate occurred during 344-331 Ma (Buckman and Aitchison, 2004;Geng et al, 2011). The ridge subduction-related magmatism, as represented by adakitic rock, high-Mg andesites, enriched-or high-Nb basaltic rocks, charnockites, and alkali-feldspar granite (Geng et al, 2009;Tang et al, 2010;Yin et al, 2010), commenced and took place between 331 and 310 Ma and probably lasted into the latest Carboniferous (302 Ma), as evidenced by the Darbut E-MORB type basalts (Liu et al, 2009). Wu et al (2018) proposed that subduction of Junggar oceanic plate started during the Early Devonian and continued to the Late Carboniferous (310 Ma), with subsequent post-collisional tectonic processes continuing to the latest Carboniferous (302 Ma).…”

Accretionary tectonics, deep structures and metallogeny of southern Altaids

“…H. Li et al (, this issue) presents petrological, zircon U–Pb geochronology, geochemical characteristics of element and Hf isotope from the Sartohay region of the Dalabute ophiolitic mélange in West Junggar. These authors found that gabbros in the Dalabute ophiolite can be divided into three groups, with the youngest age group being 307.3 ± 5 Ma.…”

Carboniferous Oceanic Basin Sediment-Gravity Flows in the Margin of the Junggar Basin, NW China: Characterisation and Implications for Hydrocarbon Potential and Evolution Pacing

“…During the Carboniferous, the Junggar region was in the prearc basin stage of its tectonic evolution (Geng et al ., 2009; Liu et al ., 2009; Tang et al ., 2010, 2009; Yin et al ., 2010). Under the influences of plate convergence, plate subduction, and volcanic activity, vast thicknesses of deep-water sediments were deposited, including gravity-flow deposits.…”