Age and geochemistry of the Zhaheba ophiolite complex in eastern Junggar of the Central Asian Orogenic Belt (CAOB): implications for the accretion process of the Junggar terrane

Abstract

We report new field observations, zircon U–Pb ages and geochemical data for the discrete members of the Zhaheba ophiolite complex in northeastern Junggar of the Central Asian Orogenic Belt (CAOB) with the aim to understand the accretion process of the eastern Junggar terrane. The zircon age data reveal that the cumulates of the Zhaheba ophiolite crystallized at ~485 Ma while the volcanic sequences erupted at ~400 Ma. Thus, the volcanic sequences are not members of the Zhaheba ophiolite. Chromian spinels from the serpentinite have comparable elemental compositions to those of spinels from MORB-type ophiolites. Similarly, the rift affinity of clinopyroxene and positive zircon εHf(t) (13–20) and mantle δ18O (+5.37‰) values of the cumulates imply that the cumulates crystallized from primitive magmas derived from a depleted mantle source. Elemental and Nd isotopic compositions indicate that the basalts in the Zhaheba area were derived from partial melting of a mantle wedge metasomatized by adakitic melts and/or subduction-related fluids. The data presented in this contribution, together with previous studies, indicate that the Zhaheba–Almantai and Kelameili ophiolites were MORB-type, which implies that there were at least two mid-ocean ridges during Ordovician to early Devonian times in the Junggar Ocean. In the earlier stage, intra-oceanic subduction led to the formation of the intra-oceanic arc, and then the Kelameili ophiolite accreted to an intra-oceanic accretionary wedge. In the later stage, the Zhaheba–Almantai ophiolite accreted to the accretionary wedge along the southern margin of the Iritish suture zone during the roll-back of the subduction zone from north to south.

Zircon U–Pb geochronology and geochemistry of Devonian plagiogranites in the Kuerti area of southern Chinese Altay, northwest China: Petrogenesis and tectonic evolution of late Paleozoic ophiolites

“…(b) Geological map of the Chinese Altay and East Junggar (modified from Wang et al, 2009). Ages shown are from Shen et al (2014) (Wu et al, 2006) Qiaoxiahala Ophiolites Pre-Carboniferous N-MORB and IAB (Wu et al, 2006) Kekesentao Ophiolites Middle-Devonian T-MORB (Niu et al, 2006) Laoshankou Picrites Middle Devonian N-MORB and IAB Shaerbulake High-Ti basalts Early-middle Devonian N-MORB, IAB and OIB (Niu et al, 2006) Habahe Mafic dykes 376 ± 5 Ma (dolerite) N-and E-MORB (Cai et al, 2010) Kuerti Ophiolites~390 Ma (plagiogranite) N-MORB and IAB (this study; Xu et al, 2003) Keketuohai Gabbros 408 ± 6 Ma (gabbro) E-MORB Alegedayi Ophiolites 439 ± 17 Ma (metagrabbro) N-, T-, E-MORB, OIB and IAB (Wong et al, 2010) Armantai Ophiolites 503 ± 5 Ma (plagiogranite) N-,E-MORB, IAB and OIB (Wang et al, 2003;Xiao et al, 2009) Zhaheba Ophiolites 485 ± 3 Ma (gabbro) N-MORB (Ye et al, 2016;Zeng et al, 2015) Note. The ages of Kekesentao ophiolites, Qiaoxiahala ophiolites, picrites, and high-Ti basalts are estimated from fossils in the stratum; all others are dated using zircon U-Pb ages.…”

“…Plagiogranites within the Zhaheba–Armantai ophiolite have zircon U–Pb ages around 500 Ma (Xiao et al, ; Zeng et al, ). The Late Cambrian Zhaheba–Armantai ophiolite has been interpreted as ancient oceanic crust from the Junggar Ocean (Deng & Wang, ; Jian et al, ; Xiao et al, ; Ye, Zhang, Zou, Yao, & Dong, ). The plagiogranites from the Kalamaili ophiolite have a zircon SHRIMP U–Pb age of 373 ± 10 Ma (Tang, Su, Liu, Hou, & Wang, ; Xu, Jiang et al, ).…”

Crustal Electrical Structure of the Zhaheba Complex Imaged by Magnetotelluric Data and Its Tectonic Implications

“…The resistive crust beneath the Zhaheba complex is uniform and stable, which indicates the Precambrian basement. During the late Cambrian to the early Ordovician period, the older basement of the Zhaheba-Aermantai ophiolite was formed by the subduction of the Palaeo-Asian Ocean to the Altai arc, which is represented by the gabbro and ultramafic rocks [58].…”

Defining the Huangcaopo complex and gabbroic magmatism in the northern Harlik Mountains (NW China): Late Cambrian to latest Permian accretionary growth of the East Junggar Arc?

“…But the magmatisms represented by diorite porphyries, diabases, granites, and rhyolites were active much later and do not belong to the Zhaheba‐Aermantai ophiolite (Luo et al, 2017). Ocean Island Basalts origin and Mid‐Ocean Ridge Basalts origin for ingredients of it have been proposed by Jin, Huang, Xu, and Li (2001) and Ye, Zhang, Zou, Yao, and Dong (2017), however, the geochemical characteristics with subduction affinity for gabbros and plagiogranites make it more likely a supra‐subduction zone (SSZ) ophiolite (Luo et al, 2017; Zeng et al, 2015). For instance, Luo et al (2017) proposed that the Zhaheba‐Aermantai ophiolite was originated from subduction initiation, later evolved as the basement of the East Junggar arc system, on which later subduction‐related magmatism developed.…”