Petrology and geochemistry of metabasalts from the Taoxinghu ophiolite, central Qiangtang, northern Tibet: Evidence for a continental back-arc basin system

Abstract

Newly discovered ophiolitic metabasalts in the Taoxinghu area of central Qiangtang on the Qinhai-Tibet Plateau, here described for the first time, have important implications for reconstructions of the tectonic history of the Paleo-Tethys Ocean. Most of the metabasalts belong to the tholeiitic basalt series and most have undergone greenschist-facies metamorphism. The distribution of rare earth elements and trace elements shows that the rocks are typical of sub-continental margin arc-basin lavas, similar to the environment of formation of the present-day Okinawa lava, suggesting that the Taoxinghu metabasalts represent the upper portions of a supra-subduction zone (SSZ)-type ophiolite that formed in a continental back-arc basin tectonic environment. The Taoxinghu metabasalts are mainly sourced from a depleted spinel mantle-source region, with a spinel lherzolite content equivalent to partial melting of 6 %-25 %. In addition, lava compositions were likely affected by melting of sediments during subduction, while the influence of aqueous fluids was minor. Combining with the existing knowledge on the ophiolites of Longmuco-Shuanghu-Lancang suture zone (LSLSZ), an evolutionary model is proposed. The LSLSZ Paleo-Tethys Ocean basin may have started to form during the Cambrian or earlier, and subducted in the early Carboniferous. As subduction proceeded, a continental back-arc basin was developed, the site of generation of most of the Taoxinghu metabasalts. The LSLSZ Paleo-Tethys Ocean finally closed in the Triassic.

Geochronology and petrogenesis of the early Silurian Zeluo mafic-ultramafic intrusion, eastern Tibet: implications for the tectonic setting and evolution of the eastern Proto-Tethys Ocean

“…Another example of middle-late Silurian intermediate-mafic magmatism was located just south of the Changning-Menglian suture zone, at 421.2 ± 1.2 Ma (Mao et al, 2012). These ages coincide with the ~450 to 400 Ma late-stage evolution of the Proto-Tethys oceanic basin (Li et al, 2016b;Wu et al, 2020). Collectively, the data (Figure 1) show that the Proto-Tethys Ocean, in the Tibetan Plateau, underwent continuous evolution during the Early Paleozoic, and that the Zeluo mafic-ultramafic rocks represent a likely final phase of the Early Paleozoic magmatism.…”

“…The Zr and Hf concentrations in the Zeluo pluton are seen to progressively decrease proportionally (Figure S1b), likely related to the crystallization properties of heavy minerals such as zircon. In reality, a near-constant Zr/Hf ratio has been observed in many magmatic suites, including low to moderate metamorphic magmas (Dostal and Chatterjee, 1995;Bryant et al, 1997;Zhang et al, 2014;Wu et al, 2016b), while the Zr/Hf ratio of most crustal rocks is close to 37 (Brooks, 1970).…”

“…In the Proto-Tethys oceanic domain there are many microcontinents/continents, including the Yangtze, Cathaysia, Tarim, Qaidam, Qilian, Indochina, north Qiangtang, and south Qiangtang blocks/micro-continental blocks which were distributed widely during the Early Paleozoic (Li et al, 2016b). Most of them were either located on the northern margin of the eastern Gondwana continent, amalgamated with the Gondwana continent, or dispersed amongst each other and the oceans (Figure 13a).…”

Petro-geochemistry, Genesis and Economic Aspects of Mafic Volcanic Rocks in the West and Southern Part of The Mamfe Basin (SW Cameroon, Central Africa)

“…The major and minor elemental concentration in seven samples (NKK3, NKK4, NKK5, NKK7, KEG, TAE, OSG) was determined by an X-ray fluorescence spectrometer in China. The analytical procedures used to acquire these results are similar to those presented in Wu et al [53]. Thirteen selected samples (e.g., NSI1, BAI3, BAI4, ARK16) were analyzed for their major, minor, trace and rare earth elements contents at ALS Chemex South Africa (Pty) Ltd, Johannesburg Gauten.…”

“…%) and lower MgO (≤ 10 wt. %) and Mg# (40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59) [1]. Some of those major element contents are within the ranges of basanite found in Mount Bamenda, Cameroon volcanic line basalts although the basanites there are consistently higher in Na 2 O contents [34].…”