Early Middle Triassic mafic dikes from the Baoshan subterrane, western Yunnan: implications for the tectonic evolution of the Palaeo-Tethys in Southeast Asia

Abstract

The time of final closure of the Palaeo-Tethys and the Sibumasu-Indochina collision in Southeast Asia represents a major unresolved geologic problem. Here, we present zircon chronology, whole-rock elemental, Sr-Nd, and zircon Hf isotopic geochemistry for newly discovered mafic dikes from the northern segment of the Sibumasu terrane, to provide constraints on this issue. Zircon U-Pb data indicate that the dikes were emplaced at 240 ± 3 Ma. These are the earliest Mesozoic magmatic rocks reported so far in the Sibumasu terrane, the late Palaeozoic passive margin of the Palaeo-Tethys. They are subalkaline tholeiites, showing geochemical characteristics similar to those of enriched mid-ocean ridge basalts (E-MORBs). They have 87 Sr/ 86 Sr(t) ratios of 0.703161-0.703826, εNd(t) of +4.8 to +7.5, and zircon εHf(t) of +9.2 to +13.3, implying strong mantle depletion. They were derived by partial melting of asthenospheric mantle and underwent subsequent fractional crystallization and lithospheric assimilation. The geologic-petrologic evidence suggests that the mafic dikes were generated in a collisional setting, when suturing of the Baoshan and Simao subterranes (the two subterranes are part of the Sibumasu and Indochina terranes, respectively) occurred. These early Middle Triassic mafic dikes provide an upper limit for Sibumasu-Indochina collision. In conjunction with previous work, we conclude that the final closure of the Palaeo-Tethys and collision of the Sibumasu and Indochina terranes took place during the late Permian to Early Triassic.

Middle Permian fusulines from the Thitsipin Formation of Shan State, Myanmar and their palaeobiogeographical and palaeogeographical implications

“…The Baoshan Block might have collided with the Simao Block in the Early Triassic (Liao et al . ). Farther to the northeast, the South Qiangtang Block might have amalgamated with the North Qiangtang Block during the Middle or Late Triassic (Zhai et al .…”

The closure of Palaeo-Tethys in Eastern Myanmar and Northern Thailand: New insights from zircon U–Pb and Hf isotope data

“…Interpretation of the tectonic setting of the Lincang batholith is controversial and ranges from island arc (e.g., Sone and Metcalfe, 2008;Liao et al, 2013), to syn-collisional (Dong et al, 2013), all the way through to post-continent-continent collision extension (Heppe, 2004;Wang et al, 2014). Some workers place the Lincang batholith within the Baoshan terrane (e.g., Dong et al, 2013).…”

Late Paleozoic Woniusi basaltic province from Sibumasu terrane: Implications for the breakup of eastern Gondwana’s northern margin

“…The Sibumasu terrane is believed to have been adjacent to NW Australia from the Devonian to Early Permian, as indicated by biogeographic, tectonostratigraphic, paleoclimatic, detrital zircon provenance, and paleomagnetic evidences (e.g., Metcalfe and Aung, 2014, and references therein). It separated from Gondwanaland in the Early Permian and subsequently drifted northward, and it fi nally accreted to southwestern China during the Mesozoic (Zhong, 1998;Liao et al, 2013;Metcalfe and Aung, 2014).…”