Cambrian magmatic flare-up, central Tibet: Magma mixing in proto-Tethyan arc along north Gondwanan margin

Accompanying Gondwana assembly, widespread but diachronous Ediacaran-early Paleozoic magmatism of uncertain origin occurred along the supercontinent's proto-Tethyan margin. We report new geochemical, isotopic, and geochronological data for Cambrian magmatic rocks (ca. 500 Ma) from the Gondwana-derived North Lhasa terrane, located in the present-day central Tibetan Plateau. The magmatic rocks are composed of basalts, gabbros, quartz monzonites, granitoids (with mafic microgranular enclaves), and rhyolites. Nd-Hf isotopic and whole-rock geochemical data indicate that these rocks were probably generated by mixing of mantle-derived mafic and crust-derived felsic melts. The mantle end-member volumes of mafic, intermediate, and felsic rocks are similar to 75%-100%, 50%-60%, and 0-30%, respectively. Integration of our new data with previous studies suggests that the North Lhasa terrane experienced long-term magmatism through the Ediacaran to Ordovician (ca. 572-483 Ma), with a magmatic flare-up at ca. 500 Ma. This magmatism, in combination with other Ediacaran-early Paleozoic magmatism along the proto-Tethyan margin, was related to an Andean-type arc, with the magmatic flare-up event related to detachment of the oceanic slab following collisional accretion of Asian micro-continental fragments to northern Gondwana. Diachroneity of the proto-Tethyan arc system along the northern Gondwanan margin (ca. 581-531 Ma along the Arabian margin and ca. 512-429 Ma along the Indian-Australian margin) may have been linked to orogenesis within Gondwana. The North Lhasa terrane was probably involved in both Arabian and Indian-Australian proto-Tethyan Andean-type orogens, based on its paleogeographic location at the northern end of the East African orogen.

Automated summary

This study reveals the significant role of the North Lhasa terrane in Cambrian magmatism, showing a long history of magmatic activity in the region through the integration of geochemical, isotopic, and geochronological data analysis, closely related to the tectonic evolution of northern Gondwana.