Ediacaran magmatism in the North Lhasa terrane, Tibet and its tectonic implications

Abstract

The origin of the North Lhasa terrane in Tibet remains enigmatic. Our study reports the first evidence for Ediacaran magmatic rocks, including gabbros (ca. 572 Ma), tonalites (ca. 568 Ma), and rhyolites (ca. 547–541 Ma), in the North Lhasa terrane, Tibet. Gabbros are calc–alkaline and exhibit arc-like (e.g., enrichments of Rb and Pb and depletions of Nb, Ta, P, and Ti) geochemical affinities. These gabbros have variable zircon εHf(t) values (−5.5 to +0.9) and they are probably derived from partial melting of an enriched lithospheric mantle source triggered by a subduction event. Tonalites are high-K calc–alkaline and exhibit negative zircon εHf(t) values (−9.1 to −0.8). They can be attributed to partial melting of a thickened lower continental crust with minor mantle-derived component. Rhyolites have negative zircon εHf(t) values (−6.1 to −1.2) and they were probably products of partial melting of Paleoproterozoic metasedimentary rocks. These Ediacaran magmatic rocks were interpreted as a result of the Andean-type subduction along the Gondwanan Proto-Tethyan margin. Coeval Andean-type magmatism has been documented along the northern Arabian margin but absent in the northern India or Australia. Integrating previous studies with the data presented in this contribution, we suggest that the North Lhasa terrane was most likely located in the transitional area between the Arabian and Indian–Australian proto-Tethyan margins in the Ediacaran and it originated from the northern segment of the East African orogen.