Petrogenesis and zircon U–Pb ages of the Thien Ke granitic pluton in the Tam Dao region: Implications for early Paleozoic tectonic evolution in NE Vietnam

Abstract

Granites of the Thien Ke pluton that are exposed in the Tam Dao region are of sub-alkaline affinity, belong to the high-K calc-alkaline series, and display typical features of S-type granite. The rocks have high ASI values of 1.14-1.41 and are characterized by high initial 87 Sr/ 86Sr ratios (0.7264-0.7270) and low ε Nd (456 Ma) values (−6.5 to −8.4). All of these characteristics, combined with~1.8 Ga T DM model ages and low Mg# of 13-22, suggest an origin in the partial melting of crustal source rocks. LA-ICP-MS zircon U-Pb analytical results from two samples revealed emplacement ages of the granite at 456 ± 28 and 449 ± 12 Ma. These ages are entirely different from those reported in earlier publications and indicate the existence of a Caledonian tectonothermal event in the study area. The Nd-Sr isotopic data, in conjunction with inherited zircon ages (721-1876 Ma), imply Paleoproterozoic to Neoproterozoic crustal material as the major components of the underlying basement. The new geochronological data provide evidence for early Paleozoic magmatism in the Tam Dao region, which has not been previously identified.

U–Pb ages and Hf isotopic composition of zircon and bulk rock geochemistry of the Dai Loc granitoid complex in Kontum massif: Implications for early Paleozoic crustal evolution in Central Vietnam

“…The consistent ages obtained by U-Pb isotopes, together with internal structures of zircon revealed by CL images, allow us to conclude that crystallization of the Dai Loc granite took place during Mid Silurian at 427-423 Ma. This age is consistent with the conclusions from the previous researchers preceding Ordovician-Silurian age in the Kontum massif (Carter, et al, 2001;Nagy et al, 2001;Vuong et al, 2004, Nakano et al, 2013, in northeastern Vietnam (Nguyen et al, 2014) and in South of China (e.g., Li, 2011). Other four zircon grains yield Neoproterozoic (976-588 Ma) to Early Cambrian (523 Ma) age.…”

“…Such age is comparable to the inferred ages of many granites in southeast Asia. Early Paleozoic magmatism has been also identified in northeast Vietnam (Nguyen et al, 2014), in eastern Tibet, western Yuannan and in the Cathaysia Block (e.g., Li, 2011). An early Paleozoic event also was identified by SHRIMP U-Pb zircon concordia ages of gneisses in Kontum massifs (407 ± 11 to 444 ± 17 Ma; Carter et al, 2001) and UPb zircon concordia ages of a granodiorite of Kontum massif (451 ± 3 Ma; Nagy et al, 2001).…”

“…Southeast Asia is a collage of some allochthonous Gondwanaland-derived microplates (Leloup et al, 1995;Nam, 1998;Carter et al, 2001;Leloup et al, 2001;Hieu et al, 2012Hieu et al, , 2013Nguyen et al, 2014). Amalgamation processes of these microplates played an important role in the evolution of the eastern Tethyan belt as well as its surrounding regions and eventually result in the formation of the SE Asian continent druing the Paleozoic and Mesozoic era (Metcalfe, 1988(Metcalfe, , 1990Lepvier et al, 2008;Nakano et al, 2013).…”