University of Tasmania
Browse

Ordo-silurian assemblage in the Indochina interior: geochronological, elemental, and Sr-Nd-Pb-Hf-O isotopic constraints of early Paleozoic granitoids in South Laos

Version 2 2024-09-18, 23:34
Version 1 2023-05-21, 12:36
journal contribution
posted on 2024-09-18, 23:34 authored by Y Wang, Y Zhang, X Qian, V Senebouttalath, C Gan, Khin ZawKhin Zaw

In order to verify the early Paleozoic accretionary assemblage in the Indochina interior and constrain the Prototethyan tectonic evolution in Southeast Asia, this study presents a set of new U-Pb geochronological, elemental, and Sr-Nd-Pb-Hf-O isotopic data for the fifty-two representative granitoids in South Laos. The granitoids from the Kontum terrane, Tam Ky-Phuoc Son tectonic zone, and southern Truong Son igneous zone in South Laos yield the crystallization ages of 464-485 Ma, 455-471 Ma, and 427-446 Ma, respectively, with a northerly younging trend within the Indochina interior. They are mainly monzogranite with A/CNK = 0.96-1.99 and K2O > Na2O, which are marked by enrichment in largeion lithophile elements and depletion in high field strength elements with remarkable NbTa, Sr-P, and Ti negative anomalies. Their initial Sr-87/Sr-86 ratios range from 0.70510 to 0.71559, epsilon(Nd)(t) from -9.5 to -3.0(Pb-206/Pb-204) from 18.65 to 19.72, (Pb-207/Pb-204) from 15.66 to 15.80, and (Pb-208/Pb-204), from 38.84 to 39.79. The corresponding zircon epsilon(Hf)(t) and delta O-18 values are in the range of -10.6 to +1.0 and 6.88 parts per thousand to 8.94 parts per thousand, respectively. In addition, their Sr-Nd-Pb and Hf-O isotopic compositions are generally similar with those of time-equivalent granitoids in South Tibet and SW Yunnan, China, and synchronous mafic-intermediate igneous rocks in South Laos, but distinctive from those of the supracrustal sedimentary-derived South China Paleozoic granite and Lincang-Sukhothai S-type granite. The early Paleozoic granitoids in South Laos might have originated from a mixed source of the wedge-derived juvenile crust coupled with supracrustal materials. All these data synthetically suggest the southward subduction of the Tam Ky-Phuoc Son Ocean and the northerly on-growing Ordo-Silurian accretionary orogenesis within the previously defined "single-ancient" Indochina block. The assemblage of the Indochina block might initiate at ca. 430 Ma in the Silurian and terminate in the Early-Middle Devonian.

History

Publication title

Bulletin of the Geological Society of America

Volume

133

Issue

1/2

Pagination

325-346

ISSN

0016-7606

Department/School

CODES ARC

Publisher

Geological Society of America

Publication status

  • Accepted

Place of publication

United States

Rights statement

Copyright 2020 Geological Society of America

Socio-economic Objectives

259999 Other mineral resources (excl. energy resources) not elsewhere classified, 250305 Precious (noble) metal ore exploration, 280107 Expanding knowledge in the earth sciences