Evolution of the Proto-Tethys in the Baoshan block along the East Gondwana margin: constraints from early Palaeozoic magmatism

2016/07/18 by Shaowei Zhao, Shao-wei Zhao, Shaocong Lai +6 · 1 citation
Earth and Planetary Sciences · #Geological and Geochemical Analysis #High-pressure geophysics and materials #earthquake and tectonic studies

paper · doi:10.1080/00206814.2016.1198994

crossref issued 2016/07/18 · crossref published 2016/07/18 · crossref published-online 2016/07/18 · openalex publication_date 2016/07/18 · crossref created 2016/07/18 · crossref published-print 2017/01/02 · crossref deposited 2020/09/05 · openalex created_date 2025/10/10 · crossref indexed 2026/07/31 · openalex updated_date 2026/08/01

Abstract

Zircon U–Pb ages and geochemical and isotopic data for Late Ordovician granites in the Baoshan Block reveal the early Palaeozoic tectonic evolution of the margin of East Gondwana. The granites are high-K, calc-alkaline, metaluminous to strongly peraluminous rocks with A/CNK values of 0.93–1.18, are enriched in SiO2, K2O, and Rb, and depleted in Nb, P, Ti, Eu, and heavy rare earth elements, which indicates the crystallization fractionation of the granitic magma. Zircon U–Pb dating indicates that they formed at ca. 445 Ma. High initial 87Sr/86Sr ratios of 0.719761–0.726754, negative ɛNd(t) values of –6.6 to –8.3, and two-stage model ages of 1.52–1.64 Ga suggest a crustal origin, with the magmas derived from the partial melting of ancient metagreywacke at high temperature. A synthesis of data for the early Palaeozoic igneous rocks in the Baoshan Block and adjacent Tengchong Block indicates two stages of flare-up of granitic and mafic magmatism caused by different tectonic settings along the East Gondwana margin. Late Cambrian to Early Ordovician granitic rocks (ca. 490 Ma) were produced when underplated mafic magmas induced crustal melting along the margin of East Gondwana related to the break-off of subducted Proto-Tethyan oceanic slab. In addition, the cession of the mafic magmatism between late Cambrian-Early Ordovician and Late Ordovician could have been caused by the collision of the Baoshan Block and outward micro-continent along the margin of East Gondwana and crust and lithosphere thickening. The Late Ordovician granites in the Baoshan Block were produced in an extensional setting resulting from the delamination of an already thickened crust and lithospheric mantle followed by the injection of synchronous mafic magma.

Citations

• Tectonic discrimination of granitoids
• Simple mixing as the major control of the evolution of volcanic suites in the Ecuadorian Andes
• Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes
• The early Palaeozoic magmatic event in the Northwest Himalaya, India: source, tectonic setting and age of emplacement
• The Saghand Region, Central Iran: U-Pb geochronology, petrogenesis and implications for Gondwana Tectonics

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