Petrogenesis and tectonic implications of ∼130 Ma diabase dikes in the western Tethyan Himalaya (western Tibet)

Abstract

Early Cretaceous mafic dikes are widely exposed in the eastern Tethyan Himalaya. However, coeval mafic rocks are limited in the western Tethyan Himalaya. We report the major and trace elements and zircon U–Pb ages of the newly discovered diabase dikes in the Zhongba area in the western Tethyan Himalaya. The ICP-MS zircon U–Pb analyses from one representative diabase dike yields a crystallization age of 129.8±1.3Ma (MSWD=6.7). These mafic dikes are characterized by high concentrations of TiO2 (2.81–3.27%), Fe2O3T (10.79–12.14%), and MgO (5.11–6.71%). The chondrite-normalized diagram indicates the enrichment of LREE and the depletion of HREE. The primitive mantle-normalized trace element patterns do not display negative anomalies of Nb, Ta, and Ti. These characteristics imply an OIB affinity. Trace element modelling (Sm/Yb vs. Sm) suggests that the dikes originated from an enriched mantle source region, composed primarily of garnet and spinel (spinel<garnet), with a low degree of partial melting (4–8%). Comparing with coeval OIB-affinity mafic rocks from the areas of Gyangze, Kangma, Cona, and Laguila, we propose that the Cretaceous mafic rocks were generated in an extensional setting along a passive continental margin and were derived from similar magma sources with some crustal contamination in the case of the Zhongba intrusives. Because of the similar geochemical characteristics, ages and tectonic settings, of the Zhongba diabase rocks and other volcanic rocks from the Kerguelen LIP, we suggest that the Zhongba diabase rocks are likely also part of the Kerguelen LIP.