Episodic continental extension in eastern Gondwana during the mid-late mesozoic: insights from geochronology and geochemistry of mafic rocks in the Tethyan Himalaya

ABSTRACT

Mesozoic extension and rifting processes of the Gondwana continent are critical for understanding the opening and formation of the Indian Ocean. Here, we report petrological, geochemical, zircon U–Pb age, and Lu–Hf isotopic data of mafic dikes in the central Tethyan Himalaya to reveal the timing and mechanism of the eastern Gondwana rifting. These mafic rocks exhibit two groups in terms of TiO₂ and MgO contents (Group I with TiO₂ < 2.0 wt.%, whereas Group II with TiO₂ > 2.0 wt.%), but (1) they have similar trace elements patterns and exhibit enriched Light Rare Earth Element (LREE) patterns without Eu anomalies and (2) they have a wide range of zircon ε_Hf(t) values. Both the above geochemical characteristics are similar to those of the Oceanic Island Basalt (OIB). However, they also show typical features of continental crust input. Compared to Group II, Group I has higher MgO, Cr, and Ni abundances (more primitive) and more depleted Nb-Ta contents, which are similar to those of lower TiO₂ Dala mafic rocks, suggesting that the continental crust signature was mainly inherited from the Greater India subcontinental lithospheric mantle (GI-SCLM). Therefore, the mafic rocks here were mainly derived from a hybrid source from both OIB-like enriched mantle and GI-SCLM. Furthermore, two groups of zircon U–Pb ages have been identified: the first group with a weight mean age of 139.9 ± 0.2 Ma, whereas the second group with a weight mean age of 163.2 ± 0.9 Ma. The Middle Jurassic zircons show similar characteristics to those of intermediate to acidic igneous rocks in the continental setting, and thus they might record a stage of magmatism associated with a tectonic extension event in the Indian passive continental margin. The Early Cretaceous ages represent the crystallization timing of the mafic dikes, which are coeval with most mafic rocks in the Tethyan Himalaya. Based on these observations and the literature data in the Tethyan Himalaya, we proposed that the Kerguelen plume was incubating underneath the Tethyan Himalaya at ca. 140 Ma, but it was not located in the triple junction among the Antarctic, Australian and Indian plates. Therefore, the Kerguelen plume might play a synergistic role in the break-up of eastern Gondwana, which had experienced at least two stages of tectonic extension during the Mid-Late Mesozoic.

KEYWORDS:

• Mafic rock
• Kerguelen plume
• Tethyan Himalaya
• Gondwana break-up

Acknowledgments

Mr Han-ao Li, Peng Wang, Ms Qi Wang, and Xue-qian Chen are gratefully acknowledged for their help in the fieldwork and laboratory analyses. This study was supported by 111 project (No. B18048). This is CUGB petrogeochemical contribution PGC-201587.

Highlights

• The mafic rocks in the central Tethyan Himalaya can be divided into two groups in terms of TiO₂ and MgO

• The mafic rocks were derived from a hybrid source from both the OIB and GI-SCLM

• The Kerguelen plume might play a synergistic role in the eastern Gondwana breakup

• The Jurassic zircons might record a tectonic extension event in the Indian passive continental margin

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed here

Additional information

Funding

This work was supported by the 111 project [B18048], CUGB petrogeochemical contribution [PGC-201587].