Exploring the tectono-magmatic evolution of intraoceanic fore-arc setting during subduction initiation: perspectives from trace and platinum group element systematics of the Jijal ultramafic arc system, NE Pakistan

ABSTRACT

The Jijal Complex is considered one of the largest Neo-Tethyan remnants in the intra-oceanic Cretaceous–Palaeogene Kohistan Arc of Pakistan. This complex largely consists of gabbros, peridotites, and chromitites. Previous studies documented the genesis of gabbros and chromitites in detail; however, detailed geochemistry and magma genesis were lacking. In this investigation, we present whole-rock geochemical and platinum group elements (PGEs) data of Jijal peridotites (dunites and harzburgites). The objectives of this study are to elucidate magmatic processes and tectonic regimes involved in the formation of peridotites, factors influencing the concentration and dispersion of PGEs in them, and their tectonic evolution. The investigated peridotite samples are depleted in magmaphile major elements (Al₂O₃: 0.23–0.57, TiO₂: 0.01–0.04, and CaO: 0.08–0.69 wt%), relative to the primitive mantle values, reflecting melt-rock interaction during their magmatic evolution. In addition, rare-earth element (REE) contents in harzburgites are relatively higher compared to the dunites; however, both rock types exhibit depletion with respect to the chondrite-normalized values. The obvious negative anomalies of Nb, Zr, and enriched LREE and large ion lithophiles collectively substantiate their association with depleted arc-type mantle components, metasomatism, and melt/fluid-rock reactions after partial melting episodes. Bulk-rock and geochemical modelling of PGEs data of the peridotites suggest their shallow depth spinel-bearing depleted heterogeneous mantle source and generation from refractory mantle residuum along with boninitic signatures in a supra-subduction zone (SSZ). The PGE’s geochemistry additionally reveals that partial melting, fractionation, metasomatism, and sulphur under-saturation were the key factors that controlled the concentration and distribution of PGEs in the studied rocks. The boninitic features of the Jijal peridotites are equated with intraoceanic fore-arc followed by subduction initiation, and melt-rock reactions in a hydrated forearc mantle, indicating robust evidence of mantle depletion and pervasive refertilisation in an embryonic Neo-Tethyan arc system. Tectonically, the investigated rocks encapsulate vestiges of the Cretaceous Tethyan Ocean and record multifaceted history from boninitic to slab-proximal island arc affinity in compliance with an intraoceanic SSZ fore-arc regime coherent with the subduction inception.

KEYWORDS:

• Origin
• PGEs
• tectonic framework
• Jijal peridotites
• Neo-Tethys
• north Pakistan

Acknowledgments

We appreciate useful comments and advice from two anonymous reviewers and editorial handling by Robert Stern which improved the text and data interpretation. This project is funded by the China Postdoctoral Science Foundation (grant number 2023M730036), awarded through the 73rd batch of general funding (8206300764). This project is also funded by Researchers Supporting Project Number (RSP 2024R455) at King Saud University, Riyadh, Saudi Arabia, and the Start-up Grant (Fund 12S155) from the United Arab Emirates University (UAEU). We would like to acknowledge the financial support of the Tibetan Plateau Scientific Expedition and Research program (grant number 2021QZKK0301) and the National Natural Science Foundation of China (NSFC) through grants 91955202 and 42022021.

Disclosure statement

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

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2024.2318573

Additional information

Funding

This project is funded by the 73rd batch of general funding (8206300764) from the China Postdoctoral Science Foundation (grant number 2023M730036). This project is also funded by Researchers Supporting Project Number (RSP 2024R455), King Saud University, Riyadh, Saudi Arabia. The authors acknowledge the financial support of the United Arab Emirates University (UAEU) by the Start-up Grant, Fund (12S155). The project was sponsored by the Tibetan Plateau Scientific Expedition and Research (2021QZKK0301) and the National Natural Science Foundation of China (NSFC) grants (91955202, 42022021)..