Cambrian (~510 Ma) ophiolites of the East Kunlun orogen, China: A case study from the Acite ophiolitic tectonic mélange

ABSTRACT

The Acite ophiolitic mélange represents a remnant of the Proto-Tethys forearc oceanic lithosphere. Two gabbros yield zircon ²⁰⁶Pb/²³⁸U ages of 510-512 Ma. The magmatic rocks are divided into three subtypes: (1) Mid-ocean ridge basalt (MORB) -like forearc basalts (FABs), (2) Low-titanium tholeiitic gabbros (LTGs), and (3) Normal calc-alkaline dacites (CADs). The FABs have comparatively higher TiO₂ concentrations (1.13–1.42 wt%) and show almost flat REE patterns. In the NMORB normalized trace element patterns, the FABs display flat distributions of high field strength element (HFSE). The ε_Nd(t) values of FABs range from +4.0 to +4.8. These features are similar to the composition of Izu-Bonin-Mariana forearc basalts (FABs). LTGs are characterized by higher contents of MgO (8.85–9.95 wt%) and lower concentration of TiO₂(0.29–0.50 wt%). They show LREE-depleted patterns, however having comparatively lower total REE contents than those of FABs. The ε_Nd(t) values of LTGs range from +7.4 to +8.4. These features show that LTG magmas originated from a progressively depleted mantle source. In contrast, the CADs having higher SiO₂ contents (63.58–70.92 wt%) have higher total REE contents. In the NMORB normalized trace element patterns, CADs are characterized by enrichment of LILEs and depletion of HFSEs. CADs have negative ε_Nd(t) values ranging from -9.8 to -10.5, which are likely suggestive of a crust-derived source. The rock association of FABs and LTGs, together with tectonic discrimination plots and regional data, suggest a forearc setting above the SSZ for Acite ophiolitic mélange.

Graphical Abstract

KEYWORDS:

• Supra-subduction zone (SSZ)
• forearc
• ophiolite
• East Kunlun
• Tibet Plateau
• Tethys
• boninite

Highlights

• Acite ophiolites formed at ca. 510–512 Ma.

• Acite ophiolitic block is remnant of forearc oceanic crust.

• Progressive evolution of forearc magmatism is presented.

• The ocean began to subduct northwards at ca. >512 Ma.

Acknowledgements

We are grateful to Dr Robert J. Stern for their constructive reviews and comments which improved the quality of the manuscript. This study has been jointly funded by the National Science Foundation of China: [Grant Numbers 41502191, 41472191, and 41172186], the Commonweal Geological Survey of the Aluminum Corporation of China and the Land–Resources Department of Qinghai Province: [Grant Number 200801], and the Special Fund for Basic Research of Central Universities: [Grant Numbers CHD2011TD020, 2013G1271091, 2013G1271092, 310827161002, 310827161006, and 310827173702].

Disclosure statement

No potential conflict of interest was reported by the authors.

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Additional information

Funding

This work was supported by the National Science Foundation of China: [Grant Numbers 41502191, 41472191, and 41172186]; Commonweal Geological Survey of the Aluminum Corporation of China and the Land–Resources Department of Qinghai Province: [Grant Number 200801]; and the Special Fund for Basic Research of Central Universities: [Grant Numbers CHD2011TD020, 2013G1271091, 2013G1271092, 310827161002, 310827161006, and 310827173702].