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Voluminous sediment recycling revealed by Pakistan volcanoes in the Makran arc

Yunying Zhang 1, Guangping Zeng1,2, Zhen Sun1, Mubashir Mehmood3

  • Affiliations:  1Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China; 2University of Chinese Academy of Sciences, Beijing 100049, China; 3Dipartimento di Scienze della Terra, dell'Ambiente e delle Risorse (DiSTAR), Università degli Studi di Napoli Federico II, 80126 Napoli, Italy

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 81

  • Programme No: 3.16.8

  • Theme 3 > Session 16

Abstract

The Makran arc forms by the subduction of the Arabian oceanic plate beneath the Eurasian plate. While the Makran arc features subduction of ~4200 m thick, carbon-rich sediments from the Indus fan, the validity of sediment recycling in this arc has not been tested. Three Late Miocene-Quaternary volcanoes (Koh-i-Sultan, Taftan, Bazman) that are constructed on 46-48 km thick continental basement with variable ages (Paleozoic-Eocene) and compositions provide a unique opportunity to investigate sediment recycling. New 40Ar-39Ar ages, whole-rock elemental and Sr-Nd-Pb isotope data for the Koh-i-Sultan volcano, combined with published data on the Bazman and Taftan volcanoes, reveal for the first time a strong, regional-scale binary mixing trends of Makran arc magmas in Sr-Nd-Pb isotope space and in Th/La vs. Sm/La diagram. The trends suggest an enriched mantle wedge strongly metasomatized by recycled sediments. Within the overarching regional-scale trends, however, the individual volcanic centers display considerable compositional diversity. For example, while individual Makran arc volcanoes plot on a single sediment-mantle mixing trend in Sr-Nd isotope space, their ratios range from MORB-type to those with 87Sr/86Sr of ~0.70676 and 143Nd/144Nd of ~0.51241. Such isotopic variability can tentatively be linked to the variable sediment thickness along the Makran trench, enhanced by differences in slab dip, convergence rate and trench-to-arc distance. However, the intra-arc variability in the fractionated incompatible trace element patterns (such as Gd/Yb), suggests that the Makran volcanoes were processed in individual ways by partial melting, fractional crystallization and melt mixing during their ascent from the mantle to the surface.