Crustal Evolution of a Paleozoic Intra-oceanic Island-Arc-Back-Arc Basin System Constrained by the Geochemistry and Geochronology of the Yakuno Ophiolite, Southwest Japan

Yoshimitsu Suda,Kosuke Kimura,Yasutaka Hayasaka

doi:10.1155/2014/652484

Yoshimitsu Suda, Kosuke Kimura + Show 1 more

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https://doi.org/10.1155/2014/652484

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Abstract

The Yakuno ophiolite in southwest Japan is considered to have been obducted by the collision between an intra-oceanic island-arc-back-arc basin (intra-OIA-BAB) system and the East Asian continent during the late Paleozoic. New SIMS (SHRIMP) zircon U-Pb determinations for amphibolite and metagabbro of BAB origin within the Yakuno ophiolite yield ages of 293.4 ± 9.5 Ma and 288 ± 13 Ma, respectively. These ages are slightly older (however, overlapping within analytical errors) than the magmatic age of arc granitoids (ca. 285–282 Ma) that intruded into the mafic rocks of BAB origin. Results from geochronological and geochemical data of the Yakuno ophiolite give rise to the following tentative geotectonic model for the Paleozoic intra-OIA-BAB system: the initial stage of BAB rifting (ca. 293–288 Ma) formed the BAB crust with island-arc basalt (IAB) signatures, which was brought to the OIA setting, and generated the arc granitoids (ca. 285–282 Ma) by anatexis of the BAB crust. A later stage of BAB rifting (<ca. 285 Ma) formed the BAB crust with IAB to MORB signatures, on which the Permian sediments were conformably deposited. These components collided with the eastern margin of the East Asian continent during the early Mesozoic.

Highlights

Ophiolites are the rock assemblages of peridotite, gabbro, basalt, and associated pelagic sediment found at the orogenic belt of a convergent plate boundary
The Yakuno ophiolite in southwest Japan originated from the crustal sections of a Paleozoic intra-oceanic island-arcback-arc basin system and formed through collision and accretion with the eastern margin of the East
The Yakuno ophiolite in the Asago area is composed of metagabbro and amphibolite of back-arc basin (BAB) origin (Figure 1) [7]

Summary

Introduction

Ophiolites are the rock assemblages of peridotite, gabbro, basalt, and associated pelagic sediment found at the orogenic belt of a convergent plate boundary. They are most commonly interpreted as the remnants of crustal components and the upper mantle beneath an ocean basin [1,2,3]. The Yakuno ophiolite in the Asago area is composed of metagabbro and amphibolite of BAB origin (Figure 1) [7] These mafic rocks are intruded by the granitoid of arc affinities. This field evidence suggests that the mafic rocks in this area originally formed as a BAB crust, which was subsequently brought to an OIA setting. The Yakuno ophiolite in this area records various lines of evidence to help understand the tectonic evolution of an intra-OIA-BAB system [7, 8]

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