International Geologiical Congress - Oslo 2008


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EID-05 Mantle petrology


Textural and fabric implications of peridotite xenoliths in basaltic rocks from Jeju island, South Korea


Jae-eun Yu, Pusan National University (Republic of Korea)
Kyounghee Yang, Pusan National University (Republic of Korea)
Bokhyun Nam, Pusan National University (Republic of Korea)
Gyorgy Falus, Eötvös University (Hungary)
Karoly Hidas, Eötvös University (Hungary)
Byoung-hoon Hwang, Pusan National University (Republic of Korea)
Casba Szabo, Eötvös University (Hungary)


Unusual peridotitic upper mantle xenoliths with fine grain size and foliated macroscopic occurrence are reported from Sinsanri (Jeju Island, South Korea). These mantle xenoliths, which have been overlooked in earlier studies from the region, provide solid evidence about the late deformation history of the upper mantle beneath the Jeju Island. Jeju Island is known as an intraplate volcano showing signatures of oceanic island basalt although the island is located at the eastern margin of the Eurasian plate which is known as convergent plate margins where Pacific and Philippine Sea plates are being subducted beneath the Eurasian Plate. These spinel peridotite xenoliths have uniform-sized tabular to mosaic pophyroclastic to equigranular texture. Detailed fabric analysis of the olivine and orthopyroxene phases of the peridotite xenoliths indicates weak to moderate fabric strength and the activation of normal {0kl}[100] slip systems, with the dominance of (010)[100]. Fine grain size together with weak fabric strength suggests that the formation of the fine-grained, foliated xenoliths may be attributed to multistage deformation, including a high temperature event dominantly taking place in the dislocation creep field, followed by one or more low temperature deformation episodes at the late stage of the evolution history of the Jeju upper mantle.

Based on the textures, geochemical evolution, LPO fabrics and their equilibrium temperatures, the studied samples went through similar deformation events and patterns representing a structural domain, indicating that they were originated from a localized, narrow, high-stress deformation zones confined to rigid lithosphere and beneath the Jeju Island. The zones may be produced by paleoseismic events in the lithosphere associated with faulting related to the ascent of basalt magma.

Key words: Jeju Island; peridotite xenoliths; fabric strength; low temperature deformation; dislocation creep


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