The Nan River mafic-ultramafic belt, northern Thailand: Geochemistry and tectonic significance

Author : Alan S. MacDonald and Sandra M. Barr
Publication : Bulletin of the Geological Society of Malaysia
Page : 209-224
Volume Number : 17
Year : 1984

Bulletin of the Geological Society of Malaysia, Volume 17, Dec.1984, pp. 209 – 224

The Nan River mafic-ultramafic belt, northern Thailand: Geochemistry and tectonic significance


Department of Geology, Acadia University, Wolfville, N.S., Canada, BOP IXO


Abstract: Reconnaissance mapping of the largest body of the Nan River mafic-ultramafic belt in northern Thailand shows that it consists mainly of metabasalt and metabasaltic andesite flows and tuffs overlying metagabbro transitional into epidote amphibolite. Ultramafic rocks along the southeast side of the body include metahornblendite, metapyroxenite and serpentite lenses within garnet amphibolite. Geochemical studies suggest that the mafic rocks closely resemble calc-alkali basalts formed in a volcanic arc, rather than in an oceanic environment. Lacking oceanic affinities, several essential components, and the systematic stratigraphy of a typical ophiolite suite, this group of mafic-ultramafic rocks, together with other occurrences farther to the southwest, should probably be termed a volcanic arc suite with associated fault-emplaced ultramafic bodies. If this belt does mark the suture between the Shan-Thai and Indosinian cratonic blocks then there was apparently no significant obduction of an intervening oceanic basin onto the Shan-Thai block.

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