S. Intasopa et al., GEOCHEMISTRY OF CENOZOIC BASALTIC AND SILICIC MAGMAS IN THE CENTRAL PORTION OF THE LOEI-PHETCHABUN VOLCANIC BELT, LOP-BURI, THAILAND, Canadian journal of earth sciences, 32(4), 1995, pp. 393-409
Cenozoic volcanic rocks outcrop in the central portion of the Loei-Phe
tchabun volcanic belt in central Thailand in the Lop Buri area. The vo
lcanic rocks range in composition from basalt to high-silica rhyolite.
In general, the volcanic rocks decrease in age from south to north. T
he oldest rocks studied are 55-57 Ma rhyolites that are isotopically a
nd geochemically distinct from younger (13-24 Ma) rhyolites that occur
farther north. Intermediate rocks (andesite and dacite) are less volu
minous than rhyolite. Basalt occurs in the central and northern parts
of the area and ranges in composition from olivine tholeiites to nephe
line normative alkali basalts. The isotopic, major, and trace element
compositions of the andesites, dacites, and younger rhyolites are cons
istent with an origin for these rocks by variable degrees of partial m
elting of metabasaltic crustal rocks, themselves derived from a deplet
ed mantle source at approximately 530 +/- 100 Ma. The apparent extent
of partial melting of metabasalt increases from rhyolite to andesite.
The isotopic and trace element systematics of the basalts are consiste
nt with a refertilized depleted mantle source with characteristics of
a mixture of normal mid-ocean ridge basalt source mantle and enriched
mantle II type mantle.