V23B-3108
DISTRIBUTION AND EVOLUTION OF VOLCANISM OF THE BOLAVEN PLATEAU, SOUTHERN LAOS

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Jason S Herrin1, Kerry Sieh1, Weerachat Wiwegwin2, Punya Charusiri3, Bradley S Singer4, Khamphao Singsomboun5 and Brian Jicha6, (1)Nanyang Technological University, Singapore, Singapore, (2)Bureau of Environmental Geology, Department of Mineral Resources, Bangkok, Thailand, (3)Chulalungkorn University, Bangkok, Thailand, (4)University of Wisconsin Madison, Madison, WI, United States, (5)Department of Geology and Mines, Geo-Information Division, Ventienne, Laos, (6)University of Wisconsin Madison, Department of Geoscience, Madison, WI, United States
Abstract:
The Bolaven Plateau of southern Laos hosts a 6000 km2 basaltic volcanic complex erupted through flat-lying Mesozoic non-marine clastic sedimentary rocks. It is among the largest of dozens of isolated intracontinental Neogene-Quaternary volcanic centers in southeast Asia. The most voluminous flow sequences are tholeiitic, but a significant component of alkalic basalt is also present as morphologically younger cinder cones and related flows that cap the Plateau. Two salient aspects of the volcanic field are these: (1) Lava compositions appear to transition temporally from tholeiitic to alkaline, suggesting that the field tapped low-degree partial melts of a fresh mantle source toward the end of its lifespan. Circumstantial evidence for this can be found in abundant spinel lherzolite, wehrlite, and olivine websterite xenoliths within the alkaline basalts. (2) The volcanic center appears to have initiated atop a pre-existing 1000 m high, 90 km wide bedrock plateau, with nearly all visible vents confined to a 30-km wide zone that extends 80-km north to south.

Our work on the Bolaven volcanic complex aims at establishment of a geochemical and temporal framework for its evolution. Using field relationships, petrologic and geochemical studies, and 40Ar/39Ar dating, we hope to unravel the genetic and age relationships of these compositionally varied lava sequences. Another objective of our investigation is to assess the possibility that lavas of the Bolaven might mask the heretofore undiscovered impact site of the Australasian tektite strewnfield (see Sieh et al, this meeting). Toward this aim, we will determine whether a sufficient expanse of the volcanic field is younger than the 0.8 Ma tektites. Finally, we intend to constrain the timing of incision of the Bolaven Plateau by the Mekong River and its tributaries.