HR: 08:30h
AN: V41A-03    [PDF]
TI: 4D constraints on melt source-rock input and granite production in continent-continent collision; a case study from a 50 km wide swath through the Himalayan magmatic arc
AU: * Edwards, M A
EM: michael.edwards@univie.ac.at
AF: Structural Processes Group Dept. of Geological Sciences University of Vienna, Althanstrasse 14, Vienna, A-1090 Austria
AU: Wiesmayr, G
EM: x@x
AF: Structural Processes Group Dept. of Geological Sciences University of Vienna, Althanstrasse 14, Vienna, A-1090 Austria
AU: Grasemann, b
EM: x@x
AF: Structural Processes Group Dept. of Geological Sciences University of Vienna, Althanstrasse 14, Vienna, A-1090 Austria
AU: Meyer, m
EM: x@x
AF: Structural Processes Group Dept. of Geological Sciences University of Vienna, Althanstrasse 14, Vienna, A-1090 Austria
AU: Hausler, h
EM: x@x
AF: Structural Processes Group Dept. of Geological Sciences University of Vienna, Althanstrasse 14, Vienna, A-1090 Austria
AU: Miller, b
EM: x@x
AF: Dept Geol. Sci., Univ of North Carolina, Chapel Hill, NC 27599z` United States
AU: Kidd, W
EM: x@x
AF: Dept Geol. Sci., SUNY, Albany, NY 12222 United States
AU: Samson, s
EM: x@x
AF: Dept. Earth Sci., Syracuse Univ., Syracuse, NY 13244, United States
AB: Detailed mapping, mountaineering and high resolution remote-sensing data from the Bhutan High Himalaya illustrate rates \& / volumes of magmatic arc growth in continent-contintent collsion. Lunana \& Gonto La, a 20 km x 30 km area with $>$3 km relief, provide 3D data for widespread, km-long, Dm-thick, sill- \& laccolith-form leucogranites. These peak-forming ($>$8000 m) Miocene plutons are typical for the ca.2500 km magmatic arc of the India-Asia continental collision. Extrapolation to geo-traverses through peaks to the east (Khula Kangri, Monlakarchung) onto a 30sec DEM provide tight datapoint 3D subsurface control for $>$4500 km$^{3}$, thereby constraining total pluton shapes and volumes. Geochemistry studies indicate exclusively decomposition melting (Harris, et al. 2002) and permit us to calculate required melt-source rock volumes for various conditions. Project INDEPTH seismic reflection profiling (conducted imm. to the N. - Nelson et al. 1996) has been used with further mapping to obtain a 50 km wide, 150 km long swath through the entire orogen. These reveal the sub-surface form of the shallow, gently N-ward dipping, crystalline, mid-crustal layer that is exposed at the High-Himalaya, the upper part of which the plutons intrude. The 4D part of our 3D swath through the magmatic arc is geochronology for the plutons and, to the north, of local granitoid protrusions from beneath the cover rocks of the melted mid-crustal layer that constrain a N-ward younging of plutonism (Copeland 1990; Edwards \& Harrison 1997; Edwards et al. 1998; Li et al. 1998). Using these time constraints together with a kinematic model incorporating dilatant flow where both lines of no-rotation are stretching and non-parallel to shearing boundaries, we link deformation with melt source-rock magmatic product volume changes. We derive a timetable for melt addition and thereby rates of magma extraction and ascent.
DE: 8020 Mechanics
DE: 8035 Pluton emplacement
DE: 8102 Continental contractional orogenic belts
DE: 8145 Physics of magma and magma bodies
DE: 8434 Magma migration
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting