Quantifying partial melt fraction in the crust beneath the Central Andes and the Tibetan plateau

An interdisciplinary approach is used to quantify partial melt fractions an d to infer the origin and distribution (melt structure) of melts located in the crust beneath the Central Andes and the Tibetan plateau. In these area s field observations of Low Velocity: Zones (LVZ) and High Conductivity Zon es (HCZ), which are commonly attributed to partial melting, are used to qua ntify melt fractions. Additional information is obtained from nu (p)/nu (S) ratios, seismic attenuation data, and heat flew density and gravity anomal ies. These data accompanied bq thermal modelling suggest that melts of main ly crustal origin are interconnected through dykes and veins. Experimental results and model calculations indicate that the minimum fraction of melt n ecessary; to describe the LVZs and HCZs in the Central Andes and the Tibeta n plateau is approximately 20 vol.%, and the melt has a non-ideal interconn ectivity. (C) 2001 Elsevier Science Ltd. All rights reserved.