Fluids and Heat along the Himalayan Plate Boundary and their Plausible Expulsion into the Subcontinent

The subduction/collision processes and consequent great Himalayan uplift are studied in the light of the plausibility that large amount of aqueous fluids may accumulate at the boundary due to (a) compaction of oceanic and marginal basin sediments, (b) various metamorphic episodes and (c) meteoric water facilitated by high topography. This would imply that during the major phase transitions in the dynamics of the plate margin, transient reservoirs of fluids and attendant heat would develop along the orogenic belt. Manifestations of related tectonomagmatic and metamorphic processes along the Himalayan arc are therefore assessed. It is noticed that epicenters of the large earthquakes, and major river-sources and morphogenic peaks seem to occur over certain nodal zones along the collision boundary as also the leucogranitic plutons. We also examine the possibility of fluid expulsion from the topographic/collision front into the foredeep basins and continental interior. It is seen that linear trends of relatively 'large' activity seem to exist over the Indian platform which nearly coincide with its basement heterogeneities (BHs) which in tum form part of the mobile belts. These BHs appear to extend upto the Himalayan arc and would thus act as subterranean links between the boundary processes and intraplate region. In particular large distance migration of fluids and thermal energy may take place through focussing offlow along these BHs because during at least the major tectonic episodes the in situ hydraulic conductivity and/or permeability along the BHs could be sufficiently raised. The plausibility of the BHs acting as hot fluid channels, is quite crucial since it may play a controlling role in the development (or remobilization) of (i) ore-deposits and hydrocarbon fields, and (ii) many geophysical features of the continental crust such as brittle-ductile transition, low velocity layer (LVL), anomalously high conductive layer (HCL), deep seismic reflectors, hydrothermal circulation, high heat flow, seismicity, etc. It is shown that indeed some of these features have been inferred along the BHs. From this possibility a tectonothermal framework emerges which may be able to integrate a number of physicochemical processes and geophysical signatures having basic as well as applied significance.