Geological Processes and Hydrothermal Mineralisation in Plate Tectonic Settings — Mineral Exploration

Abstract

The Earth’s outer layers, namely, the lithosphere and the asthenosphere have an important role in the mechanisms of plate tectonics. The outermost layer of our planet is the relatively strong and rigid lithosphere — about 100 km thick — broken up into a number of major and minor plates, whose present-day configuration is shown in Fig. 6.1. The boundaries between plates, divergent (rifting, spreading zones), convergent (subduction and collision zones) and transform faults, are the sites of intense geological activity including earthquakes, volcanism, mountain building and of course mineralisation. The lithosphere overlies the asthenosphere, a weak region of the upper mantle about 200 km thick, where temperatures approach melting point. The boundary, which is probably gradational, between these two layers is by no means well defined, and is not to be confused with the crust-mantle boundary which is defined by the Mohorovicic discontinuity. Although the reason for the movement of the lithospheric plates is not entirely understood, it is generally agreed that mantle convective motions, possibly driven by radiogenic heat, may be responsible. The spreading motion of the oceanic crust is indicated by the characteristic magnetic stripes, symmetrically disposed on either side of a mid-ocean ridge, and first described by Vine and Matthews (1963). In this chapter we examine plate tectonic settings and associated types of hydrothermal mineralisation. A schematic view of plate tectonic settings is shown in Fig. 6.2.