The mechanisms by which magma is generated and transported through continental crust and how these processes affect the chemical and mechanical evolution of the lithosphere are some of the least understood issues of continental dynamics. We report here on the evolution of an unusually well-exposed early Mesozoic arc that originally formed along the ancient margin of Gondwana and is now located in western New Zealand. The pre-Cenozoic configuration and deeply eroded character of this arc lead us to the following conclusions about magmatism and deformation at 10-50 km paleodepths: (1) The mafic-intermediate composition of the lower crust and the mineral reactions controlling melt production strongly influenced pathways of melt transfer and controlled the mechanical behavior of the lithosphere during orogenesis. (2) Evolving lithospheric strength profiles during magmatism and convergence produced transient periods of vertical coupling and decoupling of crustal layers. (3) Late orogenic extension was driven by plate interactions rather than by gravitational forces and a weak lower crust.
|Number of pages||8|
|Publication status||Published - Jan 2003|