PHANEROZOIC ANALOGUES OF ARCHAEAN OCEANIC BASEMENT FRAGMENTS: ALTAID OPHIOLITES AND OPHIRAGS

Abstract

This chapter presents an overview of the distribution, current tectonic position and mode of origin of the remnants of oceanic basement rocks in the Altaids as likely analogues of similar rocks in many Precambrian, but mainly Archaean, orogenic belts. The concept of ophiolite gained great popularity after the advent of plate tectonics, because ophiolites were thought to represent pieces of crust and upper mantle of the floors of now vanished oceans. The shape of the orogen is irregular and does not have the familiar linear/arcuate, long and narrow shapes of most Phanerozoic orogenic belts. The trend of the Altaid orogen within this confusing region could most easily be followed by tracing out the magmatic arc fronts. The Boshchekul–Tarbagatay/Zharma–Saur “bridge” had a sliding attachment to the peri-Angara accretionary systems. As the bridge tightened in the form of a south-concave pincer, its Angara end moved along the previously-assembled units in a right-lateral sense along the Irtysh shear zone.