PALEOZOIC TECTONIC EVOLUTION AND CU-PROVINCES OF KAZAKHSTAN AND TIAN SHAN

Understanding of the Paleozoic setting and evolution of Kazakhstan and Tian-Shan is crucial for assessment of prospective areas in this region, both for sediment-hosted copper and for porphyry copper deposits. The synthesis of stratigraphic, structural and geochemical data allows to identify allochthonous terranes, to reconstruct ancient arcs and to establish a correlation between accretionary events and reorganizations in arc systems. Allochthonous terranes (arcs and microcontinents) are defined as coherent blocks which display individual geological histories and are bounded by ophiolite strewn suture zones. Arc systems are reconstructed as paired belts, where volcanism (arc) and intensive deformations in deeper marine environment (wedge) occurred synchronously within parallel strips. Relative position of coeval arcs and wedges indicate polarity of arc systems. Episodes of terrane accretion are indicated by cessation of deeper marine basins in suture zones and cessation of adjacent arcs, followed by formation of unconformities, emplacement of batholiths and by jumping of the arcs toward ocean. Time of suturing is also constrained by the age of overlap assemblages and stitching intrusions. The lack of volcanic rocks in many microcontinents, the distinct differences between terranes and the presence of short-lived arcs and of non-synchronous sutures all argue against a single arc and support a model of numerous terranes, which welded together in an oceanic setting. The terranes were amalgamated by the Silurian and resulting agglomerate was deformed into a giant orocline in middle and late Paleozoic. Mechanisms of orocline include a) bending of the arc due to roll-back of the descending slab, and b) buckling and wrenching due to opposing motion of Siberia and Tarim, which squeezed Kazakhstan at the latest stages of collision. Multistage accretion of small terranes and multistage oroclinal bending led to formation of numerous arcs tightly aligned to each other, which control a bulk of porphyry copper deposits throughout the region.