The contemporaneous tectonic events of the Indian Ocean and neighbouring areas
About 140 m. y. ago, the Indian Ocean opened and the Indian plate began drifting northward. With this event began the evolution of the tectonic and magmatic pattern of the present-day Indian Ocean and its related structures. This paper deals with the temporal-tectonic coherences during the evolution of the Indian Ocean itself, of the Indian plate, the Himalayas, the Iran fold belt and the entire Afro-Arabian rift system. The authors themselves have worked in some of these areas and have also used and interpreted the voluminous and valuable literature concerning this region. During the last 140 m. y., there have been various culminations of tectonic activity which affected contemporaneously the different areas or structures of the described region. 80 to 75 m. y. ago, corresponding with magnetic anomaly 32, there was a strong acceleration of the northward drifting Indian plate. At the same time, a culmination of ophiolitic eruptions (or an intensified sea floor spreading) occurred in the Tethys region, that is along the present-day Himalayas, Karakorum, Makran, Oman, Zagros Mountains and Taurides in southern Turkey. 70 to 53 m. y. ago, following the acceleration of the Indian plate, the Indian and the Arabian plates first made contact with Asia resulting in a strong folding in Iran and the first folding phase in parts of the Karakorum and Himalayas. It is significant that the two independently moving plates contacted Asia at the same time. Intensified movements of plates combined with subduction of the continental crust of Arabia and India under Asia along the Indus suture line and the Zagros crush zone also occurred about 36, 25 and 10 m. y. ago and later. These movements corresponded with important orogenetic phases in the Himalayas and the Iran fold belt. At the same time, within the Red Sea and the Gulf of Aden an intensified sea floor spreading was in progress. The graben rifting of the East African Rift system also corresponded in time with these movements. The initial taphrogenetic phase occurred in the Afar rift 23 to 25 m. y. ago and in the Gregory Rift 10 m. y. ago. Thus, different and independent structures around the Indian Ocean showed culminations of tectonic events at the same time. The described region is extensive enough to obtain, by comparison of the varying structures, a first synopsis of temporal-tectonic activities showing how the earth's crust is influenced by contemporaneous tectonic events. Mainly, the contemporaneity of the tectonic events suggests a common origin of these dissimilar structures. Doubtless, the movements have their roots in the mantle or even in parts of the earth's core. A preliminary comparison of the tectonic culminations in the described region with those in other parts of the earth show, in the sense of Stille (1924, 1940), approximately similar periods of tectonic culminations as, for example, east and west of the Atlantic Ocean. But, in regard to the ideas of the new global tectonics, it is too early to draw any conclusions from so distant and different structures and it would be premature to speak of a contemporaneity of the global tectonics.
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