A PRELIMINARY UNDERSTANDING OF PO- LYCYCLE OF GEOSYNCLINE IN HENGDUAN MOUNTAINS
对横断山区地槽多旋回发展的初步认识

Here are presented some observations on geotectonicpolycyclic development in the Hengduan Mountains. Five focal points are included: (1) division of geotectonic cycles) (2) deep fracture and subduction zones, (3)evolution of Tethys Ocean; (4) tectonic history and (5) characteristics of poly-cyclic development. The important significance of Variscian and Indosinian cycles in Tethys evolution is emphasized.There are three major stages of tectonic development in the Hengduan Mountains. (1) Paleozoic-Prepaleozoic geosyncline-platform stage-closing stage of geosyncline (Early cycles), (2) stage of Tethys evolution-disintergration of continental crust, the spreading of oceanic crust and subduction (Principal cycles) and (3) stage of intensive northward compression and formation of Qinghai-Tibet plateau (Post cycles). Consequently, this area is of typical polycyclic development, including submarine volcanism, flysch formation, folding, granite intrusion, molasse formation, ophiolitic suites, spreading of oceanic crust subduction and resultant "trench-arc-basin" structures.