INITIAL AND BOUNDARY CONDITIONS FOR THE EVOLUTION OF THE CENTRAL ASIAN OROGENIC SYSTEM (CAOS): THE BALKATACH HYPOTHESIS

The validity of all existing tectonic models for the onset and evolution of the Central Asian Orogenic System (CAOS) critically depends on the assumed initial configuration and relative positions of the Precambrian cratons that surround the orogen. We address this issue by evaluating the tectonic relationships among the bounding cratons rather than focusing on the interactions of the cratons within the CAOS as done by nearly all previous studies. A central hypothesis we are testing is whether Baltica, Turan, Karakum, Tarim, and North China were linked as a single continental strip, with variable along-strike widths, in the Neoproterozoic. We found that most tectonic boundaries currently separating these cratonal blocks postdate the CAOS. By removing their effects, we are able to establish a >6000 km-long Neoproterozoic continental strip referred to here as Balkatach (i.e., after the Balatica-Karakum-Tarim-China connection). A contiguous Balkatach and the relative motion of its northern and southern arms (in the present coordinates) in the Paleozoic has played an important control on the evolution of the CAOS, which is best expressed by the bi-directional suturing events along the outer margin of the CAOS. Specifically, we propose that: (1) Neoproterozoic rifting of Balkatch created microcontinent blocks within the CAOS, (2) rifted microcontinents acted as nuclei for subduction to develop within the Paleo-Asian Ocean, (3) subduction of this ocean within an archipelago arc system accommodated the oroclinal bending of Balkatch around the CAOS, (4) initial collision of central Balkatch and the CAOS in the mid-Carboniferous was followed by bi-directional propagation of suturing, and (5) the complete closure of the Paleo-Asian Ocean in the Permian was accompanied by a magmatic flare up, which may have been related to the avalanche of the subducted oceanic slabs of the Paleo-Asian Ocean across the 660 km phase boundary in the mantle.