Paleomagnetism of Silurian and Devonian volcanics from the Chingiz island arc, Kazakhstan, and its bearing on tectonic evolution of the Ural-Mongol belt

Abstract

The tectonic and paleogeographic evolution of the Ural-Mongol belt between the cratons of Baltica, Siberia, and Tarim is the key to the formation of the Eurasian supercontinent during Paleozoic time, but the views on this complicated process remain very disparate and sometimes controversial. Three volcanic formations of the Middle Silurian, LowertoMiddle Devonian and Middle Devonian age from the southwestern boundary of the Chingiz Range (NE Kazakhstan) yields what are interpreted as primary paleomagnetic directions that help clarify the evolution of the belt. A singlepolarity characteristic component in midSilurian andesites yields a positive intraformational conglomerate test, whereas dualpolarity prefolding components are isolated from the two Devonian collections. These new data were evaluated together with previously published paleomagnetic results from Paleozoic rocks in the Chingiz Range, and allow us to establish with confidence the hemisphere in which the area was located at a given time. We conclude that NE Kazakhstan was steadily moving northward crossing the equator in Silurian time. These new paleomagnetic data from the Chingiz range also agree with and reinforce the hypothesis that the strongly curved volcanic belts of Kazakhstan underwent oroclinal bending between Middle Devonian and Late Carboniferous time. A comparison of the Chingiz paleolatitudes with those of Siberia shows similarities between the northward motion and rotational history of the Chingiz unit and those of Siberia, which imposes important constraints on the evolving paleogeography of the Ural-Mongol belt.