Middle-Late Paleozoic geodynamic complexes and structure of Gorny Altai and their record in gravity data

Abstract

Middle-Late Paleozoic geodynamics and structure of Gorny Altai are studied with reference to gravity data. The northern and central parts of the area belong to the Gorny Altai terrane consisting of Late Precambrian-Paleozoic rocks originated in different tectonic settings on the Siberian continental margin, including Devonian active-margin volcanoplutonic complexes. In the south and east, the Gorny Altai terrane borders the Altai-Mongolia terrane along the Charysh-Terekta-Ulagan shear zone. The Altai-Mongolia terrane is composed of Early Paleozoic turbidites of the Kazakhstan-Baikal continent, Middle Paleozoic collisional garnet-disthene-andalusite schists, and Late Paleozoic zoned andalusite-cordierite schists, with granitic plutons on their periphery. The pattern of these complexes is similar to that of Cenozoic volcanoplutonic and metamorphic domes in the Kamchatka and Chukchi Peninsulas. The Devonian volcanoplutonic complexes from the Gorny Altai terrane and the Middle-Late Paleozoic metamorphic complexes from the Altai-Mongolia terrane are well evident in the gravity field. In general, gravity anomalies in the two terranes strike in different directions: NW in the Gorny Altai terrane and W-E in the Altai-Mongolia terrane, which highlights the structural heterogeneity of the Gorny Altai region. New dates have been obtained for magmatic detrital zircons from Paleozoic sedimentary rocks of the Anui-Chuya basin in the Gorny Altai terrane. The inferred source areas of zircon hosts are igneous rocks of the Precambrian craton basement and the Vendian-Early Ordovician Kuznetsk-Altai island arc. Early Neoproterozoic (1.00-0.75 Ma) detrital zircons are abundant in the Early Paleozoic turbidites of the Altai-Mongolia terrane but are absent from samples of the Gorny Altai terrane. Populations of detrital zircons in the the Gorny Altai terrane contain Devonian and Early Neoproterozoic specimens. The reported data prove that the Kazakhstan-Baikal and Siberian continents amalgamated in the Middle-Late Paleozoic. The resulting Gorny Altai tectonic framework of that time is recorded in the gravity field and in the provenance of detrital zircons.