An analysis of Silurian-Carboniferous sedimentary and structural characteristics on both sides of Karamaili ophiolitic belt of Xinjiang and its significance

The Karamaili ophiolite belt is located on the northeastern margin of Junggar Basin, which is a very important tectonic unit in northern Xinjiang and Central Asia area. The evolution of Karamaili oceanic basin remains controversial due to hot-debated issues on the ages and characteristics of Karamaili ophiolite. This study focuses on the Paleozoic tectonic setting in the Karamaili tectonic zone revealed by a comparative study of the Silurian-Carboniferous tectono-sedimentation on its north and south sides. To the north of the Karamaili ophiolitic belt, the angular unconformities are widely developed between Upper Silurian, Lower Devonian and underlying Middle-Upper Ordovician strata and Caledonian granitoids. The Lower Silurian strata are generally absent and the underlying Middle-Upper Ordovician strata mainly consist of andesite with greenschist facies. The Middle, Upper SilurianDevonian-Lower Carboniferous sedimentary deposition system to the north of Karamaili ophiolitic belt is similar to that to the south, including conformable contact, flat occurrence and undeveloped folds, faults and metamorphism. Anticlines or synclines are mainly of short axis, which is apparently different from strong deformation shown in the Karamaili ophiolitic mélange. Besides, pyroclastics-dominated rock associations, widely existent inclined beddings and cross-beddings and abundant kinds of animals and plants fossils indicate a littoral-shallow marine environment. Therefore, during Late Paleozoic, no ocean existed in the Karamaili tectonic zone and the oceanic basin represented by the Karamaili ophiolitic mélange had been closed before Middle Silurian.