A Late Carboniferous olistostrome at the front of the Southern Tian Shan nappes (Kadamzhai and Khaidarkan deposits, Kyrgyzstan)

Abstract

A Late Carboniferous (Early Moscovian) olistostrome developed in the Kadamzhai and Khaidarkan gold-antimony-mercury deposits on the Alay Ridge northern slope (Kyrgyzstan), at the front of the Late Paleozoic Southern Tian Shan nappes, is characterized. It comprises a sub-nappe olistostrome in a collisional tectonic setting. The olistostrome contains olistoliths and olistoplaques containing parts of the mid-Paleozoic sedimentary successions belonging to the parautochthon and lower nappes of the northern Bukantau–Kokshaal branch of the Southern Tian Shan nappe belt. The olistostrome accumulated ahead the advancing nappes in the foredeep basin that was filled with turbidities and debris-flow deposits (Tolubai Formathion). The parautochthon was partly dismembered into thrust limestone sheets which disintegrated and slid into unconsolidated sediments of the foredeep basin, forming large limestone olistoliths and olistoplaques. Olistoliths containing shales and bedded cherts were slid from the lower nappes. Tectonic breccias up to melange scale are present in some olistoliths, suggesting tectonic disintegration within the nappe pile and the subsequent sliding of the tectonized blocks into the olistostrome basin. Ore-bearing silicified rocks (so-called “jasperoids”) with antimony-mercury and gold mineralization are located predominantly along the contacts of the limestone olistoliths/olistoplaques with a terrigenous matrix.