关键词: 新太古代')">

新太古代, 凝灰岩, 锆石U-Pb定年, 岩石地球化学, 岩石成因, 构造意义, 华北克拉通, 小孤山金矿床

Abstract:

The ore-bearing rock mass of Xiaogushan gold deposit in western Liaoning is a suit of pyroclastic rock assemblage, which was originally divided into Yixian Formation of Lower Cretaceous of Mesozoic. In order to accurately determine the age of this rock body, and to explore the petrogenesis and tectonic significance of the rocks in the western part of the Liaoxi region, petrography, LA-ICP-MS zircon U-Pb dating and petrogeochemical analysis were carried out on the ore-bearing tuff of the Xiaogushan gold deposit. The results show that the weighted average age of the tuff is 2 510.7-2 508.9 Ma, which is the product of Late Neoarchean magmatism. The geochemical characteristics of the major elements show that the tuff is rich in silicon (w (SiO₂) is 68.99%-71.82% ), rich in alkali and potassium (w (Na₂O+K₂O) is 7.13%-8.82%, w (K₂O) is 6.94%-8.59%), poor in magnesium (w(MgO) is 0.51%-0.66%), and poor in calcium (w (CaO) is 0.43%-0.90%). The aluminum saturation index (A/CNK) ranges from 1.16 to 1.42, which belongs to the peraluminous calc-alkaline shoshonite series rocks. The rocks are enriched in LREEs and LILEs such as Rb, Th, U, K and Pb, and depleted in HREEs and HFSEs such as Nb, Ta and P. The rare earth distribution pattern shows a right-leaning gentle low “V” curve, with obvious fractionation of light and heavy rare earth elements. (La/Yb)_N is between 15.19 and 38.23, with weak Eu anomaly (δEu is 0.60-0.72). Petrogenesis and magma source discrimination show that the rocks have the characteristics of S-type granite, and the magma originated from the partial melting of metamorphic mudstone in the lower crust. Combined with the regional tectonic evolution, tectonic discrimination and geochronological characteristics, it is believed that the ore-endowed tuffs of the Xiaogushan gold deposit were formed in the tectonic environment of syn-collision after the subduction of the Longgang block and the Langlin block in the eastern part of the North China craton, which reflects the formation and evolution of the consolidated basement of the North China craton in the Archean period, and provides evidence for the tectonic mechanism of the North China craton in the Archean.

Key words: Neoarchean')">

Neoarchean, tuff, zircon U-Pb dating, rock geochemistry, petrogenesis, tectonic significance, North China craton, Xiaogushan gold deposit ')">Xiaogushan gold deposit