Geochemistry And Tectonic Significance Of The Early Paleozoic Intrusive Rocks In The Pantuoshan Complex,Inner Mongolia

This dissertation raises a comprehensive study on the petrogenesis,intrusive pulses and tectonic significance of the Pantuoshan intrusive complex of Erlongbaoxi area in Early Palaeozoic Era,in terms of geology,petrology,mineral chemistry,element geochemistry and geochronology.This study was based on and financially supported by the State Geological 1:50000 Regional Survey.The Early Paleozoic Pantuoshan intrusion in ErlongBaoxi area is located in the southern side of the Yueyashan OPHIOLITIC MELANGE belt and belongs to the Tarim plate.The intrusive body is a multi-stage intrusive complex,which can be divided into two intrusive stages according to its intrusive age,formation mechanism and tectonic significance,namely,Middle Ordovician(465.8 +5.4 Ma)and Early Silurian(434.0 +3.5 Ma).It is an early Paleozoic intrusive rock.The Ordovician intrusive rocks are less exposed,only the Middle Ordovician medium-fine-grained granodiorite is a kind of rock type,mainly exposed in the south of the Yueyashan Mountains-Xichangjing Early Paleozoic plate suture zone,generally distributed in NW direction,basically consistent with the direction of the regional tectonic line.It belongs S-type to I-type granite and calc-alkaline series,and its magma may originate from local melting of hard sandstone in the lower crust.Formed in a compressive environment,it is a volcanic arc granites converge on the continental margin for subduction,indicating that the tectonic setting formed by it is closely related to the subduction and convergence event of the Tarim board from south to north.The Silurian intrusive rock is composed of acid rock and is a set of calcium-alkaline granite.Two kinds of rock types were disintegrated,namely: the Early Silurian plaque-like monzonitic granite and the medium-fine-grained biotite monzonitic granite.The fine-grained monzonitic granite distributed on the south side of theYueyashan Mountains-Xichangjing Early Paleozoic plate suture zone belongs to the S-type granitic,and its magma is derived from the local melting of the lower crust hard sandstone.Formed in the extrusion environment,it is the same collision granite,indicating that the Kazakhstan-Junggar plate and the Tarim block are further converging during this period,colliding and entering the closed stage.The two reflect the tectonic evolution of the Kazakhstan-Junggar plate and Tarim plate from the Middle Ordovician to the Early Silurian in the Pantuoshan of the Dilongbao area.