The Structure And Evolution Of Paleoproterozoic Lithosphere In Eastern Liaoning

The studied region covers the east part of Liaoning and Jilin provinces. Detailed work is focused on the area on the south of Shenyang-Tonghua and west of Tonghua-Dandong in the Pan-East Liaoning Peninsular. The studied area is tectonically located in the Liaoning-Jilin orogenic belt in the east of North China platform, which is adjacent to Long00Mang-Helong block on the north, neighbored by Langlin block (in DPRK) on the south, and cut by the Tan-Lu fault (Songliao Basin) on the west. Paleoproterozoic sedimentation, magmatism, mineralization and structural deformation and metamorphism are well developed in the area, forming a unique ore-bearing metamorphic formation. It is a typical intraplate splitting-orogenic mobile region.The above-mentioned geologic processes are different responses to the same crust-mantle thermodynamic process in Paleoproterozoic Era. After a synthetic study (synthesizing, connecting and confining) on the Paleoproterozoic tectonic setting of the region, this paper focuses on the characteristics of Paleoproterozoic volcanic-magmatic activities and connects the magmatic thermal events with metamorphic thermodynamic events and basin evolution to get the whole picture of lithospheric thermodynamic evolution, establish the lithospheric structure of Liaoning-Jilin orogenic belt, and discuss the evolutional process of Liaoning-Jilin orogenic belt. The result will be scientifically significant to the metamorphic dynamics of the region, and helpful for the neighboring areas in Paleoproterozoic metamorphic geologic study.The following conclusions have been obtained by preliminary research:1. The region of East Liaoning Peninsula played an important role in the Paleoproterozoic continental craton evolution of North China platform. The Paleoproterozoic Liaoning-Jilin rift zone originated at 2300 Ma. Its forming background is the convergent boundary of Archeozoic continental crust (Tl, T1T2G1, G1G2, G2), which was preliminarily cratonized (known as the second cratonization) during the developing stage of continental nucleus. In the late period of Paleoproterozoic (1900 - 1700 Ma), the rift zone underwent mountain-building by contrasting and folding, which mark the end of North China landmass cratonization (the second cratonization) and start of continental marginal developing stage of stable cap.2. The tectonic attributions of the Paleoproterozoic rift zone in East Liaoning Peninsula are obvious. It is characterized by: 1) developed hugely thick bedded metamorphic sedimentary rock series, generally named Liaohe group (Ji'an group or Lading rock group in Jilin);2) associated basic and acidic bimodal volcanic rocks;3) associated basic-acidic intrusive rocks;4) intense deformation (folding) and metamorphism (distributed in zone);and 5) richness of various polymetal and nonmetal minerals, such as copper, cobalt, gold, silver, lead, zinc, iron, uranium, sulfur, boron, talc, limestone and so on, with an evident spatial and strata controlling.3. The Paleoproterozoic metamorphic rock series can be divided into three lithologic assemblages (coincidentally with boron-bearing rock series, graphite-bearing rock series and high-aluminum rock series from bottom to top), which are the volcanic rocks and pyroclastic rock-clastic rock assemblage of Lower Subgroup (Langzishan-Lieryu formation and strata), clastic rock-carbonate rock assemblage (with minor basalt in the bottom) of Middle Subgroup (OOMaojiayu-Dashiqiao formation and strata), and clastic rock-mudstone assemblage of Upper Subgroup (OOMaixian formation and strata). The rock assemblages of the three subgroups are obviously different in sequence of strata (three clastic rock-carbonate rock super-sequences), volcanism (strong basic and acid-intermediate - minor basic - without volcanic rock) and ore-bearing formations (three source beds for: REE ores, Cu-Co ore and B-Mg-Fe ore - Pb-Zn, Au-Ag, talc and magnesite - gold deposit). Meanwhile there is a relation between them. They commonly recorded part of the evolution stages of the rift zone (splitting - isostating - pre-uplift adjusting).4. The Paleoproterozoic intrusive rocks have recorded the uplift and orogeny process of Liaoning-Jilin rift. The magmatism of the Liaoning-Jilin rift can be divided into three stages including six series: pre-orogenic magmatism (subdivided into Mg-rich basaltic magma intrusive-eruptive series and tholeiitic magma intrusive-eruptive series);synorogenic magmatism, which can further divided into pre-orogenic stage (calc-alkaline granodiorite-adamellite bedded intrusive series), main orogenic stage (peraluminous adamellite-muscovite granite intrusive series) and late orogenic stage ([meOOMa-phenocryst] K-feldspar granite and plagioclase granite);and post orogenic stage (OOMabbro and diabase dykes).5. The first two episodes of structural deformation are characterized by progressively increasing deformation. That is, from large scaled plastic-solid bedding deformation formed by gravity slide and bedding shearing with unbalance of strata led by the contraction and intrusion of magma along strata in the early stage, to large compound winding folds and reverse thrust structures with the large scaled folding and thrusting of strata by the intense contraction and strong emplacement of magma in the late stage. This is a continuous process. The regional thermodynamic field is a common activity of a relative stable thermal release and a relative abrupt thermal extrusion (thermal transmission). Besides controlled by regional thermal flow, the strength of metamorphism is also affected by the thermodynamic field of magma. The regional stress field is directly affected by the thickening of the crust. The process of contracting stress field is not negligible.