Study On Metamorphism-Deformation Of Metamorphic Rock Series Of Jiageda Formation, Manzhouli-E'ergona Region

Metamorphic series of Jiageda formation, as the important stratum of Precambrian, situates in the E'ergona block between Sino-Russian border and Deerbugan tectonic Belt. This metamorohic series experienced relative low-metamorphism from low greenschist facies - lower amphibolite facies and is made up with some complex various of rocks.. Studying area sites at the west of Deerbugan tectonic Belt of Manzhouli-E'ergona Region,belongs to Inner Mongolia Autonomous Region.The Jiageda formation exposes in the northeast of CuoGang Town and Badaguan meadow of HeiShantou Town, with a NE distribution.As a whole, there are different views about the geochemistry and ancient tectonic environment on metamorphic rock series of Jiageda formation. Xu Zhonggui(1998) consider that they are incomplete ophiolite, came from the ancient ocean basin. Lv Zhicheng(2002) believe that Jiageda fromation is continental clast formed in continental marginal depression in a acient tectonic environment of passive continental margin, and the character of sedimentary depression is a tensional fault basin in early tension period of passive continental border and later tension period of back-arc basin. These differant views mentioned above have affected the correct understanding of crustal evolutionary history. Therefore, in this gratuate project, I want to put forth some specific problems in terms of those controversy above: the rock types which compose metamorphic rock series of Jiageda formation? Characteristics of metamorphism and deformation of all rock types? Specific development time? Evolutionary sequence? Etc. In order to make sure the condition of metamorphism and deformation of metamorphic rock series of Jiageda formation and tectonic background, we do research on field attitude, rock types, facieology, age characteristics, rec-overring the initial rock building, temperature and pressure of mineral-forming. So we can offer some new evidence about amalgamation of blocks and superposition and conversion of Xing'anling-Mongolian orogenic belt.The rock types of metamorphic rock series of Jiageda formation are garnet staurolite biotite schist, biotite hornblende schist, biotite plagioclase hornblende schist, granitic gneiss, granitic mylonite, mica schist and biotite granite. Our studying area have experienced two stage of metamorphism and one stage of ductile deformation. The early metamorphic event was the magmatic rocks rebuilt Neodevonian sedimentary stratum during a partial metamorphism accompanied with occuring of metamorphic mineral-garnet and staurolite. It indicates mid-p/T metamorphic system(low-amphibolite facie). After magmatic activity, a large scale successive schistosity and gnessosity event happened and resulted in a large amount of granodioritic gneiss, and also, result in metamorphism of basic rocks. The scale of latest malleable deformation during the late stage is quite small, just existing in strongly malleable deformable zone, show as intensive gneissosity and mylonization. Murbruk and cataclast groundmass are distinct directional. The magmatic zircon SHRIMP concordia age of the garnet staurolite biotite schist is 361.0±4.7Ma;the magmatic zircon SHRIMP concordia age of the nacritid is 362.2±4.0Ma;the magmatic zircon SHRIMP concordia age of the gneissic granodiorite in Yihewula plane section is divided into two phases,one is 300.6±9.3Ma and another is 320.0～360.0Ma;the magmatic zircon SHRIMP concordia age of the granodiorite gneiss in Badaguan plane section is 211.0～148.0Ma;the magmatic zircon SHRIMP concordia age of the intrusion of aphanitic biotite granite is 130.1±1.4Ma.The 40Ar/39Ar plateau age of the biotite of the granodiorite gneiss in Yihewula plane section is 130.9±1.4Ma;the 40Ar/39Ar plateau age of the muscovite of muscovite quartz schist is 115.6±1.6Ma.By studying of geochemical analyses, original rocks recovering, and original tectonic environment recovering of six typical samples from Jiageda formation, we re-evolved rocks type original tectonic environment. Dominant rocks occurring in this region include granitic gneiss, granitic mylonite,mica schist,biotite hornblende schist and biotite plagioclase hornblende schist are ortho-metamorphic rocks.And the original rocks of granitic gneiss, granitic mylonite,mica schist, are phyric granodiorite;the original rocks of biotite hornblende schist and biotite plagioclase hornblende schis are gabbro and diabase.Garnet staurolite biotite schist are parametamorphic, the original rock is Al-rich pelitic rocks respectively.Tectonic environment of phyric granodiorite,original rock of granitic gneiss, granitic mylonite,mica schist,biotite hornblende schist included in Jiageda metamorphic series, maybe syn-orogen granite or post-orogen granite.To sum up, Jiageda metamorphic series resulted from magmatism and regional dynamic metamorphism from late Paleozoic to Mesozoic, by this we infer the geological events envolving serie since phanerozoic:①medium-acidic magma's intrusion with a large scale kept up from late Dovenian to early Carboniferous, ensued by a medium regional metamorphism evocated by magmatism;②Another medium-acidic magmatism occurred in later Carboniferous, and followed by a medium– low metamorphism and deformation of itself lasted to Triassic, and eventually formed various of gneiss and schist.③granitic magma's intrusion and large area volcanic rocks'extrusive happened in late triassic.④Partial intensive ductile-fragile extensional tectonics and evening magma's intrusion. Also, we find that the oldest rock in our studying area is not outcrop of precambrian basement, but Hercynian granite formed by orogeny, blongs to continental margin accretion building, and alleged"Jiageda formation"is just a suit of sedimentary straum of volcanic material after late Dovenian, and was arrested separately by magma after experienced orogeny and magmatism.