| Song Chay-Dulong massif is the largest igneous complex in the southwestern cornerof the South China Block. It has been thought to represent an exhumed part of thePrecambrian basement of this block. The Song Chay-Dulong dome is on the borderbetween Northern Vietnam and SW China (SE Yunnan), located between the Red Riverfaults and Van Son-Ha Giang faults. From the structural geometry point of view: SongChay has a very clear tectonic dome, extending about80km in a NS direction and about45km in an EW direction. The dome is composed of migmatites, porphyroid granites andaugen-gneisses resulting from the deformation of these granites. Metamorphism anddeformation has great significance to the multi-stage effects on intense deformation andalteration characteristics. Song Chay–Dulong has attracted the attention of manygeologists because of its distinctive location and characteristics.In this paper studies regarding several aspects of composition constituents of theSong Chay–Dulong metamorphic complex are conducted. From the Song Chay toDulong three rock types are observed:1-high-grade gneiss consisting of K-feldspar,plagioclase, perthite;2-low-grade granitic gneiss;3-Muscovite-quartz schist (mainlyquartz, no feldspar). Granite metamorphic rocks are composed mainly of quartz,plagioclase feldspar, biotite, minor hornblende, pyroxene, garnet. A typical structure of therock is equally: High grade gneiss and low grade gneiss. The rock, display a unidirectional orientation of minerals, such as quartz and feldspar and foliation in mica, which is acommon feature in strongly deformed metamorphic rocks. On the outcrops,porphyroclastic, porphyrob lastic show "σ" or "δ" shape. Deformation of porphyroclasticis elongated and directed along the direction of shear. The direction of shear movementcan be seen very clearly. Feldspar porphyroclastic rotation are directed towards thesoutheast of the upper shear deformation. And the development of the southeast-northwest mineral stretching lineation is typical geometry characteristics. This paperattempts to understand the Song Chay-Dulong igneous complex rocks, and othercharacteristics of the surrounding geological formations, in order to accurately understandthe Song Chay-Dulong igneous complex rock exhumation and significance.The Song Chay–Dulong metamorphic complex possess many differentmicrostructural phenomena in the Song Chay area and Dulong area, which are caused bytheir different metamorphic and deformation characteristics. There are manymicrostructure phenomena in the Chay–Dulong metamorphic complex, e.g: intragranularmicrofracture, undulatory extinction, mechanical twin, Static recovery–recrystallizationgrain, Dynamic recrystallization grain, porphyroclast system, banded tructure, S-C fabric,mineral fish, exsolution structure. Microstructural phenomena in high-grade plasticdeformation showed evidence later superimposed low-grade deformation transformation.In both the micro-scale and macro-scale the Chay–Dulong metamorphic complex hasundergone deformation superpositions.Song Chay-Dulong metamorphic complex analysis using EBSD fabric analysis wereobtained in quartz and show three different strain history of rock quartz group composition.Visibility is very clear early high temperature, low temperature conditions latesuperimposed deformation.Analysis activities of Song Chay-Dulong metamorphic complex have chronologicalage of442-402Ma which represent the Silurian Yangzi plate collision with Huaxia plate isthe Caledonian orogeny tectonic events, mainly S-type granites based, with the upper continental crust similar distributions in the form of trace elements. In the Mesozoic(Indosinian orogeny) Song Chay-Dulong metamorphic complex subjected to intensetectonic deformation. Massive granite magma intrusion Laojunshan formation occurs inYanshan movement.. |
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