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The Mesozoic Magmatism And Crustal Extension In Shandong Province, China-additionally Discussing The Relationship Between Lamprophyres And Gold Mineralization

Posted on:2005-10-19Degree:DoctorType:Dissertation
Country:ChinaCandidate:S LiuFull Text:PDF
GTID:1100360122480419Subject:Institute of Geochemistry
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The crustal movement was intense in Yanshanian, from 205Ma to 65Ma in Shandong Province. When the tectonic system completely changed from paleo-Asian tectonic circle to shore Pacific tectonic circle, and established the elementary tectonic framework of Shandong Province. From then on, the tectonic movements of Shandong were ascribed to the subduction (north-west-trending) of Pacific plate under Eurasian. Due to the west north direction subduction, fast collapse (delamination) may take place and the mantle plume emerged in Ludong, In addition, owing to the subduction of Pacific plate under Eurasian, there appeared left-lateral advection and extension for Tan-Lu faults (named as Yishu fault in Shandong), and together with the collapse of Yanshanian orogenic belts, all induced the crustal extension in Shandong.The Yanshanian mafic dikes, volcanic rocks and alkaline rocks resulting from extensional setting largely appeared in Shandong Province. However, it is unsubstantial for the investigation on chorology and geochemisty, and dissimilar for the research on petrogenesis and tectonic setting. Therefore, based on the isotopic chorology, petrochemistry, geochemisty and Sr, Nd, Pb isotope, the Ph.D dissertation mainly studied some Yanshanian mafic dikes, volcanic rocks and alkalic-ultramafic dikes in Shandong Province. In addition, in view of the high gold contents in the lamprophyres, and the significance of Yanshanian for gold mineralization in Shandong, the relation between lamprophyres and gold deposit is also discussed in this paper. By studying, the main conclusions have been achieved as follows:I.The volcanic rocks, as the result of the partial melting of enriched mantle, comprise calc-alkaline andesite and dacite and a few tholeiite. During diagenetic process, there may exist the fractional crystallization of clino-pyroxene, plagioclase, olivine and Ti-Fe oxide, and the accumulation of olivine. The alkalic-ultramafic dikes formed by low degree partial melting (3.4%) of enriched mantle, consist of single olivine pyroxenolite, the dominating olivine fractionation is evident. The mafic dikes also formed by the partial melting of enriched mantle, include gabbro, diabase(distributing mainly in Luxi) and lamprophyres (camptovogesite, odinite and hornblende lamprophyres) (mainly in Ludong). For all the rocks, crustal contamination was absent when magma emplaced.2. The mafic dikes, volcanic rocks and alkalic-ultramafic dikes are terrestrial, and were all formed in the extensional settings.3. The formation of the enriched mantle (EM1) is attributed to the strong metasomatism-taking place between subducted Yangtze lower crust and NC (north of China) ancient lithosphere. Due to the subduction of Pacific palte under Eurasian in early Cretaceous, at about 140 Ma, fast collapse (delamination) took place and the mantle plume emerged, both resulted in the large-scale crustal extension in Ludong. In addition, owing to the subduction of Pacific plate under Eurasian, there appeared left-lateral advection and extension for Tan-Lu faults (named as Yishu fault in Shandong), and which induced the crustal extension in Luxi. Under the cooperation of lifts and mantle fluids, the melting point of mantle peridotite fell, and then, extensive melting took place in the enriched mantle, which resulted in the appearance of abundant mafic dikes, ultramafic dikes and contemporaneous volcanic rocks in Shandong Province. Moreover, in view of the speeds of collapse, extension and magmatic emplacement were so fast that no crustal contamination in magma.4.The K-Ar isotopic data of mafic dikes vary between 72.2 ± 1 70Ma and 204.2 ± 5.4Ma, and mostly between 90 Ma and 140 Ma. Integrating the ages of the mafic dikes and alkalic-ultramafic dikes in this paper, and the known data of mafic dikes and volcanic rocks, at least, there existed four episodes Mesozoic crustal extension in Shandong Province, namely, 80Ma, 100Ma, 120 Ma and140Ma, which is similar to that of SC (South China), indicating that maybe the effect of the subductio...
Keywords/Search Tags:Mesozoic, enriched mantle, crustal extension, crustal contamination, petrogenesis, lamprophyres, gold deposit, Shandong Province
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