| The Sulu orogenic belt resulted from collision between of North China plate and Yantze plate is the largest UHP metamorphic belt in the world. Ultrahigh-pressure (UHP) metamorphism has been one of the most rapidly moving fields in geology over the last two decades. Our understanding of the UHP metamorphism has been greatly improved due to a multidisciplinary investigation used by Chinese scientists, including petrology, mineralogy, geochemistry and chronology. The eastward extension part of the Dabie-Sulu orogenic belt is a pivotal geological problem which is worthy of further study for geologists.Qiliyan uplift is in Jiaonan offshore, an extension part of Jiaonan uplift and belongs to the north part of the Sulu UHP metamorphic belt. Due to the limit by its special geographical location and natural conditions, we have low degree geological research about this area. The discovery of eclogites from Qiliyan confirmes that Qianliyan uplift is just the outcrop of the suture between North China Cration and Yantze Plate. In this thesis, the author ascertaines the protolith character of ecologites in Yangkou and Qianliyan based on analysis of geochemical features, compared with the geochemical features of ecologites in Rongcheng and Junan; we entail the basement nature of Qiliyan uplift by analysing the geochemical characteristic of the surrounding rock and compared with that of gneiss in Rongcheng and Lanshantou, this provides key constraints for discussing the collision and exhumation of North China plate and Yantze plate.Main conclusions made in this work are as followings:(1) The observations of petrography show that ecologites of Yangkou in Qingdao experience multistage retrometamorphism, there is obvious difference among mineral deformation; the degree of ecologites deformation in Qianliyan is lower than that of Yangkou, main show is multistage retrometamorphism.(2) The feature of monomineral infrared spectroscopy indicates that the garnet of ecologites of research areas is mainly composed of almandite, pyrope and grossularite, the OH- appearing in 3430cm-1 was construed as molecularwater of microscopic fluid inclusions rather than structural water in mineral; the pyroxene of ecologites, Yangkou, mainly is omphacite, the hornblende of ecologites in Qianliyan was resulted from retrometamorphism,the wide absorb peaks in typical OH vibration infrared absorb region (3000 cm-1～3800cm-1) may caused by molecularwater of fluid inclusions of omphacite.(3) The initial rocks of ecologites of Yangkou in Qingdao should be active epicontinental intraplate calc-alkaline series island arc basalt, whose diagenetic temperature approximately is 580℃～760℃; but the initial rocks of ecologites of Qianliyan belong to island arc basalt, whose geochemical properties have ocean (intra-plate) and island arc environments dual nature and its diagenetic temperature is about 680℃～760℃.(4) The analysis result of Sr isotope indicates the ecologites of Yangkou and Qianliyan were contaminated by crust which increased the ratio of 87Sr/86Sr. The characteristic of Pb isotope of Qianliyan ecologites shows the tectonic property may closely match that of Yantze plate.(5) Further study of surrounding rock suggest that K-feldspar gneiss is paragneiss, may metamorphosed from active epicontinental supracrustal sedimentary rocks. The surrounding rocks of Yangkou resemble continental crust except ultrabasite. There is much comparability among the granitic gneiss of Yangkou, I and A type granite of Rongcheng and A type granite of Lanshantou, Rizhao and this granities are post-orogenic granites, formed in active epicontinental extensional environment. Further consideration of the existiong research of the basement nature of the granite geniss in Sulu orogenic belt, the author holds that the basement of Qianliyan upift may tend to belong to Yantze plate. |
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