河南鹤壁地区金伯利岩中地幔包体地球化学研究及岩石圈地幔演化

The destruction mechanism and dynamic process of North China Craton(NCC) is the present research frontier of geological issue. Taihangshan tectonic belt is located at the central part of NCC and is as a transitional zone, in view of NCC eastern part of lithosphere was destructed while the western part keeps stable. Therefore, the research on lithosphere mantle beneath Taihangshan tectonic belt is of great importance to the destruction of NCC. Hebi region, Henan province, is located at the Taihangshan tectonic belt, and there are kimberlites occurred. Through detailed field geology work, many kinds of garnet facies mantle xenoliths were found in the kimberlites from Hebi region. Because the kimberlite and mantle xenolith samples were extensively altered, so,it is difficult to analysis the samples directly. To resolve this problem, we picked the individual minerals such as olivine, pyrope, picotitite and orthopyroxene out from mantle xenoliths separately, and picked the perovskite out from the kimberlite. Preliminary geochemical study on the placer minerals found that the minerals recorded lithosphere mantle metasomatic reaction, which indicated the destruction of NCC. This project aims to get the lithosphere mantle geochemistry information for example: the mantle character, geothermal and geobarometry condition, mechanism of lithosphere mantle metamorphism, lithosphere mantle’s geological formation age by research on olivine, pyrope, picotitite and orthopyroxene individual minerals. At the same time, we want to research the emplacement age of kimberlite through perovskite and baddelevite U-Pb geochronological dating. Combined with the above information, comparison will be made between the mantle xenoliths from the kimberlite and the xemliths from adjacent Cenozoic basalt. This project will provide the evolution information of mantle in Taihang Mountain transitional belt and help us to discuss the destruction mechanism and dynamics of the NCC.

华北克拉通的破坏机制和动力学过程是研究前沿。太行山构造带为华北克拉通东部破坏区与西部稳定区的过渡带，其深部地幔信息对华北克拉通破坏研究具有重要意义。河南鹤壁位于太行山过渡带上，产出有金伯利岩。经野外考察，在鹤壁地区金伯利岩中发现了大量的石榴石相深源地幔包体。为了克服地幔包体蚀变强烈的困难，申请人从地幔包体中分选出了橄榄石、镁铝榴石、铬尖晶石和斜方辉石等重砂矿物，从金伯利岩中分选出了钙钛矿。本项目以地幔包体为研究对象，拟在岩相学研究的基础上，通过对地幔重砂矿物的矿物化学和微量元素研究，对橄榄石的Re-Os同位素组成研究，对钙钛矿和斜锆石U-Pb年代学研究，获得鹤壁地区的地幔性质、温压条件、地幔交代机理、岩石圈地幔形成时代以及金伯利岩侵位时代等信息。综合上述研究，并与鹤壁地区新生代尖晶石相浅源地幔包体相对比，确定华北克拉通过渡带的岩石圈地幔演化，为华北克拉通破坏机制和动力学过程提供深部约束。

华北克拉通经历了破坏。太行山构造带为华北克拉通东部破坏区与西部稳定区的过渡带。河南鹤壁位于太行山过渡带上，产出有金伯利岩。在鹤壁地区金伯利岩中发现了大量的石榴石相深源地幔包体。本研究从地幔包体中分选出了橄榄石、镁铝榴石、铬尖晶石和斜方辉石等重砂矿物。这些地幔矿物携带有岩石圈地幔的丰富信息。.本研究以地幔包体为研究对象，在岩相学研究的基础上，通过对地幔重砂矿物的矿物化学和微量元素研究，获得了鹤壁地区的地幔性质、温压条件、地幔交代机理等信息。并与鹤壁地区新生代尖晶石相浅源地幔包体相对比，确定华北克拉通过渡带的岩石圈地幔演化，为华北克拉通破坏机制和动力学过程提供深部约束。.本文研究了石榴石二辉橄榄岩包体中的镁橄榄石和镁铝榴石的矿物化学特征。金伯利岩中地幔包体的镁橄榄石I(Mg#)为91.7±0.2 (n=69)。与鹤壁地区尖晶石相方辉橄榄岩相比，I(Mg#) 略偏小，指示二辉橄榄岩经历的熔融程度较低，具有过渡型地幔的特征。橄榄石-石榴石矿物温压计计算表明，包体压力在1.7~2.5 GPa之间（55~80 km），温度在641~1055 ℃之间，对应的大地热流值为50~60 mW/m2，甚至更高。指示金伯利岩侵位时对应于较高的大地热流条件。根据Grutter的镁铝榴石划分方案，镁铝榴石主要划分为G9型、G3和G4型，其中G3和G4型镁铝榴石记录了岩石圈地幔被交代的过程。根据温压条件及岩石圈地幔性质，推测认为鹤壁地区不具有形成金刚石矿的深部地质条件。.名义无水矿物（NAMs）中的结构水被证明是形成软流圈热液流体的主要来源。通过电子探针和显微傅里叶变换红外光谱等手段，对地幔包体中NAMs（主要为橄榄石、单斜辉石、斜方辉石和石榴石）的主量元素及红外吸收光谱进行了测定，获得了NAMs所对应的含水量等信息。土门橄榄石含水量在 37.33±66.10 ppm，尚峪橄榄石含水量在72.71±89.08 ppm，上峪单斜辉石249.45±199.51；土门石榴子石 49.48±45.19 ppm。.首次从河南鹤壁地区蒋家顶金伯利岩携带的橄榄岩捕虏体中分选出了铁质小球。根据铁质小球的来源、形态和成分特征，本研究推测小球是捕虏体中辉石绝热减压少量熔融的产物。