山西呂梁雜巖巖漿混合作用及界河口群形成背景
發(fā)布時間：2018-08-06 15:32
【摘要】：近年來,關(guān)于華北克拉通中部造山帶在古元古代時期的構(gòu)造演化尚存在很多爭議。呂梁雜巖體是華北中部造山帶的重要組成部分,發(fā)育新太古代末到古元古代末的多期花崗類巖石,基性巖侵入體和火山-沉積巖系。本文對其中發(fā)生的巖漿混合作用區(qū)域巖石和界河口群進行了研究。呂梁雜巖巖漿混合作用發(fā)生的時代與背景如何;對于反映中部帶構(gòu)造演化有何指示意義;以及界河口群的形成時代和物質(zhì)來源,是本文要討論的主要問題。本文關(guān)于巖漿混合作用的研究區(qū)域巖體主要為斜長角閃巖,片麻巖,對巖漿巖的鋯石進行LA-ICP-MS U-Pb定年表明,斜長角閃巖和片麻巖樣品的形成年齡分別為2104Ma和2147Ma,這兩個樣品的采樣點均為明顯的巖漿混合作用區(qū)域。據(jù)此我們推斷,巖漿混合作用發(fā)生于～2.1Ga。地球化學分析表明,基性巖樣品呈平坦的稀土配分模式,總稀土含量以及輕稀土富集程度很低,無明顯負Eu異常;巖石相對富集Cs、Rb、Ba、K等大離子親石元素,虧損Nb、Ta、P、Ti等高場強元素,Zr、Hf有負異常,為板內(nèi)亞堿性拉斑玄武巖。酸性巖樣品輕重稀土分餾明顯,Eu異常呈現(xiàn)正異常與負異常兩種模式。樣品富集Rb、Th、U、Pb、Zr和Hf,而虧損Nb、Ta、P、Ti等高場強元素,為A1型花崗巖,指示華北克拉通中部帶在～2.1Ga為大陸裂谷環(huán)境。界河口群變質(zhì)沉積巖以石英云母片巖與變質(zhì)砂巖為主,三個樣品的碎屑鋯石最小年齡峰分別為2000Ma,2048Ma和2071Ma。我們根據(jù)它們得到的加權(quán)平均年齡～2.0Ga限定了界河口群變質(zhì)沉積巖原巖的最大沉積年齡。地球化學分析表明,變質(zhì)沉積巖樣品相對富集Cs、Rb、K等大離子親石元素,虧損Ba、Nb、P、Ti等元素,大多數(shù)樣品形成于大陸島弧或活動大陸邊緣構(gòu)造背景。我們認為很有可能為弧后盆地環(huán)境。將界河口群沉積巖與西部陸塊孔茲巖帶的碎屑鋯石年齡數(shù)據(jù)進行投圖對比分析,得到了相似的年齡分布。而與TNCO和東部陸塊碎屑鋯石具有明顯差別。因此我們傾向于界河口群與東部陸塊和中部造山帶不是同源的,而是與西部陸塊孔茲巖帶相同起源,俯沖方向應為向東。界河口群為表殼巖,普遍遭受了角閃巖相的變質(zhì)作用,我們在龐泉溝剖面未觀察到上述表殼巖,從所測試的樣品看,無論是片麻巖還是斜長角閃巖,其鋯石都有明顯的巖漿鋯石特征。特別是片麻巖樣品,鋯石形態(tài)與花崗巖中的鋯石十分相似,未見具搬運特征的鋯石。兩個基性巖的形成年齡分別為～1.91Ga、～1.94Ga,而片麻巖樣品14PQG03的核部年齡為～2.12Ga,邊部年齡為～1.92Ga,前者侵入后者,在～1.92Ga經(jīng)歷一期變質(zhì)作用。綜合上述特征,我們認為,龐泉溝地區(qū)不存在代表表殼巖系的界河口群。華北中部在～2.1Ga處于大陸裂谷環(huán)境,在此之后逐漸轉(zhuǎn)變?yōu)橄驏|的俯沖島弧環(huán)境,并且最早在～2.0Ga,在呂梁地區(qū)的弧后盆地環(huán)境開始了界河口群碎屑物質(zhì)的沉積。兩個基性巖墻樣品指示了俯沖所形成的弧后盆地。
[Abstract]:In recent years, there are still many controversies about the tectonic evolution of the central North China Craton orogenic belt during the Paleoproterozoic period. The Lv Liang complex is an important part of the orogenic belt in the central part of North China. It develops multi-stage granitic rocks from the late NeoArchean to the late Gu Yuan, basic rock intrusions and volcanic-sedimentary rock series. In this paper, the rock and estuarine group in the magmatic mixing area are studied. The main problems to be discussed in this paper are the age and background of magmatic mixing in the Lv Liang complex, the indicative significance for reflecting the tectonic evolution of the central belt, and the formation age and material source of the boundary estuary group. In this paper, the magmatic mixing study area is mainly composed of amphibolite and gneiss. The LA-ICP-MS U-Pb dating of zircon from magmatic rocks shows that, The age of formation of amphibolite and gneiss samples is 2104Ma and 2147 Ma.The sampling points of these two samples are both magmatic mixing zones. Based on this, we infer that magmatic mixing occurred at 2.1 Ga. Geochemical analysis shows that the basic rock samples show a flat REE distribution pattern, the total REE content and the LREE enrichment degree are very low, and there is no obvious negative EU anomaly. There is negative anomaly in the depleted NbTa-Ta-Pa-Ti isoprestic field strength element, which is subalkaline tholeiitic basalt in the plate, and there is a negative anomaly in the zirconium HF. The fractionation of heavy and heavy rare earth elements in acid rock samples shows positive and negative EU anomalies. The samples are rich in RbPU UPbN Zr and HF, but depleted in high field strength elements such as NbCU TaPnti, which indicate that the central North China Craton belt is a continental rift environment at 2.1Ga in the North China Craton zone, which is characterized by a high field strength element, such as A 1 type granite. The metamorphic sedimentary rocks of Jiegou Group are mainly quartz mica schist and metamorphic sandstone. The minimum age peaks of zircon for the three samples are 2000 Ma 2048 Ma and 2071 Ma respectively. According to their weighted mean age of 2.0 Ga, we define the maximum sedimentary age of the metamorphic sedimentary rocks of the boundary estuary group. Geochemical analysis shows that metamorphic sedimentary rocks are relatively enriched in large ion lithophile elements, such as Csln Rbnk, and depleted in elements such as BaNbPU Ti. Most of the samples were formed in continental island arcs or active continental margin tectonic setting. We believe that it is very possible for the back-arc basin environment. The age data of detrital zircons from the sedimentary rocks of the estuarine group and the korzite belt of the western continental block are compared and analyzed, and a similar age distribution is obtained. But it is different from TNCO and the eastern continental block detrital zircon. Therefore, we tend to suggest that the boundary estuary group is not homologous with the eastern continental block and the central orogenic belt, but with the same origin as the western continental block khontzite belt, and the subduction direction should be eastward. The Jiegou Group is a epidermal rock and has generally suffered from the metamorphism of amphibolite facies. We have not observed the above-mentioned epidermal rocks in the Pang Quangou section. From the samples tested, whether they are gneiss or amphibolite, The zircon has obvious magmatic zircon characteristics. Especially for gneiss samples, the morphology of zircon is very similar to that of zircon in granite, and there is no zircon with transport characteristics. The age of formation of the two basic rocks is 1.91 Ga / 1.94 Ga, while the nuclear age of gneiss is 2.12 Ga and the edge age is 1.92 Ga. The former intruded into the latter and underwent one stage metamorphism at 1.92 Ga. Based on the above characteristics, we believe that there is no estuarine group in Pangquangou area, which represents the epidermal rock series. The central part of North China is located in the continental rift environment of 2.1Ga, then gradually transformed into an eastward subduction island arc environment, and the depositional depositions of clastic materials of the boundary estuarine group began to occur in the back-arc basin environment of Lv Liang area as early as 2.0 Ga. Two base-wall samples indicate the back-arc basin formed by subduction.
【學位授予單位】：南京大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P588.11;P542
本文編號：2168164
[Abstract]:In recent years, there are still many controversies about the tectonic evolution of the central North China Craton orogenic belt during the Paleoproterozoic period. The Lv Liang complex is an important part of the orogenic belt in the central part of North China. It develops multi-stage granitic rocks from the late NeoArchean to the late Gu Yuan, basic rock intrusions and volcanic-sedimentary rock series. In this paper, the rock and estuarine group in the magmatic mixing area are studied. The main problems to be discussed in this paper are the age and background of magmatic mixing in the Lv Liang complex, the indicative significance for reflecting the tectonic evolution of the central belt, and the formation age and material source of the boundary estuary group. In this paper, the magmatic mixing study area is mainly composed of amphibolite and gneiss. The LA-ICP-MS U-Pb dating of zircon from magmatic rocks shows that, The age of formation of amphibolite and gneiss samples is 2104Ma and 2147 Ma.The sampling points of these two samples are both magmatic mixing zones. Based on this, we infer that magmatic mixing occurred at 2.1 Ga. Geochemical analysis shows that the basic rock samples show a flat REE distribution pattern, the total REE content and the LREE enrichment degree are very low, and there is no obvious negative EU anomaly. There is negative anomaly in the depleted NbTa-Ta-Pa-Ti isoprestic field strength element, which is subalkaline tholeiitic basalt in the plate, and there is a negative anomaly in the zirconium HF. The fractionation of heavy and heavy rare earth elements in acid rock samples shows positive and negative EU anomalies. The samples are rich in RbPU UPbN Zr and HF, but depleted in high field strength elements such as NbCU TaPnti, which indicate that the central North China Craton belt is a continental rift environment at 2.1Ga in the North China Craton zone, which is characterized by a high field strength element, such as A 1 type granite. The metamorphic sedimentary rocks of Jiegou Group are mainly quartz mica schist and metamorphic sandstone. The minimum age peaks of zircon for the three samples are 2000 Ma 2048 Ma and 2071 Ma respectively. According to their weighted mean age of 2.0 Ga, we define the maximum sedimentary age of the metamorphic sedimentary rocks of the boundary estuary group. Geochemical analysis shows that metamorphic sedimentary rocks are relatively enriched in large ion lithophile elements, such as Csln Rbnk, and depleted in elements such as BaNbPU Ti. Most of the samples were formed in continental island arcs or active continental margin tectonic setting. We believe that it is very possible for the back-arc basin environment. The age data of detrital zircons from the sedimentary rocks of the estuarine group and the korzite belt of the western continental block are compared and analyzed, and a similar age distribution is obtained. But it is different from TNCO and the eastern continental block detrital zircon. Therefore, we tend to suggest that the boundary estuary group is not homologous with the eastern continental block and the central orogenic belt, but with the same origin as the western continental block khontzite belt, and the subduction direction should be eastward. The Jiegou Group is a epidermal rock and has generally suffered from the metamorphism of amphibolite facies. We have not observed the above-mentioned epidermal rocks in the Pang Quangou section. From the samples tested, whether they are gneiss or amphibolite, The zircon has obvious magmatic zircon characteristics. Especially for gneiss samples, the morphology of zircon is very similar to that of zircon in granite, and there is no zircon with transport characteristics. The age of formation of the two basic rocks is 1.91 Ga / 1.94 Ga, while the nuclear age of gneiss is 2.12 Ga and the edge age is 1.92 Ga. The former intruded into the latter and underwent one stage metamorphism at 1.92 Ga. Based on the above characteristics, we believe that there is no estuarine group in Pangquangou area, which represents the epidermal rock series. The central part of North China is located in the continental rift environment of 2.1Ga, then gradually transformed into an eastward subduction island arc environment, and the depositional depositions of clastic materials of the boundary estuarine group began to occur in the back-arc basin environment of Lv Liang area as early as 2.0 Ga. Two base-wall samples indicate the back-arc basin formed by subduction.
【學位授予單位】：南京大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P588.11;P542
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