胶东地区中生代中基性岩墙地球化学研究
发布时间：2018-08-22 15:54
【摘要】：中国东部显生宙以来发生了多次重大的地质事件,如华北克拉通的破坏,扬子板块与华北克拉通的拼合,古太平洋板块的俯冲。与此同时,岩浆作用在中国东部广泛发育,尤其是中生代时期。这些岩浆岩的源区性质、成岩过程及其地球化学动力学背景对于理解中国东部中生代岩石圈地幔的属性及其演化提供了重要的制约。胶东半岛位于中国中央造山带(秦岭-大别-苏鲁造山带)的东部,东临渤海湾,北接华北克拉通,南部毗邻苏鲁造山带,是研究深部岩石圈地幔组成和演化的天然实验室。本文以胶东半岛玲珑地区和乳山地区早白垩世中基性岩墙为研究对象,分别进行了详细的岩相学、锆石U-Pb年龄、全岩主微量元素以及Sr-Nd-Pb放射性成因同位素分析,通过结合整个山东省中生代幔源侵入岩与火山岩数据,进一步探讨研究区中生代岩石圈地幔的组成特征。玲珑地区属于胶北地体,位于胶东半岛北部,是华北克拉通的一部分。中基性岩墙的主要岩石类型为辉绿岩、煌斑岩和闪长玢岩。LA-ICPMS锆石U-Pb定年结果显示,其形成时代为121.3 ± 3.8～123.5 ± 4.6 Ma。它们具有较低的SiO2(44.53～55.05wt.%)和较高的MgO(6.77～13.26wt%,Mg#= 64～73)含量;高的K2O(1.5～4.4wt.%)含量,高Cr(383～818ppm)、Ni(135～328ppm)含量以及高的K20/Na2O比值(0.60～1.82)。在硅碱图(TAS)上主要落入辉长岩范围内。乳山地区位于胶东半岛南部的苏鲁造山带内,是大陆碰撞造山带的一部分。基性岩墙以闪长玢岩为主,LA-ICPMS锆石U-Pb定年结果表明,其形成时代为107.6±1.6～118.2±3.3Ma。与玲珑地区相比,乳山地区的样品具有较大变化范围的SiO2(45.54～60.66 wt.%)和 MgO(3.15～12.73 wt.%,Mg#= 58～76)含量。它们具有高K20(1.3～4.4 wt.%)含量,高 Cr(108～1176 ppm)、Ni(18.5～313 ppm)含量以及高的K2O/Na2O(0.47～1.71)比值。在硅碱图(TAS)上主要落入正长闪长岩、闪长岩范围内。在微量元素和稀土元素配分图上,两个地区的中基性岩墙都富集大离子亲石元素(LILE)和轻稀土元素(LREE),亏损高场强元素(HFSE)和重稀土元素(HREE),表现出明显的"弧型"微量元素分配特征。玲珑地区中基性岩墙具有较高的全岩初始87Sr/86Sr(0.7092～0.7112)、较低的εNd(t)值(-12.3～-19.6)和初始206Pb/204Pb(17.23～17.53),207Pb/204Pb(15.50～15.57),208Pb/204Pb(37.77～38.18)。与玲珑地区相比,乳山地区样品具有略低的初始87Sr/86Sr(0.7075～0.7094)、低放射性成因εNd(t)值(-10.9～-15.7)和较低的初始206Pb/204Pb(16.74～17.32),207Pb/204Pb(15.36～15.46),208Pb/204Pb(36.89～37.63)。这些地球化学特征表明,胶东地区的中基性岩墙起源于富集地幔。较低的TiO2和(Fe2O3)T含量表明它们的源区是岩石圈地幔而不是软流圈地幔。在Sr-Nd-Pb同位素表现为更接近于华北克拉通岩石圈地幔,而远离扬子克拉通岩石圈地幔。同时,初始87Sr/86Sr比值和初始εNd(t)值并不随Mg#值的变化而变化,表明其在上升过程中受到的地壳混染作用不显著,暗示着这些具有"弧型"微量元素分配特征的胶东中基性岩墙的岩浆源区为受到了交代作用的华北岩石圈地幔。另外,全岩Nb/U、Ce/Pb比值指示地幔源区有上地壳物质的贡献,其两阶段全岩Nd模式年龄与苏鲁造山带超高压变质岩一致。综合以上地球化学特点表明胶东地区中基性岩墙的地幔源区受到了扬子陆壳物质的改造。从山东省中生代幔源中基性岩浆作用整体来看,研究区的中基性岩墙地球化学特征与靠近苏鲁造山带的沂南辉长岩、方城玄武岩和胶莱盆地基性火山岩比较接近,而与华北克拉通内部济南邹平地区的基性岩有明显的差异。前者具有EM2型的富集特征而后者显示EM1型的富集特征。我们认为扬子板块的俯冲作用是两者差异的主要原因,靠近苏鲁造山带的胶东地区以及鲁西东部地区受到俯冲交代作用较大,远离造山带的华北克拉通内部受到俯冲交代作用较小。然而,从时代上来看大规模的岩浆作用形成在早白垩世,比扬子板块俯冲/碰撞作用晚约90 Ma,暗示这次造山事件与胶东地区的岩石圈地幔的熔融存在明显的时代差异。鲁西地区中生代的幔源岩浆主要集中于185～177 Ma(软流圈起源)和144～101 Ma(岩石圈起源),而胶东地区的幔源岩浆主要集中于134～102 Ma(岩石圈起源)和95～73 Ma(软流圈起源),这样的年龄分布特征与古太平洋板块的俯冲/后撤作用一致,在古太平洋平板俯冲、后撤作用下,中国东部从挤压背景转变为拉张背景,减压部分熔融是山东省早白垩世幔源岩浆作用的主要机制。
[Abstract]:Since the Phanerozoic, many important geological events have taken place in eastern China, such as the destruction of the North China Craton, the convergence of the Yangtze plate and the North China Craton, and the subduction of the Paleo-Pacific Plate. The Jiaodong Peninsula is located in the eastern part of China's Central Orogenic Belt (Qinling-Dabie-Sulu orogenic belt), east of Bohai Bay, north of North China craton, south of Sulu orogenic belt. It is a study of deep lithospheric mantle composition and evolution. Natural Laboratory of Chemistry. In this paper, the early Cretaceous intermediate-basic dykes in Linglong and Rushan areas of the Jiaodong Peninsula are studied. Detailed petrography, zircon U-Pb age, major trace elements and Sr-Nd-Pb radiogenic isotope analysis of the whole rock are carried out. The data of Mesozoic mantle-derived intrusive rocks and volcanic rocks in Shandong Province are combined. Linglong area belongs to Jiaobei terrane, located in the northern part of Jiaodong Peninsula, and is a part of the North China Craton. The main rock types of intermediate-basic dykes are diabase, lamprophyre and diorite porphyry. LA-ICPMS zircon U-Pb dating results show that the age of the formation of Linglong area is 121.3 [3.8-123]. They have lower SiO2 (44.53-55.05 wt.) and higher MgO (6.77-13.26 wt%, Mg # = 64-73), higher K2O (1.5-4.4 wt.), higher Cr (383-818 ppm), Ni (135-328 ppm) and higher K20/Na2O ratio (0.60-1.82) in the silica-alkali map (TAS). The Sulu orogenic belt in the southern part of the peninsula is a part of the continental collision orogenic belt. The basic dykes are mainly diorite porphyrite. The LA-ICPMS zircon U-Pb dating results show that the ages of these dykes are 107.6 65507 They have high K20 (1.3-4.4 wt%) content, high Cr (108-1176 ppm), Ni (18.5-313 ppm) content and high K2O/Na2O (0.47-1.71) ratio. They fall mainly into syenite diorite and diorite on the silica-alkali map (TAS). On the maps of trace elements and rare earth elements, the intermediate-basic dikes in both areas are found. Rich in large ion lithophile elements (LILE) and light rare earth elements (LREE), depleted high field strength elements (HFSE) and heavy rare earth elements (HREE), showing obvious "arc" trace element distribution characteristics. Medium-basic dykes in Linglong area have higher initial 87Sr/86Sr (0.7092-0.7112) of the whole rock and lower initial values of epsilon Nd (t) (-12.3-19.6) and 206Pb/204Pb (17.6). Compared with Linglong area, Rushan area samples have slilower initial 87Sr/86Sr (0.7075-0.7094), low initial values of 87Sr/86Sr (0.7075-0.7094), low radiogenicvalues of epsilNd (t) (-10.9-15.7) and low initial values of 206Pb/204Pb (16.74-17.32), 207Pb/204Pb (16.74-17.32), 207Pb/204Pb (15.36-15.36-15.46), 208Pb (36-15.36-15.46), 208Pb (36-15.36-15.46), 208Pb (36-18.46), 20 8 Pb (36-8 Pb (36-18.89-89.89) and 208Pb (36/89.8 Pb (36 37.63). These geochemical characteristics indicate that the intermediate-basic dykes in the eastern Shandong area originate from the enriched mantle. The lower content of TiO2 and (Fe2O3) T indicates that their source areas are lithospheric mantle rather than asthenospheric mantle. The Sr-Nd-Pb isotope shows that they are closer to the lithospheric mantle of the North China Craton and farther from the lithospheric mantle of the Yangtze craton. The initial 87Sr/86Sr ratio and initial epsilon Nd(t) values do not change with Mg# values, indicating that the crustal contamination during the ascent is not significant, suggesting that the magma source of these "arc-shaped" trace element distribution characteristics of the intermediate-basic dikes in eastern Jiaodong is the metasomatic North China lithospheric mantle. The ratios indicate that the upper crustal material contributes to the mantle source area, and the two-stage Nd model ages of the whole rock are consistent with the UHP metamorphic rocks in the Sulu orogenic belt. The geochemical characteristics of the intermediate-basic dykes in the study area are similar to those of the Yinan gabbro near the Sulu orogenic belt, Fangcheng basalt and the basic volcanic rocks in the Jiaolai basin, but different from those of the Zouping area in Jinan, North China craton. It is believed that the subduction of the Yangtze Plate is the main reason for the difference between the two. The eastern part of Jiaodong and the eastern part of Shandong are subjected to greater subduction metasomatism near the Sulu orogenic belt and the inner part of the North China craton far from the orogenic belt is subduction metasomatism less. It is about 90 Ma later than the subduction/collision of the Yangtze Plate, suggesting that the orogenic event is obviously different from the melting of the lithospheric mantle in eastern Shandong. Mesozoic mantle-derived magma in Western Shandong is mainly concentrated in 185-177 Ma (asthenospheric origin) and 144-101 Ma (lithospheric origin), while mantle-derived magma in eastern Shandong is mainly concentrated in 185-177 Ma (asthenospheric origin) and 144- 34-102 Ma (lithospheric origin) and 95-73 Ma (asthenospheric origin), such age distribution characteristics are consistent with the subduction/retraction of the Paleo-Pacific Plate. Under the subduction and retraction of the Paleo-Pacific Plate, the eastern part of China changed from compressive background to extensional background, and the decompressive partial melting was the main mantle-derived magmatism in Shandong Province during the Early Cretaceous. Mechanism.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P588.124;P534.5
，
本文编号：2197585
[Abstract]:Since the Phanerozoic, many important geological events have taken place in eastern China, such as the destruction of the North China Craton, the convergence of the Yangtze plate and the North China Craton, and the subduction of the Paleo-Pacific Plate. The Jiaodong Peninsula is located in the eastern part of China's Central Orogenic Belt (Qinling-Dabie-Sulu orogenic belt), east of Bohai Bay, north of North China craton, south of Sulu orogenic belt. It is a study of deep lithospheric mantle composition and evolution. Natural Laboratory of Chemistry. In this paper, the early Cretaceous intermediate-basic dykes in Linglong and Rushan areas of the Jiaodong Peninsula are studied. Detailed petrography, zircon U-Pb age, major trace elements and Sr-Nd-Pb radiogenic isotope analysis of the whole rock are carried out. The data of Mesozoic mantle-derived intrusive rocks and volcanic rocks in Shandong Province are combined. Linglong area belongs to Jiaobei terrane, located in the northern part of Jiaodong Peninsula, and is a part of the North China Craton. The main rock types of intermediate-basic dykes are diabase, lamprophyre and diorite porphyry. LA-ICPMS zircon U-Pb dating results show that the age of the formation of Linglong area is 121.3 [3.8-123]. They have lower SiO2 (44.53-55.05 wt.) and higher MgO (6.77-13.26 wt%, Mg # = 64-73), higher K2O (1.5-4.4 wt.), higher Cr (383-818 ppm), Ni (135-328 ppm) and higher K20/Na2O ratio (0.60-1.82) in the silica-alkali map (TAS). The Sulu orogenic belt in the southern part of the peninsula is a part of the continental collision orogenic belt. The basic dykes are mainly diorite porphyrite. The LA-ICPMS zircon U-Pb dating results show that the ages of these dykes are 107.6 65507 They have high K20 (1.3-4.4 wt%) content, high Cr (108-1176 ppm), Ni (18.5-313 ppm) content and high K2O/Na2O (0.47-1.71) ratio. They fall mainly into syenite diorite and diorite on the silica-alkali map (TAS). On the maps of trace elements and rare earth elements, the intermediate-basic dikes in both areas are found. Rich in large ion lithophile elements (LILE) and light rare earth elements (LREE), depleted high field strength elements (HFSE) and heavy rare earth elements (HREE), showing obvious "arc" trace element distribution characteristics. Medium-basic dykes in Linglong area have higher initial 87Sr/86Sr (0.7092-0.7112) of the whole rock and lower initial values of epsilon Nd (t) (-12.3-19.6) and 206Pb/204Pb (17.6). Compared with Linglong area, Rushan area samples have slilower initial 87Sr/86Sr (0.7075-0.7094), low initial values of 87Sr/86Sr (0.7075-0.7094), low radiogenicvalues of epsilNd (t) (-10.9-15.7) and low initial values of 206Pb/204Pb (16.74-17.32), 207Pb/204Pb (16.74-17.32), 207Pb/204Pb (15.36-15.36-15.46), 208Pb (36-15.36-15.46), 208Pb (36-15.36-15.46), 208Pb (36-18.46), 20 8 Pb (36-8 Pb (36-18.89-89.89) and 208Pb (36/89.8 Pb (36 37.63). These geochemical characteristics indicate that the intermediate-basic dykes in the eastern Shandong area originate from the enriched mantle. The lower content of TiO2 and (Fe2O3) T indicates that their source areas are lithospheric mantle rather than asthenospheric mantle. The Sr-Nd-Pb isotope shows that they are closer to the lithospheric mantle of the North China Craton and farther from the lithospheric mantle of the Yangtze craton. The initial 87Sr/86Sr ratio and initial epsilon Nd(t) values do not change with Mg# values, indicating that the crustal contamination during the ascent is not significant, suggesting that the magma source of these "arc-shaped" trace element distribution characteristics of the intermediate-basic dikes in eastern Jiaodong is the metasomatic North China lithospheric mantle. The ratios indicate that the upper crustal material contributes to the mantle source area, and the two-stage Nd model ages of the whole rock are consistent with the UHP metamorphic rocks in the Sulu orogenic belt. The geochemical characteristics of the intermediate-basic dykes in the study area are similar to those of the Yinan gabbro near the Sulu orogenic belt, Fangcheng basalt and the basic volcanic rocks in the Jiaolai basin, but different from those of the Zouping area in Jinan, North China craton. It is believed that the subduction of the Yangtze Plate is the main reason for the difference between the two. The eastern part of Jiaodong and the eastern part of Shandong are subjected to greater subduction metasomatism near the Sulu orogenic belt and the inner part of the North China craton far from the orogenic belt is subduction metasomatism less. It is about 90 Ma later than the subduction/collision of the Yangtze Plate, suggesting that the orogenic event is obviously different from the melting of the lithospheric mantle in eastern Shandong. Mesozoic mantle-derived magma in Western Shandong is mainly concentrated in 185-177 Ma (asthenospheric origin) and 144-101 Ma (lithospheric origin), while mantle-derived magma in eastern Shandong is mainly concentrated in 185-177 Ma (asthenospheric origin) and 144- 34-102 Ma (lithospheric origin) and 95-73 Ma (asthenospheric origin), such age distribution characteristics are consistent with the subduction/retraction of the Paleo-Pacific Plate. Under the subduction and retraction of the Paleo-Pacific Plate, the eastern part of China changed from compressive background to extensional background, and the decompressive partial melting was the main mantle-derived magmatism in Shandong Province during the Early Cretaceous. Mechanism.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P588.124;P534.5
，
本文编号：2197585
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