排序方式: 共有34条查询结果,搜索用时 15 毫秒
31.
中生代苏—鲁活动大陆边缘榴辉岩、煌斑岩、金矿及富集地幔间的成因联系 总被引:20,自引:2,他引:20
海西期末形成的初始欧亚板块,从三叠纪(250Ma)开始,便与古太平洋板块-太平洋板块发生强烈的挤压碰撞作用和俯冲作用,及由此引起的远距离效应使中国广大的东部地区从中生代开始成为活动大陆边缘,俯冲作用及构造环境的演化是控制胶东地体等大多数中生代榴0辉岩等变质岩类,花岗岩类,火山岩类,煌斑岩类以及金等矿床形成和使它们出露地表的重要因素,胶东地体中富钾的钙-碱性煌斑岩类的特征与其它活动大陆边缘和造山带中金矿有关的煌斑岩很相似,例如呈脉状产出,晚期侵位,强烈的自变质,富含大离子亲石元素(LILE)和挥发分,高的金含量,高的LREE/HREE和^87Sr/^86Sr比值,低的^143Nd/^144Nd比值,与花岗岩类,橄榄安粗岩,酸性脉岩以及热液金矿床的密切共生及它们这间与富集地幔楔的成因联系等,这些都表明它们与板块或板片俯冲过程中的去气,去碱,去ILE作用或壳-幔物质交换作用及由此形成的富集地幔楔有着紧密的联系。 相似文献
32.
Subsequent to high-pressure and temperature metamorphism of the axial zone of the Variscan foldbelt in central Europe at ca. 340 to 330 Ma, formation of lamprophyre dikes during transtensional tectonics may be viewed as the beginning of the post-collisional stage of the orogeny. We report the results of 40Ar/39Ar mica dating, major and trace element data, and isotope compositions for lamprophyre and rhyodacite samples from the southern Black Forest. The chemical compositions of these rocks shed light on the upper mantle and crust at the end of the Variscan orogeny. 40Ar/39Ar plateau ages for four phlogopite–biotite separates from lamprophyres indicate emplacement at 332 to 314 Ma. This event coincides with melting of the crust as indicated by 40Ar/39Ar biotite plateau ages of ca. 332 Ma for rhyodacite dikes which are probably related to coeval undeformed granites. Incompatible trace element patterns of the lamprophyre samples reveal the characteristics of evolved continental crust and are interpreted as evidence for melting of sediment in a subduction-modified mantle. Nd, Sr, and Pb isotope compositions indicate an enriched mantle source with Nd-values of −1.5 to −6.8 which is similar to Variscan crust. Significant contamination of the lamprophyric melts by Variscan crust can be ruled out as mantle-derived phlogopite phenocrysts have similar Nd-values as in the whole-rock samples. We propose that the isotope compositions and incompatible trace element characteristics of the lamprophyres were predominantly inherited from melted sediment. The isotope compositions of Variscan lamprophyres from western Europe suggest that enriched upper mantle was only partly delaminated when ascending hot mantle triggered melting of the lower crust, as has been invoked for the origin of post-collisional granites. The isotope compositions of Tertiary basalts and mantle xenoliths indicate a depleted upper mantle under western Europe, implying that the enriched Variscan material was efficiently removed and mixed into the convecting mantle. 相似文献
33.
34.
Cenozoic lamprophyre dykes occur widely along the Ailao-Shan-Red-River (ASRR) shear zone related to the Indian–Eurasian collision. Two generations of lamprophyres have been found at the Daping gold deposit in the southern part of the ASRR shear zone and have been investigated by using phlogopite 40Ar/39Ar dating and whole-rock major and trace element as well as Sr and Nd isotope geochemical analyses. The 40Ar/39Ar plateau ages of phlogopite from the two generations of lamprophyres bracket the emplacement of auriferous quartz veins in the Daping deposit between 36.8 ± 0.2 Ma and 29.6 ± 0.2 Ma, consistent with the timing of gold mineralization in other parts of the ASRR shear zone. Geochemical data suggest that these lamprophyres most likely originated from a subduction-modified mantle source consisting of phlogopite-bearing spinel lherzolite, which underwent partial melting with contributions from crust materials. In particular, the second generation lamprophyres are characterized by more primitive geochemical features than the first, suggesting that secular source evolution probably resulted from post-collisional slab break-off mantle convection and remelting from ascending asthenosphere after subducted lithosphere break-off. Widespread and episodic occurrences of lamprophyres and other potassic volcanism in the eastern Tibetan Plateau were probably related to the onset of transtensional tectonics along the ASRR shear zone during Oligocene. A genetic model involving transtensional tectonics has been proposed for lamprophyres and gold mineralization in the ASRR shear zone. 相似文献