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21.
东秦岭-桐柏-大别山碰撞造山带北部早古生代变质火山岩系特征及其形成环境 总被引:1,自引:0,他引:1
东秦岭-桐柏-大别山碰撞造山带北部早古生代变质火山岩系具有与大洋拉斑玄武岩相似的岩石学、岩石化学及微量元素特征,与镁铁质、超镁铁质岩块、辉绿岩墙群以及变质的沉积岩断片共同构成蛇绿混杂岩带。它们原来形成在华北断块南部大陆边缘的早古生代边缘海盆地的洋壳上。这个边缘海盆地的产生与华南洋壳海域岩石圈断块在晚前寒武纪时期向北俯冲有关,是震旦纪古边缘海继续扩张的结果。在加里东末期到海西早期,扬子断块与华北断块发生碰撞,边缘海闭合。 相似文献
22.
Houssa Ouali Bernard Briand Jean-Luc Bouchardon Paul Capiez 《Comptes Rendus Geoscience》2003,335(5):425-433
In southeastern Central Morocco, the Bou-Acila volcanic complex is considered of Cambrian age. In spite of low-grade metamorphic effect, initial volcanic texture and mineralogy can be recognized and volcanic rocks are dominated by dolerites and porphyric dolerites. The initial mineralogy is composed of plagioclases, pyroxenes and dark minerals. A secondary mineral assemblage is composed of albite, epidote, chlorite and calcite. According to their immobile elements compositions, the southeastern central Morocco metavolcanites are of within-plate continental tholeiites. This volcanism and those recognized in many other areas in Morocco confirm a Cambrian extensive episode within the Gondwana supercontinent. To cite this article: H. Ouali et al., C. R. Geoscience 335 (2003).To cite this article: H. Ouali et al., C. R. Geoscience 335 (2003). 相似文献
23.
东昆仑山清水泉镁铁质-超镁铁质岩的地球化学特征 总被引:12,自引:0,他引:12
东昆仑清水泉地区发育—套镁铁质—超镁铁质岩块组合,玄武岩Ti2O含量平均为2.11%,∑LREE/∑HREE=4.64~7.58,(La/Lu)N平均值705,稀土配分曲线平缓右倾,δEu平均值1.08;玄武岩大离子亲石元素(K、Rb、Ba、Th)富集,Sr相对亏损,高场强元素(Nb、Ta、Zr、Hf、Yb)为负异常,Th/Ta平均值51.03,(La/Nb)N=1.44~4.25,Zr/Nb=14.53~17.71,Zr/Y=4.68~6.79,Th/Yb、Ta/Yb和Ce/Yb平均值分别为6.50、0.20和23.61。这些特征显示大陆拉斑玄武岩的特征。不是蛇绿岩组成单元。 相似文献
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Katja Deckart Gilbert F raud Herv Bertrand 《Earth and Planetary Science Letters》1997,150(3-4):205-220
A detailed 40Ar/39Ar study, of mineral separates from the Jurassic Atlantic Continental Tholeiites (JACT) of Guyana (French Guyana and Surinam, South America), and Guinea (West Africa) related to the initial opening of the Central Atlantic, has been carried out. In French Guyana, plateau ages of 196.0 ± 5.7 Ma and 196.1 ± 7.5 Ma were obtained on single, small amphibole grains from NNW—SSE trending dykes. In Guinea, single biotite grains from intrusive formations from the Kakoulima and Fouta Djalon areas yielded plateau ages of 200.4 ± 0.2 Ma and 194.8 ± 0.5 Ma, concordant with high temperature apparent ages on other biotites. The bulk plagioclase samples display disturbed age spectra due to alteration and excess argon. However, intermediate temperature, weighted mean plagioclase ages are similar in both regions of Guyana and Guinea, ranging from 200.2 ± 2.4 Ma to 188.7 ± 1.9 Ma, partly in agreement with the amphibole and biotite data.
These data, combined with previous 40Ar/39Ar and U/Pb results from the northern part of the Central Atlantic margins, indicate intense magmatic activity distributed over a large area from Iberia to Liberia (ca. 4500 km long) for a short period of time (204-195 Ma, perhaps less for the bulk of the magmatism) during the initial break-up of Pangea continent. These data do not support an initiation of the magmatism from a radial volcano-tectonic system centred in the south of the region, as suggested by May [1], and the initial break-up seems to affect the whole Central Atlantic during a period of 9 Ma. 相似文献
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Gabbros at Purimetla occur in close association with the alkaline pluton. Petrography and petrochemistry of these gabbros
indicate their tholeiitic nature. Chemical variation of these tholeiites suggests that an initial undersaturated tholeiitic
magma yielded oversaturated fractions in the final stages of differentiation. Their regional distribution suggests that basic
magmatism preceded the emplacement of the alkaline rocks in the Prakasam alkaline province. 相似文献
28.
J. Escuder Viruete A. Díaz de Neira P.P. Herniz Huerta J. Monthel J. García Senz M. Joubert E. Lopera T. Ullrich R. Friedman J. Mortensen A. Prez-Estaún 《Lithos》2006,90(3-4):161-186
Located in the Cordillera Oriental of the Dominican Republic, the Early Cretaceous Los Ranchos Fm (LRF) comprises a > 3-km thick sequence of volcanic and volcaniclastic rocks with variable geochemical characteristics, which is intruded by tonalite batholiths, minor gabbro/diorite plutons and mafic dykes. From top to bottom, three main stratigraphic units have been mapped: upper basaltic, intermediate rhyodacitic and lower basaltic. Combined detailed mapping, stratigraphy, geochemistry, Rb–Sr/Sm–Nd isotopic studies and U–Pb/Ar–Ar geochronology show that the mafic rocks of the LRF include boninites and LREE-depleted island arc tholeiites (IAT) in the lower unit, both which appear genetically related, whereas normal IAT occur in the upper unit. The source for these rocks is thought to reflect variably depleted mantle, overprinted by a subduction zone component. Contemporaneous Aptian U–Pb zircon ages were obtained for a rhyodacite from the intermediate unit (116.0 ± 0.8 Ma) and a tonalite of the Zambrana batholith (115.5 ± 0.3 Ma) that intrudes the LRF. The similarity of trace element signatures in both units argues for genetic link between the felsic volcanics of the LRF and the tonalite plutonism. Low-K rhyolites and tonalite batholiths are interpreted as products of secondary melting at the base of thickened early arc crust. 40Ar/39Ar plateau ages of hornblende in most tonalites are Albian (109–106 Ma) and interpreted as final cooling ages, prior to unroofing and growth of unconformable overlying reef limestones of the Hatillo Fm (112–100 Ma). The LREE-depleted IAT and boninites of lower basaltic unit are interpreted to have formed during subduction zone initiation in the Caribbean Island arc, and the normal IAT of the upper unit are thought to represent the subsequent establishment of the volcanic front. 相似文献
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