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31.
陆相火山岩铜矿床成矿条件研究 总被引:1,自引:1,他引:1
研究陆相火山岩铜矿床的成矿条件,对于多发现新的铜矿资源有着重要的意义。本文就陆相火山岩型铜矿床的实际存在,大陆玄武岩型铜矿的成矿系列,大陆裂谷的成矿环境和热液成矿作用等方面进行讨论。 相似文献
32.
我国东部新生代玄武岩中深源岩石包体内的尖晶石类矿物属铬尖晶石和铁尖晶石,金伯利岩及其地幔岩包体和金刚石中的尖晶石类矿物主要为铝铬铁矿。玄武岩中橄榄岩类包体内的尖晶石比其辉石岩类包体中的尖晶石含Cr高,含Al低,这与Cr为相容元素、Al为不相容元素、玄武岩中橄榄岩类包体是上地幔部分熔融出玄武岩浆后的残留物及其上地幔岩石的捕虏体、而辉石岩类是玄武岩浆结晶的产物有关。玄武岩中深源岩石包体中的尖晶石明显地比金伯利岩中的粗晶、地幔岩石包体及金刚石中的尖晶石含Cr低,含Al高,其主要原因是前者比后者形成的压力低 相似文献
33.
洋岛,海山碳酸盐岩的沉积特征及其古地理意义 总被引:7,自引:1,他引:7
高出水面的洋岛和潜伏水下的海山普遍存在于现代地球表面的各大洋中,地质历史中存在的古洋岛和古海山也逐渐为人们所认识。笔者从地形特征,沉积学特征,成岩作用和生物学特征几个方面对洋岛,海山进行了分析,洋岛,海山通常具有洋岛型火山岩基底和碳酸盐盖层的双层式地层结构,具有低分异度,探讨了古洋岛,古海山的鉴别对于再造古海洋,古地理格局的现实意义。 相似文献
34.
We present the results of a detailed petrological study of a sparsely phyric basalt (MAPCO CH98-DR11) dredged along the Mid-Atlantic Ridge (30°41′N). The sample contains microphenocrysts of olivine that display four different rapid-growth morphologies. Comparison of these morphologies with those obtained in dynamic crystallization experiments allows us to constrain the thermal history of the sample. The dendritic morphology (swallowtail, chain and lattice olivine) is directly related to the final quenching during magma–seawater interaction. In contrast, the three other morphologies, namely the complex polyhedral crystal, the closed hopper and the complex swallowtail morphology result from several cycles of cooling–heating (corresponding to a maximum degree of undercooling of 20–25°C) during crystal growth. These thermal variations occurred before eruption and are interpreted to be the result of turbulent convection in a small magmatic body beneath the ridge. The results suggest that the Mid-Atlantic Ridge is underlain by a mush zone that releases batches of liquid during tectonic segregation. Aphyric basalts are emitted during eruptions controlled by the tectonic activity, whereas phyric basalts correspond to small fractions of magma from the mush zone mobilized by reinjections of primitive magmas. 相似文献
35.
Linda T Elkins-Tanton 《Earth and Planetary Science Letters》2004,222(1):17-27
Large volumes of mare basalts are present on the surface of the moon, located preferentially in large impact basins. Mechanisms relating impact basins and mare basalt eruptions have previously been suggested: lunar impacts removed low-density material that may have inhibited eruption, and created cracks for fluid flow [Icarus 139 (1999) 246], and lunar basins have long been described as catchments for magma (e.g., [Rev. Geophys. Space Phys. 18 (1980) 107] and references therein). We present a new model for melt creation under near side lunar basins that is triggered by the impacts themselves. Magma can be produced in two stages. First, crater excavation depressurizes underlying material such that it may melt in-situ. Second, the cratered lithosphere rises isostatically, warping isotherms at the lithosphere-asthenosphere boundary which may initiate convection, in which adiabatic melting can occur. The first stage produces by far the largest volume of melt, but convective melting can continue for up to 350 Ma. We propose that giant impacts account for a large portion of the volume and longevity of mare basalt volcanism, as well as for several compositional groups, including high alumina, high titanium, KREEP-rich, and picritic magmas. 相似文献
36.
峨嵋玄武岩同生流体包裹体在800℃爆裂后,2.0g/L NH4Cl溶液提取流体中Pt、Pd,C-410树脂富集-电感耦合等离子体质谱测定,方法相对误差小于25%。激光拉曼光谱与四级质谱测定包裹体的气液成分结果表明:流体中存在一定量的有机组分,这对Pt、Pd以有机螯合态形式进入流体提供了可能。 相似文献
37.
A complete dismembered sequence of ophiolite is well exposed in the south Andaman region that mainly comprises ultramafic
cumulates, serpentinite mafic plutonic and dyke rocks, pillow lava, radiolarian chert, and plagiogranite. Pillow lavas of
basaltic composition occupy a major part of the Andaman ophiolite suite (AOS). These basalts are well exposed all along the
east coast of southern part of the south AOS. Although these basalts are altered due to low-grade metamorphism and late hydrothermal
processes, their igneous textures are still preserved. These basalts are mostly either aphyric or phyric in nature. Aphyric
type exhibits intersertal or variolitic textures, whereas phyric variety shows porphyritic or sub-ophitic textures. The content
of alkalies and silica classify these basalts as sub-alkaline basalts and alkaline basalts. A few samples show basaltic andesite,
trachy-basalt, or basanitic chemical composition. High-field strength element (HFSE) geochemistry suggests that studied basalt
samples are probably derived from similar parental magmas. Al2O3/TiO2 and CaO/TiO2 ratios classify these basalts as high-Ti type basalt. On the basis of these ratios and many discriminant functions and diagrams,
it is suggested that the studied basalts, associated with Andaman ophiolite suite, were derived from magma similar to N-MORB
and emplaced in the mid-oceanic ridge tectonic setting. 相似文献
38.
The Kundal area of Malani Igneous Suite consists of volcano-plutonic rocks. Basalt flows and gabbro intrusives are associated
with rhyolite. Both the basic rocks consist of similar mineralogy of plagioclase, clinopyroxene as essential and Fe-Ti oxides
as accessories. Basalt displays sub-ophitic and glomeroporphyritic textures whereas gabbro exhibits sub-ophitic, porphyritic
and intergrannular textures. They show comparable chemistry and are enriched in Fe, Ti and incompatible elements as compared
to MORB/CFB. Samples are enriched in LREE and slightly depleted HREE patterns with least significant positive Eu anomalies.
Petrographical study and petrogenetic modeling of [Mg]-[Fe], trace and REE suggest cogenetic origin of these basic rocks and
they probably derived from Fe-enriched source with higher Fe/Mg ratio than primitive mantle source. Thus, it is concluded
that the basic volcano-plutonic rocks of Kundal area are the result of a low to moderate degree (< 30%) partial melting of
source similar to picrite/komatiitic composition. Within plate, anorogenic setting for the basic rocks of Kundal area is suggested,
which is in conformity with the similar setting for Malani Igneous Suite. 相似文献
39.
A combined gravity map over the Indian Peninsular Shield (IPS) and adjoining oceans brings out well the inter-relationships between the older tectonic features of the continent and the adjoining younger oceanic features. The NW–SE, NE–SW and N–S Precambrian trends of the IPS are reflected in the structural trends of the Arabian Sea and the Bay of Bengal suggesting their probable reactivation. The Simple Bouguer anomaly map shows consistent increase in gravity value from the continent to the deep ocean basins, which is attributed to isostatic compensation due to variations in the crustal thickness. A crustal density model computed along a profile across this region suggests a thick crust of 35–40 km under the continent, which reduces to 22/20–24 km under the Bay of Bengal with thick sediments of 8–10 km underlain by crustal layers of density 2720 and 2900/2840 kg/m3. Large crustal thickness and trends of the gravity anomalies may suggest a transitional crust in the Bay of Bengal up to 150–200 km from the east coast. The crustal thickness under the Laxmi ridge and east of it in the Arabian Sea is 20 and 14 km, respectively, with 5–6 km thick Tertiary and Mesozoic sediments separated by a thin layer of Deccan Trap. Crustal layers of densities 2750 and 2950 kg/m3 underlie sediments. The crustal density model in this part of the Arabian Sea (east of Laxmi ridge) and the structural trends similar to the Indian Peninsular Shield suggest a continent–ocean transitional crust (COTC). The COTC may represent down dropped and submerged parts of the Indian crust evolved at the time of break-up along the west coast of India and passage of Reunion hotspot over India during late Cretaceous. The crustal model under this part also shows an underplated lower crust and a low density upper mantle, extending over the continent across the west coast of India, which appears to be related to the Deccan volcanism. The crustal thickness under the western Arabian Sea (west of the Laxmi ridge) reduces to 8–9 km with crustal layers of densities 2650 and 2870 kg/m3 representing an oceanic crust. 相似文献
40.
Jean-Marie Dautria Jean-Michel Liotard Danièle Briot 《Comptes Rendus Geoscience》2004,336(11):971-981
Sr and Nd isotopic compositions of one trachyte, eight phonolites and five basalts have been measured. The isotopic characteristics of the trachyte can be explained by a combined assimilation–fractional crystallization process within an upper crustal magmatic chamber. Some phonolites display isotopic signatures identical to basalts, suggesting that they have been protected against any crustal assimilation during their formation. Some others have low Sr contents, whereas they are enriched in radiogenic Sr (0.70451<87Sr/86Sri<0.71192), and display basaltic 143Nd/144Nd ratios. Both observations could be explained by very strong alkali feldspar fractionation and by subsequent very low assimilation of surrounding rocks (between 0.3 and 4%) during intrusion. To cite this article: J.-M. Dautria et al., C. R. Geoscience 336 (2004). 相似文献