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11.
Field Evidence of Magma Mixing from Microgranular Enclaves Hosted in Palaeoproterozoic Malanjkhand Granitoids, Central India 总被引：5，自引：0，他引：5
The Malanjkhand granitoids (MG) pluton (about 1500 sq km) occurs in the Balaghat district of Madhya Pradesh. The MG (~2400 Ma) represent an episode of Palaeoproterozoic felsic magmatism in Central India and hosts potential Cu (±Mo±Au) deposits. The enclaves hosted in MG can be broadly classified into two categories: microgranular enclaves (dark-coloured, fine-grained magmatic) and xenoliths of country rocks. The microgranular enclaves (ME) may be rounded, ellipsoidal, discoid, elongated, lenticular or tabular, and their size commonly reaches up to 2 metres across. The ME have sharp and in places, diffuse contacts with their host granitoids. The shape and size of ME indicate contemporaneous flow and mingling of partly crystalline felsic-mafic magmas. Some ME exhibit dark crenulated margins giving them a pillow-like form that has been attributed to undercooling of a ME magma as globules intruded into a granitoid magma. The presence of corroded felsic and mafic minerals (xenocrysts) in ME is interpreted as the result of mechanical transfer during the mafic-felsic magma interaction and mixing event. Mafic minerals (biotite) rim the quartz xenocrysts giving rise to ocellar texture, which exhibit signatures of resorption under hybrid (enclave) magma conditions. All these features suggest an origin for the calc-alkaline intermediate granitoid magma in Malanjkhand involving a magma mixing process. 相似文献
12.
Ziyu Wu Annibale Mottana Augusto Marcelli Calogero Rino Natoli Eleonora Paris 《Physics and Chemistry of Minerals》1996,23(3):193-204
We calculated the forsterite Mg K-edge and the fayalite Fe K-edge X-ray absorption spectra both for the M 1 and M 2 sites and for the overall edge by using the one-electron multiple-scattering theory. The validity of the theoretical model is well illustrated by comparison of calculations with experimental data at the Mg K-edge of MgO (periclase) and at the Mg and Fe K-edges spectra of forsterite and fayalite. Starting from these results at room conditions, we calculated the Mg and Fe K-edges X-ray absorption spectra of forsterite and fayalite at low and high temperatures and at high pressures as well. Variations of fine structures occur mostly in the intermediate multiple scattering (IMS) regions and as a result of the applied pressure. In order to demonstrate the capability of XAS to lead to deeper knowledge of structure relevant to Earth's upper mantle we also attempted calcuating the high-P edge for Fe 2+ in low-spin using a different occupation of valence electrons. If a change in spin state really occurs in fayalite, our simple model shows that XAS would evidence it easily even with low resolution. 相似文献
13.
The Grenvillian and Pan-African orogens: World's largest orogenies through geologic time, and their implications on the origin of superplume 总被引：11，自引：11，他引：0
The Neoproterozoic Earth was shaped largely by the Grenvillian and Pan-African orogenies. Out of these, the Grenvillian orogeny has long been regarded to be of minor nature in terms of global-scale orogenic episodes, whereas the Pan-African orogeny has been widely recognized in many continental fragments, although not in major parts of Asia. Based on chronological information in zircons from major river mouths across several important terrains of the globe, we show here that the Grenvillian orogeny contributed significantly to the formation of the continental crust. The time period between 0.6 Ga and 0.8 Ga marked the climax at the dawn of the Pan-African orogeny. Continental crust formed in this period is concentrated in the Pan-African orogenic belts widely across the globe. These regions were widespread over the half hemisphere of the globe, and were subsequently reduced in size after they moved to form Laurasia. The normalized frequency distribution of zircon ages from river-mouth sand over the world clearly demonstrates that Neoproterozoic and (0.9–0.6 Ga) and Grenvillian (1.3–1.0 Ga) peaks define the largest population. This means that extensive subduction, and hence active plate tectonics, might have operated through these periods. The zircon study has also brought to light new regions of the Grenvillian orogenic belts, particularly in the continents which are now covered by thick Phanerozoic sedimentary basins. Based on the new locations of Grenvillian orogens identified in this study, and using the distribution patterns as a marker bed, we propose revised paleogeographic configurations of the Rodinia and Gondwana supercontinents.Our results demonstrate that the Neoproterozoic was the most active period of crust formation in the Earth. The cold basins, formed right after the assembly of Rodinia, exhibit a basin chain fringing the northern periphery of Rodinia, which turned into sites of mantle upwellings and led to the rifting and separation of the supercontinental assembly. The continents then moved northwards after the formation of Gondwana at ca. 540 Ma, and enlarged the northern half of the supercontinent Pangea since 250 Ma.Based on the results, we also evaluate the role of supercontinents in the mechanism of generation of superplumes addressing the enigma that the coldest mantle right above the Core–Mantle Boundary turns to the hottest one over a period of several hundreds of million years. Slab graveyard formed by the Pan-African subduction can be imaged through P-wave tomography. We postulate that the high-velocity anomaly in the D” layer underneath Gondwana has now transformed to the low-V regions to generate the African superplume. The tectonic history of solid Earth in the Phanerozoic seems to be controlled by the slab graveyards formed by the Grenvillian orogeny ca. 1.0 Ga. 相似文献
14.
Lilik Eko Widodo Tedy Agung Cahyadi Zuher Syihab Sudarto Notosiswoyo Irwan Iskandar Heru Cahya Rustamaji 《Environmental Earth Sciences》2018,77(20):721
High rainfall in equatorial regions leads to high groundwater levels or pore pressures and a high risk of landslides on the slopes of open pit mines, hindering mining operations. To lower the groundwater level surrounding a slope, a drainage system is needed. A drain hole is a part of a drainage system which utilises gravity to drain groundwater. Drain hole installation in fractured media requires the determination of the number, location, length and other parameters of the drain holes. Drain holes are frequently installed in uniform configurations or in layouts with uniform spacing, which are often ineffective and uneconomical, as some holes are not in the right positions or directions within the fractured media. This paper attempts to develop a conceptual model of an optimised configuration of drain holes by setting the drain hole parameters, or decision variables, such as number, location and length, in such a way that it produces the most effective and efficient outcome by maximising groundwater lowering and minimising cost. The optimisation is supported by the multi-stage genetic algorithm method in combination with a groundwater simulator, hereafter called the multi-stage GWSim-GA SO method. The procedure of the conceptual model will be further developed and used as a framework in the groundwater management of fractured media of an open pit mine slope. 相似文献
15.
Rino C.L. Eckert E. Siegel A. Webster T. Ochadlick A. Rankin M. Davis J. 《Oceanic Engineering, IEEE Journal of》1997,22(1):18-26
This paper reviews X-band ocean microwave backscatter data from the LOGAN (LOw Grazing ANgle) experiment conducted on the Chesapeake Light Tower by the Naval Air Warfare Center. The data were collected under varied wind, sea, and swell conditions that provide some new insights into low-grazing-angle backscatter phenomena. Transient backscatter peaks called “sea spikes” have long been associated with deep-water breaking waves; however, they have yet to be fully reconciled with backscatter and hydrodynamic theories. New analysis techniques have been applied to the LOGAN data that take advantage of the unique characteristics of sea spikes and their dynamics. High-resolution Doppler spectra are organized relative to the space-time centroids of the sea-spike clusters and conditionally averaged by RCS strength. The mean Doppler variation of the strongest sea spikes then map the breaking-wave structure just as Doppler histories measured at moderate grazing angles map the dynamics of the dominant linear surface-wave components. While breaking waves are manifest to some degree in backscatter data at all grazing angles, a non-Bragg-scatter mechanism accentuates the crest scattering at low grazing angles. The phenomena potentially can be exploited for remote ocean sensing and imaging 相似文献