Topic
Petrography
About: Petrography is a research topic. Over the lifetime, 7449 publications have been published within this topic receiving 102018 citations.
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TL;DR: In this article, the petrography and mineral composition of a mantle-derived garnet peridotite xenolith from the V. Grib kimberlite pipe (Arkhangelsk Diamond Province, Russia) was studied.
Abstract: The petrography and mineral composition of a mantle-derived garnet peridotite xenolith from the V. Grib kimberlite pipe (Arkhangelsk Diamond Province, Russia) was studied. Based on petrographic characteristics, the peridotite xenolith reflects a sheared peridotite. The sheared peridotite experienced a complex evolution with formation of three main mineral assemblages: (1) a relict harzburgite assemblage consist of olivine and orthopyroxene porphyroclasts and cores of garnet grains (Gar1) with sinusoidal rare earth elements (REE) chondrite C1 normalized patterns; (2) a neoblastic olivine and orthopyroxene assemblage; (3) the last assemblage associated with the formation of clinopyroxene and garnet marginal zones (Gar2). Major and trace element compositions of olivine, orthopyroxene, clinopyroxene and garnet indicate that both the neoblast and clinopyroxene-Gar2 mineral assemblages were in equilibrium with a high Fe-Ti carbonate-silicate metasomatic agent. The nature of the metasomatic agent was estimated based on high field strength elements (HFSE) composition of olivine neoblasts, the garnet-clinopyroxene equilibrium condition and calculated by REE-composition of Gar2 and clinopyroxene. All these evidences indicate that the agent was a high temperature carbonate-silicate melt that is geochemically linked to the formation of the protokimberlite melt.
39 citations
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01 Jan 1991
39 citations
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TL;DR: In this article, detailed petrographic studies of shales show that they consist of a wide range of components, including a wide spectrum of composite particles that were contributed to the precursor muds in the form of high-water-content suspended floccules, bedload floccule, rip-up intraclasts, pedogenic aggregates, and fully lithified shale clasts.
39 citations
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TL;DR: The spatial distribution of burial diagenetic cements in sandstones of the Frio Formation is related to permeability and fluid flow as mentioned in this paper, which implies that the modification of the rocks is largely the outcome of reactions between the detrital and authigenic minerals and the formation water in the pores.
Abstract: The spatial distribution of burial diagenetic cements in sandstones of the Frio Formation is related to permeability and fluid flow. The relationship between sandstone diagenesis and fluid flow implies that the modification of the rocks is largely the outcome of reactions between the detrital and authigenic minerals and the formation water in the pores. During burial, formation water preferentially flowed through the most porous and permeable sandstones. Diagenetic alteration is more extensive in permeable sandstones because the minerals in those rocks were exposed to significantly more pore volumes of reactive water, each of which accomplished a small amount of diagenetic work. Consequently, porous and permeable units were also the preferred sites of diagenetic mineral p ecipitation. The heterogeneous distribution of authigenic minerals in sandstones is a result of changing preferential flow paths, due to diagenetic modification, during burial. Sandstones that are not the most porous or permeable at the time of deposition commonly preserve the best reservoir quality at depth because they are less modified by diagenesis. Petrographic analyses indicate that the SiO2 needed for the quartz overgrowths in the sandstones had an allochthonous source. ^dgr18O values for diagenetic quartz imply that the mineral precipitated from rapidly ascending, hot formation water. Quartz overgrowths are most abundant in distal-shelf facies sandstones, where the isolated nature of the sandstones in a predominately shaly section maximized preferential fluid flow. Mass balance calculations show that thousands of pore volumes of formation water are required to supply the SiO2 needed for the quartz overgrowths in the sandstones. The amount of water required to produce the diagenetic modification of the sandstones is much larger than the amount of water present in the entire Frio Formation, impl ing that reuse of formation water is an important and necessary process during diagenesis.
39 citations
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TL;DR: In this article, 10 isofacial blueschist facies rocks were investigated from the Koto-Bizan District, eastern Shikoku, Japan, previously mapped by Iwasaki (1963), and 20 of the constituent minerals have been newly analysed, 17 by conventional chemical methods, and 3 by electron microprobe techniques.
39 citations