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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 paper, meteorite impacts cause conversion of kinetic energy into thermal energy, part of this thermal energy is used to form a melt sheet, part is dissipated to heat the target rocks and these together with the hot rocks that elastically rebound from the depth of several kilometres (central uplift) activate hydrothermal circulation.
Abstract: Meteorite impacts cause conversion of kinetic energy into thermal energy. Part of this thermal energy is used to form a melt sheet, part is dissipated to heat the target rocks and these together with the hot rocks that elastically rebound from the depth of several kilometres (central uplift) activate hydrothermal circulation. Impact-generated hydrothermal systems have been documented from several impact structures world-wide. Three Australian examples—Shoemaker, Woodleigh and Yarrabubba—provide evidence of hydrothermal fluid flow both within and around the structures. Field observations, and petrographic and geochemical data suggest a common evolutionary trend of post-impact hydrothermal activity from early high-temperature alkali metasomatism to a later lower temperature H+ metasomatism, resulting in the overprinting by hydrous mineral assemblages. Hydrothermal systems activated by meteorite-impact events are important because they may also form economic mineral deposits, as is documented for several imp...

35 citations

Journal ArticleDOI
TL;DR: In this paper, the use of the k-value (cation packing index is defined as the number of cation in a mole) for characterizing the degree of weathering of granitic rocks is investigated.

35 citations

Journal ArticleDOI
TL;DR: In this paper, the Gwna Group and the Gwyddel Felsitic Beds of Llŷn were shown to have formed at high grades within the facies and that the greenschist facies rocks crystallized in the higher pressure field.
Abstract: Metabasic assemblages belong to the prehnite-pumpellyite and greenschist facies. The isograds pumpellyite-in, pumpellyite-out/clinozoisite-in and biotite-in have been mapped, and divide the area into four metamorphic zones. Field and petrographic evidence indicate that the metamorphic crystallization was largely syn-and immediately post-tectonic, viz. end-Silurian to Devonian. The use of published Schreinemakers' bundles indicates that most of the prehnite-pumpellyite-bearing assemblages formed at high grades within the facies and that the greenschist facies rocks crystallized in the higher pressure field. As the amount of calcite increases so diagnostic Ca–Al silicates are reduced and eventually eliminated from assemblages. Contrary to recent claims, the evidence indicates that the Gwna Group and the Gwyddel Felsitic Beds of Llŷn were metamorphosed prior to the Arenig.

35 citations

Journal ArticleDOI
01 Sep 2006
TL;DR: In this article, the authors used geochronologic and field data to distinguish two magmatic pulses in the Pitinga Province, which are responsible for the generation of volcanic and granitic rocks of ages between 1,890 and 1,76 My.
Abstract: The Pitinga Province is responsible for 60% of the Brazilian tin product ion, and about 3% of the world production of this not ferrous metal. Associates to the Sn occurs important reserves of Nb,Ta and F (cryolite), beyond anomalous grades of Zr, Y, Rb, U, Th and HREE. The geological selling of the Pitinga Province consists in Paleoproterozoic, volcanic and granitic units or Uatuma Supergroup, younger granites related to the Madeira Suite and by the vulcano-sedimentary Urupi Formation. The granitic units of the Mapuera and Madeira Suite arc represented by eight plutons that are intrusive in to acid and intermediate volcanic rocks of the Iricoume Group. Only the granites of the Madeira Suite have previous geochronologic information. This paper shows 207 Pb/ 206 Pb zircon ages of four granitic units of the Mapuera Suite and 207 Pb/ 206 Pb zircon ages of the volcanic rocks that enclose these plutons. Petrographic, geochemical and field data, allow us to distinguish two magmatic pulses in the region. The first one is responsible for the generation of volcanic and granitic rocks of ages between 1,890 and 1,876 My. The second magmatic pulse generated A type granites with ages ranging from 1,829 and 1,798 My. Based on field and remote sensor data, the volcanic rocks of the Iricoume Group were divided in three formations, for which are proposed the names Divisor Formation, Paraiso Formation and Ouro Preto Formation. The ages of these units are around 1,89 and 1,88 Ga. The field data indicate s that the Urupi Formation shows intercalations of pyroclastic rocks. These pyroclastic rocks are interpreted as part of the Paraiso Formation; consequently it locates the Urupi Formation in the Paleoproterozoic, suggesting its correlation with Roraima Supergroup. All these lithologic units are associated with a regional, extensional, arc-shaped structure, which encloses the whole Pitinga Province. Granitic plutons of the Mapuera Suite occupy the peripheral parts of the structure, which is filled by effusive and pyroclastic rocks of the Iricoume Group, and sedimentary rocks of the Urupi Formation. The tectonic setting suggests that the emplacement of volcanic and pyroclastic rocks of the Iricoume Group, in the Pitinga Province, was controlled by extensional processes of caldera collapse. Subsequent reactivation of the extensional system allowed the emplacement of the Madeira Suite, in the central portion of this wide structure.

35 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023551
20221,098
2021370
2020344
2019310
2018291