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Principles of Petrological Analysis of Igneous Rocks
Published in O.A. Bogatikov, R.F. Fursenko, G.V. Lazareva, E.A. Miloradovskaya, A. Ya, R.E. Sorkina, Magmatism and Geodynamics Terrestrial Magmatism Throughout the Earth’s History, 2020
The calc-alkaline series contains mainly andesite, dacite and rhyolite and usually subordinate amounts of high-Al basalt and andesite-basalt. The SiO2 content varies from 52% to 70%; the groundmass contains hyperstene and pigeonite. There is no trend of enrichment in iron and low Ti content. Cerium-group TREE are more numerous as compared with those in the tholeiite series, and the total REE content is also high. At present, at least two specific series — predominantly low-Mg andesite and less commonly high-Mg boninite — can be recognized within the calc-alkaline series. The boninite series has high chromium and nickel content. The composition of the rock-forming minerals is distinctive, with the concomitant occurrence of four pyroxenes: bronzite, augite, pigeonite and pigeonite-augite; clinoenstatite is rare. The feature of the rocks is the andesitic composition of the volcanic glass in the basic and ultrabasic members of the series.
Basaltic dykes and their xenoliths from the Gerroa–Kiama region, southern Sydney Basin, New South Wales: evidence for multiple intrusive episodes
Published in Australian Journal of Earth Sciences, 2022
S. Abu-Shamma, I. T. Graham, P. Lennox, G. Bann, A. Greig
The XRD patterns were of extremely low intensity and thus unsuitable for quantitative XRD analysis; however, a total of 19 minerals were identified in eight samples. The XRD analysis in Table S7 revealed minerals previously identified in thin-section such as pyroxenes (augite, diopside, clinoferrosilite, pigeonite), quartz, plagioclase (anorthite, albite), orthoclase, amphiboles (edenite), carbonates (aragonite, calcite), pumpellyite, chlorite (clinochlore), hematite, zeolite (analcime), and clay minerals such as kaolinite and illite.
Geological setting of the Moorowie Formation, lower Cambrian Hawker Group, Mt Chambers Gorge, eastern Flinders Ranges, South Australia
Published in Australian Journal of Earth Sciences, 2020
T. J. Mount, J. B. Jago, N. R. Langsford, C. R. Dalgarno
Hydrothermal alteration is pervasive in the dolerite plugs of the major fault zones in the northern map area (Figure 5), producing epidote and minor fibrous asbestiform amphibole (uralite) in relic ophitic matrices after clinopyroxene (pigeonite and diopsidic augite to 40 vol%), plagioclase (An60; labradorite), and magnetite (5 vol%), with trace kaolinite, chlorite, apatite and opaques.
Seve terranes of the Kebnekaise Mts., Swedish Caledonides, and their amalgamation, accretion and affinity
Published in GFF, 2018
Per-Gunnar Andréasson, Ann Allen, Oskar Aurell, Daniel Boman, Jonas Ekestubbe, Ute Goerke, Anders Lundgren, Patrik Nilsson, Stefan Sandelin
The Vássačorru igneous complex (Mårma magmatic complex of Paulsson & Andréasson 2002; Mårma complex of Paulsson 1996 and Sandelin 1997) is a network of gabbroic and doleritic mafic rocks and granite (Fig. 4A, B). In addition to the main occurrence in the Kebnekaise massif, smaller bodies of the VIC occur scattered from Singis in the south (Manak gabbro; Page 1993, and Aurek gabbro; Tilke 1986) to Lake Torneträsk (Kålkuktjåkkå; N68.236058°/E19.231625°) in the north. Mafic rocks are cut by granitic dykes, some quartz-monzonitic; these are in turn cut by dolerite dykes. Narrow, very fine-grained mafic dykes with pilotaxitic plagioclase occur. Aphanitic dykes lacking chilling against country rock are interpreted as quenched liquids. Mingling and mixing between felsic and mafic magmas took place (Fig. 4). Fig. 4D shows a hybrid rock with xenoliths of metasedimentary rocks and with mafic fragments in different stages of hybridization. Fragments of all generations are rich in garnet and some are rimmed by garnet porphyroblasts and biotite. Scattered, sometimes mantled, xenocrysts of feldspar occur in both fragments and hybrid host rocks. Hybrid rocks occur also as narrow, fine-grained dykes of monzogabbroic composition. Rare evidence of igneous layering includes horizons of rusty-weathering olivine-rich gabbro, anorthositic gabbro and hornblendites. The gabbro is medium- to fine-grained, granular and composed of plagioclase, augite, hypersthene and olivine. Olivine crystals with narrow inner coronas of orthopyroxene and outer coronas of amphibole occur. Olivine-absent, orthopyroxene predominates among mafic minerals, often as hypersthene stained by iron-oxides. The dolerite is ophitic, often plagioclase porphyritic and dominated by plagioclase and augite with pigeonite exsolution lamellae. Hypersthene and inverted pigeonite are subordinate and mantled by clinopyroxene. Pyroxenes are always rimmed by hornblende. The plagioclase of some dykes is clouded by iron oxide. The clouding is confined to central parts of plagioclase laths, and the boundary to clear rims of laths is very sharp, suggesting magmatic origin (Johansson 1992). Towards the overriding Kebnekaise terrane, gabbros and dolerites of the VIC pass into amphibolites, often garnetiferous.