The Eruptive Rocks

Soil Science (Impact Factor: 0.79). 06/1948; 66(1):78.
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    • "In their modified alkali-lime index or MALI diagram (Na 2 O + K 2 O–CaO versus SiO 2 ), CB samples with b60 wt.% SiO 2 are mainly calcic, whereas high-silica samples straddle boundaries, ranging from strongly calcic to alkalic, with most samples falling on or near the calcalkalic alkali-calcic boundary (Fig. 6b). Based on aluminium saturation index (Al/(Ca + Na + K) (Shand, 1943), most CB samples are "
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    ABSTRACT: Large volume, plutonic belts, such as the ∼ 221,000 km2, ca. 1.865–1.845 Ga Cumberland batholith (CB) of the Trans-Hudson Orogen in Canada, are major components of Paleoproterozoic orogenic belts. In many cases, they have been interpreted as continental arc batholiths. The petrogenesis and tectonic context of the CB and implications for crustal growth and recycling are interpreted herein based on a 900 km geochemical-isotopic (Nd–O) transect across it and into granitoid plutons within bounding Archean cratons in central and southern Baffin Island.The mainly granulite grade CB, emplaced over an age span of between 14 and 24 Ma, consists mainly of high-K to shoshonitic monzogranite and granodiorite, but also includes low- and medium-K granitoid rocks. Metaluminous to slightly peraluminous compositions and δ18O (VSMOW) values (+ 6 to + 10‰) indicate derivation from infracrustal (I-type) sources. εNd 1.85 Ga signatures (− 12 to − 2) of both mafic and felsic units suggest a dominance of evolved sources. Isotopic signatures in the interior of the CB (− 2 to − 7) are more radiogenic than those within Archean domains in central (− 8 to − 15) and southern (− 5 to − 19) Baffin Island. The isotopic transect is interpreted as ‘imaging’ an accreted microcontinental block (Meta Incognita) and bounding Archean cratons. The CB includes granites of arc, within-plate (A-type) and post-collisional affinity and volumetrically minor mafic rocks with both arc and non-arc features. (La/Yb)CN and Sr/Y values range from < 1 to 225 and < 1 to 611, respectively. In these respects, some CB granitoid rocks resemble Paleozoic adakitic granites, interpreted as partial melts of greatly thickened crust within post-collisional settings, such as Tibet. Thus, the CB likely encompasses various non-consanguineous magmatic suites generated at deep- to mid-crustal depths. Although CB granitoid rocks undoubtedly had important crustal sources, it is hard to assess the relative contribution of mantle-derived magmas.The CB is best interpreted as a post-accretion batholith resulting from large-scale lithospheric mantle delamination followed by the upwelling of hot asthenospheric mantle leading to voluminous crustal partial melting. Contributors to crustal instability which may have facilitated such delamination included: (a) a collage of recently assembled small cratons underlain by hot, weak lithosphere with mantle-depth structural breaks within this segment of the Trans-Hudson Orogen; (b) the gabbro-eclogite phase transformation, and (c) a greatly thickened crustal section (> 60 km), as evidenced by adakitic granites.
    Lithos 06/2010; 117(1-4-117):99-118. DOI:10.1016/j.lithos.2010.02.008 · 4.48 Impact Factor
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    • "The Asarcik (Saplica, Catakhan), Eskine, and Saydere samples display linear trends in Harker FIG. 3. A. Classification of the Asarcik (Saplica, Catakhan), Eskine, and Saydere intrusives: total alkali versus SiO 2 diagram (Middlemost, 1994). B. Shand's index values (Shand, 1951). diagrams (Figs. 4 and 5). "
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    ABSTRACT: A series of Cretaceous to Eocene granitoids are present in the Eastern Pontides of northeastern Turkey. The Asarcik (Saplica, Catakhan), Eskine, and Saydere (Sebinkarahisar-Giresun) are the least-studied, thus least-understood plutons in the orogen. Rock assemblages range from monzonite to granite. They contain mainly K-feldspar, plagioclase, quartz, hornblende, biotite, and Fe-Ti oxides. They are high-K, calc-alkaline, and I-type granites. Chondrite-normalized REE patterns are fractionated and have small negative Eu anomalies. They show enrichment in LILE and LREE relative to HFSE, displaying features of arc-related granitoids. Low molar Al2O3/(FeO+MgO+TiO2) in combination with variable molar (Na2O+K2O)/(FeO+MgO+TiO2) ratios indicate that the magmas were derived from mafic lower-crustal source rocks. The Eu and Sr anomalies and unfractionated HREE suggest the presence of plagioclase and absence of garnet in the source.
    International Geology Review 06/2008; 50(6):563-582. DOI:10.2747/0020-6814.50.6.563 · 1.71 Impact Factor
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    • "). B. K 2 O versus SiO 2 diagram (classification boundaries after Le Maitre et al., 1989). C. Shand's index values of the rock types (after Shand, 1951). "
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    ABSTRACT: The western Anatolian magmatic province is typified by a large number of Late Cenozoic postcollisional granitoids. Of these magmatics, the Egrigöz pluton is one of the largest and leastunderstood plutons in the Menderes Massif. The Egrigöz intrusives are subalkaline, high-K, and calc-alkaline, and have characteristics of I-type granites. They consist mainly of granodiorite and granite. The intrusive rocks show enrichment in LILE and LREE relative to HFSE. Their chondrite-normalized REE patterns are fractionated and have small negative Eu anomalies. Geochemical characteristics of the Egrigöz pluton indicate an origin through partial melting of mafic lower-crustal source rocks. In western Anatolia, the melt generation mechanism for the intrusive rocks could be crustal extension and uplift following collision.
    International Geology Review 04/2008; 50(4):375-391. DOI:10.2747/0020-6814.50.4.375 · 1.71 Impact Factor
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