Petrogeochemistry of Amphibolites from Shivpura District Bhilwara, Rajasthan, India

Amphibolites are frequently observed in the medium- to high-grade metamorphic rocks of Shivpura. These amphibolites are the result of the metamorphism of pre-existing mafic igneous rocks under medium to high grade P-T conditions and consist essentially of hornblende–plagioclase–garnet–clinopyroxene-epidote–iron oxide. Geochemically, these orthoamphibolites are tholeiitic, show association with non-orogenic environment and shift to subalkaline derivatives with progressive differentiation. It is also clear that the parent magma for these rocks was highly evolved in nature. Paper records the petrography, geochemical characters and a probable origin of these amphibolites.Journal of Institute of Science and Technology, 2015, 20(2): 103-112

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Significance of “gneissic” rocks in the Liscomb Complex, Nova Scotia

Canadian Journal of Earth Sciences ◽

10.1139/e10-019 ◽

2010 ◽

Vol 47 (6) ◽

pp. 927-940 ◽

Cited By ~ 2

Author(s):

J. V. Owen ◽

R. Corney ◽

J. Dostal ◽

A. Vaughan

Keyword(s):

Igneous Rocks ◽

Metamorphic Rocks ◽

Low Grade ◽

High Grade ◽

Peraluminous Granite ◽

Isotopic Signatures ◽

Conventional View ◽

Basement Rocks ◽

Mineral Assemblages ◽

Intrusive Rocks

The Liscomb Complex comprises Late Devonian intrusive rocks (principally peraluminous granite) and medium- to high-grade metamorphic rocks (“gneisses”) that collectively are hosted by low-grade (greenschist facies) metasediments of the Cambro-Ordovician Meguma Group. The conventional view that these “gneisses” contain high-grade mineral assemblages and represent basement rocks has recently been challenged, and indeed, some of the rocks previously mapped as gneisses, particularly metapelites, have isotopic compositions resembling the Meguma Group. Amphibole-bearing enclaves in the Liscomb plutons, however, are isotopically distinct and in this regard resemble xenoliths of basement gneisses in the Popes Harbour lamprophyre dyke, south of the Liscomb area. Metasedimentary enclaves with Meguma isotopic signatures can contain garnets with unzoned cores (implying high temperatures) that host high-grade minerals (prismatic sillimanite, spinel, and (or) corundum) and are enclosed by retrograde-zoned rims. These features are interpreted here as having formed during and following the attainment of peak temperatures related to Liscomb magmatism. The amphibole-bearing meta-igneous rocks described here contain cummingtonite or hornblendic amphibole and occur as enclaves in granodioritic to tonalitic plutons. They are mineralogically, texturally, and isotopically distinct from Meguma metasediments and at least some of the plutonic rocks that enclose them, so remain the most likely candidate for basement rocks in the Liscomb Complex.

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The Chemical Evolution from Older (323–318 Ma) towards Younger Highly Evolved Tin Granites (315–314 Ma)—Sources and Metal Enrichment in Variscan Granites of the Western Erzgebirge (Central European Variscides, Germany)

Minerals ◽

10.3390/min9120769 ◽

2019 ◽

Vol 9 (12) ◽

pp. 769 ◽

Cited By ~ 1

Author(s):

Marion Tichomirowa ◽

Axel Gerdes ◽

Manuel Lapp ◽

Dietmar Leonhardt ◽

Martin Whitehouse

Keyword(s):

Enrichment Factors ◽

Source Rocks ◽

Metamorphic Rocks ◽

High Grade ◽

O Isotope ◽

Variscan Granites ◽

Evolution With Time ◽

Continuous Enrichment ◽

Highly Evolved ◽

And Tungsten

The sources and critical enrichment processes for granite related tin ores are still not well understood. The Erzgebirge represents one of the classical regions for tin mineralization. We investigated the four largest plutons from the Western Erzgebirge (Germany) for the geochemistry of bulk rocks and autocrystic zircons and relate this information to their intrusion ages. The source rocks of the Variscan granites were identified as high-grade metamorphic rocks based on the comparison of Hf-O isotope data on zircons, the abundance of xenocrystic zircon ages as well as Nd and Hf model ages. Among these rocks, restite is the most likely candidate for later Variscan melts. Based on the evolution with time, we could reconstruct enrichment factors for tin and tungsten starting from the protoliths (575 Ma) that were later converted to high-grade metamorphic rocks (340 Ma) and served as sources for the older biotite granites (323–318 Ma) and the tin granites (315–314 Ma). This evolution involved a continuous enrichment of both tin and tungsten with an enrichment factor of ~15 for tin and ~7 for tungsten compared to the upper continental crust (UCC). Ore level concentrations (>10–100 times enrichment) were achieved only in the greisen bodies and dykes by subsequent hydrothermal processes.

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Microscopy and Microanalysis of Magmatic and Metamorphic Minerals – Part 1: Cordierite

Microscopy Today ◽

10.1017/s1551929500061745 ◽

2008 ◽

Vol 16 (5) ◽

pp. 30-37 ◽

Cited By ~ 1

Author(s):

Robert Sturm

Keyword(s):

Regional Metamorphism ◽

Igneous Rocks ◽

Major Constituent ◽

Metamorphic Rocks ◽

High Grade ◽

Shearing Stress ◽

The Past ◽

Peraluminous Granites ◽

Wide Range ◽

Higher Temperature

Cordierite represents an orthorhombic (Mg,Fe)Al-silicate (Table 1) that is observed in a wide range of natural occurrences. As outlined in numerous mineralogical overviews published during the past decades, cordierite mainly crystallizes in thermally metamorphosed rocks, particularly in those derived from argillaceous sediments. Additionally, the mineral can be a major constituent of parageneses formed under high-grade regional metamorphism and therefore occurs in respective schists, gneisses and granulites. The metamorphic formation of cordierite is generally restricted to conditions of deficient or low shearing stress producing only moderate lithological pressures. With rising pressure due to transpression cordierite often breaks down to enstatite and sillimanite or, at higher temperature, to sapphirine and quartz (see also Fig. 5). Besides its crystallization in metamorphic rocks, cordierite is also found in specific igneous rocks like peraluminous granites and related high-grade anatectic terrains.

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Rare earth elements in high-grade metamorphic rocks from the western Alps

Lithos ◽

10.1016/0024-4937(79)90061-6 ◽

1979 ◽

Vol 12 (1) ◽

pp. 41-49 ◽

Cited By ~ 28

Author(s):

J. Dostal ◽

S. Capedri

Keyword(s):

Rare Earth ◽

Rare Earth Elements ◽

Western Alps ◽

Metamorphic Rocks ◽

High Grade

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Geochemistry of bimodal amphibolitic—felsic gneiss complexes from eastern Massif Central, France

Geological Magazine ◽

10.1017/s0016756800013637 ◽

1995 ◽

Vol 132 (3) ◽

pp. 321-337 ◽

Cited By ~ 14

Author(s):

Bernard Briand ◽

Jean-Luc Bouchardon ◽

Houssa Ouali ◽

Michel Piboule ◽

Paul Capiez

Keyword(s):

Crustal Contamination ◽

Igneous Rocks ◽

Chemical Characteristics ◽

Continental Margins ◽

High Grade ◽

Transitional Stage ◽

Crust Formation ◽

Massif Central ◽

Mantle Sources ◽

Two Populations

AbstractHigh-grade basic and acidic meta-igneous rocks are widespread in the bimodal amphibolitic—felsic gneiss complexes, which are characteristic formations of the ‘Middle Allochthonous Unit’ from eastern and southern French Massif Central. The metabasites from the Lyonnais and Doux complexes are chemically diverse and range from N-MORB type tholeiitic to transitional types. The two populations are not related by fractional crystallization or crustal contamination processes and their chemical characteristics reflect differences in their mantle sources. An ensialic setting is supported by the crustally-derived character of some of the associated felsic rocks, but the presence of N-MORB-type metabasites argues for an extensional environment. This bimodal association compares well with the magmatism of rifted continental margins and may reflect a transitional stage between continental rifting and oceanic crust formation during the Cambro-Ordovician spreading event.

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Geochronology of high-grade metamorphic rocks from the Anjul area, Lut block, eastern Iran

Journal of Asian Earth Sciences ◽

10.1016/j.jseaes.2013.12.021 ◽

2014 ◽

Vol 82 ◽

pp. 151-162 ◽

Cited By ~ 5

Author(s):

Michael Bröcker ◽

Gholamreza Fotoohi Rad ◽

Fateme Abbaslu ◽

Nikolay Rodionov

Keyword(s):

Metamorphic Rocks ◽

High Grade ◽

Lut Block ◽

Eastern Iran

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Zircon ages and the distribution of Archaean and Proterozoic rocks in the Rauer Islands

Antarctic Science ◽

10.1017/s0954102093000252 ◽

1993 ◽

Vol 5 (2) ◽

pp. 193-206 ◽

Cited By ~ 88

Author(s):

P. D. Kinny ◽

L. P. Black ◽

J. W. Sheraton

Keyword(s):

Granulite Facies ◽

Metamorphic Rocks ◽

Low Grade ◽

High Grade ◽

Ion Microprobe ◽

Rock Interaction ◽

Mafic Rocks ◽

Grade Fluid ◽

Vestfold Hills ◽

Intrusive Suite

The application of zircon U-Pb geochronology using the SHRIMP ion microprobe to the Precambrian high-grade metamorphic rocks of the Rauer Islands on the Prydz Bay coast of East Antarctica, has resulted in major revisions to the interpreted geological history. Large tracts of granitic orthogneisses, previously considered to be mostly Proterozoic in age, are shown here to be Archaean, with crystallization ages of 3270 Ma and 2800 Ma. These rocks and associated granulite-facies mafic rocks and paragneisses account for up to 50% of exposures in the Rauer Islands. Unlike the 2500 Ma rocks in the nearby Vestfold Hills which were cratonized soon after formation, the Rauer Islands rocks were reworked at about 1000 Ma under granulite to amphibolite facies conditions, and mixed with newly generated felsic crust. Dating of components of this felsic intrusive suite indicates that this Proterozoic reworking was accomplished in about 30–40 million years. Low-grade retrogression at 500 Ma was accompanied by brittle shearing, pegmatite injection, partial resetting of U-Pb geochronometers and growth of new zircons. Minor underformed lamprophyre dykes intruded Hop and nearby islands later in the Phanerozoic. Thus, the geology of the Rauer Islands reflects reworking and juxtaposition of unrelated rocks in a Proterozoic orogenic belt, and illustrates the important influence of relatively low-grade fluid-rock interaction on zircon U-Pb systematics in high-grade terranes.

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