Metamorphic zonal sequences of pelitic schists and gneisses from the area around Kandra (Jharkhand): Constraints from field and textural relationship

2017 ◽  
Vol 89 (2) ◽  
pp. 139-144 ◽  
Author(s):  
Divya Prakash ◽  
Dhananjay Kumar Patel ◽  
Suparna Tewari ◽  
Manoj Kumar Yadav ◽  
Roopali Yadav
Keyword(s):  
Textural Relationship

Petrological and geochemical characterization of the arc-related Suru–Thasgam ophiolitic slice along the Indus Suture Zone, Ladakh Himalaya

2021 ◽  
pp. 1-20
Author(s):  
I.M. Bhat ◽  
T. Ahmad ◽  
D.V. Subba Rao ◽  
N.V. Chalapathi Rao
Keyword(s):  
Suture Zone ◽  
Secondary Mineral ◽  
High Field Strength ◽  
Geochemical Characterization ◽  
Rock Types ◽  
Ladakh Himalaya ◽  
Magnesian Olivine ◽  
Textural Relationship ◽  
Ree Patterns

Abstract The Ladakh Himalayan ophiolites preserve remnants of the eastern part of the Neo-Tethyan Ocean, in the form of Dras, Suru Valley, Shergol, Spongtang and Nidar ophiolitic sequences. In Kohistan region of Pakistan, Muslim Bagh, Zhob and Bela ophiolites are considered to be equivalents of Ladakh ophiolites. In western Ladakh, the Suru–Thasgam ophiolitic slice is highly dismembered and consists of peridotites, pyroxenites and gabbros, emplaced as imbricate blocks thrust over the Mesozoic Dras arc complex along the Indus Suture Zone. The Thasgam peridotites are partially serpentinized with relict olivine, orthopyroxene and minor clinopyroxene, as well as serpentine and iron oxide as secondary mineral assemblage. The pyroxenites are dominated by clinopyroxene followed by orthopyroxene with subordinate olivine and spinel. Gabbros are composed of plagioclase and pyroxene (mostly replaced by amphiboles), describing an ophitic to sub-ophitic textural relationship. Geochemically, the studied rock types show sub-alkaline tholeiitic characteristics. The peridotites display nearly flat chondrite-normalized rare earth element (REE) patterns ((La/Yb)N = 0.6–1.5), while fractionated patterns were observed for pyroxenites and gabbros. Multi-element spidergrams for peridotites, pyroxenites and gabbros display subduction-related geochemical characteristics such as enriched large-ion lithophile element (LILE) and depleted high-field-strength element (HFSE) concentrations. In peridotites and pyroxenites, highly magnesian olivine (Fo88.5-89.3 and Fo87.8-89.9, respectively) and clinopyroxene (Mg no. of 93–98 and 90–97, respectively) indicate supra-subduction zone (SSZ) tectonic affinity. Our study suggests that the peridotites epitomize the refractory nature of their protoliths and were later evolved in a subduction environment. Pyroxenites and gabbros appear to be related to the base of the modern intra-oceanic island-arc tholeiitic sequence.

scholarly journals MINERAL CHEMISTRY AND GEOCHEMISTRY OF HYPERSTHENE-BEARING DIORITE FROM ERUSU AKOKO, SOUTHWESTERN NIGERIA

2020 ◽  
Vol 4 (1) ◽  
pp. 13-18
Author(s):  
E. J. Oziegbe ◽  
V. O. Olarewaju ◽  
O. O. Ocan
Keyword(s):  
Chemical Composition ◽  
Chemical Properties ◽  
Mineral Chemistry ◽  
Accessory Mineral ◽  
Southwestern Nigeria ◽  
Hydrous Minerals ◽  
Icp Ms ◽  
Composition Of Minerals ◽  
Textural Relationship ◽  
Opaque Minerals

Samples of mafic intrusive rock were analyzed for their mineralogical and chemical properties. The textural relationship was studied using the petrographic microscope, elemental composition of minerals was determined using the Electron Microprobe and the whole rock chemical analysis was done using the XRF and ICP-MS. The following minerals were observed in order of abundance; pyroxene, amphibole, plagioclase, biotite, opaque minerals, quartz and chlorite, with apatite and zircon occurring as accessory mineral. Two types of pyroxenes were observed; orthopyroxene (hypersthene) and clinopyroxene. Texturally, amphiboles have inclusions of plagioclase and pyroxene. The plagioclase has undergone sericitization. The chemical composition of the pyroxene is En51.95Fs44.53Wo3.52, biotite has Fe/(Fe+Mg):0.42, Mg/(Fe+Mg):0.59, and plagioclase is Ab63.5An34.55Or1.95. Whole rock chemistry shows a chemical composition; SiO2: 45.15 %, Al2O3: 14.04 %, Fe2O3: 16.01 %, MgO: 5.65 %, CaO: 7.58 % and TiO2: 3.59 %. There is an enrichment of LREE and a depletion of HREE. Based on the minerals, mineral chemistry and the geochemistry of the studied rock, the rock is mafic and hydrous minerals formed by hydration recrystallization of pyroxene. The rock has extensively retrogressed but has not been affected by any form of deformation.

Deciphering the brittle failure of eclogites at high-pressures: hydrofractures as fluid-escape pathways

2020 ◽  
Author(s):  
Michał Bukała ◽  
Károly Hidas ◽  
Carlos J. Garrido ◽  
Christopher Barnes ◽  
Iwona Klonowska ◽  
...  
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Outer Zone ◽  
Passive Margin ◽  
National Agency ◽  
Vein Formation ◽  
Iapetus Ocean ◽  
Eclogite Facies ◽  
Textural Relationship ◽  
Opening And Closing

<p>The Tsäkkok lens (northern Scandinavian Caledonides) represents the outermost part of the rifted Baltica passive margin and consists of sediments and pillow basalts of MORB affinity that were metamorphosed in eclogite facies. The Tsäkkok eclogites underwent metamorphism in a cold subduction regime (~8 °C/km) at the onset of the Iapetus Ocean closure. These rocks record pervasive high-pressure, fracturing during prograde dehydration at eclogite-facies conditions reaching up to 2.2 GPa and 590 ºC. Locally, the omphacite-dominated groundmass is transected by fractures sealed either by omphacitite or garnetite veins. Garnetite veins form a dense network that disrupt intact eclogite blocks, whereas omphacitite is found in rare, single veins. The garnetite veins are dominated by dense, poikiloblastic garnet clusters and display two chemically different zones, i.e., a high-Mn inner zone and a low-Mn outer zone. Detailed microstructural and geochemical mapping by EDS-EBSD SEM revealed that the high-Mn inner zone is disrupted and sealed by the low-Mn garnet zone. Garnets in the vein usually show little elongation and moderate intracrystalline substructure that is dominated by slightly changing misorientations without clear subgrain boundaries. By contrast, garnets of the sealed domain display an abrupt grain size reduction and anomalously high density of sharp intracrystalline misorientations in equant grains. The interstitial space between garnet grains in both of the inner and outer zones of the vein is infilled by omphacite + rutile + quartz + phengite + glaucophane.</p><p>The textural relationship between the inner- and outer zones of the garnetite vein implies syn-deformation growth of the outer zone, while the mineral assemblage attests for high-pressure conditions of the vein formation. Considering the lack of significant offset along the vein, we interpret the observed microstructures as formed during the sudden opening and closing of a brittle fracture, typical of hydrofracturing, and fast crystal growth assisted by high-pressure fluids. Presumably, these fractures constitute a fluid escape pathway during dehydration at prograde/peak conditions.</p><p>Research funded by NCN project no. 2019/33/N/ST10/01479 (M.Bukała) and no. 2014/14/E/ST10/00321 (J.Majka), as well as the The Polish National Agency for the Academic Exchange scholarship no. PPN/IWA/2018/1/00046/U/0001 given to M.Bukała.</p><p> </p>

Palaeoenvironmental significance of iron carbonate concretions from the Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn, Kraków-Silesia Homocline, Poland

2012 ◽  
Vol 62 (3) ◽  
pp. 307-324 ◽  
Author(s):  
Magdalena Witkowska
Keyword(s):  
Sedimentation Rate ◽  
Middle Jurassic ◽  
Iron Carbonate ◽  
Reactive Iron ◽  
Carbonate Concretions ◽  
Mode Of Occurrence ◽  
Characteristic Features ◽  
Textural Relationship ◽  
Redox Boundary ◽  
Sediment Layers

ABSTRACT Witkowska, M. 2012. Palaeoenvironmental significance of iron carbonate concretions from the Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn, Krakow-Silesia Homocline, Poland. Acta Geologica Polonica, 62 (3), 307-324. Warszawa. Iron carbonate concretion horizons are characteristic features of the Bathonian (Middle Jurassic) claystone-mudstone succession at Gnaszyn. They occur in single horizons, which generally represent the same genetic type. The siderite concretions are the main type of iron carbonate concretions at Gnaszyn; a second type is represented by phosphate-siderite concretions. On the basis of the fieldwork, and their petrographical and mineralogical characteristics, the genesis of the concretions and their palaeoenvironmental significance is discussed. The results of this study (based on the localization, mode of occurrence, mineralogy of iron carbonate concretions and also the textural relationship between the concretions and host sediment layers) suggest an early diagenetic origin of the concretions. The preferential occurrence of the concretion horizons in single layers in the ambient sediments was associated with particular conditions of their deposition and early diagenesis, favored by a slower sedimentation rate and more intense bioturbation, and related primarily to the greater availability of reactive iron ions. From the viewpoint of physicochemical conditions the horizons with iron carbonate concretions in the study area reflect the redox boundary between oxic/bioturbated and anoxic/non-bioturbated zones. The conditions favoring the formation of such horizons was possibly due to longer periods of diminished sedimentation rate when the redox boundary remained in the same position within the sediment.

scholarly journals UM MODELO PARA A EVOLUÇÃO MICROESTRUTURAL DOS MINÉRIOS DE FERO DO QUADRILÁTEO FERRÍFERO. PARTE I - ESTRUTURAS E RECRISTALIZAÇÃO

1993 ◽  
Author(s):  
Carlos Alberto Rosière ◽  
Farid Chemale Jr. ◽  
Marcelo L.V. Guimarães
Keyword(s):  
Iron Ore ◽  
Banded Iron Formations ◽  
Lower Proterozoic ◽  
Ore Bodies ◽  
Quadrilátero Ferrífero ◽  
Textural Relationship ◽  
Iron Formations ◽  
Ore District ◽  
Proterozoic Age

In the Quadrilátero Ferrífero iron ore district, the Cauê Formation of the Minas Supergroup comprise banded iron formations, called itabirites, of Lower Proterozoic age enclosing iron rich ore bodies. Although many ore bodies are associated with syntectonic enrichment processes, due to the leaching of gangue minerals like quartz and carbonates, others are probably of sedimentary origin and were recrystallized during the tectonometamorphic development of the region.Three generations of magnetite and four of hematite are recognized in these rocks. They display a clear textural relationship in zones of high and low strain, with the development of two main deformational events under variable metamorphic conditions and different tectonic levels.The first part of this paper one describes the recrystallization phenomena and its relation to the main structures, while in the second part the developed textures and its association to the strain are presented.

scholarly journals Garnet-sillimanite bearing gneisses from Darjeeling, eastern Himalaya: Textural relationship and P–T conditions

2015 ◽  
Vol 124 (6) ◽  
pp. 1187-1199 ◽  
Author(s):  
Divya Prakash ◽  
Suparna Tewari
Keyword(s):  
Eastern Himalaya ◽  
Textural Relationship

Textural Relationship of Sulfide Ores, PGE, and Sr-Nd-Os Isotope Compositions of the Triassic Piaohechuan Ni-Cu Sulfide Deposit in NE China

2015 ◽  
Vol 110 (8) ◽  
pp. 2041-2062 ◽  
Author(s):  
Bo Wei ◽  
Christina Yan Wang ◽  
Nicholas T. Arndt ◽  
Hazel M. Prichard ◽  
Peter C. Fisher
Keyword(s):  
Sulfide Deposit ◽  
Sulfide Ores ◽  
Ne China ◽  
Textural Relationship ◽  
Relationship Of ◽  
Os Isotope

Spatial Association Between Platinum Minerals and Magmatic Sulfides Imaged with the Maia Mapper and Implications for the Origin of the Chromite-Sulfide-PGE Association

2021 ◽  
Author(s):  
Stephen J. Barnes ◽  
Chris Ryan ◽  
Gareth Moorhead ◽  
Rais Latypov ◽  
Wolfgang D. Maier ◽  
...  
Keyword(s):  
Close Association ◽  
Spatial Association ◽  
Ore Deposits ◽  
Sulfide Liquid ◽  
X Ray ◽  
Magmatic Sulfides ◽  
Array Technology ◽  
Magmatic Sulfide ◽  
Textural Relationship

ABSTRACT The spatial association between Pt minerals, magmatic sulfides, and chromite has been investigated using microbeam X-ray fluorescence (XRF) element mapping and the Maia Mapper. This lab-based instrument combines the Maia parallel energy dispersive (ESD) detector array technology with a focused X-ray beam generated from a liquid metal source. It proves to be a powerful technique for imaging Pt distribution at low-ppm levels on minimally prepared cut rock surfaces over areas of tens to hundreds of square centimeters, an ideal scale for investigating these relationships. Images of a selection of samples from the Bushveld Complex and from the Norilsk-Talnakh ore deposits (Siberia) show strikingly close association of Pt hotspots, equated with the presence of Pt-rich mineral grains, with magmatic sulfide blebs in all cases, except for a taxitic low-S ore sample from Norilsk. In all of the Bushveld samples, at least 75% of Pt hotspots (by number) occur at or within a few hundred microns of the outer edges of sulfide blebs. In samples from the leader seams of the UG2 chromitite, sulfides and platinum hotspots are also very closely associated with the chromite seams and are almost completely absent from the intervening pyroxenite. In the Merensky Reef, the area ratio of Pt hotspots to sulfides is markedly higher in the chromite stringers than in the silicate-dominated lithologies over a few centimeters either side. We take these observations as confirmation that sulfide liquid is indeed the prime collector for Pt and, by inference, for the other platinum group elements (PGEs) in all these settings. We further propose a mechanism for the sulfide-PGE-chromite association in terms of in situ heterogeneous nucleation of all these phases coupled with transient sulfide saturation during chromite growth and subsequent sulfide loss by partial re-dissolution. In the case of the amygdular Norilsk taxite, the textural relationship and high PGE/S ratio is explained by extensive loss of S to an escaping aqueous vapor phase.

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