Mineralogical and chemical characteristics of newer dolerite dyke around Keonjhar, Orissa: Implication for hydrothermal activity in subduction zone setting
TL;DR: The newer dolerite dykes around Keonjhar within the Singbhum Granite occur in NE-SW, NW-SE and NNE-SSW trends as mentioned in this paper.
Abstract: The newer dolerite dykes around Keonjhar within the Singbhum Granite occur in NE–SW, NW–SE and NNE–SSW trends. The mafic dykes of the present study exhibit several mineralogical changes like clouding of plagioclase feldspars, bastitisation of orthopyroxene, and development of fibrous amphibole (tremolite–actinolite) from clinopyroxene, which are all considered products of hydrothermal alterations. This alteration involves addition and subtraction of certain elements. Graphical analyses with Alteration index and elemental abundances show that elements like Rb, Ba, Th, La and K have been added during the alteration process, whereas elements like Sc, Cr, Co, Ni, Si, Al, Fe, Mg and Ca have been removed. It is observed that in spite of such chemical alteration, correlation between major and trace elements, characteristic of petrogenetic process, is still preserved. This might reflect systematic Alteration (addition or subtraction) of elements without disturbing the original element to element correlation. It has also been established by earlier workers that the evolution of newer dolerite had occurred in an arc-back arc setting which may also be true for newer dolerites of the present study. This is evident from plots of pyroxene composition and whole rock composition of newer dolerite samples in different tectonic discrimination diagrams using immobile elements. The newer dolerite dykes of the Keonjhar area may thus be considered to represent an example of hydrothermal activity on mafic rocks in an arc setting.
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TL;DR: In this article, the authors reported eight new Pb-Pb baddeleyite ages and paleomagnetic results on a series of hitherto unknown NNE-SSW trending mafic dyke swarms intruding the Paleoarchean basement rocks in the Singhbhum craton, eastern India.
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TL;DR: In this article, the authors reported the first key paleopole as a result of paleomagnetic study on a precisely dated 1765, which was used in this study to propose the paleogeographic reconstruction of India with Baltica Craton and North China Craton.
35 citations
TL;DR: The Bangriposi Granite Gneiss as discussed by the authors is composed of quartz, alkali feldspar, ferroan biotite (Fe/Fe+Mg: 0.7-0.9), titanite, illmenite, hastingsite, apatite, and numerous U-ThREE bearing accessory phases.
27 citations
TL;DR: The Singhbhum Craton in eastern India is host to at least seven sets of mafic dyke swarms and the dykes range in composition from basalt to andesite and have transitional tholeiitic to calc-alkaline affinities as discussed by the authors.
14 citations
TL;DR: In this article, the authors investigated the petrography and geochemistry of 19 NNE-SSW to NE-SW trending dolerite dykes in two sectors in the northern and southwestern part of Bahalda town, Odisha, India.
Abstract: The mafic dyke swarm, newer dolerite dykes (NDDs) intrudes the Archaean Singbhum granite of the Singhbhum craton, eastern India. The present investigation focuses on the petrography and geochemistry of 19 NNE–SSW to NE–SW trending NDDs in two sectors in the northern and south-western part of Bahalda town, Odisha, Singhbhum. Chondrite normalised rare earth element (REE) patterns show light REE (LREE) enrichment among majority of the 13 dykes while the remaining six dykes show a flat REE pattern. Critical analyses of some important trace element ratios like Ba/La, La/Sm, Nb/Y, Ba/Y, Sm/La, Th/La, La/Sm, Nb/Zr, Th/Zr, Hf/Sm, Ta/La and Gd/Yb indicate that the dolerite dykes originated from a heterogeneous spinel peridotite mantle source which was modified by fluids and melts in an arc/back arc setting. REE modelling of these dolerite dykes were attempted on LREE-enriched representative of NDD which shows that these dykes might have been generated by 5–25% partial melting of a modified spinel peridotite source which subsequently suffered around 30% fractional crystallisation of olivine, orthopyroxene and clinopyroxene. The reported age of ~2.75–2.8 Ma seems to be applicable for these dykes and this magmatism appears to be contemporaneous with major scale anorogenic granitic activity in the Singhbhum craton marking a major event of magmatic activity in eastern India.
11 citations
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Journal Article•
TL;DR: The early Proterozoic Bundelkhand Granite Massif of India is extensively intruded by NW-SE and NE-SW trending mafic and ultramafic dykes as mentioned in this paper.
Abstract: The early Proterozoic Bundelkhand Granite Massif of
Central India is extensively intruded by NW–SE and
NE–SW trending mafic and ultramafic dykes. These
dykes are mostly dolerites with subordinate pyroxenite
or lamproites, and geochemical signatures are different
for the NW–SE and NE–SW trending dyke suites.
40Ar/39Ar age determinations of the dolerite dykes
suggest two phases of dyke activity at ca. 2150 Ma and
2000 Ma and supported by palaeomagnetic results in
this region. Apart from other magmatic emplacements,
there are younger deformational events recorded by
minerals (1800 Ma event recorded by some mafic regions
of dykes and 692–750 Ma given by plagioclase feldspars) subsequent to their magmatic emplacements. The dolerites are typically tholeiites and quartz normative types, while the ultramafics are komatiite or basaltic komatiite in composition and show an olivinenormative character. Most of the tholeiites display incompatible elements pattern indicative of an enriched mantle source, while those of the ultramafics indicate a depleted source.
79 citations
Journal Article•
TL;DR: Taking the Pulse of Planet Earth as discussed by the authors is a multidisciplinary "big science" project for Canada's solid earth sciences, aiming at providing the most comprehensive and multidisdisciplinary knowledge base of the complete record of mafic magmatism in and around Canada, and through stimulating international cooperation, around the world.
Abstract: Herein I propose a vision for a new multidisciplinary "big science" project for Canada's solid earth sciences. I call this proposed project: "Taking the Pulse of Planet Earth". At a modest cost, and over a 5 to 10 year life-span, it would aim at providing the most comprehensive and multidisciplinary knowledge base of the complete record of mafic magmatism in and around Canada, and through stimulating international cooperation, around the world.
A complete record of mafic magmatism (spatial distribution, ages, periodicities, rates, volume estimates, estimated geochemical fluxes to atmosphere and hydrosphere, tectonic settings, structural trends, sequence stratigraphic framework, evolving major and trace element compositions, evolving isotopic ratios, paleomagnetic information, paleo-intensities, associated ore deposits, etc.) constitutes critical input data for numerous first-order questions about the past and present evolution of our planet. Many of such questions relate to issues that are currently a focus of attention: global change, past climate extremes, complex Earth systems, planetary evolution, extinction events, flood volcanism, potential relationships with large impact events, and the discovery of new ore resources.
The proposed project is a focused, "smart", and highly efficient approach to solve a large number of these seemingly unrelated but first-order questions in contemporary earth science. At its core, it would have a large dating program, aiming to provide approximately 200 new, high-precision ages of mafic magmatic events across Canada and adjacent regions. A Supporting Geoscience grant system would ensure that other aspects of the magmatic record receive equal attention. Finally, I illustrate the impact this project would have on paleo-continental reconstructions. As part of this illustration, I synthesize existing data on two dyke swarms, the ca. 2.45 Ga Matachewan and Kaminak swarms, respectively, and propose a novel Superior-Hearne reconstruction within supercraton Superia.
SOMMAIRE
Je propose ci-contre l'idee d'un nouveau projet multidisciplinaire de grande envergure dans le domaine des sciences des roches solides au Canada. J'ai nomme ce projet « Prendre le pouls de la planete Terre ». D'un cout modeste et s'echelonnant sur cinq a dix ans, ce projet constituerait la base de connaissances multidisciplinaire la plus complete de tout le repertoire des evenements magmatiques mafiques au Canada et a son pourtour, cela, en profitant des effets stimulant de la cooperation internationale.
Un repertoire complet des evenements magmatiques mafiques (distribution spatiale, âges, periodicites, taux, estimations des volumes, estimations geochimiques des flux dans l'atmosphere et l'hydrosphere, cadres tectoniques, styles structuraux, cadres stratigraphiques des sequences, compositions des suites evolutives des elements majeurs et en trace, evolution des ratios isotopiques, donnees paleomagnetiques, paleo-intensites, gisements associes, etc.) constitue un registre de donnees de base cruciales pour nombres de grandes questions sur l'evolution passee et actuelle de notre planete. Plusieurs de ces grandes questions sont liees a des problemes actuels qui mobilisent l'attention, tels : les changements a l'echelle planetaire, les evenements climatiques extremes du passe, les systemes planetaires complexes, l'evolution de la planete, les grandes extinctions biotiques, les grands epanchements volcaniques, les liens eventuels avec de grands impacts meteoritiques, ainsi que la decouverte de nouvelles sources de minerai.
Le projet propose constitue une approche ciblee, « habile », et tres efficace permettant de solutionner un grand nombre de ces grands problemes, sans liens apparents, des geosciences contemporaines. Au cœur du projet on retrouve un grand programme de datation visant a etablir quelques 200 nouvelles datations de grande precision d'evenements magmatiques au Canada et dans les regions peripheriques. Un systeme de subvention d'appoint permettrait d'assurer que d'autres aspects de la problematique magmatique recoivent autant d'attention. Finalement, a titre d'illustration, je decris les repercussions escomptees d'un tel projet sur les reconstitutions paleocontinentales. Dans le cadre de cette illustration, je presente une synthese des donnees disponibles concernant deux reseaux de dykes, soit les reseaux de Matachewan et de Kaminak de 2,45 Ga, respectivement, et propose une nouvelle reconstitution Superieur-Hearne dans le super-craton Superia.
77 citations
"Mineralogical and chemical characte..." refers background in this paper
...Mafic dykes are important components of the Proterozoic rock record and act as significant time markers within stabilized Archean cratons (Ernst and Buchan 2001; Bleeker 2004)....
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TL;DR: In this article, five zones are recognized in the Troodos ophiolite and in situ oceanic crust: (1) a sea-floor weathering zone (SWZ), (2) a low-temperature zone (LTZ),(3) a transition zone, (4) an upper dike zone (UDZ), and (5) a mineralized zone (MZ).
Abstract: Aging of the upper oceanic crust produces alteration zones that have distinct mineralogical and geochemical characteristics. Five zones are recognized in the Troodos ophiolite and in situ oceanic crust: (1) a sea-floor weathering zone (SWZ), (2) a low-temperature zone (LTZ), (3) a transition zone (TZ), (4) an upper dike zone (UDZ), and (5) a mineralized zone (MZ). The MZ may be overlain by the SWZ, LTZ, or TZ, but in the known examples it is always underlain by the UDZ. The development of the SWZ is dependent upon the duration of cold-seawater circulation, which is dependent upon seafloor topography and the rate and nature of sedimentation. The boundary between the low- and high-temperature zones is largely controlled by permeability contrasts. Lateral variation in the depth of this boundary indicates that the thermal gradient is not uniform within the crust. This, along with the evidence for disequilibrium assemblages, implies that regional metamorphic zones are not appropriate to describe the distribution of alteration effects.
76 citations
Journal Article•
TL;DR: In this paper, various theories to account for the formation of clouded plagioclase are reviewed, and it is shown that such feldspars cannot be used as sole criteria for thermal metamorphism.
Abstract: Various theories to account lor clouded plagioclase are reviewed. Observations indicate that the particles causing this efiect may consist of different minerals, and that many minerals, besides plagioclase, may show clouding. It is suggested that in clouded minerals there are minute surfaces of physical discontinuity which provide adequate passages for difiusion of material into and out of the crystals. In intermediate plagioclases these surfaces may consist of internal phase boundaries in the unmixed feldspar. Slight clouding is probably due to exsolution of iron present in the feldspar lattice at the time of its formation, but more intense clouding is believed to be the result of the migration of iron and other elements into the crystal after its formation. The geological significance of clouded plagioclase is discussed and it is shown that such feldspars cannot be used as sole criteria for thermal metamorphism.
50 citations