Geochemical trends in tholeiite dykes of different ages from Guiana

Choudhuri, Asit

doi:10.1016/0009-2541(78)90022-0

Cited by 12 publications

(6 citation statements)

References 17 publications

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“…2, 6a, 7, and 8). Some early Mesozoic tholeiitic dike provinces include those of Surinam (Choudhuri, 1978) and Liberia (Testa, 1978). Major oxide compositional data collected from each of these Triassic and Jurassic provinces, when plotted on another HTQ normalization diagram (Fig.…”

Section: Triassic and Jurassic Flood Basaltsmentioning

confidence: 99%

Eastern North American flood basalts in the context of the incipient breakup of Pangea

Puffer

1992

Geological Society of America Special Papers

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The eastern North America (ENA) Mesozoic flood basalt province, particularly the part of the province north of central Virginia, is dominated by quartz-normative tholeiites. High-titanium quartz-normative (HTQ) basalts are the first and most widespread Mesozoic extrusions that flowed across several North Atlantic margin rift basins, including the Fundy, Hartford, Newark, and Culpeper basins of North America and the Argana basin of Morocco, Africa. These initial flows are chemically uniform and appear to be largely unchanged by fractionation from their mantle source. Isotopic data for 87 Sr/ 86 Sr and ,43 Nd/ 144 Nd are consistent with a lithospheric subcontinental mantle source that was either undepleted or slightly enriched through previous subduction events. The mantle source presumably underwent adiabatic decompressive melting during Mesozoic North Atlantic rifting.The HTQ flood basalts are chemically the same as the dominant members of flood-basalt provinces that were penecontemporaneously extruding from rifts along the South Atlantic margin (the Lesotho basalts of South Africa and the adjacent Patagonian basalts of Argentina), and from the Siberian platform of Asia. This world-wide distribution of virtually identical basalts associated with Pangean rifting implies the uniform operation of some fundamental petrogenetic controls and a diminished likelihood that localized processes unique to any single basin were dominant controlling factors of the regional HTQ composition.The HTQ flood basalts also chemically resemble some of the least-evolved flows of several other continental flood-basalt provinces. Most world-wide continental provinces, however, are dominated by basalts that are relatively enriched in incompatible elements, as if they were contaminated or fractionated to varying degrees. Perhaps the Pangean rifting event responsible for the flood basalts of the North and South Atlantic margins and the Siberian platform was uniquely powerful enough to allow for the rapid delivery of large quantities of unfractionated and uncontaminated magma directly from shallow undepleted or enriched mantle sources after a prolonged period of insulation and thermal accumulation under the Pangean "supercontinent."The HTQ flows are chemically distinct from other quartz-normative tholeiites of the ENA Mesozoic flood-basalt province that quickly followed them. Flows overlying the HTQ flows are a chemically diverse array including several varieties of high-iron quartz-normative, low-titanium quartz-normative, and possibly olivine-normative types that were probably generated at mantle sources chemically modified by previous HTQ partial melting or from mantle sources independent of the HTQ source. The diverse array of extrusive basalts that followed the HTQ flows seems to have undergone the varying degrees of contamination and fractionation typical of other continental floodbasalt provinces.

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Section: Triassic and Jurassic Flood Basaltsmentioning

confidence: 99%

Eastern North American flood basalts in the context of the incipient breakup of Pangea

Puffer

1992

Geological Society of America Special Papers

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“…At Omai, these bodies may represent subvolcanic equivalents of the overlying mafic volcanic rocks (Voicu and Bardoux, 1995). Younger Basic Group rocks yielded ages between 1.6 and 1.8 Ga by K-Ar and Rb-Sr methods (Snelling and McConnell, 1969), similar to ages of the Mesoproterozoic Avanavero Suite, which has been described throughout the Guiana Shield (Hawkes, 1966;Choudhuri, 1978;Gibbs, 1987b;Teixeira, 1990;Choudhuri et al, 1990).…”

Section: Regional Geologymentioning

confidence: 65%

Géologie, géochimie et métallogénie du gisement d'or Omai, Bouclier Guyanais, Amérique du Sud =

Voicu¹

1999

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IVdépôt de la minéralisation à Ornai (basse température, pression, salinité, et contenu en CO 2 , pH légèrement acide à neutre, fugacités modérées de l'oxygène et du soufre, fugacité élevée des tellurures), l'implication de l'eau de surface, la présence des structures hôtes de la minéralisation de nature essentiellement cassante et la localisation dans un terrain faiblement métamorphisé sont autant de critères permettant de classer Ornai dans la catégorie des gîtes épithermaux. D'autres caractéristiques majeures tels que: le style d'altération; le cadre géodynamique; l'emplacement tardi-orogénique/syn-à tarditectonique; la présence des fluides d'une source profonde et; de manière moins directe, la paragénèse minéralogique se rattachent à la définition des gîtes mésothermaux plus profonds. La superposition des caractéristiques épi-et mésothermales d'Omai correspond donc à la partie supérieure du "continuum model" proposé pour les gisements archéens de type "gold-only" et définie comme le domaine crustal dit épizonal. Ornai serait donc un premier exemple de gîte orogénique aurifère d'âge paléoprotérozoïque de type épizonal associé aux granitoïdes et aux roches vertes. Il représente un équivalent de ce type de gîte ayant été décrit uniquement dans certains cratons archéens (Yilgarn et Zimbabwe).Mots clé: Guyana, Paléoprotérozoïque, or, géochimie, métallogénie ABSTRACTThe Omai gold mine is located in the Barama-Mazaruni Supergroup, part of the Paleoproterozoic greenstone belt of the north-central Guiana Shield. The lithological sequence consists of mafic volcanic (and genetically related subvolcanic maficultramafic bodies) to felsic volcanic cycles with intercalated sediments. The volcanosedimentary unit was intruded by a quartz monzodiorite plug (the Omai stock) and several irregularly-shaped quartz-feldspar porphyry and rhyolite dikes. Postmineralization mafic dikes and sills were intruded discontinuously from Mesoproterozoic to Triassic. The Barama-Mazaruni volcano-sedimentary sequence has been metamorphosed to lower greenschist faciès. The local structure is relatively simple and consists of two deformational phases (Dl and D2). Dl phase resulted in the ESE-WNW trending/steeply dipping regional scale foliation and ductile shear zones, whereas the D2 event caused brittle± ductile fracturing with moderate dips, oriented perpendicularly to Dl shear zones. D2 structures provided the main pathways for the mineralizing fluids.The Omai deposit consists of two gold mineralized zones exploited in open pit operations referred to as Fennell and Wenot. Fennell mineralization is mainly hosted by the Omai stock and to a lesser extends by the volcanic rocks (tholeiitic basalts and calcalkaline andésites). Wenot mineralization is mainly hosted by tabular quartz-feldspar porphyry dikes as well as by strongly silicified rhyolite dikes, and subordinately by andésites and metapelites.The geological features and geochronological data of these ore zones suggest that they are genetically related and represent a contemporaneous metallo...

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“…Rocks of the Cuchivero Group and its equivalents have been considered as both orogenic related to the Trans-Amazonian collision and deformation and as anorogenic (De Vletter and Kroonenberg, 1984). Supporters of the orogenic interpretation suggest that the contact between the felsic 19782Berrange, 19773Priem and others, 19714Basei and Teixeira, 19755 Amaral and Halpern, 1975 *As reported by Priem and others, 1971 **As reported by Basei and Teixeira, 1975 4.63 volcanic rocks and rocks of the underlying greenstone belt is conformable and therefore include the Cuchivero Group and its equivalents as a second, dominantly magmatic, stage of the Trans-Amazonian orogeny between about 2,000 and 1,870 Ma (Bosma and others, 1983;De Vletter and Kroonenberg, 1984;Teixeira and others, 1984). However, as noted above, deformation and metamorphism in the Cuchivero Group are significantly different from that in the greenstone-belt rocks, and, therefore, a conformable contact is considered extremely unlikely.…”

Section: Age and Origin Of The Cuchivero Groupmentioning

confidence: 98%

“…The Proterozoic diabases are lower in total iron, titanium, vanadium, volatile content (water, carbon dioxide, fluorine, and chlorine as measured by loss on ignition), and possibly copper than the Mesozoic diabase suite (Teggin and others, 1985;Sial and others, 1986). It has been suggested, on the basis of these and other chemical differences between the Proterozoic and Mesozoic diabases, that the Proterozoic intrusions represent differentiates of parent magmas with the same composition that underwent pre-intrusive, shallow level (crustal) differentiation (Choudhuri, 1978) or that were derived from a shallower region in the mantle (Sial and others, 1986). In contrast, the Mesozoic dike swarms represent magmas derived directly from the mantle, possibly related to a hot spot or mantle plume, during the breakup of Gondwanaland and the formation of the Atlantic Ocean (Choudhuri, 1978;Sial and others, 1986).…”

Section: Avanavero Suitementioning

confidence: 99%

“…The dike rocks are fine-to medium-grained, with subophitic to ophitic texture (Hargraves, 1978), and contain plagioclase (commonly labradorite) and augite with minor pigeonite, relict olivine cores in pyroxene, biotite, green amphibole, apatite, opaque minerals such as titaniferous magnetite, ilmenite, rare chalcopyrite and pyrrhotite, and minor interstitial granophyric intergrowths of quartz and microcline microperthite (Hawkes, 1966a;Hargraves, 1978;Choudhuri and others, 1984). These rocks are quartz-saturated tholeiite with a continental basalt affinity (Choudhuri and others, 1984), and they generally have a higher concentration of titanium, total iron, vanadium, volatile content (water, carbon dioxide, fluorine, and chlorine as measured by loss on ignition), and possibly copper than those in the Avanavero Suite (Choudhuri, 1978;Teggin and others, 1985). Their chemistry suggests that the Mesozoic dike swarms were derived directly from an undepleted mantle source, possibly related to a mantle plume and hot spot, during the breakup of Gondwanaland and the separation of South America from Africa (Choudhuri and others, 1984).…”

Section: Mesozoic Diabase Dikesmentioning

confidence: 99%

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Geology of the Venezuelan Guayana Shield and its relation to the entire Guayana Shield

Sidder¹,

Mendoza²

1991

Open-File Report

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The Guayana Shield in Venezuela is composed of five lithotectonic provinces: 1) an Archean amphibolite-to granulite-facies gneiss terrane; 2) an Early Proterozoic greenstone-granite terrane(s); 3) an Early Proterozoic unmetamorphosed volcanoplutonic complex; 4) Early to Middle Proterozoic continental sedimentary rocks; and 5) Middle Proterozoic anorogenic rapakivi-type granite. Early Proterozoic rocks in the Amazon Federal Territory of western Venezuela are undivided and their relation to other rocks of the Venezuelan Guayana Shield is unclear. Early to Middle Proterozoic continental tholeiitic dikes, sills, and small irregular intrusive bodies and Mesozoic dikes emplaced during the opening of the Atlantic Ocean cut all of the lithotectonic provinces. Major mineral deposits of the Venezuelan Guayana Shield include gold, iron, bauxite, and diamonds. The Archean Imataca Complex, the oldest unit, consists of gneiss and granulite with minor dolomite and banded iron-formation (BIF). Large isoclinal folds, which have been refolded into relatively open folds, are common in the Imataca Complex. Metamorphic grade ranges from granulite facies in the northeast part of the belt to amphibolite facies in the southwest. Deposits of enriched BIF in the Imataca Complex contain more than 2 billion metric tons of iron ore. During the Pre-Trans-Amazonian tectonomagmatic event, between about 2,800 and 2,700 Ma, granitic rocks intruded the Imataca Complex, and injection gneisses and migmatite were developed. The Early Proterozoic greenstone belts, which formed between about 2,250 and 2,100 Ma, consist of a submarine sequence of tholeiitic mafic volcanic rocks, a sequence of tholeiitic to calc-alkaline basalt to rhyolite, and an interval of turbiditic graywacke, volcaniclastic rocks, and chemical sedimentary rocks that characterize the basal, middle, and upper parts, respectively. Layered mafic complexes also occur in the greenstone belts. The greenstone-belt rocks range in metamorphic grade from greenschist to amphibolite facies. Low-sulfide gold-quartz veins are hosted by Early Proterozoic greenstone-belt rocks cut by major shear zones. Deposits of volcanogenic manganese are mined elsewhere in the Guayana Shield; in Venezuela, a moderate potential exists for the discovery of additional deposits of manganese in the greenstone belts. Platinum-group elements (PGE) and chromium are present in anomalous values in the layered mafic complex at Piston de Uroy, Venezuela. Also, PGE are anomalous in mafic metavolcanic and metagabbroic rocks adjacent to an exhalative (Homestake-type) gold prospect in the Cerro La Pinto area. Granitic domes of the Supamo Complex intruded the greenstone-belt rocks between about 2,230 and 2,050 Ma and divided the metasedimentary and meta-igneous greenstonebelt rocks into branching synclinoria between intrusive uplifts. The Trans-Amazonian orogeny was a period of continental collision between about 2,150 and 1,960 Ma, during which the Imataca Complex and the greenstonegranite terranes were deformed and metamorphose...

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Geochemical trends in tholeiite dykes of different ages from Guiana

Cited by 12 publications

References 17 publications

Eastern North American flood basalts in the context of the incipient breakup of Pangea

Eastern North American flood basalts in the context of the incipient breakup of Pangea

Géologie, géochimie et métallogénie du gisement d'or Omai, Bouclier Guyanais, Amérique du Sud =

Geology of the Venezuelan Guayana Shield and its relation to the entire Guayana Shield

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