Geology and U-Pb geochronology of rocks of the Eokuk Uplift: a pre-2.8 Ga basement inlier in the northwestern Slave Province, Nunavut, Canada

1999 ◽  
Vol 36 (7) ◽  
pp. 1061-1082 ◽  
Author(s):  
K A Emon ◽  
V A Jackson ◽  
G R Dunning
Keyword(s):  
Granite Gneiss ◽  
Granulite Facies ◽  
High Grade ◽  
Zircon Age ◽  
Crustal Component ◽  
Slave Province ◽  
Zircon Crystallization ◽  
Intrusive Rocks ◽  
High Grade Metamorphism ◽  
Combined Data

Rocks of the Eokuk Uplift have been mapped in detail along the coast of Coronation Gulf and 10 key units have been dated by U-Pb analysis of zircon, monazite, and titanite. The combined data indicate that this inlier of the Slave Province has a >3.2 Ga crustal component, evidence of a granulite-grade orogenic event predating 2.8 Ga and a lack of evidence for any significant orogenic activity corresponding to the 2.7-2.6 Ga events common in the rest of the Slave Province. The oldest rocks in the study area are a succession of granitoid and supracrustal gneisses that have been metamorphosed to amphibolite to granulite facies. From field relationships, the oldest rock is a granodiorite to tonalite orthogneiss, with a zircon crystallization age of 3254+13-6 Ma. A granite gneiss, which may be a small felsic intrusion or an anatectic melt of the tonalite gneiss, yields a zircon age of 3216+14-13 Ma. A K-feldspar megacrystic monzogranite gneiss contains old, discordant, possibly inherited zircons with 207Pb/206Pb ages ranging from 3103 to 3039 Ma, together with coexisting 2879 ± 3 Ma zircon and monazite. These high-grade gneisses are intruded by two megacrystic granite plutons, dated at 2887 ± 2 and 2881+4-3 Ma. The absence of extensive recrystallization and complex structures in these plutons indicates that this igneous event postdated the high-grade metamorphism. An amphibolite-grade synplutonic metamorphic event is dated at ~2880 Ma by new monazite in the older gneiss units. A series of variably deformed mafic to felsic dykes and pegmatites intrude both the granites and gneisses and constrain the end of penetrative deformation in the area. Of these, a boudinaged diorite dyke, with a strong internal foliation parallel to the regional fabric, is dated at 2877 ± 3 Ma. A younger granodiorite dyke that crosscuts the regional fabric at a high angle and has only a weak internal foliation yields an age of 2864+3-9 Ma. An undeformed syenogranite pegmatite, which represents a suite that intrudes all other units in the study area, has a combined zircon-monazite age of 2852 ± 3 Ma. The varying degrees of deformation in these minor intrusive rocks constrains the end of deformation in the study area to ca. 2850 Ma. This contrasts with data from the rest of the Slave Province, where the main phases of deformation, metamorphism, and synmetamorphic plutonism have been dated at ca. 2.62-2.59 Ga. Metamorphic titanite ages from the diorite and granodiorite dykes indicate two lower amphibolite to greenschist facies metamorphic events: one at ca. 2705 Ma and one at ca. 2646 Ma. The youngest Archean magmatic event in the area is represented by granite intrusions at 2594+3-2 Ma, coeval with crystallization of titanite at greenschist-grade conditions in some of the older gneissic and intrusive rocks.

Geology of the Bunger Hills area, Antarctica: implications for Gondwana correlations

1993 ◽  
Vol 5 (1) ◽  
pp. 85-102 ◽  
Author(s):  
John W. Sheraton ◽  
Robert J. Tingey ◽  
Lance P. Black ◽  
Robin L. Oliver
Keyword(s):  
Granulite Facies ◽  
Mobile Belt ◽  
High Grade ◽  
Yilgarn Craton ◽  
Zone Formation ◽  
Zircon Age ◽  
Peak Metamorphism ◽  
High Grade Metamorphism ◽  
Subsequent Deformation ◽  
Hills Area

The Bunger Hills area of the East Antarctic Shield consists of granulite-facies felsic orthogneiss, with subordinate paragneiss and mafic granulite. The igneous precursors of granodioritic orthogneiss were emplaced 1500-1700 Ma ago, and late Archaean (2640 Ma) tonalitic orthogneiss occurs in the nearby Obruchev Hills. Peak metamorphism (M1) (at about 750-800°C and 5-6kb) occurred 1190 ±15 Ma ago (U-Pb zircon age), and was accompanied by the first of three ductile deformations (D1). Emplacement of voluminous, mainly mantle-derived plutonic rocks, ranging from gabbro, through quartz monzogabbro and quartz monzodiorite, to granite, followed between 1170 (during D3) and 1150 Ma. Intrusion of abundant dolerite dykes of four chemically distinct suites at about 1140 Ma was associated with shear zone formation, indicating at least limited uplift; all subsequent deformation was of brittle-ductile type. Alkaline mafic dykes were emplaced 500 Ma ago. Marked geochronological similarities with the Albany Mobile Belt of Western Australia suggest that high-grade metamorphism occurred during collision between the Archaean Yilgarn Craton of Australia and the East Antarctic Shield about 1200 Ma ago.

Ages of detrital and metamorphic zircons and monazites from a pre-Taltson magmatic zone basin at the western margin of Rae Province

1994 ◽  
Vol 31 (8) ◽  
pp. 1353-1364 ◽  
Author(s):  
H. H. Bostock ◽  
O. van Breemen
Keyword(s):  
Isotope Geochemistry ◽  
Granulite Facies ◽  
Metamorphic Grade ◽  
Detrital Zircons ◽  
Ultramafic Rocks ◽  
Crustal Accretion ◽  
The West ◽  
Slave Province ◽  
Basin Formation ◽  
High Grade Metamorphism

The western edge of Rae Province, prior to indentation of Slave Province, is conceived as a compressional tectonic margin in which Archean plutonic rocks were intruded by syntectonic granites of 2.4–2.3 Ga age as a result of eastward subduction. Subsequently this margin was intruded by the 2.0–1.90 Ga granites that characterize the Taltson magmatic zone. The latter granites engulf remnants of a widespread supracrustal assemblage of lower granulite facies metamorphic grade, the age of which has heretofore been unknown. We use U–Pb zircon and monazite geochronology to limit the age of cessation of deposition of these metasediments in a pre-Taltson granite basin to between 2.13 and 2.09 Ga.Similarities in geochronology and isotope geochemistry between western Rae Province and Buffalo Head domain, together with the presence of mafic to ultramafic rocks both within the basin and along the western Rae margin, suggest that basin formation was by rifting. Influx of 2.15 Ga detrital zircons probably from the west, and high-grade metamorphism accompanying basin closure at 2.09 Ga, suggest an eastward (inward) movement of magmatism at that time. A second similar eastward migration of magmatism occurred in association with the Slave–Churchill collision (2.0–1.9 Ga). These relations suggest a complex record of crustal accretion within Buffalo Head and Chinchaga domains, the details of which remain to be established.

scholarly journals Search for Archaean basement in the Caledonian fold belt of North-East Greenland

1994 ◽  
Vol 162 ◽  
pp. 129-133
Author(s):  
A.P Nutman ◽  
F Kalsbeek
Keyword(s):  
High Grade ◽  
Metamorphic Zircon ◽  
Fold Belt ◽  
Pb Isotope ◽  
Zircon Age ◽  
East Greenland ◽  
Early Proterozoic ◽  
North East ◽  
History Of ◽  
High Grade Metamorphism

SHRIMP U-Pb isotope data on zircon crystals from a gneiss sample near Danmarkshavn, where the presence of Archaean rocks has earlier been documented, show that the rock has undergone a complex history of igneous and metamorphic zircon growth. At least three generations of zircon are present with ages of c. 3000 Ma, c. 2725 Ma and 1967 ±8 Ma (2 α). Apparently the rock was formed from an Archaean protolith which underwent high grade metamorphism during the early Proterozoic. Another sample from the easternmost exposures of the Caledonian basement, collected further north, yielded only early Proterozoic zircons with an age of 1963 ± 6 Ma. Together with a SHRIMP U-Pb zircon age of 1974 ± 17 Ma reported earlier, these results give evidence of a major igneous and metamorphic event in North-East Greenland about 1965 Ma ago.

Silicate, Oxide and Sulphide Trends in Neo-Archean Rocks from the Nilgiri Block, Southern India: the Role of Fluids During High-grade Metamorphism

2019 ◽  
Vol 60 (5) ◽  
pp. 1027-1062 ◽  
Author(s):  
Vinod O Samuel ◽  
Daniel E Harlov ◽  
Sanghoon Kwon ◽  
K Sajeev
Keyword(s):  
Granulite Facies ◽  
Southern India ◽  
Sulphide Mineral ◽  
High Grade ◽  
Regional Trend ◽  
Granulite Facies Metamorphism ◽  
Facies Metamorphism ◽  
High Grade Metamorphism ◽  
Specific Oxidation

Abstract The Nilgiri Block, southern India represents an exhumed section of lower, late Archean (2500 Ma) crust. The northern highlands of the Nilgiri Block are characterized by metagabbros with pyroxenite inlayers. A two-pyroxene granulite zone acts as a transition between the metagabbros and charnockites, which are exposed in the central and southern part of the Nilgiri highlands. Thermobarometry results indicate a SW–NE regional trend both in temperature (∼650–800°C) and in pressure (700–1100 MPa) over the Nilgiri highlands. In the charnockites, composite rutile–ilmenite grains are the dominant oxide assemblage. In the two-pyroxene granulites, hemo-ilmenite–magnetite is dominant with coexisting rutile–ilmenite composite grains in a few samples in the vicinity of the boundary with the charnockites. In the metagabbros, hemo-ilmenite–magnetite is the dominant oxide assemblage. The principal sulphide mineral in the charnockite is pyrrhotite with minor pyrite–chalcopyrite exsolution lamellae or blebs. In the two-pyroxene granulites and the metagabbros, the principal sulphide assemblage consists of discrete pyrite grains with magnetite rims and pyrite–pyrrhotite–chalcocopyrite associations. From these observations, a specific oxidation trend is seen. The northern granulite-facies metagabbros and two-pyroxene granulites of the Nilgiri highlands are highly oxidized compared with the charnockites from the central and southern regions. This higher oxidation state is proposed to be the result of highly oxidizing agents (probably as SO3) in low H2O activity grain boundary NaCl saline fluids with a dissolved CaSO4 component present during granulite-facies metamorphism of the metagabbros and two-pyroxene granulites. Eventually these agents became more reducing, owing to the inherent buffering of the original tonalite–granodiorite granitoids at the graphite–CO2 buffer, such that S took the form of H2S during the granulite-facies metamorphism of the charnockites. At the same time, these saline fluids were also responsible the solid-state conversion of biotite and amphibole to orthopyroxene and clinopyroxene in the metagabbro, two-pyroxene granulite, and charnockite.

Zircon geochronology of anatectic melts and residues from a highgrade pelitic assemblage at Ihosy, southern Madagascar: evidence for Pan-African granulite metamorphism

1996 ◽  
Vol 133 (3) ◽  
pp. 311-323 ◽  
Author(s):  
A. Kröner ◽  
I. Braun ◽  
P. Jaeckel
Keyword(s):  
Source Region ◽  
Granulite Facies ◽  
Detrital Zircons ◽  
High Grade ◽  
Left Behind ◽  
Granulite Metamorphism ◽  
Mozambique Belt ◽  
High Grade Metamorphism ◽  
Depositional Age ◽  
Heterogeneous Source

AbstractWe report U—Pb and207Pb/206Pb zircon ages for a granulite facies gneiss assemblage exposed in a large quarry at Ihosy, southern Madagascar. The granulites are derived from pelitic to arkosic sediments and attained equilibrium conditions at 650–700°C and 4–5 kbar. HigherP—Tconditions of 750–800°C and 6 kbar in the presence of low water activities have led to dehydration melting processes. The formation of granitic melts, which (partly) moved away from their source region, intruded into upper parts of the metapelitic gneisses as small granitic veins and left behind granulitic garnet-cordierite-quartz bearing rocks. Detrital zircons in a sample of metapelite and a sample of quartzofeldspathic gneiss yielded ages between ˜720 and ˜1855 Ma, suggesting a chronologically heterogeneous source region and a depositional age of less than ˜720 Ma for these rocks. High-grade metamorphism and anatexis are documented by zircon ages between 526 ±34 and 557 ±2 Ma with a mean age of about 550 Ma. The broad lithologies, metamorphic grades and ages recorded in the Ihosy rocks are similar to those in the Wanni Complex of northwestern Sri Lanka and in high-grade assemblages of southernmost India and support the contention that all these terrains were part of the Mozambique belt which formed as a result of collision of East and West Gondwana in latest Precambrian time.

SHRIMP U–Pb zircon geochronology of gneisses from the Gweta borehole, northeast Botswana: implications for the Palaeoproterozoic Magondi Belt in southern Africa

2001 ◽  
Vol 138 (3) ◽  
pp. 299-308 ◽  
Author(s):  
R. B. M. MAPEO ◽  
R. A. ARMSTRONG ◽  
A. B. KAMPUNZU
Keyword(s):  
Central Zone ◽  
Granulite Facies ◽  
Eastern Africa ◽  
High Grade ◽  
Zircon Geochronology ◽  
Granulite Facies Metamorphism ◽  
Grade Metamorphism ◽  
Facies Metamorphism ◽  
High Grade Metamorphism ◽  
Limpopo Belt

This paper presents new U–Pb zircon analyses from garnet–sillimanite paragneisses from the Gweta borehole in northeast Botswana. Concordant to near-concordant analyses of zircon from these rocks reveal a billion year history from 3015 ± 21 Ma for the oldest detrital grain measured, to the age of high-grade metamorphism, 2027 ± 8 Ma. The maximum age of sedimentation in the Magondi belt is constrained by the age of the youngest concordant detrital zircon at 2125 ± 6 Ma. This contrasts with the age of sedimentation in the Central Zone of the Limpopo belt which is Archaean. The comparison of our results with U–Pb zircon data from the Magondi belt in Zimbabwe suggests that the granulite-facies metamorphism in this belt extended between c. 2027–1960 Ma. Granulite-facies rocks with U–Pb zircon ages in this interval are also known in the Ubendian belt and lend support to the correlation of these two segments of Palaeoproterozoic belts in southern and central–eastern Africa. The granulite facies metamorphism in the Magondi belt is coeval with the high-grade metamorphism and granitoids documented further south in the Central Zone of the Limpopo Belt.

scholarly journals MAPEAMENTO GEOLÓGICO DA REGIÃO DA SERRA DOS TURVOS, CARATINGA (MG), SETOR SUL DO ORÓGENO ARAÇUAÍ

2012 ◽  
Author(s):  
Gláucia Queiroga ◽  
Tiago Novo ◽  
A. C. Pedrosa-Soares
Keyword(s):  
Sedimentary Cover ◽  
Granulite Facies ◽  
Geological Mapping ◽  
Iron Formation ◽  
High Grade ◽  
Crystalline Core ◽  
High Grade Metamorphism ◽  
Iron Formations ◽  
Araçuaí Orogen ◽  
Southern Section

A área de estudo situa-se na parte sul do núcleo cristalino do Orógeno Araçuaí, próximo à fronteira com o Orógeno Ribeira. A característica fundamental da região é a abundância de rochas de alto grau metamórfico, na transição de fácies anfibolito-granulito. Uma cobertura metassedimentar neoproterozóica é a unidade dominante e está representada por paragnaisse migmatítico, bandado, com intercalações de quartzito, formação ferrífera micácea e formação ferrífera maciça. Corpos de anfibolito, pegmatito e charnockito também ocorrem na área. A principal estrutura dúctil é a foliação (Sn) regional, paralela ao bandamento composicional do granada-biotita paragnaisse. Fraturas são abundantes no quartzito e formação ferrífera maciça. As formações ferríferas são ricas em magnetita e formam corpos lenticulares com espessura decamétrica a centimétrica, concordantes com o bandamento composicional do granada-biotita paragnaisse. Preliminarmente, interpreta-se a gênese dessas formações ferríferas como sedimentar, durante a deposição dos protolitos areno-pelíticos do paragnaisse.Palavras-chave: metamorfismo de alto grau, formação ferrífera, Orógeno Araçuaí. ABSTRACT: GEOLOGICAL MAPPING OF THE SERRA DOS TURVOS REGION, CARATINGA (MG), SOUTHERN SECTION OF THE ARAÇUAÍ OROGEN. The study area is located in the southern part of the crystalline core of the Araçuaí orogen, close to the boundary with the Ribeira orogen. The main feature of the region is the abundance of high-grade metamorphic rocks of the amphibolite-granulite facies transition. A Neoproterozoic sedimentary cover is the dominant unit in the area and consists of migmatitic banded paragneiss with intercalations of quartzite, mica-bearing iron formation and massive iron formation. Amphibolite, pegmatite and charnockite bodies are also found in the area. The main ductile structure is the regional foliation (Sn) which is parallel to the compositional banding of the garnet-biotite paragneiss. Fractures are abundant in the quartzite and massive iron formation. The iron formations form lenticular bodies ranging in thickness from centimeters to decameters, which are concordant to the banding and foliation of the garnet-biotite paragneiss. Accordingly to field data, a sedimentary genesis can be suggested for the iron formations.Keywords: high grade metamorphism, iron formation, Araçuaí Orogen

Decoding 3-D monazite textures using LA-ICP-MS raster mapping

2020 ◽  
Author(s):  
Owen Weller ◽  
Simon Jackson ◽  
William Miller ◽  
Marc St-Onge ◽  
Nicole Rayner
Keyword(s):  
Trace Element ◽  
Inductively Coupled Plasma ◽  
Granulite Facies ◽  
High Grade ◽  
Study Region ◽  
Inductively Coupled ◽  
Plasma Mass Spectrometry ◽  
High Grade Metamorphism ◽  
Metamorphic Terranes ◽  
Melt Crystallisation

<p>Texturally complex monazite grains within two granulite-facies pelitic migmatites from southern Baffin Island, Arctic Canada, were mapped by laser ablation-inductively coupled plasma-mass spectrometry to quantitatively determine the spatial variation in trace element chemistry with a 4-5 μm resolution (with up to 1883 analyses per grain). The maps demarcate growth zones, some of which were cryptic with conventional imaging, highlighting the 3-D complexity of monazite grains that have experienced multiple episodes of growth and resorption during high-grade metamorphism. Associated monazite trace element systematics are highly variable, both within domains interpreted to have grown in a single event, and between samples that experienced similar metamorphic conditions and mineral assemblages. This result cautions against generalised petrological interpretations being made about monazite trace element signatures as it suggests sample-specific controls. Nevertheless, by quantifying monazite textures, a related U-Pb dataset is re-interpreted, allowing ages to be extracted from a continuum of concordant data. The results reveal a ~45 Myr interval between prograde metamorphism and retrograde melt crystallisation in the study region, emphasising the long-lived nature of heat flow in high-grade metamorphic terranes. Careful characterisation of monazite grains suggests that continuum-style U-Pb datasets can be decoded to provide insights into the rates of metamorphic processes.</p>

scholarly journals Fluid-induced metamorphism and anatexis of refractory Ni-Co-Cu sulphides in subduction-related rocks

2019 ◽  
Vol 98 ◽  
pp. 08008
Author(s):  
Nikita Kepezhinskas
Keyword(s):  
Granulite Facies ◽  
High Grade ◽  
Accretionary Complex ◽  
Sulfide Mineralization ◽  
Granulite Facies Metamorphism ◽  
Grade Metamorphism ◽  
Facies Metamorphism ◽  
High Grade Metamorphism ◽  
Bay Islands

The role of metamorphism on refractory sulfides is not well constrained. Although experiments have displayed the effectiveness of high grade metamorphism, namely granulite facies metamorphism, on sulfide anatexis, its role in the presence of other variables is still poorly understood. Rocks from the Bay Islands Accretionary Complex in Honduras and the Ildeus-Lucha Complex in Russia exhibit extensive metamorphism. Sulfide mineralization is prolific in these rocks suggesting that metamorphism has played an important role in re-concentrating these sulfides during amphibolite and granulite facies metamorphism.

scholarly journals Persistence of melt-bearing Archean lower crust for >200 m.y.—An example from the Lewisian Complex, northwest Scotland

Geology ◽  
2019 ◽  
Vol 48 (3) ◽  
pp. 221-225 ◽  
Author(s):  
Richard J.M. Taylor ◽  
Tim E. Johnson ◽  
Chris Clark ◽  
Richard J. Harrison
Keyword(s):  
Trace Element ◽  
Lower Crust ◽  
Mafic Magma ◽  
High Grade ◽  
Trace Element Data ◽  
Metamorphic Zircon ◽  
Geochronological Data ◽  
Zircon Age ◽  
Gneiss Complex ◽  
High Grade Metamorphism

Abstract Geochronological data from zircon in Archean tonalite–trondhjemite–granodiorite (TTG) gneisses are commonly difficult to interpret. A notable example is the TTG gneisses from the Lewisian Gneiss Complex, northwest Scotland, which have metamorphic zircon ages that define a more-or-less continuous spread through the Neoarchean, with no clear relationship to zircon textures. These data are generally interpreted to record discrete high-grade events at ca. 2.7 Ga and ca. 2.5 Ga, with intermediate ages reflecting variable Pb loss. Although ancient diffusion of Pb is commonly invoked to explain such protracted age spreads, trace-element data in zircon may permit identification of otherwise cryptic magmatic and metamorphic episodes. Although zircons from the TTG gneiss analyzed here show a characteristic spread of Neoarchean ages, they exhibit subtle but key step changes in trace-element compositions that are difficult to ascribe to diffusive resetting, but that are consistent with emplacement of regionally extensive bodies of mafic magma. These data suggest suprasolidus metamorphic temperatures persisted for 200 m.y. or more during the Neoarchean. Such long-lived high-grade metamorphism is supported by data from zircon grains from a nearby monzogranite sheet. These preserve distinctive trace-element compositions consistent with derivation from a mafic source, and they define a well-constrained U-Pb zircon age of ca. 2.6 Ga that is intermediate between the two previously proposed discrete metamorphic episodes. The persistence of melt-bearing lower crust for hundreds of millions of years was probably the norm during the Archean.

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