Contrasting types of bladed olivine in ultramafic rocks from the Archean of Labrador

1976 ◽  
Vol 13 (3) ◽  
pp. 442-450 ◽  
Author(s):  
Kenneth D. Collerson ◽  
C. Wayne Jesseau ◽  
David Bridgwater
Keyword(s):  
Granulite Facies ◽  
Metamorphic Grade ◽  
Coarse Grained ◽  
Ultramafic Rocks ◽  
Host Rocks

Exceptionally coarse grained, interlocking olivine crystals up to 1 m long occur in small lenticular ultramafic bodies within the Nain Province of Labrador. The ultramafic rocks occur in association with Archean gneisses that vary in metamorphic grade from amphibolile fades to granulite facies. Some of the interlocking textures (i.e. near Hopedale) are interpreted as relict cumulate or harrisitic growths, mimicked by olivine regrowlh during metamorphism and preserved in structurally isotropic enclaves in their host rocks. Others (e.g. near Saglek) are regarded as solely of metamorphic origin. None of the olivine growths resemble spinifex textures reported in Archean ultramafic rocks elsewhere.

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 Magma Mixing Genesis of the Mafic Enclaves in the Qingshanbao Complex of Longshou Mountain, China: Evidence from Petrology, Geochemistry, and Zircon Chronology

Minerals ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 195 ◽  
Author(s):  
Wenheng Liu ◽  
Xiaodong Liu ◽  
Jiayong Pan ◽  
Kaixing Wang ◽  
Gang Wang ◽  
...  
Keyword(s):  
Host Rock ◽  
Inductively Coupled Plasma ◽  
Magma Mixing ◽  
Coarse Grained ◽  
Calc Alkaline ◽  
Quartz Crystals ◽  
Alkaline Rocks ◽  
Mafic Enclaves ◽  
Normal Zoning ◽  
Host Rocks

The Qingshanbao complex, part of the uranium metallogenic belt of the Longshou-Qilian mountains, is located in the center of the Longshou Mountain next to the Jiling complex that hosts a number of U deposits. However, little research has been conducted in this area. In order to investigate the origin and formation of mafic enclaves observed in the Qingshanbao body and the implications for magmatic-tectonic dynamics, we systematically studied the mineralogy, petrography, and geochemistry of these enclaves. Our results showed that the enclaves contain plagioclase enwrapped by early dark minerals. These enclaves also showed round quartz crystals and acicular apatite in association with the plagioclase. Electron probe analyses showed that the plagioclase in the host rocks (such as K-feldspar granite, adamellite, granodiorite, etc.) show normal zoning, while the plagioclase in the mafic enclaves has a discontinuous rim composition and shows instances of reverse zoning. Major elemental geochemistry revealed that the mafic enclaves belong to the calc-alkaline rocks that are rich in titanium, iron, aluminum, and depleted in silica, while the host rocks are calc-alkaline to alkaline rocks with enrichment in silica. On Harker diagrams, SiO2 contents are negatively correlated with all major oxides but K2O. Both the mafic enclaves and host rock are rich in large ion lithophile elements such as Rb and K, as well as elements such as La, Nd, and Sm, and relatively poor in high field strength elements such as Nb, Ta, P, Ti, and U. Element ratios of Nb/La, Rb/Sr, and Nb/Ta indicate that the mafic enclaves were formed by the mixing of mafic and felsic magma. In terms of rare earth elements, both the mafic enclaves and the host rock show right-inclined trends with similar weak to medium degrees of negative Eu anomaly and with no obvious Ce anomaly. Zircon LA-ICP-MS (Laser ablation inductively coupled plasma mass spectrometry) U-Pb concordant ages of the mafic enclaves and host rock were determined to be 431.8 5.2 Ma (MSWD (mean standard weighted deviation)= 1.5, n = 14) and 432.8 4.2 Ma (MSWD = 1.7, n = 16), respectively, consistent with that for the zircon U-Pb ages of the granite and medium-coarse grained K-feldspar granites of the Qingshanbao complex. The estimated ages coincide with the timing of the late Caledonian collision of the Alashan Block. This comprehensive analysis allowed us to conclude that the mafic enclaves in the Qingshanbao complex were formed by the mixing of crust-mantle magma with mantle-derived magma due to underplating, which caused partial melting of the ancient basement crust during the collisional orogenesis between the Alashan Block and Qilian rock mass in the early Silurian Period.

A garnet peridotite and a garnet-amphibole pyroxenite from South Harris, Outer Hebrides, and their bearing on the South Harris eclogite facies status

1967 ◽  
Vol 36 (279) ◽  
pp. 380-388 ◽  
Author(s):  
A. Livingstone
Keyword(s):  
Optical Properties ◽  
Granulite Facies ◽  
Garnet Peridotite ◽  
Ultramafic Rocks ◽  
Chemical Analyses ◽  
The South ◽  
Outer Hebrides ◽  
Eclogite Facies

SummaryA garnet-olivine metaperidotite and a garnet-amphibole pyroxenite are described. Chemical analyses are presented for six rocks and optical properties and chemical analyses are tabulated for clinopyroxene, almandine-pyrope garnet, and hastingsitie amphibole from the garnet-amphibole pyroxenite. A possible origin for the garnet peridotite and chemically similar granulite facies ultramafic rocks is suggested. The eclogite facies in South Harris is reinstated in the light of the data presented.

Perovskite, loparite and Ba-Fe hollandite from the Schryburt Lake carbonatite complex, northwestern Ontario, Canada

1994 ◽  
Vol 58 (390) ◽  
pp. 49-57 ◽  
Author(s):  
R. Garth Platt
Keyword(s):  
Fluid Phase ◽  
Ultramafic Rocks ◽  
Subsequent Reaction ◽  
Carbonatite Complex ◽  
Silicate System ◽  
Northwestern Ontario ◽  
Intimate Association ◽  
Free Mica ◽  
Host Rocks ◽  
Light Rare Earth Elements

AbstractWithin a suite of felsic-free, mica-rich alkaline ultramafic rocks of the Schryburt Lake carbonatite complex of northwestern Ontario, loparite and Ba-Fe hollandite occur in intimate association with perovskite. The host rocks have variable modal proportions of Mg-olivine, phlogopite, magnetite, ilmenite, apatite and carbonate (generally calcite) with minor Mg-salite. Thus, they correspond to ultramafic lamprophyres (i.e. aillikites), in the sense of Rock (1990) or the lamprophyric facies of the melilitite clan, in the sense of Mitchell (1993).Perovskite is the principal titanate phase, forming both euhedral and anhedral grains, the latter showing evidence of marginal resorption. It exhibits complex zonal patterns due principally to variations in the light rare earth elements, Na and Nb. In the nomenclature suggested, they may be termed perovskite and cerian perovskite. Loparite forms as small euhedral overgrowths on corroded perovskite cores. Chemically they are essentially solid solutions of loparite, lueshite and perovskite. Consequently, they may be termed calcian-loparite, calcian niobian loparite, niobian calcian loparite, loparite and niobian loparite. Titanates of the hollandite group are rare accessory minerals whose composition closely approach that of the septatitanate BaFe2+Ti7O16.The complex zoning of the perovskite grains has been attributed to the periodic introduction of carbonatite-derived fluids enriched in REE, Na and Nb into the silicate system during perovskite crystallization. Subsequent reaction of the early perovskite with F-bearing fluids leads to a localized environment enriched in Ti, Na, Nb and REE derived from both the fluid phase and the unstable perovskite. Loparite subsequently crystallizes from these micro-chemical environments.

scholarly journals The country rocks of Devonian magmatism in the North Patagonian Massif and Chaitenia

2018 ◽  
Vol 45 (3) ◽  
pp. 301 ◽  
Author(s):  
Francisco Hervé ◽  
Mauricio Calderón ◽  
Mark Fanning ◽  
Robert Pankhurst ◽  
Carlos W. Rapela ◽  
...  
Keyword(s):  
Metamorphic Grade ◽  
Oceanic Island ◽  
Detrital Zircons ◽  
Island Arc ◽  
Ultramafic Rocks ◽  
The West ◽  
Metasedimentary Rocks ◽  
The North ◽  
The Andes ◽  
Late Neoproterozoic

Previous work has shown that Devonian magmatism in the southern Andes occurred in two contemporaneous belts: one emplaced in the continental crust of the North Patagonian Massif and the other in an oceanic island arc terrane to the west, Chaitenia, which was later accreted to Patagonia. The country rocks of the plutonic rocks consist of metasedimentary complexes which crop out sporadically in the Andes on both sides of the Argentina-Chile border, and additionally of pillow metabasalts for Chaitenia. Detrital zircon SHRIMP U-Pb age determinations in 13 samples of these rocks indicate maximum possible depositional ages from ca. 370 to 900 Ma, and the case is argued for mostly Devonian sedimentation as for the fossiliferous Buill slates. Ordovician, Cambrian-late Neoproterozoic and “Grenville-age” provenance is seen throughout, except for the most westerly outcrops where Devonian detrital zircons predominate. Besides a difference in the Precambrian zircon grains, 76% versus 25% respectively, there is no systematic variation in provenance from the Patagonian foreland to Chaitenia, so that the island arc terrane must have been proximal to the continent: its deeper crust is not exposed but several outcrops of ultramafic rocks are known. Zircons with devonian metamorphic rims in rocks from the North Patagonian Massif have no counterpart in the low metamorphic grade Chilean rocks. These Paleozoic metasedimentary rocks were also intruded by Pennsylvanian and Jurassic granitoids.

Thermometry and barometry of some amphibolite–granulite facies rocks from the Otter Lake area, southern Quebec

1982 ◽  
Vol 19 (9) ◽  
pp. 1759-1774 ◽  
Author(s):  
Dexter Perkins III ◽  
Eric J. Essene ◽  
Louise Annette Marcotty
Keyword(s):  
New York ◽  
Thermal Gradient ◽  
Granulite Facies ◽  
Metamorphic Grade ◽  
Lake Area ◽  
Temperature And Pressure ◽  
East West

Grenville rocks from a 2500 km2 area centered on Otter Lake, Quebec (some 75 km northwest of Ottawa) are in the uppermost amphibolite to lower granulite facies; orthopyroxene occurs occasionally in both metabasic and charnockitic rocks. The temperature of metapmorphism was approximately 675 °C, based upon oxide, feldspar, and garnet–clinopyroxene thermometry. Little thermal gradient could be detected across the area. Carbonate thermometry, using reintegrated calcite compositions, yielded lower temperatures of 600 °C (maximum), while garnet–biotite and other Kd thermometers yielded scattered and for the most part unreasonable results. Metamorphic pressure, calculated from the reaction anorthite = grossular + sillimanite + quartz, was 5.0 ± 0.5 kbar(500 ± 50 MPa). Similar calculations based upon the reactions garnet + quartz = anorthite + orthopyroxene and garnet + quartz = anorthite + clinopyroxene yielded pressures of 5.5–7.0 kbar (550–700 MPa). Pressure calculations based upon assemblages of cordierite–garnet–sillimanite–quartz were less precise, but agreed with the outer estimates. Similar metamorphic temperatures and slightly lower pressures have been estimated for the Adirondack Lowlands of New York. In the Morin Highlands, 100 km east of Otter Lake, and in the Adirondack Highlands, 100 km east of the Adirondack Lowlands, temperatures of metamorphism (700–800 °C) and pressures of metamorphism (6–9 kbar (600–900 MPa)) are both higher. Thus it appears that over an approximate 300 km north–south direction nearly constant metamorphic conditions prevailed at Grenville time. In the east–west direction significant variations in metamorphic grade are recorded; both temperature and pressure markedly increase to the east.

Archean rocks from the eastern Lac Seul region of the English River Gneiss Belt, northwestern Ontario, part 1. Petrology, chemistry, and metamorphism

1976 ◽  
Vol 13 (9) ◽  
pp. 1201-1211 ◽  
Author(s):  
N. B. W. Harris ◽  
A. M. Goodwin
Keyword(s):  
Complex Structure ◽  
Granulite Facies ◽  
Metamorphic Grade ◽  
Amphibolite Facies ◽  
Northwestern Ontario ◽  
Southern Margin ◽  
Field Evidence ◽  
Facies Metamorphism

The eastern Lac Seul region of the English River Gneiss Belt is divided into two domains defined by contrasting petrology and structure. The northern domain is underlain by east-trending, steeply south-dipping, migmatized metasediments, intruded by occasional granite sills, and the southern domain by gneissic tonalite and trondhjemite, with abundant amphibolite inclusions, intruded by granite dykes and diapirs: this domain has a complex structure with gently east-plunging open folds of about 5 km wavelength. Field evidence suggests that metasediments of the northern domain have been deposited on the tonalite trondhjemite basement, which was subsequently mobilized, thereby producing the steeply dipping paragneiss belt of the northern domain.The grade of metamorphism throughout the region lies in the upper amphibolite facies, rising locally to the granulite facies. Within 15 km of the southern margin of the gneiss belt, the metamorphic grade decreases to the greenschist facies.U–Pb dating of zircons indicates that the tonalite gneiss was emplaced at least 3040 m.y. ago, and the granite plutons at 2660 m.y., coeval with migmatization and upper amphibolite facies metamorphism. Late pegmatites were emplaced at 2560 m.y.

Metamorphic evolution of the Karimnagar granulite terrane, Eastern Dharwar Craton, south India

2010 ◽  
Vol 148 (1) ◽  
pp. 112-132 ◽  
Author(s):  
D. PRAKASH ◽  
I. N. SHARMA
Keyword(s):  
Granulite Facies ◽  
Dharwar Craton ◽  
Ultramafic Rocks ◽  
Chemical Compositions ◽  
Eastern Dharwar Craton ◽  
Geochronological Data ◽  
Rock Types ◽  
Wide Range ◽  
The Subject ◽  
Lower Crustal

AbstractThe Karimnagar granulite terrane is an integral part of the Eastern Dharwar Craton (EDC), India, having been the subject of much interest because of the only reported granulite facies rocks in the EDC. It shows a large variety of rock types with a wide range of mineral parageneses and chemical compositions, namely charnockites (Opx+Pl+perthite+Qtz±Bt±Grt), gneisses (Opx+Crd+Bt+Pl+Qtz+perthite±Sil±Grt±Spl; Bt+Qtz+Pl±Crd±Hbl±Spl), mafic granulites (Cpx+Pl+Qtz±Opx±Hbl), quartz-free granulites (Spr+Spl+Bt+Crd+Kfs+Crn; Bt+Crd+Kfs±Crn±Spl±Krn; And+Bt+Kfs+Chl), granites (Qtz+Pl+Kfs±Bt±Hbl), altered ultramafic rocks (Chl+Trem+Tlc), metadolerites (Cpx+Pl±Bt±Qtz±Chl), banded magnetite quartzites and quartzites. Andalusite- and chlorite-bearing assemblages presumably suggest a retrograde origin. Investigation of quartz-free granulites of the area brings out some interesting and important observations, reflecting the presence of refractory phases. These granulites are devoid of sillimanite and contain corundum instead. Reaction textures in the gneisses include breakdown of garnet to form coronas and symplectites of orthopyroxene+cordierite, formation of cordierite from garnet+sillimanite+quartz and late retrograde biotite and biotite+quartz symplectites. In the mafic granulites, inclusions of quartz and hornblende within orthopyroxene are interpreted as being a part of the prograde assemblage. At a later stage orthopyroxene is also rimmed by hornblende. The quartz-free granulites display a variety of spectacular coronas, for example, successive rims on corundum consisting of spinel+sapphirine+cordierite±orthopyroxene, rare skeletal symplectitic intergrowth of sapphirine+cordierite+potash feldspar, and late retrograde formation of chlorite, corundum, spinel and andalusite from sapphirine±cordierite. Based on chemographic relationships and petrogenetic grids, a sequence of prograde, isothermal decompressive and retrograde reactions have been inferred. Quartz-free sapphirine granulites and mafic granulites record the highest P–T conditions (~7 kbar, 850°C), whereas the gneisses were formed at lower P–T conditions (~5 kbar, 800°C). In addition, the presence of andalusite-bearing rocks suggests a pressure of around 2.5 kbar. This change in pressure from 7 kbar to around 2.5 kbar suggests a decompressive path for the evolution of granulites in the study area, which indicates an uplift for the granulite-facies rocks from lower crustal conditions. The implications for supercontinent history are also addressed in light of available geochronological data.

Temperatures of Neoproterozoic Regional Carbonate Alteration in the Eastern Desert of Egypt

2020 ◽  
Author(s):  
Arman Boskabadi ◽  
Tobias Kluge ◽  
Iain Pitcairn ◽  
Rabea Ali ◽  
Mokhles Azer ◽  
...  
Keyword(s):  
Low Temperature ◽  
Homogenization Temperature ◽  
Eastern Desert ◽  
Ultramafic Rocks ◽  
Wide Range ◽  
Two Samples ◽  
Ophiolitic Rocks ◽  
Clumped Isotope ◽  
Host Rocks ◽  
Different Sources

<p>Neoproterozoic ophiolites in the Eastern Desert (ED) of Egypt are pervasively carbonated and listvenitized. Two types of carbonation are recognized: 1) intergrown magnesite (and to lesser extent dolomite) with serpentine and talc that in cases form pure carbonate veins, and 2) cryptocrystalline magnesite veins filling the fractures crosscutting other ophiolitic host rocks. Few studies address the conditions of carbonate alteration of ultramafic rocks, especially the temperature of altering fluids. We employ clumped isotope thermometry on natural dolomite and magnesite from 17 variably carbonated ophiolitic rocks and veins in the ED. Five samples of antigorite-bearing serpentinite, talc-carbonate, and associated carbonate veins yield wide range temperatures of magnesite and dolomite between 213 to 426°C (285±73°C). These temperatures are comparable with previous fluid inclusion thermometry carried out on some of the vein samples (homogenization temperature between 225 to 383°C; Boskabadi et al. 2017). Ten samples of fully quartz-carbonate altered peridotites (i.e. listvenites) record even a wider range of clumped isotope carbonation temperatures between 90 and 452°C (227±112°C). In contrast, two samples of late-stage veins of cryptocrystalline magnesite record lower temperatures of 19 and 28°C. While the constraints on the pressure of carbonation are lacking, the wide range of temperatures for the carbonates in antigorite-bearing serpentinite, talc-carbonate, and listvenite lithologies suggest that carbonation probably occurred at variable depths, whereas the low temperature of cryptocrystalline magnesite veins points to conditions nearer the surface most likely associated with post-obduction processes. Therefore, different sources of carbon and CO<sub>2</sub>-bearing fluids should have been responsible for the formation of high- and low-temperature carbonates in the region.</p><p> </p><p>  Boskabadi et al. 2017. International Geology Review 59, 391–419.</p>

scholarly journals Metamorphic and Metasomatic Kyanite-Bearing Mineral Assemblages of Thassos Island (Rhodope, Greece)

Minerals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 252 ◽  
Author(s):  
Tarantola ◽  
Voudouris ◽  
Eglinger ◽  
Scheffer ◽  
Trebus ◽  
...  
Keyword(s):  
Crystal Size ◽  
Near Infrared ◽  
Coarse Grained ◽  
Fluid Circulation ◽  
Large Crystal ◽  
Northern Greece ◽  
Quartz Veins ◽  
Mineral Assemblages ◽  
Mineral Compositions ◽  
Host Rocks

The Trikorfo area (Thassos Island, Rhodope massif, Northern Greece) represents a unique mineralogical locality with Mn-rich minerals including kyanite, andalusite, garnet and epidote. Their vivid colors and large crystal size make them good indicators of gem-quality materials, although crystals found up to now are too fractured to be considered as marketable gems. The dominant lithology is represented by a garnet–kyanite–biotite–hematite–plagioclase ± staurolite ± sillimanite paragneiss. Thermodynamic Perple_X modeling indicates conditions of ca. 630–710 °C and 7.8–10.4 kbars. Post-metamorphic metasomatic silicate and calc-silicate (Mn-rich)-minerals are found within (i) green-red horizons with a mineralogical zonation from diopside, hornblende, epidote and grossular, (ii) mica schists containing spessartine, kyanite, andalusite and piemontite, and (iii) weakly deformed quartz-feldspar coarse-grained veins with kyanite at the interface with the metamorphic gneiss. The transition towards brittle conditions is shown by Alpine-type tension gashes, including spessartine–epidote–clinochlore–hornblende-quartz veins, cross-cutting the metamorphic foliation. Kyanite is of particular interest because it is present in the metamorphic paragenesis and locally in metasomatic assemblages with a large variety of colors (zoned blue to green/yellow-transparent and orange). Element analyses and UV-near infrared spectroscopy analyses indicate that the variation in color is due to a combination of Ti4+–Fe2+, Fe3+ and Mn3+ substitutions with Al3+. Structural and mineralogical observations point to a two-stage evolution of the Trikorfo area, where post-metamorphic hydrothermal fluid circulation lead locally to metasomatic reactions from ductile to brittle conditions during Miocene exhumation of the high-grade host-rocks. The large variety of mineral compositions and assemblages points to a local control of the mineralogy and fO2 conditions during metasomatic reactions and interactions between hydrothermal active fluids with surrounding rocks.

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