Mineral assemblages and phase equilibria of metabasites from the prehnite–pumpellyite to amphibolite facies, with the Flin Flon Greenstone Belt (Manitoba) as a type example

2019 ◽  
Vol 38 (1) ◽  
pp. 71-102 ◽  
Author(s):  
Paul G. Starr ◽  
David R. M. Pattison ◽  
Doreen E. Ames
Keyword(s):  
Phase Equilibria ◽  
Greenstone Belt ◽  
Amphibolite Facies ◽  
Mineral Assemblages ◽  
Flin Flon

Paleomagnetism of the Flin Flon – Snow Lake Greenstone Belt, Manitoba and Saskatchewan

1975 ◽  
Vol 12 (8) ◽  
pp. 1272-1290 ◽  
Author(s):  
J. K. Park
Keyword(s):  
Greenstone Belt ◽  
Amphibolite Facies ◽  
Retrograde Metamorphism ◽  
General Direction ◽  
Thermoremanent Magnetization ◽  
Flin Flon ◽  
K 12 ◽  
Very High

The Flin Flon – Snow Lake greenstone belt is of Archean or Aphebian age and has been metamorphosed to greenschist or low amphibolite facies during the Hudsonian orogeny. It contains four rock units — the Amisk Group, the Missi Group, metadiorite and metagabbro bodies, and the Boundary Intrusions. The rocks contain two main magnetizations, an early B magnetization and a later A magnetization. Both magnetizations contain reversals. The A magnetization (43 sites, direction 168°, +73°, k = 17, α95 = 5°, pole 24°N, 095°W) is found in all rock units. It can be divided into three parts (1, 2 and 3) which have the same general direction, but which are significantly different from one another. It is suggested that A1 is a viscous partial thermoremanence (vptrm), and A2 possibly a chemical remanence (crm). Both are considered to have been acquired during uplift (1600–1700 m.y.) following the Hudsonian orogeny. A3 is possibly a crm acquired during late fault movements and appears to be carried by hematite developed during retrograde metamorphism. A3 is considered to be about 1600 m.y. old. The B magnetization (7 sites, 129°, +04°, k = 12, α95 = 18°, pole 20°S, 046°W) occurs in all rock units except the Missi. It is particularly well developed in the Boundary Intrusions where it is considered to be a primary thermoremanent magnetization (trm). In other rock units B is considered to be a vptrm acquired during heating at the time of emplacement of the Boundary Intrusions. The B magnetization is considered to be about 1800 m.y. old. Some enigmatic magnetizations with very high blocking temperatures above 700 °C were observed. Formulas for calculating the coercivities in rocks with more than one magnetization are given.

Pressure–temperature conditions of Early Proterozoic metamorphism during the Trans-Hudson Orogen as determined from rocks straddling the Flin Flon – Kisseynew boundary at Niblock and File lakes, Manitoba

1992 ◽  
Vol 29 (11) ◽  
pp. 2497-2507 ◽  
Author(s):  
William Briggs ◽  
C. T. Foster
Keyword(s):  
Amphibolite Facies ◽  
Lake Area ◽  
Relative Timing ◽  
Early Proterozoic ◽  
Temperature Conditions ◽  
Mineral Assemblages ◽  
Flin Flon ◽  
The Town

The Niblock Lake and File Lake areas straddle the boundary between the Kisseynew gneiss belt and the Flin Flon belt, near the town of Snow Lake, Manitoba. The region contains pelitic schists metamorphosed to lower to middle almandine–amphibolite facies. Metamorphic conditions were studied by examining relative timing of growth of metamorphic minerals by geothermobarometry of selected samples. Calculated temperatures and pressures are compared with those estimated from mineral assemblages and reactions on a petrogenetic grid.Two metamorphic (M1 and M2) and deformation (D1 and D2) phases have been recognized in the Niblock Lake and File Lake areas. M1 (contemporaneous with D1 folding) was characterized by growth of micas but no higher grade minerals. Temperatures and pressures of M1, therefore, were probably less than about 475 °C and 3.5 kbar (1 kbar = 100 MPa). Peak conditions, reached during M2 (late- to post-D2 folding), resulted in growth of garnet, staurolite, sillimanite, and (in the Niblock Lake area) andalusite. In the Niblock Lake area, M2 temperatures range from 525 to 625 °C, with most samples between 550 and 600 °C; pressures range from 2.5 to 5 kbar, with most samples between 2.5 and 4 kbar. In the File Lake area, M2 temperatures range from approximately 560 to 625 °C; pressures range from 3.3 to 4.6 kbar.

Oxidized and reduced mineral assemblages in greenstone belt rocks of the St. Ives gold camp, Western Australia: vectors to high-grade ore bodies in Archaean gold deposits?

2007 ◽  
Vol 43 (3) ◽  
pp. 363-371 ◽  
Author(s):  
Peter Neumayr ◽  
John Walshe ◽  
Steffen Hagemann ◽  
Klaus Petersen ◽  
Anthony Roache ◽  
...  
Keyword(s):  
Western Australia ◽  
Greenstone Belt ◽  
Gold Deposits ◽  
High Grade ◽  
Ore Bodies ◽  
Mineral Assemblages

A retrogressive sapphirine-cordierite-talc paragenesis in a spinel-orthopyroxenite from southern Karnataka, India

1993 ◽  
Vol 57 (387) ◽  
pp. 273-288 ◽  
Author(s):  
C. R. L. Friend ◽  
A. S. Janardhan ◽  
N. Shadakshara Swamy
Keyword(s):  
Dharwar Craton ◽  
Amphibolite Facies ◽  
Coarse Grained ◽  
Cooling History ◽  
Metamorphic History ◽  
Gneiss Complex ◽  
Igneous Origin ◽  
Mineral Assemblages ◽  
History Of ◽  
Granoblastic Texture

AbstractWithin amphibolite facies Peninsular gneisses in the south of the Dharwar craton, units of Sargur supracrustal rocks contain ultrabasic enclaves. One of these enclaves is an orthopyroxenite which comprises bronzite, spinel and minor phlogopite preserving coarse-grained, relic textures of probable igneous origin. After incorporation into the gneisses the enclave evolved through several distinct stages, elucidation of which allow an assessment of its metamorphic history.Firstly, deformation during closed system, anhydrous recrystallisation caused the coarse-grained textures to be partially overprinted by similar mineral assemblages but with a granoblastic texture. Secondly, open system hydration caused retrogression of the bronzite to alumino-gedrite at the margins of the enclave. Subsequently, the penetration of these fluids along grain boundaries caused reactions between spinel and bronzite to produce reaction pockets carrying assemblages of peraluminous sapphirine associated with cordierite and talc. The differences in the mineral assemblages in each pocket coupled with slight variations in their chemistry, suggest that equilibrium did not develop over the outcrop. Because sapphirine + magnesite is present in some pockets, it is evident that CO2 was also a component of the fluid.Phase relations from the MASH portion of the FMASH system, to which the chemistry of the reaction pockets approximates, suggest that the hydrous metamorphism causing the changes depended upon the assemblage enstatite + spinel + vapour which exists at PT conditions above the position of I16, ∼760°C at 3 kbar and below I21 at ∼765°C at 5.6 kbar (Seifert, 1974, 1975), where sapphirine is replaced by kornerupine. The suggested path of reaction occurred between I18 and I21. Subsequent reactions related to I20 cause the formation of cordierite. Talc formation has to be modelled in a different reaction grid.The metamorphism recorded by these reactions is thus at a maximum of amphibolite facies and is interpreted to have formed during the uplift and cooling history of the gneiss complex when hydrous fluids were free to migrate. Given the complex high-grade metamorphic history of this part of the Dharwar craton this event is likely to be late Archaean or Palaeoproterozoic in age.

Paragenesis of the metasomatic actinolite-bearing rocks from the Khetri copper belt, Rajasthan, India

1967 ◽  
Vol 36 (277) ◽  
pp. 22-28 ◽  
Author(s):  
S. P. Das Gupta
Keyword(s):  
Amphibolite Facies ◽  
Granitic Rocks ◽  
The South ◽  
Sulphide Mineralization ◽  
South Eastern ◽  
Pale Pink ◽  
Mineral Assemblages ◽  
Metasomatic Fluid ◽  
Metasomatic Replacement ◽  
Khetri Copper Belt

SummaryIn the south-eastern part of the Khetri copper belt, actinolite occurs in association with alteration assemblages resulting from the Fe-Mg metasomatism that accompanied sulphide mineralization, and more commonly with albite-bearing rocks formed by albitization of quartzites and schists near granitic rocks. Within the latter occur many coarse, massive, and unoriented aggregates of actinolite crystals, individuals being commonly more than 10 cm long. Locally fluorite-bearing veins oecur within granitic and albite-quartz rocks. The actinolite is pleochroic from pale pink to green; γ: [001] = 26°; γ = 1·642 ± 0·003; 2Vα = 80°. The composition of the analysed actinolite closely compares with those published in the literature excepting in (OH), which is low. The mineral assemblages, formed by metasomatic replacement of pre-existing rocks, are equivalent to those of albite-epidote-amphibolite facies. The metasomatic fluid was apparently rich in Ca, F (indicated by fluorite), and oxygen (indicated by magnetite, ilmenite, and hematite).

Phase equilibria and mixed parageneses of metabasites in lowgrade metamorphism

1985 ◽  
Vol 49 (352) ◽  
pp. 321-333 ◽  
Author(s):  
J. G. Liou ◽  
S. Maruyama ◽  
M. Cho
Keyword(s):  
Phase Equilibria ◽  
Model System ◽  
Metamorphic Grade ◽  
Low Grade ◽  
Qualitative And Quantitative ◽  
Basaltic Rocks ◽  
Mineral Assemblages ◽  
The Common ◽  
Invariant Points ◽  
Model Phase

AbstractThe system Na2O-CaO-MgO Al2O3-SiO2-H2O is proposed to model phase equilibria and mineral parageneses for low-temperature metamorphism of basaltic rocks. Univariant reactions marking the transitions between various sub-greenschist facies are identified and some have been experimentally determined. The introduction of Fe2O3 into the model system at fixed FeO/MgO ratio creates continuous reactions for facies boundaries and discontinuous reactions for invariant points of the model system. Both qualitative and quantitative effects on P-T displacement and phase compositions are discussed. The XFe3+ isopleths for epidote were plotted to exemplify the transition from the zeolite through prehnite-pumpellyite to prehnite-actinolite facies. T-XFe3+ relations were established for continuous and discontinuous reactions relating such facies transitions. Because of the common occurrence of two or three Ca-Al hydrosilicates in low-grade metabasites, an isobaric Al-Ca-Fe3+ projection from chlorite may be used to illustrate mineral assemblages and compositions of the coexisting Ca-Al silicates in the presence of quartz, albite, and chlorite. Reported occurrences in several classic burial metamorphic terrains and ocean-floor metabasites in ophiolites are described. Only the composition of a mineral from a buffered assemblage can constrain the intensive properties for metamorphism; previously reported compositional trends for pumpellyite and epidote with increasing metamorphic grade are oversimplified.

Multi-stage metamorphism of the South Altyn ultrahigh-pressure metamorphic belt, West China: insights into tectonic evolution from continental subduction to arc–backarc extension

2021 ◽  
Author(s):  
Jie Dong ◽  
Chunjing Wei
Keyword(s):  
Late Stage ◽  
Tectonic Evolution ◽  
Granulite Facies ◽  
Amphibolite Facies ◽  
Ultrahigh Pressure ◽  
Garnet Amphibolite ◽  
The South ◽  
Metamorphic Belt ◽  
Mineral Assemblages ◽  
Eclogite Facies

Abstract The South Altyn ultrahigh-pressure (UHP) metamorphic belt is claimed to host the deepest subducted continental crust based on the discovery of former stishovite, and thus can provide unique insights into the tectonic evolution from deep continental subduction and exhumation to arc–backarc extension. In this paper, we present detailed studies of petrography, mineral chemistry, phase equilibria modelling and zircon U-Pb dating for three representative samples involving garnet amphibolite (A1531 & A1533) and associated garnet-biotite gneiss (A1534) from the UHP belt. Three phases of metamorphism are inferred for the rocks. The first phase high pressure (HP)–UHP-type eclogite facies is represented by the mineral assemblages of garnet and phengite inclusions in zircon and garnet cores with the high grossular (XGrs = 0.33–0.34). The Si contents of 3.40–3.53 and 3.24–3.25 p.f.u. in phengite inclusions yield pressure conditions of >1.7–2.3 GPa for A1533 and 2.5–2.55 GPa for A1534 at a fixed temperature of 770 °C. The second phase medium-pressure (MP)-type overprinting of garnet amphibolite facies shows P–T conditions of 0.8–1.2 GPa/750–785 °C based on the stability fields of corresponding mineral assemblages, the measured isopleths of Ti contents in biotite and amphibole cores, and XGrs in garnet. The third phase low-pressure (LP) type overprinting includes early-stage heating to peak granulite facies followed by cooling towards a late-stage amphibolite facies. The peak granulite facies is represented by the high Ti amphibole mantle, high Zr titanite and the intergrowths of clinopyroxene + ilmenite in A1533 & A1531, with P–T conditions of 800–875 °C/0.80–0.95 GPa. The late-stage is defined by the solidus assemblages, giving P–T conditions of 0.5–0.7 GPa/720–805 °C. U-Pb geochronology on metamorphic zircons from A1533 and A1534 gives three ages of c. 500 Ma, c. 482 Ma and c. 460 Ma. They are interpreted to represent the HP–UHP, MP and LP types of metamorphism respectively, based on cathodoluminescence images, mineral inclusions and trace element patterns. Combining the regional geology and metamorphic evolution from the Altyn Orogen, a tectonic model is inferred, including the following tectonic scenarios. The small Altyn Microcontinent was subducted to great mantle depths with dragging of the surrounding vast oceanic lithosphere to undergo the HP–UHP eclogite facies metamorphism during the early subduction stage (c. 500 Ma) of the Proto-Tethys Ocean. Then, the subducted slabs were exhumed to a thickened crust region to be overprinted by the MP-type assemblages at c. 482 Ma. Finally, an arc–backarc extension was operated within the thickened crust region due to the retreat of subduction zones. It caused evident heating and the LP-type metamorphic overprinting at c. 460 Ma, with a fairly long interval of 30–40 Myr after the HP–UHP metamorphism, distinct from the short interval of <5–10 Myr in the Bohemian Massif.

The texture and composition of tourmaline in metasediments of the Sinai, Egypt: Implications for the tectono-metamorphic evolution of the Pan-African basement

2007 ◽  
Vol 71 (1) ◽  
pp. 17-40 ◽  
Author(s):  
M. M. Abu El-Enen ◽  
M. Okrusch
Keyword(s):  
Regional Metamorphism ◽  
Metamorphic Grade ◽  
Crystalline Basement ◽  
Amphibolite Facies ◽  
Metamorphic Rocks ◽  
Pan African ◽  
Chemical Signatures ◽  
Mineral Assemblages ◽  
The Matrix ◽  
Metamorphic Facies

AbstractAccessory tourmaline in metasediments from the Sinai crystalline basement exhibits textural and chemical signatures that relate to the evolution of regional metamorphism and deformation during the Pan-African orogeny and testifies to different P-T path segments. Tourmaline inclusions in various porphyroblasts were formed during the prograde phase of metamorphism; acicular to prismatic crystals in the matrix, oriented sub-parallel to, and enveloped by, the main foliation crystallized syntectonically under prograde and peak metamorphic conditions; tourmaline cross-cutting the main foliation may have formed just after the peak or during the retrograde phase of metamorphism. Some of the cores in tourmaline crystals, showing different colours, are interpreted as former detrital grains. The abundance of tourmaline decreases with increasing peak metamorphic conditions. The tourmaline investigated belongs to the schorl-dravitess group, generally with XMg of 0.42–0.73 and XCa = Ca/(Ca+Na+K+□) of 0.02–0.24, typical of tourmalines in metapelites and metapsammites; whereas detrital cores have been derived from various sources, including former tourmaline-quartz and pre-existing high-metamorphic rocks. Tourmaline of the Sinai metasediments was formed during metamorphism of the sedimentary precursors, essentially in a closed system, where clay minerals and organic matter, together with detrital tourmaline, served as the source of boron. Although a metamorphic facies should be defined by characteristic mineral assemblages present in metamorphic rocks, tourmaline chemistry is a good monitor of P-T conditions in the metapelites and semi-metapelites investigated, showing an increase in XMg with increasing metamorphic grade, where XturMg = 0.60 distinguishes between greenschist and lower-amphibolite facies, while XturMg = 0.65 could distinguish lower- from middle- to upper-amphibolite facies. The results of tourmaline-biotite geothermometry compare well with our former temperature estimates using conventional geothermometry and phase-diagram modelling.

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