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.

XII.—Petrology and Petrogenesis of some Garnetiferous Peridotites

1963 ◽  
Vol 65 (12) ◽  
pp. 251-314 ◽  
Author(s):  
M. J. O'Hara ◽  
F. H. Stewart
Keyword(s):  
South Africa ◽  
Crystalline Rocks ◽  
Chemical Analyses ◽  
X Ray ◽  
Metamorphic History ◽  
Igneous Origin ◽  
Mineral Assemblages ◽  
History Of ◽  
Reliable Interpretation ◽  
Recent Experimental Work

SynopsisGarnetiferous peridotite masses which occur among gneisses in the Tafjord district of Norway are cold intrusions emplaced as crystalline rocks late in the metamorphic history of the region. No relationship other than similarity of mineral facies can be established between the peridotites and the eclogite bodies in the surrounding gneiss. Chemical analyses of twelve olivines, fourteen orthopyroxenes, nine chrome diopsides, nine garnets, three amphiboles and two rocks are presented, representing material from the Tafjord and Almklovdalen districts of Norway, a garnetiferous peridotite mass near Bellinzona, Switzerland, and the garnet-peridotite inclusions in the kimberlite pipes of South Africa. Optical and X-ray data for the analyzed and some unanalyzed assemblages are also presented. The mineral assemblages of these rocks are compared with each other, and with data from the peridotites of layered tholeiitic intrusions, alpine-type peridotites and the peridotite nodules in basalts. The garnet-peridotites of Norway, Switzerland and South Africa are believed to be little altered fragments of the mantle, whereas the peridotite nodules in basalts and the alpine-type peridotites are believed to be of igneous origin. Examination of the distribution of cations between the coexisting phases suggests that there are too many variables to permit a reliable interpretation of the results.The orthopyroxenes from the garnetiferous peridotites are not rich in A1203, contrary to expectations based upon recent experimental work.

Mineralogy of vesicles in an olivine leucitite at Cosgrove, Victoria, Australia

1980 ◽  
Vol 43 (329) ◽  
pp. 597-603 ◽  
Author(s):  
W. D. Birch
Keyword(s):  
Late Stage ◽  
Rock Type ◽  
Early Stage ◽  
Coarse Grained ◽  
Residual Liquid ◽  
Cooling History ◽  
History Of

SummaryAn olivine-titanomagnetite-apatite-clinopyroxene-mica-nepheline-feldspar assemblage occurs in late-stage vesicles in a small outcrop of olivine leucitite at Cosgrove, Victoria. The vesicles were formed by exsolution of volatiles at an early stage in the cooling history of the lava. Subsequently, a volatile-rich residual liquid filled cavities and fractures, giving rise to a coarse-grained pegmatoid rock type similar in over-all mineralogy to the vesicles. The volatiles facilitating crystallization in both the vesicles and the pegmatoid were probably enriched in F, CO2, and P. A number of geothermometers applied to the vesicle assemblage failed to agree on likely crystallization temperatures.

Mineralogy and metamorphic history of norite dykes within granulite facies gneisses from Sand Mata, Rajasthan, NW India

1987 ◽  
Vol 51 (360) ◽  
pp. 207-215 ◽  
Author(s):  
Ram S. Sharma ◽  
Jane D. Sills ◽  
M. Joshi
Keyword(s):  
Country Rock ◽  
Granulite Facies ◽  
Slow Cooling ◽  
Granulite Facies Metamorphism ◽  
Tholeiitic Magma ◽  
Metamorphic History ◽  
Gneiss Complex ◽  
Corona Formation ◽  
History Of ◽  
Mineral Compositions

AbstractMetanorite dykes intrude the Banded Gneiss Complex at various places in Rajasthan, N.W. India. They show neither chilled margins nor gradational contacts with the country rock amphibolite or granulite facies gneisses. They have ophitic to subophitic texture with strongly zoned subcalcic clinopyroxene and orthopyroxene, olivine and plagioclase, with subsidiary biotite. During slow cooling a series of reaction coronas developed with garnet forming round biotite, ilmenite and orthopyroxene; hornblende round pyroxenes and orthopyroxene, hornblende ± spinel round olivine, which may be totally replaced. It is inferred that the dykes crystallised from a tholeiitic magma at about 1100-1150 °C and were intruded during the waning stages of granulite facies metamorphism. The corona minerals grew at about 650–700 °C. A series of reactions to account for the development of the coronas is proposed using measured mineral compositions. Although these reactions do not balance for individual corona formation, metamorphism was probably isochemical with Ca, Na, K, Ti, Si and H2O only mobile on the scale of a thin section. Si and H2O were possibly mobile on a larger scale.

scholarly journals The Archaean gneiss complex of northern Labrador A review of current results, ideas and problems

1991 ◽  
Vol 39 ◽  
pp. 153-166
Author(s):  
D. Bridgwater ◽  
L. Schiøtte
Keyword(s):  
Major Part ◽  
Granulite Facies ◽  
High Grade ◽  
Late Archaean ◽  
West Greenland ◽  
Metamorphic History ◽  
Gneiss Complex ◽  
History Of ◽  
Augen Gneiss ◽  
Dominant Phase

1. The early Archaean rocks in northern Labrador can be subdivided into the ea. 3.78 Ga Nulliak supracrus­tal association, the migmatitic Uivak I gneisses, the dominant phase of which was emplaced at ea. 3.73 Ga, and the Uivak II augen gneiss. Inherited low-U rounded inclusions within igneous zircons in the Uivak I gneisses have ages between 3.73 and 3.86 Ga and are more likely to have been derived from a pre-existing high-grade metamorphic gneiss complex than from the Nulliak association. In the early Archaean there were probably several rapid cycles of sedimentary deposition and volcanism followed by emplacement of major plutons. Mid Archaean gneisses are more abundant in northern Labrador than previously realised. The late Archaean metamorphic history of these gneisses is different from the history of the early Archaean gneisses. Whereas an important part of the mid Archaean suite was emplaced in granulite facies and retrogressed at the time of granitoid veining at ea. 2.99 Ga, the major part of the early Archaean rocks were reworked under granulite facies conditions in a sequence of closely spaced events between 2. 7 and 2.8 Ga. The two groups of gneisses had different metamorphic histories until ea. 2.7 Ga, but late and post-tectonic granites of 2.5- 2. 7 Ga age cut across both. It is suggested that the terrane model in southern West Greenland can be extended to Labrador and that tectonic intercalation of early and mid Archaean gneisses took place around 2.7 Ga. Correlation between the Maggo gneisses around Hopedale, mid Archaean gneisses in northernmost Labrador and gneisses from the Akia terrane in West Greenland is suggested. Like the Malene supracrustals in West Greenland the Upernavik supracrustals in Labrador are composite associations, the youngest of which are thought to have been deposited around 2. 7 Ga.

scholarly journals Controls of metamorphic grade in shear belts

1979 ◽  
Vol 89 ◽  
pp. 47-62
Author(s):  
J Grocott
Keyword(s):  
Vertical Displacement ◽  
Metamorphic Grade ◽  
Perfect Equilibrium ◽  
Horizontal Gradients ◽  
Metamorphic History ◽  
Mineral Assemblages ◽  
History Of ◽  
Set Up ◽  
The Relationship ◽  
Shear Belt

The relationship between metamorphic grade and deformation is examined for shear belts occurring in Precambrian shields. A particular case, where isotherms have fallen continuously relative to an originally horizontal datum surface, for some time prior to the initiation of the shear belt and throughout its life, is examined in detail. Such behaviour of isotherms appears to be common. A type of syn-tectonic metamorphic boundary occurring within shear belts and not coinciding with a strain gradient is discussed in detail. Such boundaries are called active facies boundaries, as mineral assemblages on each side tend to maintain perfect equilibrium with metamorphic conditions during deformation. The orientation of active facies boundaries depends on the vertical displacement rate. In ductile thrust zones horizontal gradients in metamorphic conditions can be set up, and folIowing erosion once active facies boundaries may be exposed. The metamorphic history of rocks in such zones will vary vertically, and, under certain circumstances, laterally. A model is set up to predict these variations, and is applied to the northem boundary of the Ikertoq shear belt, western Greenland.

Metamorphic history of the Hemlo gold deposit from Al2SiO5 mineral assemblages, with implications for the timing of mineralization

1999 ◽  
Vol 36 (1) ◽  
pp. 33-46 ◽  
Author(s):  
Wayne G Powell ◽  
David RM Pattison ◽  
Paul Johnston
Keyword(s):  
Gold Deposit ◽  
Quartz Veins ◽  
Metamorphic History ◽  
Fluid Infiltration ◽  
Mineral Assemblages ◽  
Metamorphic Assemblage ◽  
The Matrix ◽  
History Of ◽  
T Path ◽  
Late Growth

Textural relations between Al2SiO5 phases, and deformation fabrics, provide constraints on the metamorphic history of the Hemlo gold deposit. Kyanite in the deposit is most common within and on the margins of boudinaged quartz ± realgar veins, and less commonly as rotated porphyroblasts within the matrix of schistose rocks. Kyanite predates the main (D2) schistosity. Sillimanite postdates kyanite, occurring irregularly as discrete knots and foliae that run parallel to, but sometimes cut across, the principal (D2) foliation, indicating that sillimanite postdates the D2 foliation. We regard kyanite to be part of the peak metamorphic assemblage, with sillimanite representing a partial later overprint most likely related to fluid infiltration. Rare andalusite occurs in two associations: as late-stage, clean, idioblastic crystals; and as large, fractured grains, locally overprinted by sillimanite, in boudinaged quartz-realgar veins. We suggest two possible origins for this second form of andalusite, one involving generally late growth, the second involving early growth prior to the development of peak metamorphic kyanite. Although not unambiguous, we prefer the second scenario. P-T conditions from petrogenetic grid constraints, and new geothermobarometric estimates, indicate 6-7 GPa, 600-650°C for the peak kyanite grade metamorphism (ca. 2677 Ma?), and 4-5 GPa, 600°C for the later sillimanite overprint (ca. 2672 Ma?). We see these two events as part of an evolving P-T path in a single metamorphic event. In our early andalusite scenario, the andalusite may have formed from pyrophyllite breakdown at 2-4 GPa, 450°C, possibly associated with emplacement of the regional suite of granodiorite plutons (ca. 2686 Ma). Late andalusite formed sporadically on the retrograde path. The occurrence of deformed andalusite and aligned kyanite in and on the margins of boudinaged auriferous realgar-stibnite-quartz veins provides evidence in support of a premetamorphic mineralization event.

The Proterozoic magmatic and metamorphic history of the Banded Gneiss Complex, central Rajasthan, India: LA-ICP-MS U–Pb zircon constraints

2006 ◽  
Vol 151 (1-2) ◽  
pp. 119-142 ◽  
Author(s):  
I.S. Buick ◽  
C. Allen ◽  
M. Pandit ◽  
D. Rubatto ◽  
J. Hermann
Keyword(s):  
Metamorphic History ◽  
Gneiss Complex ◽  
Icp Ms ◽  
History Of

scholarly journals Two garnet growth events in polymetamorphic rocks in southwest Spitsbergen, Norway: insight in the history of Neoproterozoic and early Paleozoic metamorphism in the High Arctic

2015 ◽  
Vol 52 (12) ◽  
pp. 1045-1061 ◽  
Author(s):  
Jarosław Majka ◽  
Karolina Kośmińska ◽  
Stanisław Mazur ◽  
Jerzy Czerny ◽  
Karsten Piepjohn ◽  
...  
Keyword(s):  
Large Scale ◽  
High Arctic ◽  
Amphibolite Facies ◽  
Garnet Growth ◽  
Original Structure ◽  
Clockwise Rotation ◽  
Passive Rotation ◽  
Metamorphic Basement ◽  
Mineral Assemblages ◽  
History Of

Geochronological studies in northern Wedel Jarlsberg Land, southwestern Svalbard (Norway), showed that the Tonian (c. 950 Ma) igneous rocks were subjected to metamorphism during the Torellian (c. 640 Ma) and early Caledonian (470–460 Ma) events. Predominant augen gneisses, derived from a Tonian protolith, are intercalated in that area, with schists comprising two distinct metamorphic mineral assemblages. The M1 (Torellian) assemblage containing garnet-I + quartz + plagioclase-I + biotite-I + muscovite-I was formed under amphibolite-facies conditions at c. 550–600 °C and 5–8 kbar (1 kbar = 100 MPa). The M2 (Caledonian) assemblage comprising garnet-II + quartz + plagioclase-II + biotite-II + muscovite-II + zoisite + chlorite crystallized at c. 500–550 °C and 9–12 kbar, corresponding to epidote–amphibolite facies conditions. The M2 mineral assemblage constitutes the pervasive Caledonian fabric of the schists that was subsequently reactivated in a left-lateral strike-slip shear regime. The subsequent c. 70° clockwise rotation of the original structure to its present position was caused by a large-scale passive rotation during the Paleogene Eurekan orogeny. The new pressure–temperature estimates suggest that metamorphic basement in the study area was consolidated during the Torellian middle-grade event and then overprinted by Caledonian moderate- to high-pressure subduction-related metamorphism. A following sinistral shear zone assembled the present structure of basement units. Our results pose a question about the possible extent of Torellian precursor to the Caledonian basement across the High Arctic and the scale of its subsequent involvement in early Caledonian subduction. In conjunction with previous studies, the results suggest a possible correlation between southwestern Spitsbergen and the Pearya Terrane in Ellesmere Island.

The structural and metamorphic history of the Taconic unconformity in western Massachusetts

1978 ◽  
Vol 15 (12) ◽  
pp. 1941-1953
Author(s):  
A. B. Uzuakpunwa ◽  
Arthur H. Brownlow
Keyword(s):  
Volcanic Rock ◽  
Island Arc ◽  
Amphibolite Facies ◽  
Middle Ordovician ◽  
Angular Unconformity ◽  
Basic Volcanic Rock ◽  
Metamorphic History ◽  
History Of ◽  
Basic Volcanic ◽  
Pegmatitic Granite

Evidence from detailed structural and petrographic studies in western Massachusetts shows that the Cambro-Ordovician Rowe Schist and the Middle Ordovician Moretown Formation have different depositional, structural, and metamorphic histories and are separated by a pre-Taconic angular unconformity. The Rowe Schist (pelitic and semi-pelitic schists and minor lenticular amphibolites) underwent multiple periods of deformation and amphibolite facies grade of metamorphism before the deposition of the Moretown Formation. The latter is composed of the Chester Amphibolite, chlorite–muscovite schist, and staurolite–garnet–biotite schists. The predominant structures and metamorphism in the Moretown Formation are those of the Acadian Orogeny. Both the Rowe Schist and the Moretown Formation are transected by a foliated pegmatitic granite (Middlefield – Blair Pond Pluton). A dyke of the granite cuts the composite tectonic fabric in the Rowe Schist (which it post-dates), but it is generally deformed by the earliest and regional schistosities found in the Moretown Formation (which it pre-dates). The base of the Moretown Formation is defined by the Chester Amphibolite. It represents a recrystallized basic volcanic rock associated with an island arc system.

scholarly journals 40 Ar/39/Ar dating and cooling history of the Pangeon granitoids, Rhodope Massif (Eastern Macedonia, Greece)

2001 ◽  
Vol 34 (3) ◽  
pp. 911 ◽  
Author(s):  
G. ELEFTHERIADIS ◽  
W. FRANK ◽  
K. PETRAKAKIS
Keyword(s):  
Lower Limit ◽  
Coarse Grained ◽  
Cooling History ◽  
History Of

The Pangeon granitoids are distinguished into two pétrographie types with sharp contacts: (a) heterogranular, medium- to coarse-grained, hornblende+biotite- bearing porphyritic tonalités and granodiorites (PTG), and, (b) equigranular, medium-grained, biotite±muscovite-bearing granodiorites and granites (MGG). Dark-coloured, medium-grained monzodioritic enclaves occur in PTG rocks. Hornblende 40Ar/39Ar spectra from the PTG rocks yielded cooling ages of 21.7±0.5 Ma to 18.8±0.6 Ma. With the exception one sample, the corresponding hornblende ages from enclaves coincide well with the above ages. The age of 21.7±0.5 Ma is considered as the lower limit for the PTG rocks emplacement. Muscoviteplateau ages of c. 15.7±0.5 Ma and total gas biotite ages of 15.2±0.4 Ma to 13.8±0.5 Ma from the studied rocks, constrain the cooling history of the Pangeon granitoids (with some local variations) in the range 430 - 300Ί C.

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