Pressure--Temperature--Time Paths of Regional Metamorphism II. Their Inference and Interpretation using Mineral Assemblages in Metamorphic Rocks

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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Metamorphism of the Settler Schist, southwest of Yale, British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/e76-042 ◽

1976 ◽

Vol 13 (3) ◽

pp. 405-421 ◽

Cited By ~ 19

Author(s):

Lee C. Pigage

Keyword(s):

British Columbia ◽

Linear Regression ◽

Microprobe Analysis ◽

Regional Metamorphism ◽

Fluid Phase ◽

Contact Metamorphism ◽

Major Constituent ◽

Minor Components ◽

Mineral Assemblages ◽

Regression Techniques

Pelitic metasediments immediately southwest of Yale, British Columbia contain mineral assemblages characteristic of staurolite through sillimanite zones of the Barrovian facies series. Microprobe analyses of major constituent phases in the pelites are combined with linear regression techniques to formulate probable kyanite- and sillimanite-forming reactions.A zone some 3 km wide contains the assemblage staurolite–kyanite–garnet–biotite–muscovite–quartz–plagioclase-ilmenite-rutile, which is univariant in AFM projection. Within precision limits of microprobe analysis, this assemblage is also univariant using linear regression techniques. Univariant relations are possible if [Formula: see text] with the composition of the fluid phase being buffered by the progressing reaction. This assemblage emphasizes the need for precise analyses when using the regression method, since minor components are often within permissible error limits rather than being balanced.Pelitic and calc-silicate assemblages from the metasediments restrict estimates of pressure–temperature conditions during regional metamorphism to 6–8 kbar and 550–770 °C. Pseudomorphs after andalusite indicate that contact metamorphism preceded regional upgrading of the pelites.

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Petrology of the metamorphic rocks (gravels) from Bhajanpur area in Panchagarh District, Bangladesh

Journal of Life and Earth Science ◽

10.3329/jles.v5i0.7357 ◽

1970 ◽

Vol 5 ◽

pp. 91-96

Author(s):

Md Rahat Hossain ◽

Ismail Hossain ◽

ASM Zahid Hossain ◽

Prodip Kumar Biswas

Keyword(s):

Key Words ◽

Metamorphic Rock ◽

Metamorphic Rocks ◽

Mica Schist ◽

Mineral Assemblages ◽

Temperature Ranges ◽

Garnet Zone ◽

Opaque Minerals ◽

Mineralogical Compositions ◽

Chlorite Schist

The present study deals with petrology of the detrital gravelly rocks from Bhajanpur area, Panchagarh, Bangladesh. The results of detailed petrography of gravelly rocks indicate the presence of quartz (monocrystalline and polycrystalline quartz), K-feldspar, plagioclase, chlorite, muscovite and biotite as major mineralogical compositions. Other minor minerals are garnet, kyanite, graphite and opaque minerals. Based on definitive mineral assemblages, blueschist and greenschist facies sequences are recognized. Correspondingly, index minerals provide chlorite zone, biotite zone, garnet zone, kyanite zone, and graphite zone. The P-T conditions of the studied rocks demonstrate the possible temperature ranges 300-550°C and pressure ranges 2-10 kbar. Most common varieties of metamorphic rocks in the study area are garnet mica schist, chlorite schist, gneiss and few quartzites. Characteristics of garnet mica schist and chlorite schist are equivalent with the lesser Himalayan metamorphic rock sequence in Sikkim area, whereas gneiss from Bhajanpur area has similar precursor as Darjeeling gneiss. Therefore, the sources of detrital metamorphic rocks in Bhajanpur area obviously come from the lesser Himalayan sequence in Sikkim and Darjeeling areas, India. Key words: Petrology; metamorphic rocks; gravels; P-T conditions; Panchagarh; lesser Himalayan sequence DOI: 10.3329/jles.v5i0.7357 J. Life Earth Sci., Vol. 5: 91-96, 2010

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Nature of the Quetico–Wabigoon boundary in the de Courcey – Smiley Lakes area, northwestern Ontario

Canadian Journal of Earth Sciences ◽

10.1139/e76-078 ◽

1976 ◽

Vol 13 (6) ◽

pp. 737-748 ◽

Cited By ~ 5

Author(s):

Manfred M. Kehlenbeck

Keyword(s):

Regional Metamorphism ◽

Sedimentary Rocks ◽

Metamorphic Grade ◽

Boundary Zone ◽

Present Level ◽

Metasedimentary Rocks ◽

The North ◽

Northwestern Ontario ◽

Multiple Phase ◽

Mineral Assemblages

In the de Courcey – Smiley Lakes Area, the boundary between the Quetico and Wabigoon Belts is expressed by a sequence of pelitic to semi-pelitic schists and gneisses. At the present level of erosion, these metasedimentary rocks are in contact with granodioritic gneisses, granites, and pegmatites, which are exposed to the south.To the north of this area, regional metamorphism of volcanic and sedimentary rocks has resulted in greenschist facies assemblages, which characterize the Wabigoon Belt in general. In the boundary zone, the metamorphic grade increases southward toward de Courcey and Smiley Lakes.Formation of three distinct foliation surfaces was accompanied by syn-tectonic as well as post-tectonic recrystallization, producing polymetamorphic schists.In the boundary zone, mineral assemblages comprising andalusile, sillimanite, cordierite, garnet. biotite, and muscovite form a facies series of the Abukuma type.The boundary between the Quetico and Wabigoon Belts in this area is a complex zone in which rocks of both belts have been reconstituted by multiple-phase metamorphism and partial melting.

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Viscous relaxation of mineral Inclusions and its implications for reaction overstepping calculations in metamorphic rocks

10.5194/egusphere-egu2020-7568 ◽

2020 ◽

Author(s):

Evangelos Moulas ◽

Xin Zhong ◽

Lucie Tajcmanova

Keyword(s):

Independent Method ◽

Metamorphic Rocks ◽

Additional Method ◽

Natural Systems ◽

Long Period ◽

Mineral Inclusions ◽

Large Peak ◽

Viscous Relaxation ◽

T Path ◽

Temperature Time

Over the recent years, Raman elastic barometry has been developed as an additional method to calculate metamorphic conditions in natural systems. A major advantage of Raman elastic barometry is that it does not depend on thermodynamic databases and classic geobarometry methods but relies on mechanical calculations. As a consequence, Raman elastic barometry offers an independent method for estimating the pressure conditions that prevailed at the time of entrapment of minerals during growth of their hosts.The difference between the pressure calculated using elastic geobarometry and that calculated by phase equilibria methods has recently been employed to estimate the extent of metamorphic reaction overstepping in natural systems. Quantification of the latter however implicitly assumes that the rheology of the inclusion-host system is perfectly elastic. This assumption may not hold at high temperatures, where viscous creep of minerals takes place.The amount of viscous relaxation of a host-inclusion system is a path-dependent quantity which mostly depends on the temperature-time (T-t) path followed. Here, we present examples of visco-elastic relaxation of mineral inclusions and calculate the apparent reaction overstepping which results by assuming that the mechanical system is purely elastic. Our modelling shows that host-inclusion systems that experienced large peak temperatures for long periods of time will retain inclusion residual pressures that cannot be simply related to the growth of their hosts and should therefore not be used for reaction overstepping calculations.

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Compositional variation in högbomites from north Connemara, Ireland

Mineralogical Magazine ◽

10.1180/minmag.1985.049.354.03 ◽

1985 ◽

Vol 49 (354) ◽

pp. 649-654 ◽

Cited By ~ 7

Author(s):

N. S. Angus ◽

R. Middleton

Keyword(s):

Chemical Composition ◽

Regional Metamorphism ◽

The Other ◽

Partial Substitution ◽

Compositional Variation ◽

Physical Parameters ◽

Chemical Heterogeneity ◽

High Grade ◽

Thermal Metamorphism ◽

Mineral Assemblages

AbstractHögbomite occurs in two contrasting mineral assemblages within the Currywongaun-Dough-ruagh intrusion of north Connemara: a cordierite-rich pelitic xenolith and an orthopyroxenite. In the latter, högbomite and green spinel form blebs within magnetite-ilmenite grains. The högbomite displays significant compositional variation from grain to grain: TiO2 (3.0–6.3%), FeO (21.6–21.3%), MgO (10.0–7.5%), ZnO (3.6–2.4%). This chemical heterogeneity appears to represent variable degrees of partial substitution of Mg and Zn by Ti, in the replacement of spinel by högbomite. By contrast, in the cordierite-hornfels, the högbomite compositions are more notably enriched in iron: TiO2 (4.7–7.0%), FeO (29.6–24.3%), MgO (4.2–6.2%), ZnO (2.7–2.1%). This iron-rich högbomite appears to have formed primarily by interaction between opaque ore and adjacent cordierite, rather than by replacement of spinel.Two high-grade metamorphic episodes appear to be necessary for högbomite growth, one determining chemical composition and the other appropriate physical parameters. In the Connemara occurrences thermal metamorphism and partial melting, coupled with contamination of the surrounding magma, controlled the formation of mineral assemblages rich in Fe, Mg, Al, Ti, and Zn. Emplacement of the intrusion was accompanied by amphibolite facies regional metamorphism and it is to this metamorphic event that the growth of högbomite may be attributed.

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Whole-Rock Rb/Sr Ages of Metamorphic Rocks from Northern Ellesmere Island, Canadian Arctic Archipelago. I. The Gneiss Terrain between Ayles Fiord and Yelverton Inlet

Canadian Journal of Earth Sciences ◽

10.1139/e75-010 ◽

1975 ◽

Vol 12 (1) ◽

pp. 90-94 ◽

Cited By ~ 5

Author(s):

A. K. Sinha ◽

Thomas Frisch

Keyword(s):

Regional Metamorphism ◽

Canadian Arctic ◽

Ellesmere Island ◽

Metamorphic Rocks ◽

Canadian Arctic Archipelago ◽

Fold Belt ◽

Late Precambrian

The first Precambrian ages from the Northern Ellesmere Fold Belt are reported. Six rocks from the largest gneiss terrain in northern Ellesmere Island yield a Late Precambrian age (minimum 742 ± 12 m.y.) of regional metamorphism. Relatively high initial 87Sr/86Sr suggests that the rocks were derived from crustal materials.

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Petrochemistry of metamorphosed pillows, and the geochemical status of the amphibolites (Proterozoic) from the Sirohi district, Rajasthan, India

Geological Magazine ◽

10.1017/s001675680002999x ◽

1984 ◽

Vol 121 (5) ◽

pp. 465-473 ◽

Cited By ~ 14

Author(s):

P. K. Bhattacharyya ◽

A. D. Mukherjee

Keyword(s):

Regional Metamorphism ◽

Element Distribution ◽

Island Arcs ◽

Oceanic Sediments ◽

Crystalline Core ◽

Mineral Assemblages ◽

Trace Element Contents ◽

Closed Systems ◽

Low K ◽

Middle Proterozoic

AbstractRelic pillows in the middle Proterozoic amphibolites, occurring in the Sirohi Road–Abu Road tract of Rajasthan, India exhibit contrasted mineral assemblages from core to rim – mimetic after the crystalline core, the zone of incipient crystallization, and the rim of the original pillows. The major element distribution pattern across the pillows indicates exchange of Na–Al for Ca (Mg, Fe) in an inner reaction zone, surrounding the core and in the inner margin of the rim, and Fe–Al exchange for Ca–Si at the outer margin of the rim.Despite such exchanges around the rims, these pillows have retained their initial geochemical characteristics internally and thus have largely acted as closed systems during post-emplacement metamorphism. Mineral parageneses indicate that the contrasted mineral assemblages could evolve from domainal characters of the co-existing fluids, the compositions of which were only buffered by the reacting minerals during regional metamorphism.The major, minor and trace element contents of the pillows and of amphibolites of diverse petrographic character in the region further establish that the pillow interiors and the massive amphibolites were least modified during metamorphism(s), and represent oceanic tholeiites. Their average 2300 ppm K, 4.5 ppm Rb, 150 ppm Sr, along with the K/Rb and K/Sr ratios of 510 and 15 respectively resemble that of the low K-tholeiites, occurring nearest to the trenches in modern island arcs. On the other hand, the higher values of 17300 ppm K, 4.9 ppm Rb, and 210 ppm Sr of the banded and the schistose amphibolites indicate that they were contaminated in various magnitudes by oceanic sediments.

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Whole rock major element influences on monazite growth: examples from igneous and metamorphic rocks in the Menderes Massif, western Turkey

Mineralogia ◽

10.2478/v10002-008-0002-8 ◽

2008 ◽

Vol 39 (1-2) ◽

pp. 7-30 ◽

Cited By ~ 3

Author(s):

Elizabeth Catlos ◽

Courteney Baker ◽

Ibrahim Çemen ◽

Cenk Ozerdem

Keyword(s):

Major Element ◽

Bulk Composition ◽

Metamorphic Rocks ◽

Western Turkey ◽

Menderes Massif ◽

Tectonic History ◽

Major Element Chemistry ◽

Element Chemistry ◽

Multi Stage ◽

Mineral Assemblages

Whole rock major element influences on monazite growth: examples from igneous and metamorphic rocks in the Menderes Massif, western TurkeyMonazite (LREEPO4) is a radiogenic, rare-earth bearing mineral commonly used for geochronology. Here we examine the control of major element chemistry in influencing the crystallization of monazite in granites (Salihli and Turgutlu bodies) and garnet-bearing metamorphic assemblages (Bozdag and Bayindir nappes) from the Menderes Massif, western Turkey. In S-type granites from the massif, the presence of monazite correlates to the CaO and Al2O3content of the whole rock. Granites with monazite only are low Ca (0.6-1.8 wt% CaO). As CaO increases (from 2.1-4.6 wt%), allanite [(Ce, Ca, Y)2(Al, Fe3+)3(SiO4)3(OH)] is present. Higher Al2O3(>15 wt%) rocks contain allanite and/or monazite, whereas those with lower Al2O3contain monazite only. However, examining data reported elsewhere for A-type granites, the correlation between major element chemistry and presence of monazite is likely restricted to S-type lithologies. Pelitic schists of the Menderes Massif show no correlation between major element chemistry and presence of monazite. One Bayindir nappe sample contains both prograde garnets and those affected significantly by diffusion. These rocks have likely experienced a complicated multi-stage tectonic history, which influenced their current mineral assemblages. The presence of monazite in a metamorphic rock can be influenced by the number, duration, and nature of events that were experienced and the degree to which fluids were involved. The source of monazite in the Bayindir and Bozdag samples was likely reactions that involved allanite. These reactions may not have significantly changed the bulk composition of the rock.

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A model for the origin of the Lac St. Jean anorthosite massif

Canadian Journal of Earth Sciences ◽

10.1139/e76-040 ◽

1976 ◽

Vol 13 (2) ◽

pp. 389-399 ◽

Cited By ~ 7

Author(s):

R. A. Frith ◽

K. L. Currie

Keyword(s):

Experimental Data ◽

Partial Melting ◽

Metamorphic Rocks ◽

High Grade ◽

Calc Alkaline ◽

Grenville Province ◽

Thermal Event ◽

Anorthosite Massif ◽

Mineral Assemblages ◽

Potassic Rocks

An ancient tonalitic complex becomes migmatitic around the Lac St. Jean massif, ultimately losing its identity in the high grade metamorphic rocks surrounding the anorthosite. Field relations suggest extreme metamorphism and anatexis of tonalitic rocks. Experimental data show that extensive partial melting of the tonalite leaves an anorthositic residue. The same process operating on more potassic rocks would leave monzonitic or quartz syenitic residues. Synthesis of experimental data suggests that the process could operate at pressures of 5–8 kbar and temperatures of 800–1000 °C, which are compatible with mineral assemblages around the anorthosite massif. Slightly higher temperatures at the end of the process could generate magmatic anorthosite.Application of the model to the Grenville province as a whole predicts generation of anorthosite during a long-lived thermal event of unusual intensity. Residual anorthosite would occur as a substratum in the crust, overlain by high-grade metamorphic rocks intruded by anorthosite and syenitic rocks, while higher levels in the crust would display abundant calc-alkaline plutons and extrusives.

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