Characterization and metamorphic evolution of Mesoproterozoic granulites from Sonapahar (Meghalaya), NE India, using EPMA monazite dating

2020 ◽  
Vol 157 (9) ◽  
pp. 1409-1427
Author(s):  
Shyam Bihari Dwivedi ◽  
Kevilhoutuo Theunuo ◽  
Ravi Ranjan Kumar
Keyword(s):  
Metamorphic Stage ◽  
Radioactive Materials ◽  
Tectonic Event ◽  
Monazite Dating ◽  
Pan African ◽  
Mineral Phases ◽  
Ne India ◽  
Mineral Assemblages ◽  
Isothermal Decompression ◽  
Grenvillian Orogeny

AbstractThis paper presents three different age domains, obtained by electron microprobe monazite dating, for granulitic gneisses collected from the Shillong-Meghalaya Gneissic Complex in Sonapahar, NE India, which contain radioactive materials, e.g. thorium (3.32–7.20 wt %), uranium (0.133–1.172 wt %) and lead (0.101–0.513 wt %). The microprobe analyses of monazite grains in the rock samples show that the monazites have three different ages ranging from Mesoproterozoic to Neoproterozoic. The oldest age (1571 ± 22 Ma) represents a peak metamorphic event, the youngest dominant age indicates the Pan-African tectonic event (478 ± 7 Ma) and the intermediate age marks the Grenvillian orogeny (1034 ± 91 Ma) or may be a mixing artefact; these ages are located at the cores, rims and intermediate parts of the monazite grains, respectively. The equilibrium mineral phases calculated for the granulitic gneisses from Sonapahar lie in a P–T range from 5.9 kbar/754 °C to 8.3 kbar/829 °C in the NCKFMASH system. Plotting the P–T conditions of the granulitic gneisses reveals a clockwise P–T path. Two major metamorphic events are observed in Sonapahar. The M1 metamorphic stage is represented by peak mineral assemblages of prograde garnet-forming reactions (8.2 kbar/∼713 °C) during Mesoproterozoic time (1571 ± 22 Ma). The M2 metamorphic stage featured decompression (3.9 kbar/∼701 °C) in which garnet–sillimanite broke down to form cordierite along an isothermal decompression path during the Pan-African tectonic event (478 ± 7 Ma).

Timing and rate of isothermal decompression in Pan-African granulites from Rundvågshetta, East Antarctica

2000 ◽  
Vol 18 (4) ◽  
pp. 441-454 ◽  
Author(s):  
G. Fraser ◽  
I. McDougall ◽  
D. J. Ellis ◽  
I. S. Williams
Keyword(s):  
East Antarctica ◽  
Pan African ◽  
Isothermal Decompression

Paragenesis of Cu-Fe ores from Ocna de Fier-Dognecea (Romania), typifying fluid plume mineralization in a proximal skarn setting

2001 ◽  
Vol 65 (3) ◽  
pp. 351-372 ◽  
Author(s):  
N. J. Cook ◽  
C. L. Ciobanu
Keyword(s):  
Trace Mineral ◽  
Mineral Phases ◽  
Initial Stage ◽  
Mineral Assemblages ◽  
Skarn Deposits ◽  
Additional Constraints

AbstractTrace mineral assemblages in the bornite- and chalcopyrite-rich Cu-Fe zone of the Ocna de Fier-Dognecea skarn deposits, Banat, SW Romania provide additional constraints on the genesis of this classic zoned skarn system. Observed assemblages substantiate a model, in which the Cu-Fe zone forms the proximal fluid-plume root of the system. Observed trace mineral assemblages in the magnesian forsterite-bearing skarns crystallized at ~650°C in a volatile-rich environment, evidenced by widespread phlogopite, ludwigite, valleriite and apatite. The entire assemblage thus belongs to the initial stage of skarn formation. Prolonged cooling led to sequential exsolution of trace mineral phases from bornite and chalcopyrite during the retrograde stage, although still at temperatures in excess of 500°C. Bornite is typified by the abundance of exsolved phases along cleavage planes and along crystal margins, notably chalcopyrite and pyrrhotite, but also cobalt pentlandite, carrollite, wittichenite, galena, mawsonite, silver and electrum. Chalcopyrite hosts cobalt pentlandite, carrollite, wittichenite, galena and a sequence of Se- and Te-bearing minerals (kawazulite, bohdanowiczite, hessite, volynskite), along, although not restricted to, grain margins. The assemblage bornite-chalcopyrite-magnetite, with the trace phases, cobalt pentlandite, carrollite, wittichenite and various Se- and Te-bearing minerals represents a characteristic assemblage common to a disparate range of deposits formed at temperatures in excess of 500°C in the presence of volatiles and typified by relatively low fS2 fluids.

scholarly journals Powder diffraction of yellow and red natural earths from Lessini Mountains in NE Italy

2015 ◽  
Vol 30 (2) ◽  
pp. 122-129 ◽  
Author(s):  
Giovanni Cavallo ◽  
Maria Pia Riccardi ◽  
Roberto Zorzin
Keyword(s):  
Powder Diffraction ◽  
Raw Materials ◽  
Mineralogical Composition ◽  
Degree Of Crystallinity ◽  
Ne Italy ◽  
Mineral Phases ◽  
Mineral Assemblages ◽  
Parent Rocks ◽  
Materials Used ◽  
The Degree Of Crystallinity

A first attempt to differentiate goethite- and hematite-based natural materials, used for several purposes during the Late Palaeolithic in the Lessini Mountains (Italy), is here proposed. All raw materials were collected from known geological sites within a distance of about 20 km from archaeological excavations (Tagliente and Fumane caves) where ochre fragments were found. X-ray powder diffraction allowed the mineralogical composition of samples collected from carbonate and volcanic geological host and parent rocks to be inferred; in addition, a preliminary distinction based on the different mineral assemblages, on the presence of distinctive mineral phases and on the degree of crystallinity of some compounds such as hematite, became possible. The acquired data thus represent a sort of preliminary inventory for provenance studies on archaeological samples originating in the same region, for which ancillary micro-analytical and geochemical techniques are planned.

The origins of granulites: a metamorphic perspective

1989 ◽  
Vol 126 (3) ◽  
pp. 215-247 ◽  
Author(s):  
S. L. Harley
Keyword(s):  
Large Range ◽  
Crustal Extension ◽  
Mineral Assemblages ◽  
Moderate Rate ◽  
Complex Models ◽  
Isothermal Decompression ◽  
Normal Thickness ◽  
Thinning Process ◽  
Tectonic Exhumation ◽  
Very High

AbstractAlthough many recent reviews emphasize a uniformity in granulite pressure–temperature (P–T) conditions and paths, granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation. A thorough survey of over 90 granulite terranes or occurrences reveals that over 50% of them recordP–Tconditions outside the 7.5 ± 1 kbar and 800 ± 50 °C average granulite regime preferred by many authors. In particular, an increasing number of very high temperature (900−1000 °C) terranes are being recognized, both on the basis of distinctive mineral assemblages and geothermobarometry. Petrogenetic grid and geothermobarometric approaches to the determination and interpretation ofP–Thistories are both evaluated within the context of reaction textures to demonstrate that the large range inP–Tconditions is indeed real, and that both near-isothermal decompression (ITD) and near-isobaric cooling (IBC)P–Tpaths are important. Amphibolite–granulite transitions promoted by the passage of CO2-rich fluids, as observed in southern India and Sri Lanka, are exceptional and not representative of fluid-related processes in the majority of terranes. It is considered, on the contrary, that fluid-absent conditions are typical of most granulites at or near the time of their recorded thermal maxima.ITD granulites are interpreted to have formed in crust thickened by collision, with magmatic additions being an important extra heat source. Erosion alone is not, however, considered to be the dominant post-collisional thinning process. Instead, the ITD paths are generated during more rapid thinning (1−2 mm/yr exposure) related to tectonic exhumation during moderate-rate or waning extension. IBC granulites may have formed in a variety of settings. Those which show anticlockwiseP–Thistories are interpreted to have formed in and beneath areas of voluminous magmatic accretion, with or without additional crustal extension. IBC granulites at shallow levels (< 5 kbar) may also be formed during extension of normal thickness crust, but deeper-level IBC requires more complex models. Many granulites exhibiting IBC at deep crustal levels may have formed in thickened crust which underwentveryrapid (5 mm/yr) extensional thinning subsequent to collision. It is suggested that the preservation of IBC paths rather than ITD paths in many granulites is primarily related to therateandtimescaleof extensional thinning of thickened crust, and that hybrid ITD to IBC paths should also be observed.Most IBC granulites, and probably many ITD granulites, have not been exposed at the Earth's surface as a result of the tectonic episodes which produced them, but have resided in the middle and lower crust for long periods of time (100−2000 Ma) following these events. The eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation.

Quaternary caldera-forming eruptions from north to south Sumatra (Indonesia)

2021 ◽  
Author(s):  
Francesca Forni ◽  
Jeffrey A. Oalmann ◽  
Giuditta Fellin ◽  
Steffen Eisele ◽  
Marcus Phua ◽  
...  
Keyword(s):  
Explosive Volcanism ◽  
Mineral Chemistry ◽  
Upper Crust ◽  
Similar Frequency ◽  
Mineral Phases ◽  
Dating Methods ◽  
Mineral Assemblages ◽  
Tephra Layers ◽  
Geochemical Analyses ◽  
Central Sumatra

&lt;p&gt;Large volumes of silicic tuffs deposited during highly explosive eruptions associated with caldera-collapses are widespread on the island of Sumatra (Indonesia) from north to south. Among them, only the Toba tuffs have been studied in great detail, while others have so far received less attention.&lt;/p&gt;&lt;p&gt;This study is aimed at determining the age and characteristics of a number of these tuffs from northern Sumatra (Sinkgut and Hopong-Sipirok), central Sumatra (Maninjau and Kerinci-Lempur) and southern Sumatra (Pasomah, Ranau and Lampong), in order to reconstruct the distribution and frequency of caldera-forming eruptions in the region. Furthermore, since most of the information about the volcanic activity in Sumatra comes from marine tephra layers with unknown sources, linking the temporal and compositional information to the terrestrial sources contributes a foundation for tephrostratigraphic correlations in south-east Asia.&lt;/p&gt;&lt;p&gt;We performed textural and geochemical analyses to characterize the crystallinity &amp;#160;and major and trace element compositions of bulk-rock, matrix glasses and mineral phases from the studied ignimbrites and derive information about the pre-eruptive conditions. We used a variety of geochronological methods (including U/Th, U/Pb and U/Th-He zircon dating together with &lt;sup&gt;14&lt;/sup&gt;C and &lt;sup&gt;40&lt;/sup&gt;Ar/&lt;sup&gt;39&lt;/sup&gt;Ar) and statistical analyses to estimate the eruption ages and magma residence times. Multiple dating methods were often applied to the same deposits thus allowing comparison between independent age results.&lt;/p&gt;&lt;p&gt;Our research indicates that between ~1200 and 30 ka the region experienced at least 10 caldera-forming eruptions, in addition to 4 from Toba (between ~1.2 Ma and 74 ka) and 1 from Masurai (~33 ka): 3 from northern Sumatra at ~44 ka (Singkut), ~400 ka and ~580 ka (Hopong-Sipirok), 5 from central Sumatra at ~51 ka (Maninajau), ~150, 210, and 220 ka (Kerinci-Lempur) and 3 from southern Sumatra at ~35 ka (Ranau), ~480 ka (Pasomah), and ~1200 ka (Lampong). Each of these eruptions involved tens to hundreds of km&lt;sup&gt;3&lt;/sup&gt; of rhyolitic magmas (VEI&gt;6) and produced calderas with diameters between ~5 and 30 km. Geothermobarometers and hygrometers indicate that prior to eruption, magmas were stored in the upper crust in similar conditions but the geochemical signatures (in particular the K&lt;sub&gt;2&lt;/sub&gt;O content), mineral assemblages and mineral chemistry define clear differences between the northern, central and southern sectors of the Sumatran volcanic arc, presumably linked to the regional geodynamics and structural setting.&lt;/p&gt;&lt;p&gt;This study allows to redefine the number of caldera-forming eruptions in Sumatra from 7 (previously dated) to 15 over the last 1.2 Ma. A similar frequency of VEI&gt;6 eruptions during the Quaternary is reported for the Japan arc [1]. However, a significant number of eruptions, potentially better preserved in the marine record, might still be missing from our reconstruction.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;[1] Schindlbeck, J. C. et al. One Million Years Tephra Record at IODP Sites U1436 and U1437: Insights into explosive volcanism from the Japan and Izu arcs. Isl. Arc. https://doi.org/10.1111/iar.12244 (2018).&lt;/p&gt;

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.

Progressive metamorphism of pelitic and quartzofeldspathic rocks in the Grenville Province of western Labrador — tectonic implications of bathozone 6 assemblages

1983 ◽  
Vol 20 (12) ◽  
pp. 1791-1804 ◽  
Author(s):  
T. Rivers
Keyword(s):  
Experimental Data ◽  
Pressure Gradient ◽  
Granulite Facies ◽  
Lithostatic Pressure ◽  
Lower Grade ◽  
High Grade ◽  
Tectonic Zone ◽  
Grenville Province ◽  
Mineral Assemblages ◽  
Grenvillian Orogeny

Aphebian metapelites and quartzofeldspathic rocks from the Grenville Province south of the Labrador Trough display progressive changes in mineral assemblages as a result of Grenvillian metamorphism, consistent with variation in grade from greenschist to upper amphibolite facies. The following metamorphic zones have been delineated: (i) chlorite–muscovite; (ii) chlorite–muscovite–biotite; (iii) chlorite–muscovite–biotite–garnet; (iv) muscovite–staurolite–kyanite; (v) muscovite–garnet–biotite–kyanite; (vi) muscovite–garnet–biotite–kyanite–granitic veins; (vii) K–feldspar–kyanite – granitic veins; (viii) K-feldspar–sillimanite–granitic veins. Reactions linking the lower grade metamorphic zones are interpreted to be dehydration phenomena, whilst anatectic reactions occur at higher grades. At lower metamorphic grades aH2O was high [Formula: see text] but it declined progressively as water entered the melt phase during higher grade anatectic reactions. With the onset of vapour-absent anatexis, the restite assemblage became essentially "dry" [Formula: see text], and biotite breakdown occurred in granulite-facies rocks east of the study area. Consideration of available experimental data suggests that metamorphic temperatures ranged from approximately 450 to 750 °C across the study area. Lithostatic pressure during metamorphism reached about 8 kbar (800 MPa) in the high-grade zones, with estimates at lower grades being poorly constrained; however, a steep pressure gradient across the map area is postulated.This is the first reported occurrence of bathozone 6 assemblages from a progressive metamorphic sequence, and it indicates the presence of an unusually great thickness of supracrustal rocks during the Grenvillian Orogeny. This was achieved by imbricate stacking of thrust slices, perhaps doubling the thickness of the crust in the Grenville Front Tectonic Zone, creating a huge gravity anomaly of which a remnant still persists today.

Preparation and Characterization of a Calcium Phosphate Ceramic for the Immobilization of Chloride-containing Intermediate Level Waste

2002 ◽  
Vol 757 ◽  
Author(s):  
Brian L. Metcalfe ◽  
Ian W. Donald ◽  
Randy D. Scheele ◽  
Denis M. Strachan
Keyword(s):  
Calcium Phosphate ◽  
Rate Data ◽  
Volatile Species ◽  
Calcium Phosphate Ceramic ◽  
Radioactive Materials ◽  
Mineral Phases ◽  
Simulated Waste ◽  
High Concentrations ◽  
The Individual

ABSTRACTAttention has recently been given to the immobilization of special categories of radioactive wastes, some of which contain high concentrations of actinide chlorides. Although vitrification in phosphate glass has been proposed, this was rejected because of the high losses of chloride through the mobilization of volatile species.On the basis of non-radioactive and, more recently, radioactive studies, we have shown that calcium phosphate is an effective host for immobilizing the chloride constituents [1]. In this instance, the chlorine is retained as chloride, rather than evolved as a chlorine-bearing gas. The immobilized product is in the form of a free-flowing, non-hygroscopic powder, in which the chlorides are chemically combined within the synthetic mineral phases chlorapatite [Ca5(PO4)3Cl] and spodiosite [Ca2(PO4)Cl]. Data from studies on non-radioactive simulated waste consisting of a mixture of CaCl2 and SmCl3, and radioactive simulated waste composed of CaCl2 with PuCl3 or PuCl3 and AmCl3, are presented and compared.The XRD data confirm the presence of chlorapatite and spodiosite in the non-radioactive and radioactive materials. The durability of all specimens was measured with a modified MCC-1 test. Normalized releases of Cl after 28 days were 1.6 × 10-3 g m-2 for the non-radioactive specimens and 7 × 10-3 g m-2 for the Pu bearing specimens. Releases of Ca after 28 days were 0.3 × 10-3 and 2.0 × 10-3 g m-2 for the non-radioactive composition and the Pu composition, respectively, whilst release of Pu from the radioactive specimens was higher for the mixed Pu/Am specimen at 1.2 × 10-5g m-2 than for the Pu only specimens. The release of Am from the mixed Pu/Am composition was exceptionally low at 2.4 × 10-7 g m-2. Overall, the release rate data suggest that the ceramics dissolve congruently, followed by precipitation of Sm, Pu and Am as less soluble phases, possibly oxides or phosphates. The differences in behaviour noted between non-radioactive and radioactive specimens are interpreted in terms of the crystal chemistry of the individual systems.

scholarly journals Zinc systematics quantify crustal thickness control on fractionating assemblages of arc magmas

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
M. Chiaradia
Keyword(s):  
Balance Model ◽  
Systematic Change ◽  
Continuous Transition ◽  
Porphyry Deposits ◽  
Magmatic Arc ◽  
Arc Magmas ◽  
Mineral Phases ◽  
Chemical Variability ◽  
Mineral Assemblages

AbstractUnderstanding the processes leading to the broad chemical variability of arc magmas is an essential, yet not fully elucidated, issue in Earth Sciences. Here, I show that Zn–MgO–SiO2 systematics of magmatic arc rocks correlate significantly with arc thickness. Because Zn–MgO–SiO2 systematics are mostly controlled by fractionation of different mineral phases, this suggests a systematic change in the proportions of fractionating mineral assemblages depending on arc thickness. Using a mass balance model with a Monte Carlo approach, I show that Zn–MgO–SiO2 systematics can be quantitatively explained by a continuous transition from plagioclase-dominated fractionating assemblages in thin arcs to amphibole-garnet-magnetite-dominated assemblages in increasingly thicker arcs. Most likely, such a systematic change results from the increase of average depth of magma differentiation that is ultimately controlled by arc thickness. Results presented have implications on the causes of different geochemical trends in arcs, the role of arcs as H2O filters, and their association with porphyry deposits.

Can mineral equilibrium modelling provide additional details on metamorphism of the Barberton garnet amphibolites?

2021 ◽  
Author(s):  
J.F.A. Diener ◽  
A. Dziggel
Keyword(s):  
Greenstone Belt ◽  
Main Body ◽  
Tectonic Event ◽  
Tectonic Model ◽  
Barberton Greenstone Belt ◽  
Cool Environment ◽  
Mineral Assemblages ◽  
The Stability ◽  
Lower Crustal ◽  
Good Agreement

Abstract The Stolzburg domain to the south of the Barberton Greenstone Belt preserves evidence for a 3.23 Ga subduction–collision tectonic event. Garnet amphibolite greenstone remnants have previously yielded conventional thermobarometric P-T estimates of 12 to 15 kbar at 600 to 650°C, 8 to 11 kbar at 650 to 700°C and 7.5 to 8.5 kbar at 560 to 640°C from, respectively, the Inyoni shear zone along the western margin of the Stolzburg domain, the central part of the domain and from the Tjakastad schist belt on the boundary with the main body of the Barberton Greenstone Belt. Pseudosection calculations constrain the stability conditions of the peak metamorphic assemblages at the three localities to be 10 kbar at 675 to 690°C, ~10 kbar at 700°C and ~7 and 10 kbar at 660°C respectively. Although it is possible that the peak metamorphic assemblages may be displaced to somewhat lower conditions if Mn is considered in the calculations, these estimates are generally in good agreement with existing estimates, and confirm that the Stolzburg domain exposes an intact mid- to lower-crustal section that was metamorphosed in a relatively cool environment at 3.23 Ga. Our results do not support previously documented higher-pressure conditions, and we contend that the mineral assemblages used to derive these estimates can equally reflect the conditions determined here. The presence of albite-epidote inclusion assemblages in garnet indicates that the likely prograde path involved a component of heating at depth, which is typical of subduction–collision environments and markedly different from the heating–burial paths expected for sinking greenstones in a vertical tectonic model.

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