scholarly journals Mineral chemistry of eclogites to investigate the evolutionary metamorphic history of UHP rocks from Tso-Morari region, Ladakh, India

2010 ◽  
Vol 40 ◽  
pp. 13-20
Author(s):  
Rameshwar Rao ◽  
Hakim Rai
Keyword(s):  
High Pressures ◽  
Mineral Chemistry ◽  
Textural Features ◽  
Mineral Inclusions ◽  
Metamorphic History ◽  
Facies Metamorphism ◽  
History Of ◽  
T Path ◽  
Si Content ◽  
Tso Morari

Micro textures of metabasics from the Tso-Morari region, Ladakh were studied in order to understand the evolutionary metamorphic history of eclogites. The mineral chemistry, paragenesis of mineral inclusions in garnet, and zoning in omphacite, garnet and amphibole suggest three main metamorphic stages: (i) an eclogite stage with late blueschist facies metamorphism, (ii) a medium-pressure amphibolite facies stage, and (iii) a low-pressure amphibolite to greenschist facies stage. The high Si content in phengite, presence of rutile besides almandine-rich garnet and omphacite in eclogites indicate the attainment of high pressures. Also, the textural features and composition of amphiboles indicate that blueschist facies conditions represented by growth of glaucophane at high pressure and low temperature were followed by a lower-pressure stage of metamorphism represented by partial and in some cases complete reaction of glaucophane to calcic green amphibole such as magnesio-hornblende. The relationships define a clock-wise P-T path with the involvement of an isothermal uplift path for the eclogites and associated garnet-amphibolites of Tso-Morari region.

scholarly journals Multiple Metamorphic Events Recorded within Eclogites of the Chandman District, SW Mongolia

Minerals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 495
Author(s):  
Terbishiinkhen O. Javkhlan ◽  
Akira Takasu ◽  
Md Fazle Kabir ◽  
Dash Batulzii
Keyword(s):  
Mineral Chemistry ◽  
Orogenic Belt ◽  
Metamorphic Complex ◽  
Multiple Events ◽  
Metamorphic History ◽  
Central Asian ◽  
Lake Zone ◽  
The World ◽  
Facies Metamorphism ◽  
History Of

The eclogite-bearing Alag Khadny metamorphic complex in the Lake Zone, SW Mongolia occupies the central region of the Central Asian Orogenic Belt, the largest Phanerozoic orogenic belt in the world. The complex consists mainly of orthogneisses intercalated with eclogites and micaschists in a mélange zone. Most of eclogites are strongly amphibolitized. In this study, we examined petrography and mineral chemistry of eclogites and amphibolitized eclogites, respectively. The result of our research shows that Chandman eclogites experienced multiple events of metamorphism in throughout their subduction and subsequent collision history. We revealed that eclogites were subjected to blueschist facies metamorphism before the peak eclogite facies stage. In addition, we have studied amphibolitized eclogite, and revealed that another distinct progressive medium pressure (MP) epidote-amphibolite facies metamorphic event took place in the eclogite, consistent with collision process. The multiple events of metamorphism in eclogites have been revealed by zonation textures of HP amphiboles zoned with glaucophane→barroisite→Mg-hornblende and MP amphiboles zoned with actinolite/winchite→barroisite→Mg-hornblende/tschermakite/Fe-pargasite. These amphiboles with different zonation textures reflect their metamorphic history of subduction to collision events.

Multistage Exhumation History of Ultra-cool Oceanic (U)HP eclogites: New evidence from the Nagaland Ophiolite Complex (NOC), NE India

2020 ◽  
Author(s):  
Santanu Kumar Bhowmik ◽  
Mayashri Rajkakati
Keyword(s):  
Large Scale ◽  
Mature Stage ◽  
Ophiolite Complex ◽  
Subduction Channel ◽  
Ne India ◽  
Facies Metamorphism ◽  
History Of ◽  
Eclogite Facies ◽  
T Path ◽  
Exhumation History

<p>Despite significant progress in our understanding of the thermal history of ultra-high pressure (UHP) metamorphosed oceanic eclogite, the mechanisms of detachment and exhumation of these rocks in the subduction channel are still debatable. Opinions vary from their exhumation as detached blocks due to circulation in a weak and loose serpentinite mélange to coherent bodies in large-scale imbricated slices. In this study, we integrate published metamorphic P-T path and peak P-T data with new metamorphic reconstruction of oceanic eclogites from two locations in the Nagaland Ophiolite Complex (NOC), NE India to establish its UHP signature and complicated  multistage exhumation history. Previous studies reveal the NOC to be the largest exposed remnant of an array of HP/LT metamorphic rocks within the eastern Neo-Tethys with the subduction burial-exhumation cycle of eclogites being bracketed between ca. 205 and 172 Ma. In both the locations near Thewati and Mokie villages, the eclogites occur as ~5 to ~50 m long and ~2-5 m wide tectonic lenses within a lawsonite blueschist facies metamorphosed package of oceanic basalt-limestone-radiolarian chert (peak P-T at ~11.5 kbar, ~340<sup>o</sup>C).  The Thewati eclogite records a clockwise (CW) P-T path of evolution with an epidote blueschist facies prograde burial at ~18.8 kbar, 555°C, peak epidote eclogite  facies metamorphism at ~25–28 kbar, ~650°C and a two stage exhumation: an early one along a steep dP/dT gradient in amphibole-eclogite facies at ~18.3 kbar, 630°C and a later one along a gentler dP/dT gradient through epidote blueschist facies to the transitional lawsonite blueschist and greenschist facies metamorphic conditions at ~6 kbar, 300°C. In the Mokie locality, thin discontinuous stringers of highly magnesian (Mg# = 73) and eclogite facies altered basaltic crust (peak P-T at ~23.8 kbar and ~555°C) separate the eclogitic core (Mg# = 44) from the blueschist host. The Mokie eclogite core records an epidote blueschist facies prograde burial at ~12.5 kbar, ~510°C, peak UHP epidote eclogite facies metamorphism at ~32.0 kbar, ~700°C, an initial, eclogite facies exhumation at ~17.3 kbar, 560<sup>o</sup>C that retraces the prograde burial path, but at a higher temperature, a subsequent phase of eclogite facies prograde heating and the final exhumation and cooling at metamorphic conditions transitional between lawsonite blueschist and prehnite-pumpellyite facies. We interpret the P-T history of the Nagaland blueschists and eclogites in terms of a Jurassic-aged ultra-cool (thermobaric ratio at metamorphic peak between ~220<sup>o</sup>C/GPa and ~300<sup>o</sup>C/GPa) intra-oceanic subduction system within the Neo-Tethys, subduction burial of the Mokie eclogite core to ~100 kms of depth, putting it in the select category of rare global UHP oceanic eclogite facies metamorphism during the cold mature stage of subduction and a change in its exhumation style from an initial buoyancy-driven material transport in a rheologically weak and fluidised subduction channel, often involving prograde heating of partially exhumed rocks to later thrust stacking and tectonic mixing of the eclogites from different crustal levels with the cooler, prograde blueschists at shallower crustal levels (P~5-6 kbar). This stage two exhumation led to the assembly of the Nagaland Accretionary Complex.</p>

Microstructures and mineral chemistry in amphibolites from the western Tauern Window (Eastern Alps), and P-T deformation paths of the Alpine greenschist-amphibolite facies metamorphism

1995 ◽  
Vol 59 (397) ◽  
pp. 641-659 ◽  
Author(s):  
Bernhard Schulz ◽  
Claude Triboulet ◽  
Claude Audren
Keyword(s):  
Mineral Chemistry ◽  
Eastern Alps ◽  
Amphibolite Facies ◽  
Tauern Window ◽  
Metamorphic History ◽  
Lithostratigraphic Units ◽  
Facies Metamorphism ◽  
Austroalpine Basement ◽  
T Deformation Paths ◽  
Extension Axis

AbstractAmphibolites in the Mesozoic part of the parautochthonous Lower Schieferhülle (LSH), the allochthonous Upper Schieferhülle (USH) and the overlying Austroalpine basement (AA) in and around the western Tauern Window (Eastern Alps) suffered a progressive Alpine deformation. Lineations and foliations L1-S1, L2-S2 defined by preferentially oriented (Na-Ca) amphiboles as well as F3 folds and further foliations Smyl and S4 in the metabasites are structures of successive deformational stages with a constant W-E main extension axis of strain. The (Na-Ca) amphiboles in assemblages with epidote, chlorite, albite/oligoclase and quartz are zoned with similar continuous zonation trends from early actinolite in the cores to magnesio-hornblende and tschermakitic hornblende, and from magnesio-hornblende to late actinolite in the rims in the three lithostratigraphic units. Geothermobarometry involving tremolite-edenite and (pargasite-hastingsite)-tremolite end-member equilibria in amphiboles allowed us to reconstruct prograde-retrograde P-T paths for the Alpine greenschist-amphibolite facies event. The paths passed P/Tmax at 6–7 kbar/600°C. Similar shapes of the paths in AA, USH and Mesozoic LSH indicate a common metamorphic history and a stacking of these units prior to or during the pre-Pmax evolution. Moderate P-T ratios are characteristic for the temperature-dominated compression paths and indicate continental collisional rather than subduction zone metamorphism. The middle to late Alpine greenschist-amphibolite facies event appears as an independent metamorphism along a complete P-T loop which may have followed an earlier and poorly documented high-pressure/low-temperature event.

Polymetamorphism in the Archean Hemlo – Heron Bay greenstone belt, Superior Province: P–T variations and implications for tectonic evolution

1993 ◽  
Vol 30 (5) ◽  
pp. 985-996 ◽  
Author(s):  
Yuanming Pan ◽  
Michael E. Fleet
Keyword(s):  
Greenstone Belt ◽  
Regional Metamorphism ◽  
Mineral Chemistry ◽  
Superior Province ◽  
Low Grade ◽  
Garnet Porphyroblasts ◽  
Metamorphic History ◽  
Tectonic Environment ◽  
History Of ◽  
Archean Greenstone Belt

The tectono-metamorphic history of the late Archean (2800–2600 Ma) Hemlo – Heron Bay greenstone belt in the Superior Province has been delineated from textural relationships, mineral chemistry, and P–T paths in metapelites, cordierite–orthoamphibole rocks, and metabasites from the White River exploration property, Hemlo area, Ontario. An early low-temperature, medium-pressure metamorphism (about 500 °C and 6–6.5 kbar (1 kbar = 100 MPa)) is indicated by the occurrence of relict kyanite and staurolite porphyroblasts and zoned garnet porphyroblasts in metapelites and the presence of zoned calcic amphiboles in metabasites. This early metamorphism appears to have been coeval with the previously documented D1 deformation that is associated with, for example, low-angle thrusts. A second regional metamorphism predominates in the Hemlo – Heron Bay greenstone belt and is generally of relatively low grade, at about 510–530 °C and 3.2–3.5 kbar, over most of the study area and increases to medium grade (550–650 °C and 4–5 kbar) towards the southern margin with the Pukaskwa Gneissic Complex and along the central axis enclosing the Hemlo Shear Zone. The second regional metamorphism was contemporaneous with the D3 deformation and was probably related to plutonism. This type of polymetamorphism in the Hemlo – Heron Bay greenstone belt may be equivalent to those in Phanerozoic subduction complexes and therefore supports the arc–arc accretion model for the development of the southern Superior Province. Although the Hemlo – Heron Bay greenstone belt most likely represents a single tectonic environment (an oceanic island arc), the restricted occurrence of the relict kyanite and staurolite indicates that the central portion of this Archean greenstone belt probably was at a deeper crustal level at the time of the first metamorphic event.

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.

Regional geothermobarometry in the granulite facies terrane of South India

1983 ◽  
Vol 73 (4) ◽  
pp. 221-244 ◽  
Author(s):  
M. Raith ◽  
P. Raase ◽  
D. Ackermand ◽  
R. K. Lal
Keyword(s):  
South India ◽  
Analytical Data ◽  
Granulite Facies ◽  
Critical Discussion ◽  
Granulite Facies Metamorphism ◽  
Northern Margin ◽  
Mineral Equilibria ◽  
Metamorphic History ◽  
Facies Metamorphism ◽  
History Of

ABSTRACTIn the southern part of the Archaean craton of South India, an approximately 3.4–2.9 b.y. old migmatite–gneiss terrane (Peninsular gneiss complex) has been subjected to granulite facies metamorphism about 2.6 b.y. ago. During this event, the extensive charnockite-khondalite zone of southern India developed. A younger metamorphism (Proterozoic?) led to retrogression of the charnockites and khondalites, mainly under the conditions of the amphibolite facies.The physical conditions of metamorphism have been evaluated by applying methods of geothermobarometry to the widespread charnockitic assemblages with garnet, orthopyroxene, clinopyroxene, plagioclase, and quartz. The interpretation of the P–T estimates includes a critical discussion of potential error sources, e.g. errors of the analytical data and the calibrations of the models, and takes into account the complex metamorphic history of the rocks and the kinetics of the mineral equilibria.P-T estimates were obtained for seven subareas from the rim compositions of the coexisting minerals: Shevaroy Hills 680±55°C—7·4±1 kb; Kollaimalai area 680±40°C—8·6± 1 kb; Nilgiri Hills 680±90°C—6·6±0.8kb (upland massif) and 705±60°C—9·3±0.8 kb (northern margin); Bhavani Sagar area 650±50°C—7·2± 1 kb; Sargur-Mysore area 690±60°C—7·6 kb; Bangalore-Kunigal-Satnur area 760±50°C—6 kb. Except for the last subarea, the P-T model data reflect the conditions of a late annealing stage probably related to the retrogressive metamorphism. Conditions near the peak of granulite facies metamorphism (730–800°C—6·5–9·5 kb) are recorded by the core compositions of the minerals. Although a rather uniform cooling history of the main part of the charnockite-khondalite terrane is suggested from the temperature data, differential uplift of smaller blocks is indicated by the regional variation of the pressure data.

Petrologic constraints on subduction zone metamorphism from a coesite-bearing metapelite in the Northern Appalachian Orogen

2021 ◽  
Author(s):  
Joseph P. Gonzalez ◽  
Suzanne L. Baldwin ◽  
Jay B. Thomas ◽  
William O. Nachlas ◽  
Paul G. Fitzgerald ◽  
...  
Keyword(s):  
Trace Element ◽  
Subduction Zone ◽  
Uhp Metamorphism ◽  
Mineral Inclusions ◽  
Metamorphic History ◽  
Iapetus Ocean ◽  
Hp Metamorphism ◽  
History Of ◽  
Appalachian Orogen ◽  
Zr In Rutile

<p>The Caledonian orogen formed following Paleozoic subduction of the Iapetus Ocean and preserves evidence of ultrahigh-pressure (UHP) metamorphism and exhumation of crustal rocks from mantle depths. The Appalachian orogen similarly formed in the Paleozoic following subduction of Iapetus Ocean crust, but evidence for (U)HP metamorphism in exhumed Appalachian rocks has been challenging to identify. We present results from a metapelite from high-pressure rocks of the Tillotson Peak Complex in the northern Appalachians, which formed during the middle-Ordovician Taconic orogeny. This sample contained mm-cm scale garnet porphyroblasts that host abundant mineral inclusions. Confocal Raman microspectroscopy of inclusions in the rims of a garnet porphyroblast identified relic coesite, preserved as a bi-mineralic inclusion composed of coesite in α-quartz. Raman depth profiling and 2-dimensional mapping indicate the relic coesite is ~10 μm<sup>3</sup>, suggesting that mineralogical evidence of UHP metamorphism in the Appalachians may be preserved only as μm-scale inclusions contained in polymetamorphosed rocks. We applied quantitative WDS X-ray maps acquired with electron microprobe, quartz-in-garnet elastic thermobarometry, and Zr-in-rutile trace element thermometry to further constrain the metamorphic history of the coesite-bearing metapelite. Garnet zoning patterns in conjunction with elastic and trace element thermobarometry applied to co-entrapped mineral inclusions suggest that garnet nucleated at 14-15.5 kbar and 420-520 °C, and continuously crystallized to 15-19.5 kbar and 470-560 °C during subduction zone metamorphism. Peak metamorphic conditions based on the stability field of coesite and on Zr-in-rutile thermometry from inclusions in the garnet rims suggest UHP metamorphism at >28 kbar and 530 °C. UHP metamorphism of pelitic sediments within the Taconic paleo-subduction zone invite comparisons with similar UHP rocks in the Caledonian orogeny. Future studies of UHP metamorphism in the Appalachian orogen will focus on constraining: 1) the spatial and temporal scales of UHP metamorphism, 2) the retrograde/exhumation P–T path of the coesite-bearing metapelite, and 3) the P–T history of other nearby metamorphic units, such as the Tillotson peak metabasites, to evaluate if these units shared a similar metamorphic history.</p>

Mineral chemistry, geothermobarometry and pre-Alpine high-pressure metamorphism of eclogitic amphibolites and mica schists from the Schobergruppe, Austroalpine basement, Eastern Alps

1993 ◽  
Vol 57 (387) ◽  
pp. 189-202 ◽  
Author(s):  
Bernhard Schulz
Keyword(s):  
High Pressure ◽  
Mineral Chemistry ◽  
Eastern Alps ◽  
Upper Ordovician ◽  
Progressive Deformation ◽  
Tauern Window ◽  
High Pressure Metamorphism ◽  
Facies Metamorphism ◽  
Austroalpine Basement ◽  
T Path

AbstractAlternating eclogitic amphibolites, mica schists and orthogneisses in the Schobergruppe to the south of the Tauern Window suffered a post-Upper-Ordovician progressive deformation D1-D2which produced parallel planar-linear structures in all the rocks. Zoned garnets, preferentially oriented zoned clinopyroxenes (Jd 35-42%) and albite (An 7-9%) give evidence of high-pressure metamorphism (550-650°C 14-16 kbar) of the metabasites. Ca-amphiboles crystallized during subsequent decompression. In a kyanite-staurolite-garnet mica schist 300 metres below the metabasites, garnetbearing assemblages grew synchronous with the development of foliations S1and S2. Garnets are zoned with increasing XMgand decreasing-increasing-rcdecreasing Xcafrom cores to rims. Albitic plagioclase (An 1-3%) and micas are enclosed in garnet cores and rims, are in contact with garnet, and occur with garnet in microlithons. When these minerals are used for geothermobarometry, a prograde P-T evolution (460 to 680°C with coeval pressure variations which reach high-pressure conditions can be estimated. This suggests that garnet-plagioclase geobarometry with albitic plagioclase works in the relevant P-T field. Similar garnet zonation trends and a similarly shaped P-T path from mica schists of an adjacent region with late-Variscan cooling ages, points to an eady-Variscan age of the syn-D1-D2high-pressure and subsequent amphibolite-facies metamorphism.

scholarly journals Zircon record of the igneous and metamorphic history of the Fiskenæsset anorthosite complex in southern West Greenland

1969 ◽  
Vol 20 ◽  
pp. 67-70 ◽  
Author(s):  
Nynke Keulen ◽  
Tomas Næraa ◽  
Thomas F. Kokfelt ◽  
John C. Schumacher ◽  
Anders Scherstén
Keyword(s):  
North Atlantic ◽  
Layered Intrusion ◽  
Mineral Chemistry ◽  
Joint Project ◽  
West Greenland ◽  
Metamorphic History ◽  
The North ◽  
History Of ◽  
The North Atlantic ◽  
North Atlantic Craton

The Fiskenæsset complex in southern West Greenland is part of the North Atlantic craton and is a layered intrusion consisting of gabbro, ultramafic and anorthositic rocks that was deformed during multiple episodes of folding and metamorphism (Myers 1985). We collected late-stage magmatic hornblenditic dykes and adjacent anorthosites and studied these samples integratively with several in situ techniques to determine the igneous and metamorphic history of the Fiskenæsset complex. The work presented here is part of an ongoing joint project between the Greenland Bureau of Minerals and Petroleum and the Geological Survey of Denmark and Greenland (GEUS). Here we report on new radiometric ages and mineral chemistry data from anorthosites from the North Atlantic craton in southern West Greenland (Fig. 1).

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