Geochemical signatures of metasedimentary rocks of high-pressure granulite facies and their relation with partial melting: Carvalhos Klippe, Southern Brasília Belt, Brazil

2012 ◽  
Vol 40 ◽  
pp. 63-76 ◽  
Author(s):  
Caue Rodrigues Cioffi ◽  
Mario da Costa Campos Neto ◽  
Brenda Chung da Rocha ◽  
Renato Moraes ◽  
Renato Henrique-Pinto
Keyword(s):  
High Pressure ◽  
Partial Melting ◽  
Granulite Facies ◽  
Metasedimentary Rocks ◽  
High Pressure Granulite

Metamorphic micro-textural variations and their bearing on rock technical properties. A case study of the transition from greenschist- to high-pressure granulite-facies in the Eastern Segment, Sveconorwegian orogen

2020 ◽  
Author(s):  
Cindy Urueña ◽  
Charlotte Möller ◽  
Jenny Andersson ◽  
Mattias Göransson ◽  
Jan Erik Lindqvist ◽  
...  
Keyword(s):  
Grain Size ◽  
High Pressure ◽  
Los Angeles ◽  
Partial Melting ◽  
Granulite Facies ◽  
Gradual Change ◽  
Average Grain Size ◽  
High Pressure Granulite ◽  
Eastern Segment ◽  
Technical Properties

<p>The Precambrian shield in southern Sweden exposes a granitic bedrock segment that represents a part of an ancient eroded mountain belt and expose a gradual change in metamorphic grade from cold (<300°C), little affected by recrystallization, to hot (>800°C) and partially molten sections at the west coast (Möller and Andersson, 2018). This area – the Eastern Segment – offers a large scale study of the interdependence of metamorphism, deformation, partial melting, and functional properties of crushed rock aggregates.</p><p>In the petrological community, it is well-known that the evolution of a metamorphic unit (e.g. a high-pressure unit) with respect to pressure, temperature, time, and deformation holds key information on its tectonic history. It has rarely been emphasized, however, that the same factors determine the physical properties of the rock and thus, its technical properties. Basic research in metamorphic petrology thus contributes with a fundament to applied and technical science, e.g. by providing data that lead to quarrying of proper materials.</p><p>This study assesses the variations of technical properties with the metamorphic state, primarily metamorphic temperature and partial melting during metamorphism. Our first results show the correlation between the petrological characteristics and technical properties of felsic orthogneiss within a migmatized eclogite-bearing terrane and its high-pressure granulite-bearing footwall.</p><p>Measurements include the Los Angeles and Micro-Deval value tests. The Los Angeles value is a measure of the resistance to fragmentation (EN 1097-2, 2010). The Micro-Deval test measures the resistance to wear.</p><p>High values of the Los Angeles and Micro-Deval analyses for felsic orthogneiss in the eclogite-bearing domain reflect poor technical properties and are largely linked to that the rocks underwent partial melting. Orthogneisses in the footwall, which recrystallized under high-temperature, dry conditions, and without partial melting, tend to have lower values. This group includes high-quality rocks for the production of aggregates suitable for asphalt base courses and unbound road layers.</p><p>Micro-textures in the orthogneisses are linked with these metamorphic conditions. The clinopyroxene-bearing orthogneisses have complex grain boundaries and micro-perthitic feldspars, finer average grain size, lower biotite content, and absence of migmatitic segregation or penetrative veining. These textures in the footwall orthogneisses contrast with those in the migmatitic orthogneisses from the eclogite-bearing domain, which have a coarser average grain size, even-grained and granoblastic texture, and lack of perthitic texture in feldspars. Thus, these petrographic parameters govern the technical differences.</p><p>Our ongoing research addresses the relations between macro-fabric, micro-texture and technical properties of felsic orthogneiss and metagabbro, respectively, along 120 km profile across the metamorphic field gradient from greenschist- to high-pressure granulite-facies in the Eastern Segment.</p>

Pétrologie des niveaux trondhjémitiques de haute pression associés aux éclogites et amphibolites des complexes leptyno-amphiboliques du Massif Central français

1978 ◽  
Vol 15 (5) ◽  
pp. 696-707 ◽  
Author(s):  
C. Nicollet ◽  
A. Leyreloup
Keyword(s):  
High Pressure ◽  
Partial Melting ◽  
Granulite Facies ◽  
Massif Central ◽  
Granulite Facies Metamorphism ◽  
High Pressure Granulite ◽  
Greenstone Belts ◽  
Metamorphic Terranes ◽  
Archean Greenstone Belts ◽  
Initial Mineral

High pressure trondhjemitic rocks interbedded with eclogites and high pressure amphibolites have been recognized in the leptyno-amphibolitic series of the Rouergue and Marvejols metamorphic terranes. These rocks appear to have been derived by partial melting of the surrounding amphibolites (or amphibole-gabbro) at [Formula: see text] (<7 × 105 kPa). The initial mineral assemblage of these layers (Q, Pl, Ky, Ga, Zo, etc.) is suggested by microstructural evidence to have crystallized directly under high pressure granulite facies conditions (12.5 kbar <PT <20 kbar (12.5 × 105 kPa < PT <20 × 105 kPa); 750 °C<T<840 °C) from the trondhjemitic liquid. The partial melting has taken place before the well-known Barrovian metamorphism that has affected the whole crystalline basement of the French Massif Central. This older metamorphic event is considered to be equivalent to the high pressure granulite facies metamorphism recognized in the Variscan of Europe. This acid–basic high pressure bimodal association argues for a close similarity between Archean greenstone belts and the leptyno-amphibolitic series.

scholarly journals Building a continental arc section: Constraints from Paleozoic granulite-facies metamorphism, anatexis, and magmatism in the northern margin of the Qilian Block, northern Tibet Plateau

2021 ◽  
Author(s):  
Yinbiao Peng ◽  
Shengyao Yu ◽  
Jianxin Zhang ◽  
Yunshuai Li ◽  
Sanzhong Li ◽  
...  
Keyword(s):  
High Pressure ◽  
Partial Melting ◽  
Lithospheric Mantle ◽  
Lower Crust ◽  
Granulite Facies ◽  
Granulite Facies Metamorphism ◽  
Northern Margin ◽  
Metasedimentary Rocks ◽  
Continental Arc ◽  
Facies Metamorphism

Continental arcs in active continental margins (especially deep-seated arc magmatism, anatexis, and metamorphism) can be extremely significant in evaluating continent building processes. In this contribution, a Paleozoic continental arc section is constructed based on coeval granulite-facies metamorphism, anatexis, and magmatism on the northern margin of the Qilian Block, which record two significant episodes of continental crust growth. The deeper layer of the lower crust mainly consists of medium-high pressure mafic and felsic granulites, with apparent peak pressure-temperature conditions of 11−13 kbar and 800−950 °C, corresponding to crustal depths of ∼35−45 km. The high-pressure mafic granulite and local garnet-cumulate represent mafic residues via dehydration melting involving breakdown of amphibole with anatectic garnet growth. Zircon U-Pb geochronology indicates that these high-grade metamorphic rocks experienced peak granulite-facies metamorphism at ca. 450 Ma. In the upper layer of the lower crust, the most abundant rocks are preexisting garnet-bearing metasedimentary rocks, orthogneiss, and local garnet amphibolite, which experienced medium-pressure amphibolite-facies to granulite-facies metamorphism at depths of 20−30 km at ca. 450 Ma. These metasedimentary rocks and orthogneiss have also experienced partial melting involving mica and rare amphibole at 457−453 Ma. The shallow to mid-crust is primarily composed of diorite-granodiorite batholiths and volcanic cover with multiple origin, which were intruded during 500−450 Ma, recording long-term crustal growth and differentiation episode. As a whole, two episodes of continental crust growth were depicted in the continental arc section on the northern margin of the Qilian Block, including: (a) the first episode is documented in a lithological assemblage composing of coeval mafic-intermediate intrusive and volcanic rocks derived from partial melting of modified lithospheric mantle and subducted oceanic crust during southward subduction of the North Qilian Ocean at 500−480 Ma; (b) the second episode is recorded in mafic rocks derived from partial melting of modified lithospheric mantle during transition from oceanic subduction to initial collision at 460−450 Ma.

Discussion of ‘Metamorphic P–T and retrograde path of high-pressure Barrovian metamorphic zones near Cairn Leuchan, Caledonian orogen, Scotland’

2014 ◽  
Vol 151 (4) ◽  
pp. 758-763 ◽  
Author(s):  
K. Aoki ◽  
B. F. Windley ◽  
S. Maruyama ◽  
S. Omori
Keyword(s):  
High Pressure ◽  
Granulite Facies ◽  
Geological Structure ◽  
Metamorphic Rocks ◽  
New Paradigm ◽  
Zircon Age ◽  
Tectonic Model ◽  
High Pressure Granulite ◽  
Future Publication ◽  
Western Ireland

K. Aoki, B. F. Windley, S. Maruyama & S. Omori reply: First, we thank Viete, Oliver & Wilde for their interesting and thought-provoking comments on the timing of the high-pressure granulite facies (HGR) metamorphism recorded in metamorphic rocks at Cairn Leuchan, Scotland, published by Aoki et al. (2013). Based on new metamorphic data of garnetites and garnet-amphibolites at Cairn Leuchan and new zircon U–Pb ages of amphibolitized eclogite at Tomatin, we suggested in our publication that the HGR metamorphism was retrograde after eclogite facies before the c. 470 Ma ‘Barrovian metamorphism’. Viete, Oliver & Wilde however speculate that the HGR metamorphism at Cairn Leuchan may have occurred at c. 1000 Ma, as a result of their new U–Pb zircon age of the Cowhythe Gneiss at Portsoy and from previous studies of the geological structure and geochronology. We are grateful for this opportunity to describe, albeit in a preliminary manner, our new understanding and tectonic model of the Caledonian orogen in Scotland and western Ireland of which the Barrovian metamorphism is a key component. A reply to a comment is not the correct place to propose an entirely new paradigm for such a classic orogen, but we will present our model more fully in a future publication.

Asymmetric zoning profiles in garnet from HP-HT granulite and implications for volume and grain-boundary diffusion

1999 ◽  
Vol 63 (2) ◽  
pp. 227-238 ◽  
Author(s):  
P. J. O’Brien
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Grain Boundary ◽  
Boundary Diffusion ◽  
Sharp Decrease ◽  
Fluid Phase ◽  
Granulite Facies ◽  
Grain Boundary Diffusion ◽  
Diffusion Models ◽  
High Pressure Granulite

AbstractDetailed electron-microprobe line profiles and small-area compositional maps of zoned garnets in a sample of high-pressure-high-temperature granulite show features inconsistent with commonly applied diffusion models. Larger grains of an early garnet generation have their highest Ca contents in domains away from the rim or inclusions but show a sharp fall in Ca balanced by increased Mg and Fe (and slightly higher XMg) towards inclusions and the rim. In domains with secondary biotite, the sharp decrease in Ca is accompanied by variations in XMg dependent upon proximity to biotite, thus producing one-sided, asymmetric profiles with XMg lower against biotite. As a consequence, rim compositions of the same grain are different on the sides adjacent and away from biotite and there is no relationship between grain size and rim XMg. Such a zoning pattern requires that grain-boundary diffusion is as slow as volume diffusion and implies the absence of a diffusion-enhancing grain-boundary fluid phase during the majority of the rock's high-temperature exhumation history. Diffusion models ignoring this probability could yield either cooling rates that were too fast, or extrapolated ages based on closure temperature models that were too old.A second garnet generation in the same rock, grown in a Ca-rich domain resulting from kyanite breakdown, has irregularly distributed patches, identified by compositional mapping, containing higher Ca than the first-formed garnet but at lower XMg. Use of such garnet compositions for geothermobarometrical determination of the high-pressure granulite stage would clearly lead to erroneous results. The presence of such contrasting garnet compositions in a granulite-facies rock is clearly evidence of disequilibrium, and further supports the proposition that there was a lack of an effective transport medium even at the mm scale.

A Discussion on the evolution of the Precambrian crust - Geochemistry of granulite facies rocks and problems of their origin

1973 ◽  
Vol 273 (1235) ◽  
pp. 429-442 ◽  
Keyword(s):  
High Pressure ◽  
Continental Crust ◽  
Major Element ◽  
Granulite Facies ◽  
Sr Isotope ◽  
Average Surface ◽  
Magmatic Rocks ◽  
Mineral Associations ◽  
High Pressure Granulite ◽  
Critical Mineral

Occurrences of granulite facies rocks are widespread in continental regions where they mostly are parts of stable shield areas. Granulite facies terrains are classified as low-, medium- or high-pressure terrains on the basis of critical mineral associations. Special interest is attached to the medium- and highpressure terrains, as they are representative of the deepest crustal levels available for study in any areal extent on the surface, and may give information about the composition of the lower continental crust. Granulite facies terrains are mainly composed of metamorphic and metasomatic rocks, but magmatic rocks with primary igneous textures interpreted as formed by crystallization of magmas under granulite facies conditions are frequent in some areas. Examples of such rocks are anorthosites, gabbros and mangerites. The low-pressure—high-temperature granulite facies rocks are chemically indistinguishable from the amphibolite facies gneisses with which they characteristically occur. It is therefore important to make a distinction between these and the higher pressure types. The medium- to high-pressure granulite facies terrains are characterized by a less ‘acidic’ average major element compositions, and significant depletions in Rb, Cs, Th and U compared with average surface shield compositions. Available data also indicate low initial Sr isotope ratios, even in the gneissic types. In the author’s opinion the important problem associated with granulite facies rocks is not that of their origin, but rather of their importance as constituents of the continental crust, and how they attained their present chemistry.

Local rapid exhumation and fast cooling in a long-lived Paleoproterozoic orogeny

2020 ◽  
Author(s):  
Y Zou ◽  
x Chu ◽  
Q L Li ◽  
R N Mitchell ◽  
M G Zhai ◽  
...  
Keyword(s):  
High Pressure ◽  
Temporal Resolution ◽  
Plate Tectonics ◽  
Granulite Facies ◽  
High Grade ◽  
Promising Alternative ◽  
High Pressure Granulite ◽  
Fast Cooling ◽  
Thermal Excursion ◽  
Uht Metamorphism

Abstract The exhumation and cooling rates of high-grade metamorphic rocks are crucial for inferring orogenic processes and understanding the regimes of heat transport in Earth's crust. Quantification of these rates remains challenging for Precambrian terranes, because the temporal resolution of geochronology becomes coarser in deeper geologic time. This limitation is partly reflected by a striking lack of Proterozoic or older short-duration events (&lt;10 Myr), most documented cases of fast metamorphism are confined to the Phanerozoic. In this study, we use garnet geospeedometry to explore the metamorphic rates of Paleoproterozoic high-grade rocks from two representative areas within the long-lived (1.95–1.80 Ga) Jiao-Liao-Ji orogenic belt, North China Craton. The pelitic granulites in the Taipingzhuang area record high-pressure granulite-facies (HPG) metamorphism of ∼12 kbar and ∼800 °C, followed by a fast decompression-cooling to ∼5 kbar and ∼600 °C within ∼5 Myr, at ca. 1.87 Ga. The pelitic granulites in the Rizhuang area document a brief (&lt;1 Myr) thermal excursion to ultra-high-temperature (UHT) metamorphism of ∼8 kbar and ∼940 °C at ca. 1.85 Ga, followed by a fast cooling to ∼600 °C within 1–5 Myr. In light of available geological data, the fast decompression-cooling of HPG granulites is interpreted as the syn-collisional exhumation of thickened lower crustal segments at ca. 1.87 Ga, most likely through tectonic extrusion. The thermal excursion transiently reaching UHT conditions is inferred to be triggered by localized syn-metamorphic mafic intrusions in association with magmatic underplating during post-collisional extension at ca. 1.85 Ga. These metamorphic pulses were interspersed within the protracted Paleoproterozoic orogenesis and require geodynamic processes resembling modern plate tectonics. Notably, these ancient rapid events are beyond the temporal resolution of commonly-used in-situ geochronology that tends to yield apparent longer durations given errors and uncertainties. We therefore note that most ancient metamorphic rates might be underestimated using geochronological data, and recommend garnet geospeedometry as a promising alternative approach. The largely similar rates recorded by Paleoproterozoic and Phanerozoic orogens, as well as high-pressure metamorphism at 1.9–1.8 Ga, support the operation of modern plate tectonics in Paleoproterozoic time.

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