Chapter 15 Polyphase (1.9–1.8, 1.5–1.4 and 1.0–0.9 Ga) deformation and metamorphism of Proterozoic (1.9–1.2 Ga) continental crust, Eastern Segment, Sveconorwegian orogen

2020 ◽  
Vol 50 (1) ◽  
pp. 351-396 ◽  
Author(s):  
Michael B. Stephens ◽  
Carl-Henric Wahlgren
Keyword(s):  
High Pressure ◽  
Variable Temperature ◽  
Active Continental Margin ◽  
Granulite Facies ◽  
Metavolcanic Rocks ◽  
High Pressure Granulite ◽  
Facies Metamorphism ◽  
Eastern Segment ◽  
Sveconorwegian Orogen ◽  
East West

AbstractThe Eastern Segment in the Sveconorwegian orogen comprises Paleoproterozoic–Mesoproterozoic magmatic suites, which formed along an active continental margin, and Mesoproterozoic suites emplaced during intracratonic extension. Zn–Pb sulphide and Fe oxide mineralizations in 1.9 Ga metavolcanic rocks form a significant mineral resource cluster in the northeastern part. Deformation and metamorphism under low-pressure (≤5 kbar) and variable-temperature conditions, including anatexis and granulite facies, prevailed during 1.9–1.8 Ga (Svecokarelian) and 1.5–1.4 Ga (Hallandian) accretionary orogenies. Sveconorwegian tectonothermal reworking initiated at c. 0.99–0.98 Ga in structurally lower levels. Crustal shortening, underthrusting with eclogite facies metamorphism (18 kbar), exhumation by eastwards thrusting (D1) during continued shortening and high-pressure granulite (8–12 kbar) to upper amphibolite facies metamorphism prevailed. Anatexis and folding around east–west axial surfaces with west-northwesterly constrictional strain (D2) followed at c. 0.98–0.95 Ga, being consanguineous with crustal extension. Structurally higher levels, northwards and eastwards, consist of high-pressure (10–12 kbar) orthogneisses, not affected by anatexis but also showing polyphase deformation. Sveconorwegian convergence ceased with upright folding along north–south axial surfaces and, in the uppermost frontal part, greenschist facies shearing with top-to-the-foreland normal followed by reverse displacement after 0.95 Ga. The normal shearing detached the upper compartment from the underlying gneisses.

Extensional exhumation of a high-pressure granulite terrane in Payer Land, Greenland Caledonides: structural, petrologic, and geochronologic evidence from metapelites

2002 ◽  
Vol 39 (8) ◽  
pp. 1169-1187 ◽  
Author(s):  
Jane A Gilotti ◽  
Synnøve Elvevold
Keyword(s):  
High Pressure ◽  
Granulite Facies ◽  
Crustal Thickening ◽  
Low Grade ◽  
Granulite Facies Metamorphism ◽  
High Pressure High Temperature ◽  
High Pressure Granulite ◽  
Two Samples ◽  
Facies Metamorphism ◽  
Southern Half

The Payer Land gneiss complex is unique among the mostly amphibolite-facies, mid-crustal gneiss complexes in the East Greenland Caledonides due to its well-preserved, regional high-pressure (HP) granulite-facies metamorphism. High-pressure – high-temperature (HP–HT) assemblages are recognized in mafic, ultramafic, granitic, and metasedimentary lithologies. Anatectic metapelites contain the assemblage garnet + kyanite + K-feldspar + antiperthite (exsolved ternary feldspar) + quartz ± biotite ± rutile and record approximately the same peak metamorphic conditions (pressure (P) = 1.4–1.5 GPa, temperature (T) = 800–850°C) as those of the neighboring mafic HP granulites. The HP granulite-facies metamorphism is Caledonian based on in situ U–Th–Pb electron microprobe dating of monazite from two samples of the aluminous paragneiss. The monazites are found along garnet–kyanite phase boundaries, as inclusions in garnet and kyanite, and within small leucocratic melt pods (K-feldspar + plagioclase + kyanite ± garnet) within the HP–HT paragneisses. Mylonitic equivalents of the metapelites contain a detrital monazite age signature that suggests the Payer Land paragneisses correlate with other Mesoproterozoic metasedimentary sequences in the area. The gneisses form a metamorphic core complex that is separated from the overlying low-grade sedimentary rocks of the Neoproterozoic Eleonore Bay Supergroup by an extensional detachment. This newly recognized Payer Land detachment is part of a system of prominent extensional faults located in the southern half of the Greenland Caledonides (i.e., south of 76°N). The HP granulites preserve the deepest level of crust exposed in this southern segment of the orogen and attest to significant crustal thickening.

Granulite-facies metamorphism of the Palaeoproterozoic – early Palaeozoic gneiss domains of NE Mozambique, East African Orogen

2016 ◽  
Vol 154 (3) ◽  
pp. 491-515 ◽  
Author(s):  
A. K. ENGVIK ◽  
B. BINGEN
Keyword(s):  
High Pressure ◽  
Granulite Facies ◽  
Crustal Thickening ◽  
Northwestern Part ◽  
Granulite Facies Metamorphism ◽  
Medium Pressure ◽  
Nappe Complex ◽  
High Pressure Granulite ◽  
Facies Metamorphism ◽  
Early Palaeozoic

AbstractGranulite-facies metamorphism recorded in NE Mozambique is attributed to three main tectonothermal events, covering more than 1400 Ma from Palaeoproterozoic – early Palaeozoic time. (1) Usagaran–Ubendian high-grade metamorphism of Palaeoproterozoic age is documented in the Ponta Messuli Complex by Grt-Sil-Crd-bearing metapelites, estimated to pressure (P) 0.75 ± 0.08 GPa and temperature (T) 765 ± 96°C. The post-peak P-T path is characterized by decompression followed by near-isobaric cooling. (2) Irumidian medium- to high-pressure granulite-facies metamorphism is evident in the Unango and Marrupa complexes of late Mesoproterozoic – early Neoproterozoic age. High-pressure granulite-facies is documented by Grt-Cpx-Pl-Rt-bearing mafic granulites in the northwestern part of the Unango Complex, with peak conditions up to P = 1.5 GPa and T = 850°C. Medium-pressure granulite-facies conditions recording P of c. 1.15 GPa and T of 875°C are documented by Grt-Opx-Cpx-Pl assemblage in mafic granulites and charnockitic gneisses of the central part of the Unango Complex. (3) Tectonothermal activity during the Ediacaran–Cambrian Kuunga Orogeny is recorded in the Mesoproterozoic gneiss complexes as amphibolite facies to medium-pressure granulite-facies metamorphism. Granulite facies are documented by Grt-Opx-Cpx-Pl-bearing mafic granulites and charnockitic gneisses, reporting P = 0.99 ± 13 GPa at T = 738 ± 84°C in the Unango Complex and P = 0.92 ± 18 GPa at T = 841 ± 135°C in the Marrupa Complex. This metamorphism is attributed to crustal thickening related to overriding of the Cabo Delgado Nappe Complex, and shorthening along the Lurio Belt during the early Palaeozoic Kuunga Orogeny.

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>

Sign in / Sign up

Export Citation Format

Share Document