Lithological and Structural Controls on Regional 3-D Fluid Flow Patterns during Greenschist Facies Metamorphism of the Dalradian of the SW Scottish Highlands
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Journal Article Lithological and Structural Controls on Regional 3-D Fluid Flow Patterns during Greenschist Facies Metamorphism of the Dalradian of the SW Scottish Highlands Get access ALASDAIR D. L. SKELTON, ALASDAIR D. L. SKELTON * 1DEPARTMENT OF GEOLOGY AND GEOPHYSICS, UNIVERSITY OF EDINBURGHEDINBURGH EH9 3JW, SCOTLAND *Corresponding author. Telephone: 0131-650-5885 Fax: 0131-668-3184 E-mail: askelton@glg.ed.ac.uk Search for other works by this author on: Oxford Academic Google Scholar COLIN M. GRAHAM, COLIN M. GRAHAM 1DEPARTMENT OF GEOLOGY AND GEOPHYSICS, UNIVERSITY OF EDINBURGHEDINBURGH EH9 3JW, SCOTLAND Search for other works by this author on: Oxford Academic Google Scholar MIKE J. BICKLE MIKE J. BICKLE 2DEPARTMENT OF EARTH SCIENCES, UNIVERSITY OF CAMBRIDGECAMBRIDGE CB2 3EQ, UK Search for other works by this author on: Oxford Academic Google Scholar Journal of Petrology, Volume 36, Issue 2, April 1995, Pages 563–586, https://doi.org/10.1093/petrology/36.2.563 Published: 01 April 1995 Article history Received: 01 April 1994 Accepted: 17 October 1994 Published: 01 April 1995Keywords:
Dalradian
Greenschist
Queen (butterfly)
The Alpine metamorphic evolution of the Cycladic Crystalline Complex of the Aegean aera of Greece is characterized by an Eocene eclogite-to-blueschist facies metamorphism and an Oligocene/ Miocene greenschist-to-amphibolite facies metamorphism. High pressure assemblages are well preserved in the north of Sifnos island (Blueschist Unit), whereas the rest of the island is dominated by greenschist-facies rocks (Greenschist Unit). However, rocks from Sifnos island preserve a complex record of both metamorphic events at all scales. In this paper we combine structural and petrological observations with major and trace geochemistry and stable-isotope data to characterize (a) the fluid involvement during highpressure and greenschist-facies metamorphism and (b) the nature of the retrogression from blueschist to greenschist facies rocks.
Fluid pressure
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Greenschist
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New data on petrography, geochemistry and geochronology of metamorphic rocks sampled from Neoproterozoic basement of Wrangel Island are presented. Oceanic affinity for mafic rocks underwent greenschist to amphibolite facies conditions (350600C) has been established by geochemical data. Protolith of this rock belongs to products of the evolution of magmatic melts parental for MORB. Protoliths age is 61713 and 69812 Ma was determined by U-Pb isotope dating of Zircons from these rocks (SHRIMP II and La-ICP MS). There are two main stage of metamorphism could be established: Neoproterozoi Early Paleozoi (amphibolite and greenschist facies conditions) and Middle Cretaceous (greenschist facies condition only), Last stage of metamorphism related to Chukcha deformation events accompanied by formation of folded nappes structure and consequent extension. An comparison of studied rocks with samples dredged at Chukcha Borderland evidenced for certain similarity existing between these rock assemblages judging by their petrography and chemistry.
Greenschist
Protolith
Basement
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Reconstruction of deformation and metamorphic processes and conditions can be carried out by studying micro-features of rock and minerals. This paper has investigated the microstructures, quartz fabrics, and mineral chemistry of mylonites from the ductile shear zone of the granite-greenstone belt in Seerteng area, Inner Mongolia. Synthetic analyses reveal that the mylonites underwent four evolutionary processes of deformation and metamorphism, such as lower-amphibolite facies regional metamorphism, retrograde epidote-amphibolite facies metamorphism and deformation, progressive recrystallization and retrograde greenschist facies metamorphism and deformation. The temperature and pressure combination of four metamorphic stages defines a clockwise p-T path, with the superimposition of a later anticlockwise p-T path.
Greenschist
Mylonite
Clockwise
Recrystallization (geology)
Blueschist
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Metamorphic minerals are widely developed in Laoling Group of southern Jilin Province.Based on a detailed analysis of the metamorphic minerals in rock samples,the authors hold that the main minerals in lower sub-group of Laoling Group can be divided into two generations:M1 and M2,which represent two metamorphic stages.Researches on metamorphic assemblage,distribution characteristics and division of metamorphic facies show that M1 is characterized by low-to-moderate temperature regional dynamic heat flow metamorphism which can be divided into two metamorphic facies:lower greenschist facies and high greenschist facies.By contrast,M2 is represented by local thermal metamorphism which can be divided into three metamorphic facies:lower greenschist facies,high greenschist facies and lower amphibolitic facies.Comprehensive studies show that metamorphism of the sub-group of Laoling Group in southern Jilin Province is characterized by reduction of influencing area and decrease of intensity from early to late.This tendency suggests hat the earth's crust became stable in Paleo Proterozoic.
Greenschist
Isograd
Diachronous
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Several dolomitic marble lenses were found at the western margin of the metadiorite subzone in the central basic belt of the Brno Massif. Phase relations and mineral compositions indicate two metamorphic events in surrounding amphibolites. Thermometric estimations indicate metamorphic conditions of early metamorphism in epidote amphibolite facies conditions (for 6 kbar T = 650 - 690 °C) and later in greenschist facies conditions. Mineral assemblages in marbles: Tr + Cal ± Chl ± Qtz and Tr + Dol ± Chl indicate metamorphism only in greenschist facies. Tremolite formed throuhg metasomatic reactions of SiO2-rich hydrothermal fluids with dolomite in centre of marbles boudins. This process is related to tectonic deformation of pure dolomitic marbles during metamorphism in greenschist facies.
Greenschist
Massif
Metasomatism
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Abstract The east sector of the southern Qinling belt is, lithologically, composed mainly of metapelites, ***qüartzites, marbles and small amount of metabasites and gneisses, whose protoliths are the Silurian, Devonian and less commonly the Sinian and Upper Palaeozoic. They have been subjected at least to two epochs of metamorphism. The early epoch belongs to progressive metamorphism which is centered on high amphibolite‐granulite fades in the Fuping area and changed outwards into low amphibolite facies (staurolite‐kyanite zone), epidote amphibolite facies (garnet zone) and greenschist facies (chlorite and biotite zones), the metamorphic age of which is about 220–260 Ma. This early‐epoch metamorphism belongs to different pressure types: the rocks from greenschist to low amphibolite facies belong to the typical medium‐pressure type which shows geothermal gradients of about 17–20 ***C/km and was probably produced by a crustal thickening process related to continental collision, and the high amphibolite‐granulite facies belongs to the low‐pressure type which shows geothermal gradients of about 25–38 ***C/km and was probably affected by some magmatic heats. Based on the basic characteristics of the P‐T paths of the different facies calculated from the garnet zonations, it can be deduced that the metamorphism of medium‐pressure facies series took place during an imbricated thickening process, rather than during the uplifting process after thickening. The late‐epoch metamorphism belongs to dynamic metamorphism of greenschist facies which is overprinted on the early‐epoch metamorphic rocks and is Yanshanian or Himalayan in age, probably related to intracontinental orogeny.
Greenschist
Orogeny
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