scholarly journals Metamorphism of the Dizi Series Rocks (the Greater Caucasus): Petrography, Mineralogy and Evolution of Metamorphic Assemblages

Baltica ◽  
2021 ◽  
pp. 185-202
Author(s):  
Irakli Javakhishvili ◽  
David Shengelia ◽  
Tamara Tsutsunava ◽  
Giorgi Chichinadze ◽  
Giorgi Beridze ◽  
...  
Keyword(s):  
Regional Metamorphism ◽  
Crystalline Basement ◽  
Contact Metamorphism ◽  
Maximum Temperature ◽  
Metamorphic Rocks ◽  
Southern Slope ◽  
Greater Caucasus ◽  
The Core ◽  
Icp Ms ◽  
Higher Temperature

The Dizi Series is exposed within the Southern Slope zone of the Greater Caucasus, in the core of the Svaneti anticlinorium. It is mainly composed of terrigenous, volcanogenic and carbonate rocks faunistically dated from the Devonian to the Triassic inclusive. Regional and contact metamorphism of the Dizi Series rocks was studied. It is stated that the degree of regional metamorphism corresponds to the chlorite-sericite subfacies of the greenschist facies, occurring at a temperature of 300–350°C and a pressure of 1.5–2.3 kbar. As a result of the action of the Middle Jurassic intrusive rock bodies, the regionally metamorphosed rocks of the Dizi Series underwent contact metamorphism. Three zones of contact metamorphism were distinguished corresponding to albite-epidote-hornfels, andalusite-biotite-muscovite-chlorite-hornfels and andalusite-biotite-muscovite-hornfels subfacies. Contact metamorphism took place at a significantly higher temperature and lower pressure than the preceding regional metamorphism. The maximum temperature of the contact metamorphism reached ≈ 570°С, while pressure varied within the range of ≈ 0.3–0.8 kbar. The evolution of rock associations of regional and contact metamorphism of the Dizi Series was studied. The fields of facies and subfacies of regional and contact metamorphism are shown in the Ps-T diagram. Three age populations of zircons were identified using U-Pb LA-ICP-MS dating of the diorite-porphyrite intrusion in the Dizi Series: Zrn1 (ca. 2200 Ma) and Zrn2 (458 ± 29 Ma) that were captured by the diorite-porphyrite magma from the ancient magmatic and metamorphic rocks of the crystalline basement, and Zrn3 (166.5 ± 4.6 Ma) that corresponds to the age of diorite-porphyrite crystallization.

On the possible analogy between the Dizi Series of the Southern slope zone of the Greater Caucasus and the folded basement of the plain Crimea: composition, metamorphism, magmatism and age

2021 ◽  
Author(s):  
Irakli Javakhishvili ◽  
David Shengelia ◽  
Tamara Tsutsunava ◽  
Giorgi Chichinadze ◽  
Giorgi Beridze ◽  
...  
Keyword(s):  
Middle Jurassic ◽  
Regional Metamorphism ◽  
Geological Structure ◽  
Greenschist Facies ◽  
Igneous Rocks ◽  
Contact Metamorphism ◽  
Southern Slope ◽  
Quartz Syenite ◽  
Greater Caucasus ◽  
Geological Conditions

<p>The Dizi Series is exposed within the Southern slope zone of the Greater Caucasus that occurs as a complex geological structure, which constitutes an integral part of the Mediterranean (Alpine-Himalayan) collisional orogenic belt. It is built up of terrigenous and volcanogenic-sedimentary rocks faunistically dated from the Devonian to Triassic inclusive (Somin, 1971; Somin, Belov, 1976; Kutelia 1983). Most of them are metamorphosed under conditions of chlorite-sericite subfacies of the greenschist facies of regional metamorphism (chlorite-phengite-albite±quartz, graphite-sericite-quartz phyllites and marbleized limestones), and only a minor part represented by clay-carbonaceous, phengite-chlorite-carbonaceous and prehnite-chlorite-carbonate schists underwent anchimetamorphism (Shengelia et al., 2015). The Dizi Series is intruded by numerous magmatic bodies of gabbro-diabases, diabases, diorites, diorite-porphyries, syenites, monzo-syenites and granitoids. The age of the intrusions was defined by K-Ar method at 176-165 Ma (Dudauri, Togonidze, 1998) and by U-Pb LA-ICP-MS zircon dating at 166.5 ± 4.6 Ma (authors` unpublished data) and corresponds to the Bathonian orogeny. The Middle Jurassic intrusions caused intense contact metamorphism of the rocks of the Dizi Series resulted in the formation of various hornfelses containing andalusite, cordierite, corundum, biotite, plagioclase, potassium feldspar, clinozoisite, hornblende, cummingtonite, clinopyroxene, wollastonite and scapolite. These rocks correspond to albite-epidote-hornfels, andalusite-biotite-muscovite-chlorite-hornfels and andalusite-biotite-muscovite-hornfels subfacies of the contact metamorphism (Javakhishvili et al., 2020). The analogues of the Dizi Series rocks have not previously been established either in the Greater Caucasus or in the neighboring regions. In our view, Paleozoic rocks similar to the Dizi Series occur under the Cretaceous and Jurassic deposits within the folded basement of the plain Crimea where they were recovered by wells. Most of these rocks, as in the Dizi Series, underwent metamorphism of chlorite subfacies of the greenschist facies and, to a lesser extent, deep epigenesis (clayey-carbonaceous, sericite-carbonaceous, actinolite-chlorite-prehnite, muscovite-albite-chlorite, epidote-actinolite-chlorite and graphite-talc-quartz schists) (Chernyak, 1969). These rocks are also intruded by Middle Jurassic igneous rocks, including gabbro-diabases, diabases, diorites, syenites, monzo-syenites, granite-porphyries, etc. (Shniukova, 2016; Shumlyanskyy, 2019). As a result of the contact metamorphism of the basement rocks, muscovite-quartz-cordierite and cordierite-quartz-feldspar micaceous hornfelses were formed. Quartz syenite yielded a K-Ar age of 158 Ma (Scherbak, 1981), while monzo-syenite was dated at 170 ± 5 Ma applying 40Ar/39Ar method (Meijers, 2010). Thus, based on the rock associations, the nature of metamorphism, the age of the metamorphic and igneous rocks, and on the spatial position of the Dizi Series and folded basement of the plain Crimea we assume that these units developed coevally in similar environment and geological conditions.<br><br>Acknowledgements.This work was supported by Shota Rustaveli National Science Foundation (SRNSF) [PHDF-19-159, Regional and Contact Metamorphism of the Dizi Series].</p>

Regional and Contact Metamorphism of the Dizi Series (the Greater Caucasus)

2020 ◽  
Author(s):  
Irakli Javakhishvili ◽  
Tamara Tsutsunava ◽  
David Shengelia ◽  
Giorgi Chichinadze ◽  
Giorgi Beridze
Keyword(s):  
General Scheme ◽  
Regional Metamorphism ◽  
Geological Structure ◽  
Contact Metamorphism ◽  
Maximum Temperature ◽  
Greater Caucasus ◽  
Mineral Associations ◽  
Mineral Assemblages ◽  
Characteristic Features ◽  
Composition Of Minerals

<p>The Greater Caucasus - the complex geological structure of the Caucasus is an integrated part of the Mediterranean (Alpine-Himalayan) collision orogenic belt. The Dizi series is exposed within the Greater Caucasus Southern Slope zone, in the core of Svaneti anticlinorium. It is composed of faunistically dated from the Devonian to the Triassic inclusively thin-striped and crenulated terrigenous deposits, various volcanites and marbles. Despite the well-studied stratigraphy and tectonics of the Dizi series, the issues of metamorphism, unlike the other rocks of the pre-Alpine crystalline basement of the Greater Caucasus are less studied. The rocks of the Dizi series underwent regional metamorphism of the greenschist facies chlorite-sericite sub-facies under a temperature of 300-340°С and pressures of ≈ 2-2.5 kbar. Characteristic mineral assemblages are established on the basis of microprobe analysis of chlorite, K-mica, plagioclase, actinolite, actinolitic hornblende and prehnite. Due to the contact impact of the Bathonian intrusions on the regionally metamorphosed rocks of the Dizi series, various hornfelses, spotted schists and skarns were formed. Composition of minerals of contact-metamorphism - biotite, cordierite, muscovite, plagioclase, cummingtonite, hornblende, chlorite, clinopyroxene, clinozoisite and K-feldspar is determined. According to the results of studies of key mineral assemblages of contact-metamorphosed rocks, three exocontact zones are distinguished, corresponding to the albite-epidote-hornfels, andalusite-biotite-muscovite-chlorite-hornfels and andalusite-biotite-muscovite-hornfels sub-facies conditions. The first zone is marked by the appearance of biotite, muscovite and plagioclase of oligoclase-andesine series in metapelites; hornblende, biotite and clinozoisite in metabasites and amphibole schists; wollastonite and clinozoisite in carbonate-silicate schists. The beginning of the second zone is marked in the appearance of cordierite, corundum in metapelites and of scapolite in metabasites and carbonate-silicate schists. By the disappearance of chlorite in the metapelites, the appearance of cummingtonite in metabasites and garnet in carbonate-silicate schists, a transition to the third zone is established. In the high-temperature part of the last zone, in the metapelites fibrolite is formed. The maximum temperature in the aureole of contact metamorphism is 550⁰С, and the pressure is about 0.5-1 kbar. Due to very low pressure during the re-crystallization of rocks pyralspite garnet is missing in the mineral associations of the Dizi series rocks. Instead of garnet, the association of chlorite-quartz-muscovite appeared. Under the conditions of increasing temperature during the metamorphism a change in the characteristic features of the mineral composition is shown graphically. Based on the accessible data the authors have drawn the contact metamorphism fields on the existing general scheme of facies and subfacies of regional metamorphism.</p>

scholarly journals U–Pb LA–ICP–MS dating of zoned zircons from the Greater Caucasus pre-Alpine crystalline basement: Evidence for Cadomian to Late Variscan evolution

2020 ◽  
Vol 71 (3) ◽  
pp. 249-263
Author(s):  
Irakli Gamkrelidze ◽  
David Shengelia ◽  
Giorgi Chichinadze ◽  
Yuan-Hsi Lee ◽  
Avtandil Okrostsvaridze ◽  
...  
Keyword(s):  
Crystalline Basement ◽  
Greater Caucasus ◽  
Icp Ms

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.

Contact metamorphism of the Tethyan Sedimentary Sequence, Upper Mustang region, west-central Nepal

2020 ◽  
Vol 157 (11) ◽  
pp. 1917-1932 ◽  
Author(s):  
Iva Lihter ◽  
Kyle P. Larson ◽  
Sudip Shrestha ◽  
John M. Cottle ◽  
Alex D. Brubacher
Keyword(s):  
Regional Metamorphism ◽  
Contact Metamorphism ◽  
Metamorphic Rocks ◽  
Upper Crust ◽  
Sedimentary Sequence ◽  
The North ◽  
Central Nepal ◽  
West Central ◽  
Metamorphic Temperature ◽  
Local Movement

AbstractThe Upper Mustang region of west-central Nepal contains exposures of metamorphosed Tethyan Sedimentary Sequence rocks that have been interpreted to reflect either contact metamorphism related to the nearby Mugu pluton or regional metamorphism associated with the North Himalayan domes. New monazite geochronology results show that the Mugu leucogranite crystallized at c. 21.3 Ma, while the dominant monazite age peaks from the surrounding garnet ± staurolite ± sillimanite schists range between c. 21.7 and 19.4 Ma, generally decreasing in age away from the pluton. Metamorphic temperature estimates based on Ti-in-biotite and garnet–biotite thermometry are highest in the specimens closest to the pluton (648 ± 24°C and 615 ± 25°C, respectively) and lowest in those furthest away (578 ± 24°C and 563 ± 25°C, respectively), while pressure estimates are all within uncertainty of one another, averaging 5.0 ± 0.5 kbar. These results are interpreted to be consistent with contact metamorphism of the rocks in proximity to the Mugu pluton, which was emplaced at c. 18 ± 2 km depth after local movement across the South Tibetan detachment system had ceased. While this new dataset helps to characterize the metamorphic rocks of the Tethyan Sedimentary Sequence and provides new constraints on the thickness of the upper crust, it also emphasizes the importance of careful integration of metamorphic conditions and inferred processes that may affect interpretation of currently proposed Himalayan models.

4. Rocks transformed

2016 ◽  
pp. 51-65
Author(s):  
Jan Zalasiewicz
Keyword(s):  
Chemical Composition ◽  
High Pressures ◽  
Regional Metamorphism ◽  
Contact Metamorphism ◽  
Metamorphic Rocks ◽  
Mountain Belt ◽  
Different Types ◽  
High Pressures And Temperatures ◽  
Contact And Impact

‘Rocks transformed’ outlines the processes of metamorphism and describes the different types of metamorphism: regional, contact, and impact. Regional metamorphism is the most common form and occurs in mountain belt zones where the crust is much thicker. High pressures and temperatures result in recrystallization in the rocks. As temperatures and pressures increase, the new crystals that form are bigger. The original chemical composition of the rocks affects the resulting metamorphic rocks. Muds become slates and mica-schists, while limestones become marbles. Contact metamorphism takes place at the boundaries of magma bodies and impact metamorphism is seen when meteorites crash into the Earth’s surface.

scholarly journals VII. Regional metamorphism

1885 ◽  
Vol 38 (235-238) ◽  
pp. 425-432
Keyword(s):  
Regional Metamorphism ◽  
Igneous Rocks ◽  
Contact Metamorphism ◽  
Metamorphic Rocks

Metamorphic rocks hare been divided into two classes—1. Those in which local changes have been caused by contact with heated eruptive rocks; 2. Those extending over wider areas, in which the rocks are in no apparent relation to eruptive or igneous rocks. The first has been termed Contact Metamorphism , and the second Normal or Regional Metamorphism , the latter two terms having been used to express the same phenomena and treated as synonymous. The object of this paper is briefly to show that there may be another cause for metamorphic action, for which, not to introduce a new term, I would propose to transfer and restrict the term of “ Metamorphism ."

scholarly journals Metamorphic Age Comparison and Its Implications between the Zuoquan and Zanhuang Complexes in the Central North China Craton, Based on LA-ICP-MS Zircon U–Pb Dating

Minerals ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 780 ◽  
Author(s):  
Ling-Ling Xiao ◽  
Min-Hua Chen
Keyword(s):  
Phase I ◽  
Phase Ii ◽  
North China Craton ◽  
North China ◽  
Regional Metamorphism ◽  
Metamorphic Rocks ◽  
The North ◽  
South Central ◽  
Icp Ms ◽  
Two Phases

The Trans-North China Orogen (TNCO) is well-known as an early Precambrian orogenic belt in the North China Craton (NCC). Three meaningful groups of metamorphic ages have been reported in the metamorphic complexes throughout the TNCO, including c. 1.85 Ga, c. 1.95 Ga, and c. 2.5 Ga. The spatial distributions and relationships of these ages provide notable insight into the formation timing and tectonic evolution of the NCC basement. The Zuoquan and Zanhuang complexes are exposed in the south–central TNCO and are adjacent to the Eastern Block. In order to place new constraints on the timing of two phases of metamorphism that occurred in the complexes, combined U–Pb and rare earth element analyses were performed on zircons from different types of metamorphic rocks. Uranium–Pb zircon dating in this study shows that two groups of metamorphic ages of 1.88–1.85 Ga and 2.48–2.46 Ga were commonly recorded by metamorphic rocks in the Zanhuang and Zuoquan complexes, respectively. Our previous geochronological studies showed that metamorphic ages of c. 2.51 Ga and c. 1.90 Ga were locally recorded in the Zanhuang and Zuoquan complexes, respectively. These data indicate that metamorphic rocks in the two complexes underwent at least two phases of metamorphism, i.e., 2.51–2.46 Ga (Phase I) and 1.90–1.85 Ga (Phase II). In combination with previous studies regarding reaction microstructures, metamorphic pressure–temperature paths, and geochronology, the Phase II metamorphic ages are interpreted to be linked to the collision between the Western and Eastern Blocks along the TNCO between 1.97 Ga and 1.80 Ga, whereas the Phase I metamorphic ages, as a result of an earlier and extensive tectono-thermal event that occurred in the Eastern and Western Blocks of the NCC, were related to underplating of mantle-derived magma. It is inferred that the rocks with c. 2.51–2.46 Ga metamorphic ages in the two complexes formed in the Eastern Block and underwent regional metamorphism during that period, and then were tectonically involved in the TNCO and experienced c. 1.90–1.85 Ga metamorphism. Metamorphic peaks occurred at different crustal levels in the orogen, resulting in distinct metamorphic ages and peak conditions preserved by metamorphic rocks in the two complexes.

scholarly journals Microscopy and Microanalysis of Magmatic and Metamorphic Minerals – Part 1: Cordierite

2008 ◽  
Vol 16 (5) ◽  
pp. 30-37 ◽  
Author(s):  
Robert Sturm
Keyword(s):  
Regional Metamorphism ◽  
Igneous Rocks ◽  
Major Constituent ◽  
Metamorphic Rocks ◽  
High Grade ◽  
Shearing Stress ◽  
The Past ◽  
Peraluminous Granites ◽  
Wide Range ◽  
Higher Temperature

Cordierite represents an orthorhombic (Mg,Fe)Al-silicate (Table 1) that is observed in a wide range of natural occurrences. As outlined in numerous mineralogical overviews published during the past decades, cordierite mainly crystallizes in thermally metamorphosed rocks, particularly in those derived from argillaceous sediments. Additionally, the mineral can be a major constituent of parageneses formed under high-grade regional metamorphism and therefore occurs in respective schists, gneisses and granulites. The metamorphic formation of cordierite is generally restricted to conditions of deficient or low shearing stress producing only moderate lithological pressures. With rising pressure due to transpression cordierite often breaks down to enstatite and sillimanite or, at higher temperature, to sapphirine and quartz (see also Fig. 5). Besides its crystallization in metamorphic rocks, cordierite is also found in specific igneous rocks like peraluminous granites and related high-grade anatectic terrains.

Low-pressure metamorphism of the mafic volcanic rocks of the Rossland Group, southeastern British Columbia

1996 ◽  
Vol 33 (10) ◽  
pp. 1402-1409 ◽  
Author(s):  
Wayne G. Powell ◽  
Edward D. Ghent
Keyword(s):  
Regional Metamorphism ◽  
Volcanic Rocks ◽  
Temperature Limit ◽  
Maximum Temperature ◽  
Metamorphic Rocks ◽  
Widespread Occurrence ◽  
Extensive Region ◽  
Homogenization Temperatures ◽  
Structural Levels ◽  
Contact Aureoles

Mafic volcanic rocks of the Rossland Group have been metamorphosed in the subgreenschist to lower amphibolite faciès. Subgreenschist-facies regional metamorphic rocks are subdivided into prehnite–pumpeilyite zone and prehnite–epidote zone. Fluid inclusions in two subgreenschist-facies veins yielded mean homogenization temperatures of 139 and 151 °C. Assuming a reasonable maximum temperature limit of 275 °C for the subgreenschist fades, the fluid-inclusion isochores indicate a pressure <250 MPa for regional metamorphism in the subgreenschist facies. This is consistent with the widespread occurrence of prehnite–chlorite-bearing assemblages. Metamorphic grade increases sharply northward approaching the large plutons of the Nelson suite. The contact aureoles of the Nelson batholith and the related Bonnington pluton encompass most of the region, producing an extensive region underlain by rocks within the hornblende–oligoclasc zone. Intrusion of the Nelson plutonic suite overlapped with the development of the Hall Creek syncline and Silver King shear zone. The pattern of isograds across the Rossland Group indicates superimposed contact and regional metamorphism rather than progressively deeper structural levels northward.

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