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 ."

Ultramafic and mafic protoclastic intrusions in the Dahomeyan gneiss of Ghana

1973 ◽  
Vol 110 (6) ◽  
pp. 557-564 ◽  
Author(s):  
R. F. Holm
Keyword(s):  
Regional Metamorphism ◽  
Mafic Magma ◽  
Igneous Rocks ◽  
Contact Metamorphism ◽  
Partial Recrystallization ◽  
Anorthite Content

SummaryCharacteristics of mineralogy and texture, together with systematic changes in the enstatite content of orthopyroxene and in the anorthite content of plagioclase, indicate that intrusions of pyroxenite, norite and gabbro, and diorite and leucocratic diorite in the Dahomeyan gneiss of Ghana are genetically related, and that they belong to a subalkaline comagmatic series derived from a parental mafic magma. Partial recrystallization (deuteric) of the igneous rocks during and after intrusion and protoclasis produced minerals characteristic of temperatures higher than those that existed during the medium-grade regional metamorphism of the Dahomeyan gneiss, thus indicating that emplacement of the igneous rocks occurred late during, or perhaps after, the metamorphism. Contact metamorphism appears to have resulted in higher than normal anorthite contents of the plagioclase in the surrounding Dahomeyan gneiss.

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>

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.

XIX.—Metamorphic History of the Schichallion Complex (Perthshire)

1958 ◽  
Vol 63 (2) ◽  
pp. 413-431 ◽  
Author(s):  
N. Rast
Keyword(s):  
Regional Metamorphism ◽  
Igneous Rocks ◽  
Metamorphic Rocks ◽  
Present Contribution ◽  
Scottish Highlands ◽  
Metamorphic History ◽  
Fine Grain ◽  
Tectonic History ◽  
History Of ◽  
Garnet Zone

SynopsisThe Schichallion complex is situated in the Central Highlands of Scotland between the villages Struan and Kinloch Rannoch. The area is of considerable geological interest and has been investigated stratigraphically and structurally by E. M. Anderson and Bailey and McCallien. As a consequence of their researches a complete stratigraphical succession has been established. Thus, the metamorphic rocks of the area are classified into the Moinian and Dalradian systems, which are separated by a plane of tectonic discontinuity known as the Boundary Slide. The Moinian rocks are quartz-felspathic granulites, whereas the Dalradian system includes pelitic schists, quartzites, limestones as well as a variety of meta-igneous rocks.In his previous research the present author has established the tectonic history of the complex. In particular three episodes of folding (F1to F3) and a much later episode of faulting (F4) were recognized. Of these the F3episode is of least significance. Consequently, events after the F2movements can be in many cases regarded as post-folding.The present contribution is concerned essentially with the mapping of the metamorphic zones (garnet and staurolite-kyanite) and with a detailed study of the mineralogical evolution of regionally metamorphosed rocks within these zones.In the field it is possible to prove that the staurolite-kyanite zone is essentially post-folding, since the kyanitepegmatites are found to cut across the minor F2-folds. In this respect textural studies confirm the field observations. The study of the internal inclusions in garnets indicates that the garnet zone has a much longer history, since pre-F2garnets are found in the southern part of the complex and throughout the central part of the area syn-tectonic F2garnets are apparent. The pre-F2garnets contain a very fine-grain F1fabric. Hence the garnets in relation to the F1movements are post-tectonic. Thus, the regional metamorphism can be subdivided into three phases: the F1metamorphism, the F2metamorphism and the post-F2metamorphism. The latter, on structural evidence appears to be at least in part contemporaneous with the F3movements.The meta-igneous rocks of the area are grouped into the hornblende-schists and granular epidiorites. The hornblende-schists appear to have suffered deformation and recrystallization during F1and F2episodes of movement. On the other hand the granular epidiorites are later than the F1and the F2movements. Although in the southern parts of the district the epidiorites have been slightly deformed, elsewhere they preserve the original ophitic texture and cut across the F1and F2folds. The deformation in the south is attributed to the effects of the F3folding. The epidiorites have been evidently emplaced as dolerites after the F2movements and before the F3metamorphism.The localized retrogressive metamorphism is associated with the F4movements, which are responsible for the Loch Tay Fault. The Fault is later than the minor intrusives associated with the Younger Granites of the Scottish Highlands and is suggested to be of a Lower or Middle O.R.S. age.On the basis of the chemical composition of the plagioclase felspars it is proposed to include all the staurolite and kyanite bearing rocks into the epidote-amphibolite facies. In this respect temperature and the hydrostatic pressure are assumed to have been the main factors, since similar minerals came into existence during static and dynamic stages of metamorphism alike.

Further Observations on the Ballantrae Igneous Complex, South Ayrshire

1937 ◽  
Vol 74 (1) ◽  
pp. 20-33 ◽  
Author(s):  
D. Balsillie
Keyword(s):  
Field Work ◽  
Igneous Rocks ◽  
Contact Metamorphism ◽  
Metamorphic Rocks ◽  
Considerable Difficulty ◽  
Short Account ◽  
Thermal Metamorphism ◽  
South West ◽  
Interesting Paper ◽  
Characteristic Effect

In the southern belt of the Ballantrae serpentine, stretching south-west from Millenderdale, there occur many exposures of altered and more or less recrystallized dolerite and gabbro. Some of these rocks have afforded considerable difficulty to previous observers and they have been variously interpreted. Thus Dr. G. W. Tyrrell, in an interesting paper published twenty-five years ago (Trans. Geol. Soc. Glas., xiii, 283), regarded some of the rocks on Littleton Hill as “relics of an older mass of dolerite or gabbro” that had “become enveloped by the later serpentine”. But this expression of opinion does not appear to have been founded upon conviction, since quite recently Tyrrell states (Proc. Geol. Assoc, xliv, 59) “contact metamorphism presumably by the enveloping serpentine seems to have been developed in rocks on Littleton Hill which may originally have been spilites and diabase porphyrites”. At the time of writing a previous paper (GEOL. MAG., LXIX, 1932, 107) I hadalready inferred that the metamorphic rocks seen on Littleton Hill must have been derived from dolerites and gabbros, but the nature of their association with the serpentine was then merely a matter of surmise. In continuing field work in the province, therefore, I keptin mind the requirement to determine, if possible, the true geological relationships of these rocks, and to that end I have re-investigated carefully the whole southern outcrop of the serpentine and its accompanying metamorphic masses. A short account of the results of the field and laboratory work is given below. Firstly, however, I take leave to acknowledge the very helpful character of Mr. A. G. Macgregor's researches on felspar clouding, “a characteristic effect that is often produced in the fresh plagioclase felspars of igneous rocks by thermal metamorphism” (see Min. Mag., xxii, 524).

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 Geology of Zagros metamorphosed volcaniclastic sandstones: a key for changing the Mawat Ophiolite Complex to a metamorphic core complex, Kurdistan Region, NE-Iraq

2021 ◽  
Vol 906 (1) ◽  
pp. 012024
Author(s):  
Kamal Haji Karim
Keyword(s):  
Regional Metamorphism ◽  
Metamorphic Core Complex ◽  
Igneous Rocks ◽  
Contact Metamorphism ◽  
High Mountain ◽  
Core Complex ◽  
Ophiolite Complex ◽  
Volcanic Source ◽  
Different Types ◽  
Metamorphic Core

Abstract Mawat Ophiolite Complex is located about 36 km to the northeast of Sulaimani city and directly to the east-northeast of Mawat town near the border of Iran in the northeastern Iraq. The complex has about 600-km2 surface area and consists of high mountain terrains that subjected to intense geological investigations from the fiftieth of previous century till now. According to previous studies, the complex contains tens of igneous rocks such as basalt, metabasalt, tuff, diabase, metadiabase, diorite dykes, periodotite, serpentinite, serpentinite-matrix mélange, gabbro, metagabbro, harzbergite, pyroxenite, plagiogranite, pegmatite, granitiod rocks and dunite. They added occurrences of the volcanic and subvolcanic rocks in the form of dykes or basaltic flows. The present study tries to change the petrology and tectonics of whole complex from Ophiolite Complex to Metamorphic Core Complex. The revision includes refusal of all the above igneous rocks, instead they considered as medium grade regional metamorphism of different types of volcaniclastic sandstones (volcanic wackes), arenites and greywackes (impure sandstones) which sourced predominantly from remote volcanic source area inside Iran. The revision depended on several conjugate field and laboratory evidences inside the complex. These evidences such as absence of pillow basalt, volcanic flows, glass shards, volcanic cones, dykes, sills, contact metamorphism, dilatational structures and flow structures. Other evidences are presence of cross beddings, erosional surfaces, lensoidal channel fills, metamorphosed conglomerate, exposures of thousands of laminated planar beds and transition from fresh volcaniclastic sandstones to its medium grade metamorphosed counterparts, which previously considered as igneous rocks of ophiolite types. Another, evidence, in contrast to ophiolite section, the basalt location is at the base of the claimed ophiolite section while plutonic (dunite and peridotite) rocks located at its top. These locations of the two rocks contradict the definition of ophiolites. Accordingly, the present study changed the geological map of the whole Mawat area from igneous outcrops to metamorphosed volcaniclastic sandstones, arenites and greywackes that belong to Walash-Naoperdan Series. The parent rocks of the series transformed to different types of regionally metamorphosed rocks by deep burial during Eocene. During the burial, diageneses and metamorphisms enhanced by complex mixture of materials from different source areas and seawaters environments. Later, they uplifted, unroofed and exhumed during Pliocene as a core complex.

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.

Revised stratigraphy of the Mesozoic rocks of southern Cyprus

1980 ◽  
Vol 117 (6) ◽  
pp. 547-563 ◽  
Author(s):  
R. E. Swarbrick ◽  
A. H. F. Robertson
Keyword(s):  
Oceanic Crust ◽  
Continental Margin ◽  
Late Cretaceous ◽  
Sedimentary Cover ◽  
Igneous Rocks ◽  
Late Triassic ◽  
Metamorphic Rocks ◽  
Southern Cyprus

SummaryRecent resurgence of interest in the Mesozoic rocks of SW and southern Cyprus necessitates redefinition of the Mesozoic sedimentary and igneous rocks in line with modern stratigraphical convention. Two fundamentally different rocks associations are present, the Troodos Complex, not redefined, a portion of late Cretaceous oceanic crust, and the Mamonia Complex, the tectonically dismembered remnants of a Mesozoic continental margin. Based on earlier work, the Mamonia Complex is divided into two groups, each subdivided into a number of subsidiary formations and members. The Ayios Photios Group is wholly sedimentary, and records the evolution of a late Triassic to Cretaceous inactive continental margin. The Dhiarizos Group represents Triassic alkalic volcanism and sedimentation adjacent to a continental margin. Several other formations not included in the two groups comprise sedimentary mélange and metamorphic rocks. The Troodos Complex possesses an in situ late Cretaceous sedimentary cover which includes two formations of ferromanganiferous pelagic sediments, radiolarites and volcaniclastic sandstones. The overlying Cainozoic calcareous units are not redefined here.

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