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.

scholarly journals Geology and Mineral Resources of Phalamdada-Dhuwakot Section of West-Central Nepal, Lesser Himalaya

2018 ◽  
pp. 59-64
Author(s):  
Arjun Bhattarai ◽  
Kabiraj Paudyal
Keyword(s):  
Mineral Resources ◽  
Geological Mapping ◽  
Metamorphic Rocks ◽  
Low Grade ◽  
Lesser Himalaya ◽  
Central Nepal ◽  
West Central ◽  
Metallic Mineral ◽  
Geological Control ◽  
Core Part

Geological mapping was carried out along the Phalamdanda-Dhuwakot section of west-central Nepal in the Lesser Himalaya. The aim of geological mapping was to prospect the metallic mineral resources in the area especially to assess the geological control of mineralization as prognostic mapping and study the genesis of mineralization. The area has developed low-grade metamorphic rocks of the Nawakot Group. Geological rock units like the Kuncha Formation, Fagfog Quartzite, Dandagaon Phyllite, Nourpul Formation and Dhading Dolomite are mapped in the area. Jal Bhanjyang Thrust carries the more older rocks of the Nourpul Formation over the Dhading Dolomite. The area is highly deformed as indicated by presence of folds. Outliers of Fagfog Quartzite and Dhading Dolomite are developed at the core part of the syncline. Phalamdada iron and Anbu Khaireni as well as Dharapani copper are the major metallic deposits reported in the area. Both deposits are considered as the syngenetic in nature. Bulletin of Department of Geology, vol. 20-21, 2018, pp:59-64

scholarly journals Tracing the Mahabharat Thrust (MT) on the basis of lithology and microstructures around Bhainse-Manahari area, central Nepal

2016 ◽  
Vol 51 ◽  
pp. 39-48
Author(s):  
Laxman Subedi ◽  
Kamala Kant Acharya
Keyword(s):  
Hanging Wall ◽  
Strain Analysis ◽  
Metamorphic Rocks ◽  
Foot Wall ◽  
Low Grade ◽  
The North ◽  
Central Nepal ◽  
Complex Shear ◽  
Thrust Zone ◽  
Quartz Grains

Lithological and microstructural study carried out in Bhainse –Manahari area, central Nepal reveals that the rock sequences of the Bhainse–Manahari area can be divided into two successions: the Nawakot Complex and the Kathmandu Complex. These two Complexes are separated by a distinct thrust boundary, the Mahabharat Thrust (MT). The Nawakot Complex consists of low-grade metamorphic rocks like slate, phyllite, quartzite and limestone while the Kathmandu Complex comprises medium grade (up to garnet grade) metamorphic rocks like garnet-schist, marble and mica-schist. The Mahabharat Thrust (MT) and the Manahari Thrust (MnT) are the two major thrusts in the study area. The MT separates the rocks of the Nawakot Complex (foot wall) in the south from the rocks of the Kathmandu Complex (hanging wall) in the north. The Manahari Thrust in the western part of the study area separates the Dunga Quartzite and the older Benighat Slates lying above it. The microstructure analysis reveals that the rocks in the thrust zone show higher deformation than in the neighboring rocks, and this gradually decreases away from the MT zone. The strain analysis of quartz grains reveals that the rock sequences of the hanging wall of the MT showed pure, simple and complex shear senses and the rocks of the footwall also showed the same pattern indicating MT as a stretching fault.

scholarly journals Study of regional geological structures in Ridi-Shantipur area of Gulmi district, Lesser Himalaya, west-central Nepal

2019 ◽  
Vol 58 ◽  
pp. 111-118
Author(s):  
Shrawan Shakya ◽  
Kabi Raj Paudyal
Keyword(s):  
Regional Scale ◽  
Lesser Himalaya ◽  
The North ◽  
Central Nepal ◽  
West Central ◽  
Continuous Shear ◽  
Deformation Event ◽  
Middle Member ◽  
Geological Units ◽  
The Himalaya

The study was carried out in the Lesser Himalaya between Ridi-Shantipur area of the Gulmi District, west-central Nepal. Two geological units: the Nourpul Formation and the Dhading Dolomite were mapped in the area. These units belong to the Nawakot Group as explained by several researchers in central Nepal. The Nourpul Formation can further be divided into three members based on distinct mappable lithology, which are named as the Lower Member, the Middle Member and the Upper Member, respectively. The area is highly folded with several local and regional anticlines and synclines; Ridi Khola Anticline, Ridi-Karikot Syncline, Ruru Anticline, Baletaksar-Gwadi Syncline, Huga-Bamgha Anticline, Rimuwa-Rudrabeni Syncline, Juhan-Eksing Anticline, Juniya-Limgha Syncline, Bharse-Thaple Anticline, and Chiureko Syncline, respectively from the south to the north. All the folds are trending along to the ESE-WNW direction. The origin of these folds can be linked with the thrust propagation in the Himalaya that can be explained with the deformation event D4. The Harewa Khola Thrust is the only one regional scale thrust mapped in the area. The thrust carries the older Nourpul Formation over the Dhading Dolomite with the indications of thrust related features like slickensides and fault-breccias. The thrust seems to propagate to the north. There is a continuous shear zone mapped in the outcrops from the Tal Khola-Aslewa-Eksingh-Gudrung-Juhang- Rupakot region as an indicator of the presence of the Badi Gad Fault in the region.

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.

scholarly journals Geology and mineral resources of Khudi-Bahundanda area of west-central Nepal along Marshyangdi Valley

2019 ◽  
Vol 58 ◽  
pp. 97-103
Author(s):  
Shashi Tamang ◽  
Sandeep Thapa ◽  
Kabi Raj Paudyal ◽  
Frédéric Girault ◽  
Frédéric Perrier
Keyword(s):  
Large Scale ◽  
Mineral Resources ◽  
Main Central Thrust ◽  
Quartz Veins ◽  
The North ◽  
Central Nepal ◽  
West Central ◽  
Geological Map ◽  
Scale Structures ◽  
Garnet Zone

Geological study was carried out along the Khudi-Bahundanda area of the Marshyangdi Valley in the west central Nepal. The area lies partly in the Main Central Thrust (MCT) zone and partly in the Higher Himalayan Crystalline Zone. The aim of the study was to prepare a detail geological map and cross section in the scale of 1:25,000 to work out on stratigraphy, metamorphism and mineral resource potential of the area. The rocks of the Higher Himalaya have been mapped under a single unit as Formation I. This unit consists of kyanite-garnet para-gneiss. The lithological units of the MCT zone are mapped into three units as the Benighat Slate, the Malekhu Formation and the Robang Formation from the bottom to the top, respectively. The Benighat Slate consists of dark grey to black schist with some carbonate beds as members. The Malekhu Formation consists of creamy white siliceous dolomite marble with parting of schist. The Robang Formation comprises of light grey psammitic schist with garnet and white micaceous quartzite in various proportion. Many secondary structures are observed in the study area, but primary structures are missing due to extreme metamorphism. The large-scale structures are the MCT, which separates the Lesser Himalayan rocks to the south from the Higher Himalaya to the north, and the Bahundanda Thrust (BT). Numerous outcrop-scale structures like meso-scale folds, quartz veins, boudinage and ptygmatic folds are abundant. Folds in the MCT zone are mostly E-W trending, and rocks have experienced multiple metamorphism and dynamic crystallization of minerals. The Lesser Himalayan rocks resemble the garnet zone while the Higher Himalayan rocks resemble to the kyanite grade of metamorphism. As in the other sections of the Himalaya, the present section also clearly shows the inverted metamorphism in the MCT zone. The MCT zone is considered as the potential site for precious and semi-precious stones, of which the most potential ones are the garnet and kyanite.

Fabric developments and the evolution of the Periadriatic Lineament in southeast Austria

1989 ◽  
Vol 126 (1) ◽  
pp. 55-71 ◽  
Author(s):  
W. von Gosen
Keyword(s):  
Regional Metamorphism ◽  
Southern Alps ◽  
Contact Metamorphism ◽  
Polyphase Deformation ◽  
The North ◽  
Late Tertiary ◽  
Intrusive Activity

AbstractThe Periadriatic Lineament Zone which forms the boundary between the Eastern and Southern Alps in the Karawanken region of Austria has a complex history spanning the Variscan and Alpine orogenies. Variscan regional metamorphism and polyphase deformation followed by Late to Post Variscan intrusive activity with accompanying contact metamorphism affects a belt of structurally complex rocks referred to as the Eisenkappel Zone to the north of the lineament. Weak Early Alpine deformation in the Southern Alpine rocks can also be recognized in the Eisenkappel Zone. The Young Alpine intrusion of the Karawanken Tonalite was followed by lateral fault displacements associated with the formation of the Periadriatic Lineament. Late Tertiary sediments, caught up in the northward directed thrusting responsible for the uplift of the Karawanken chain, record the youngest deformation in the area.

Metamorphic rocks of the 1985 Tibet Geotraverse, Lhasa to Golmud

1988 ◽  
Vol 327 (1594) ◽  
pp. 203-213 ◽  
Keyword(s):  
Tibetan Plateau ◽  
Regional Metamorphism ◽  
Metamorphic Grade ◽  
Metamorphic Rocks ◽  
The Tibetan Plateau ◽  
Crustal Anatexis ◽  
Prograde Metamorphism ◽  
Lhasa Terrane ◽  
The North ◽  
Peak Metamorphism

Two examples of uplifted basement have been studied in the Lhasa Terrane of the Tibetan Plateau. The Nyainqentanglha orthogneisses are bounded by staurolite-garnet schists to the north which record prograde metamorphism at 5 .0 ± 1.3 kbar, 610 ± 70 °C. Garnet sillimanite xenoliths within the orthogneiss suggest that peak temperatures reached at least 700 ± 70 °C at 5.1 ± 2 .5 kbar. These P / T fields reflect high T /low P metamorphism during Eocene subduction, and indicate that the syntectonic Nyainqentanglha orthogneiss was emplaced at depths greater than 10 km. Sillimanite-bearing assemblages from the Amdo gneisses in the northern Lhasa Terrane provide evidence of crustal anatexis at temperatures > 680 °C. This event is poorly constrained in time but is probably Cambrian or earlier. Within the Kunlun Terrane, biotite and garnet isograds north of the Xidatan Fault indicate an increase in metamorphic grade from north to south, reaching peak metamorphism at 470 ± 30 °C, 4 .3 ± 1.5 kbar synchronous with the emplacement of the Triassic batholith. Regional metamorphism was followed by uplift of at least 2 km before emplacement of post-tectonic, early Jurassic granites.

scholarly journals Neogene fluvial systems in the Siwalik Group along the Tinau Khola section, west central Nepal Himalaya

2001 ◽  
Vol 25 ◽  
Author(s):  
Prakash Das Ulak ◽  
Katsuhiro Nakayama
Keyword(s):  
System Development ◽  
Major Change ◽  
Fluvial System ◽  
Facies Association ◽  
The North ◽  
Central Nepal ◽  
Main Boundary Thrust ◽  
West Central ◽  
Facies Associations ◽  
Siwalik Group

Along the Tinau Khola section of west central Nepal, the Siwalik Group is a 4 km thick pile of fluvial sedimentary sequence of mudstone, sandstone and conglomerate. It is exposed between the Main Boundary Thrust (MBT) to the north and the Frontal Churia Thrust (FCT), also known as the Main Frontal Thrust (MFT), in the south. The Siwalik Group is lithologically divided into the Arung Khola, Binai Khola and Chitwan formations, in ascending order. Six facies associations (FA1 to FA6) are recognised within the group based on grain size distribution, nature of bedforms, and sandstone-mudstone ratio. The fine-grained sediments of the Lower and Middle members of the Arung Khola Formation belong to the FA1-facies association and were interpreted to have deposited by a low-discharge, low -relief meandering fluvial system. The multiple accumulated thin-layered muddy sandstone sequence in the Upper Member of the Arung Khola and the Lower Member of the Binai Khola formations belong to FA2 and FA3- facies associations and were deposited by a flood flow-dominated meandering fluvial system. The deep sandy braided facies association (FA4) and shallow sandy braided facies association (FA5) are well developed in the Middle and Upper members of the Binai Khola Formation, respectively. The gravelly braided facies association (FA6) is recognised in the Chitwan Formation. The palaeomagnetically well-studied section of the Tinau Khola allows precise dating of the major change of fluvial system during the deposition of the Siwalk Group. The environment of predominantly shallow meandering rivers with low­ relief and low-discharge during the time of deposition of the Arung Khola Formation changed at 9.9 Ma and flooding in the rivers dramatically increased due to the intensification of monsoon precipitation. This hydrographic change also brought the change in facies from the earlier FA1 facies to FA2 and FA3 facies. Change from meandering to braided system occurred at 8.2 Ma because of the obvious regional tectonic upliftment of the Higher Himalaya bringing into FA4 and FA5-facies associations. Finally the FA6-facies association was developed due to the large gravelly braided system development at 2.5 Ma as a result of the Main Boundary Thrust movement along the frontal part of the Himalaya.

scholarly journals Linking metamorphism, magma generation, and synorogenic sedimentation to crustal thickening during Southern Appalachian mountain building, USA

Lithosphere ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 722-749
Author(s):  
H.H. Stowell ◽  
J.J. Schwartz ◽  
S.B. Ingram ◽  
J. Madden ◽  
C. Jernigan ◽  
...  
Keyword(s):  
Regional Metamorphism ◽  
Foreland Basin ◽  
Progressive Increase ◽  
Crustal Thickening ◽  
Garnet Growth ◽  
Metamorphic Rocks ◽  
Blue Ridge ◽  
Magma Generation ◽  
The North ◽  
North American Craton

Abstract The nature of metamorphism, magma compositions, the spatial distribution of plutons, and foreland sediments reflect, in part, the character and thickness of continental crust. We utilized metamorphic pressure-temperature-time (P-T-t) paths, garnet Sm-Nd ages, zircon U-Pb ages, and pluton compositions to estimate paleocrustal thickness and temporal changes in crustal magma sources in the Blue Ridge of the southernmost Appalachians. Garnet Sm-Nd ages for amphibolite-facies metamorphic rocks range from 331 ± 4 to 320 ± 3 Ma. Low- and high-Sr/Y plutons that intruded these metamorphic rocks have zircon U-Pb ages of 390 ± 1 to 365 ± 1 Ma and 349 ± 2 to 335 ± 1 Ma, respectively. Therefore, garnet growth began during regional metamorphism synchronous with or shortly after intrusion of the youngest high-Sr/Y trondhjemite plutons. Phase diagram sections and thermobarometry indicate that garnet growth initiated at ∼5.8 kbar and 540 °C and grew during temperature increases of 60–100 °C and pressure increases of 2–3 kbar. The older, low-Sr/Y magmas are inferred to have been sourced in the crust at depths <∼30 km, insufficient for garnet to be stable. However, the younger, high-Sr/Y magmas are inferred to have been sourced at >30 km depths where garnet was stable. Hafnium isotopic compositions for all the plutons, but one, exhibit a range from negative initial εHf(i) to weakly positive initial εHf(i), indicating incomplete mixing of dominantly crustal sources. Our data require minimum crustal thicknesses of ∼33 km at 331 Ma; however, Alleghanian crustal thicknesses must have locally reached 39 km, based on crustal reconstruction adding the Alleghanian thrust sheet beneath the eastern Blue Ridge. We infer the presence of hot, tectonically thickened crust during intrusion of the early Alleghanian high-Sr/Y plutons and conclude that garnet growth and plutonism reflect a progressive increase in crustal thickness and depth of magma generation. The crustal thickening was synchronous with deposition of Mississippian to early Pennsylvanian sediments in the foreland basin of the Appalachian orogen between 350 and 320 Ma. This crustal thickening may have preceded emplacement of the Alleghanian thrust sheets onto the North American craton.

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.

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