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 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 Scion Image Analysis in rocks of the hanging wall and foot wall of the MCT, central Nepal

1970 ◽  
Vol 5 (7) ◽  
pp. 15
Author(s):  
Kamala Kant Acharya ◽  
Bernhard Grasemann
Keyword(s):  
Image Analysis ◽  
Hanging Wall ◽  
Foot Wall ◽  
Special Issue ◽  
Central Nepal ◽  
Scion Image

DOI = 10.3126/hjs.v5i7.1227Himalayan Journal of Sciences Vol.5(7) (Special Issue) 2008 p.15  

scholarly journals Inverted metamorphic zonation in the hanging and foot walls of the Mahabharat Thrust, Kathmandu-Trishuli area, central Nepal

1970 ◽  
Vol 14 ◽  
pp. 51-58
Author(s):  
Sobit Prasad Thapaliya ◽  
Lalu Prasad Paudel
Keyword(s):  
High Temperature ◽  
Hanging Wall ◽  
Contact Metamorphism ◽  
Foot Wall ◽  
Central Nepal ◽  
Garnet Zone

Geological study was carried out along the Pasang Lahmu Highway from Kathmandu to Trishuli Bazaar covering both theLesser Himalayan autochthonous unit and the Kathmandu Nappe. The Lesser Himalayan rocks in the study area belong to theKunchha Formation, Benighat Slate and the Robang Formation of the Nawakot Complex. The Kathmandu Nappe (KathmanduComplex) comprises the Kalitar Formation, Gneiss Zone, Tistung Formation, Sopyang Formation and the Chandragiri Limestone.Petrographic study was carried out in the samples representing all the lithological units along the Pasang-Lahmu Highway.The study shows that the Kunchha Formation belongs to the biotite zone. The overlying units (Benighat Slate and RobangFormations) belong to the garnet zone. It is a clear evidence of inverted metamorphic zonation at the foot wall of the KathmanduNappe. The rocks of the Kathmandu Complex above the Mahabharat Thrust north of Kakani also show an inverse metamorphiczonation, i.e., the garnet zone is overlain by the sillimanite zone. However, in the southern part, the metamorphic zonation isnormal with biotite zone overlain by the chlorite zone. Although the inverted metamorphic zonation at the hanging wall of theMahabharat Thrust may be related to the high temperature contact metamorphism by pegmatite injection, the inverted metamorphismat the footwall needs an explanation.DOI: http://dx.doi.org/10.3126/bdg.v14i0.5439Bulletin of the Department of Geology, Vol. 14, 2011 pp. 51–58 

scholarly journals Mode of Occurrence of Nepheline Syenites in the Gorkha-Ampipal Area, Central Nepal Lesser Himalaya

1995 ◽  
Vol 11 ◽  
Author(s):  
M. R. Dhital
Keyword(s):  
Nepheline Syenite ◽  
Hot Springs ◽  
Country Rock ◽  
Hanging Wall ◽  
Hydrothermal Activity ◽  
Contact Metamorphism ◽  
Low Grade ◽  
Main Central Thrust ◽  
The North ◽  
Ore Minerals

In the Gorkha-Ampipal area, low-grade metamorphic rocks of the Kuncha Formation are delimited in the north by the Masel Thrust. The Kuncha Formation is characterised by doubly-plunging, en-echelon types of noncylindrical folds which are 2 to 20 km long (essentially in NW-SE direction), and have wavelengths of a few km. Mineral and stretching lineations are gently plunging due NNE or SSW. The hanging wall of the Masel Thrust is represented by garnet-biotite schists and gneisses. The schists and gneisses make up a steeply northward dipping homocline. In contrast to the rocks of the footwall, they are generally gently dipping and constitute several mesoscopic folds. Further north, the homocline is discordantly overlain by the intensely deformed unit of phyllites, graphitic schists, marbles, crystalline limestones, and calcareous quartzites. The Main Central Thrust sharply overrides the latter unit and brings with it gently northward dipping kyanite-garnet-biotite schists, quartzites, feldspathic schists, and mylonitic gneisses. There are several nepheline syenite intrusive bodies in the Kuncha Formation in the vicinity of the villages Harmi Bhnnjyang, Ampipal, Chanp Bhanjyang, Bhulbhule Khar, and Luintel Bhanjyang. Two separate bodies are also encountered at the confluence of the Masel Khola and the Daraundi Khola. The nepheline syenite bodies observed in the study area vary widely in their shape, size, and orientation. The largest pluton is observed in the vicinity of the villages Ampipal and Chanp Bhanjyang. It is about 7.5 km long in NNE-SSW direction and about 2 km wide. The second largest body is observed between the villages Bandre and Luintel Bhanjyang. It is about 2.5 km long approximately in east-west direction and 300 m wide. Numerous other smaller bodies ranging in size from hundreds of m to a few cm also occur in the region. The nephelinesyenites show sharp and irregular contacts with the country rock, they are crosscut by numerous dykes, and occasionally the effect of contact metamorphism is also observed in the country rock. The northeastern part of the largest nepheline syenite pluton (which occurs between Ampipal and Chanp Bhanjyang) is covered by about 500 m thick band of impure marbles. Rare, thin alternations of impure marble with phyllite as well as large (more than 10 m in diameter) scattered marble boulders areseen on the slopes NE of Chanp Bhanjyang, N of Bhulbhule Khar, at the saddle of Lagamkot, and at Khanigaun. The secondary mineralisation in the marbles is represented by magnetite, actinolite, biotite, and chlorite. There exist a few old iron mine workings in the magnetite mineralisation zones. Similar minerals are also seen in the nepheline syenite suggesting a direct relationship between the mineralisation in the nepheline syenite and the marbles. Generally, the nepheline syenite bodies exhibit the same trends of foliation and lineation as those of the country rock, and therefore, they must be intruded before the development of the secondary structures. There are a few hot springs at Bhulbhule Khar, which contain a high amount of H2S gas and sulphur, and are coming through the nepheline syenite. The development of copper as well as other secondary ore minerals and several generations of veins in the country rock, and the presence of hot springs probably indicate a continued hydrothermal activity in that area up to the recent times.

scholarly journals The Geology of the Rolwaling-Lapchi Kang Himalayas, East-Central Nepal: preliminary findings

1987 ◽  
Vol 4 ◽  
Author(s):  
Daniel Schelling
Keyword(s):  
Brittle Deformation ◽  
The South ◽  
Main Central Thrust ◽  
East Central ◽  
The North ◽  
Central Nepal ◽  
Main Boundary Thrust ◽  
Structural Discontinuity ◽  
Thrust Zone

Between the Tethyan sediments to the north and the Main Boundary Thrust to the south ten lithotectonic units have been identified in the Rolwaling-Lapchi Kang Himalayas and the Tamba Kosi region of east-central Nepal. These are (1) the Rolwaling Granites, (2) the Rolwaling Paragneisses, (3) the Rolwaling Migmatites, (4) the Alampu Schists, (5) the Khare Phyllites , (6) The Chagu-ChilangkaAugen Gneisses; (7) The Laduk Phyllites, (8) the Suri Dhoban Augen Gneisses, (9) the Rarnechap Group, and (10) the Mahabharat Crystallines. The Main Central Thrust (MCT) is a major lithologic, metamorphic and structural discontinuity separating the overthrust Higher Himalayan crystallines from the underthrust Lesser Himalayan metasediments. The Mahabharat Crystallines are an outlying klippe of Higher Himalayan rocks, underlain by the MCT, that has been thrust a minimum of 80 kilometers over the underlying Lesser Himalayan metasediments. Extending approximately 5 km below the MCT and 15 km above the MCT the Himalayas are a shear-thrust zone exhibiting ductile, brittle-ductile and brittle deformation as well as an inverted metamorphic sequence.

Deformation of the Archean Quetico–Shebandowan subprovince boundary in the Canadian Shield near Kashabowie, northern Ontario

1991 ◽  
Vol 28 (1) ◽  
pp. 116-125 ◽  
Author(s):  
Graham Borradaile ◽  
Robert Spark
Keyword(s):  
Strain Analysis ◽  
Canadian Shield ◽  
Vertical Position ◽  
Low Grade ◽  
Northern Ontario ◽  
Southern Boundary ◽  
The North ◽  
Shear Component ◽  
East West ◽  
Compressional Component

The southern boundary of the Quetico metasedimentary subprovince of the Superior Province of the Canadian Shield near Kashabowie, Ontario, is a vertical, east–west feature affected by dextral transpression that had a north-northwest – south-southeast compressional component. A synmetamorphic, locally D1 microfabric and magnetic-susceptibility fabric with an east-directed extension lineation is kinematically compatible with this pattern. It shows the same bedding–cleavage relationship and the same direction of structural facing on D1 in both the Quetico metasediments and the Shebandowan greenstone subprovince on the south side of the Quetico subprovince. In the low-grade rocks of the study area, there is a single phase of penetrative deformation, giving a nearly vertical schistosity at a consistent angle, anticlockwise with respect to the now nearly vertical east–west-striking strata. The absence of penetrative polyphase deformations may be due to the near parallelism of the subprovince boundary with the shear component of dextral transpression. Strain analysis indicates that the minimum shortening of the greywackes is 40% in a north–south direction. It is tentatively suggested that the shortening, the steepening of strata into a vertical position, and some of the S1 fabric development may have occurred prior to the climax of metamorphism and transpression. If this sequence is correct, the strata would have dipped gently to the north prior to the steepening event, with the embryonic schistosity dipping to the west.

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 Petrography of low-grade metamorphic rocks of the Lesser Himalaya from Malekhu area, central Nepal

2015 ◽  
Vol 3 ◽  
pp. 28-35
Author(s):  
Rajendra Acharya ◽  
Kabiraj Paudyal
Keyword(s):  
Metamorphic Rocks ◽  
Low Grade ◽  
Lesser Himalaya ◽  
Thin Sections ◽  
Rock Types ◽  
Central Nepal ◽  
Geological Unit ◽  
The Individual ◽  
Petrographic Study ◽  
Representative Samples

Petrographic study was carried out in the rocks of the Nawakot Group from the Malekhu area. Representative samples from all the units were collected systematically. The area is occupied by low-grade metamorphic rocks of the Lesser Himalaya. The main lithology of this study area consists of phyllite, quartzite, metasandstone, dolomite, slate and metabasics. The main aim of this study was to distinguish the individual rock types based on the petrographic characteristics. Necessity of this type of study is felt because about each geological unit has similar type of rocks. In the case of complex geological setting due to faults and thrusts, distinction between the macroscopically similar rocks is possible only under the thin sections. Keeping this geological problem in mind, altogether 12 thin sections of representative rocks were prepared and studied for mineral paragenesis, texture, microscopic structures, deformation characteristics and metamorphic grade. Chlorite is found in all pelitic rocks as a metamorphic index mineral.

scholarly journals Tourmaline chemistry in the metamorphic rocks of the central Nepal Himalaya

2002 ◽  
Vol 26 ◽  
Author(s):  
Santa Man Rai ◽  
Patrick Le Fort
Keyword(s):  
Hanging Wall ◽  
Low Grade ◽  
Structural Level ◽  
Nepal Himalaya ◽  
Central Nepal ◽  
Fe Content ◽  
Almost All ◽  
End Members ◽  
Host Rocks ◽  
Mg Content

Tourmaline occurs in various tectonic units of the Himalaya. It is found in almost all formations, from the Lesser Himalaya to the Tibetan-Tethys Sedimentary Series. They are also found in the Cambro-Ordovician granite of the Kathmandu nappe and Miocene leucogranites of the Higher Himalaya. The chemical composition of tourmalines from the central Nepal Himalaya is presented in schorlite (Fe)-dravite (Mg)­ elbaite (Al) diagram. The variation in chemistry of tourmaline in different types of rock is found to depend on the composition of the host rocks, the grade of metamorphism and the position in the structural edifice. The chemical results show that the Mg-rich tourmaline (dravite) is found to be concentrated in marble, calcic gneiss, whereas schorlite elbaite end members are found in the pelitic gneiss, mica schist, migmatitc, and quartzite, with little increase of elbaite content. The Lesser Himalayan tourmalines show a correlation between their chemistry and the grade of metamorphism of the host rocks. The Mg content of the tourmaline increases whereas Fe and Al contents decrease from chlorite to kyanite isograd. In the chlorite isograd rocks, the tourmalines are detritic in origin and are affected very little by the low-grade metamorphism. With increasing grade of metamorphism, the fluids rich in boron are mobilized in the schist and quartzite, and reacted with aluminium silicate associated elements resulting in the crystallization of the tourmalines. In the Higher Himalayan Crystallines, where the temperature remains constant and the pressures decreases upward in the hanging wall of the MCT, the composition of the tourmaline is found to be evolved with an increase of Fe content and decrease of Mg and Al contents in the higher structural level.

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