scholarly journals Geology along the Arniko Highway between Barabise and Kodari (China-Nepal Boarder) area, central Himalaya

2011 ◽  
Vol 42 ◽  
pp. 41-50
Author(s):  
Santa Man Rai
Keyword(s):  
Amphibolite Facies ◽  
Retrograde Metamorphism ◽  
Mica Schist ◽  
Lower Section ◽  
Main Central Thrust ◽  
Central Nepal ◽  
Pelitic Schist ◽  
Deformation Event ◽  
Augen Gneiss ◽  
Black Schist

The area between Barabise and Kodari in central Nepal along the Arniko Highway is geologically located into Higher Himalayan Crystallines (HHC) and Lesser Himalayan Sequence (LHS) that is separated by the Main Central Thrust (MCT). The HHC consists of amphibolite facies rocks (pelitic schist, psamitic schist, pelitic gneiss and quartzite), while LHS is comprised by green schist to amphibolite facies rocks (phyllite, calcareous phyllite, garnet-mica schist, black schist, quartzite and augen gneiss) in uppermost section and carbonate (dolomite and limestone) with phyllite, and metasandstone in lower section. The MCT in the area is oriented in E-W direction with about 30° dip due north and S-C structure preserved in augen gneiss of LHS characterizes the top-to-south sense of shearing, which could be related to the movement along the MCT. Mineral lineation marked by stretched mica indicates N to NNE direction in both HHC and LHS. Metamorphism of inverse grade from biotite at stratigraphically lower most section of Kuncha Formation to garnet at the uppermost section having schist and augen gneiss is obvious close to the MCT in the section. However, the Kuncha Formation contains tiny crystals of garnet in the rocks of greenschist facies. Kyanite and sillimanite isograds are developed in pelitic and psamitic schists, and pelitic schists appeared at the basal part of HHC above the MCT. The transformation of garnet to chlorite at the margin and fractures and formation of chlorite within bulk rocks of the MCT zone and HHC are the indicators of traces of retrograde metamorphism because of dropping in pressure-temperature probably related to post deformation event.

scholarly journals Early Proterozoic granite of the Taplejung Window, far eastern Lesser Nepal Himalaya

2003 ◽  
Vol 28 ◽  
Author(s):  
B. N. Upreti ◽  
S. M. Rai ◽  
H. Sakai ◽  
D. R. Koirala ◽  
Y. Takigam
Keyword(s):  
Alkali Feldspar ◽  
Main Central Thrust ◽  
Triangular Diagram ◽  
Nepal Himalaya ◽  
Central Nepal ◽  
Marginal Part ◽  
Normative Quartz ◽  
Augen Gneiss ◽  
Bottom To Top ◽  
Far Eastern

The Lesser Himalayan Sequence of the Taplejung Window in the far eastern Nepal Himalaya can be divided into Taplejung Formation, Mitlung Augen Gneiss and Linkhim Schist (from bottom to top respectively). The window is a large domal shaped anticline plunging to the east. Two-mica granite bodies (Amarpur Granite, Kabeli Khola Granite and Tamor River Granite) have intruded the metasediments of Taplejung Formation. The granite bodies are discordant to subconcordant in relation to the country rocks. Quartz, alkali feldspar, plagioclase, muscovite, biotite and tourmaline are the main constituent minerals of the granite. Generally, the core of granite bodies is undeformed, whereas the marginal part is gneissfied with S-C mylonitic texture showing the top to south sense of shear. This sense of shear is related to the movement along the Main Central Thrust (MCT). All the samples from the granitic bodies fall under the granite field in the normative quartz-alkali feldspar-plagioclase (QAP) triangular diagram. The mineral composition shows that the granite is peraluminous in nature. The Kabeli Khola Granite has yielded a 40Ar/ 39Ar muscovite age older than 1.6 Ga indicating its magmatic age. The granites of the study area can also be correlated with the 1.8 Ga Ulleri type augen gneiss of central Nepal.

scholarly journals Zinc-Lead mineralisation in Ganesh Himal region of central Nepal

1982 ◽  
Vol 2 (1) ◽  
Author(s):  
C. K. Chakrabarti
Keyword(s):  
Host Rock ◽  
High Grade ◽  
Dolomitic Limestone ◽  
Mica Schist ◽  
Main Central Thrust ◽  
Central Nepal ◽  
The Himalaya ◽  
Simple Nature

High grade mineralisation of zinc and lead sulphides occur near the Main Central Thrust (MCT) Zone of the Himalaya in the lower regions of Ganesh Himal Range in Nepal. The host rock is crystalline dolomitic limestone showing tremendous flow in a highly folded sequence of garnetiferous mica-schist, quartzites, calcareous schists, and bands of hornblende gneiss. The stratigraphic control and the simple nature of mineralisations suggest a syn-sedimentary genesis.

scholarly journals Characteristics and field relation of Ulleri Augen Gneiss to country rocks in the Lesser Himalaya: A case study from Syaprubesi-Chhyamthali area, central Nepal

2019 ◽  
Vol 58 ◽  
pp. 89-96
Author(s):  
Jharendra K.C. ◽  
Kabi Raj Paudyal
Keyword(s):  
Geological Mapping ◽  
Lesser Himalaya ◽  
Main Central Thrust ◽  
Nepal Himalaya ◽  
Field Relation ◽  
Central Nepal ◽  
Thrust Zone ◽  
Augen Gneiss ◽  
Host Rocks

The distribution of Ulleri Augen Gneiss and its origin in the Lesser Nepal Himalaya adjacent to the Main Central Thrust zone is stilla debate among the geo-scientists. Geological mapping was carried out along the Syaprubesi-Chhyamthali area of central Nepal with the aim to study the field relation, distribution, deformation and metamorphism of the Ulleri Augen Gneiss. During mapping, close traverses were set to observe the field relation and a number of systematic samples were collected for analysis of composition and texture. Some preliminary findings were obtained related to its geological position and distribution. This gneiss is hosted within the Kuncha Formation, the oldest unit of the Nawakot Group in the Lesser Himalaya. It has been evolved within this unit as a tabular form in some places and lenses in other places. It shows both concordant (i.e., sill type) and discordant (i.e., dike type) relationship with the host rock. It is characterized by augen-shaped porphyroblasts of K-feldspar and S-C mylonitic texture showing top to the SW sense of shear. The S-C structures and lineated textures shown by the minerals are associated with the shearing caused by the movement along the MCT during the syn-MCT metamorphic deformation. It is characterized in different types of lithologies such as augen gneiss, banded gneiss and two-mica gneiss. An attempt is made to explain the petrological characteristics and field relation of the Ulleri Augen Gneiss with the host rocks along with structural aspects. Based on the field relation and texture analysis, the evolution of the protolith of this Ulleri Augun Gneiss can be interpreted as a multi-story emplacement within the host rocks during and immediately after the sedimentation.

scholarly journals Geology, geochemistry, and radiochronology of the Kathmandu and Gosainkund Crystalline nappes, central Nepal Himalaya

2001 ◽  
Vol 25 ◽  
Author(s):  
Santa Man Rai
Keyword(s):  
Granulite Facies ◽  
Tectonic Block ◽  
Lesser Himalaya ◽  
Main Central Thrust ◽  
Nepal Himalaya ◽  
Magmatic Origin ◽  
The North ◽  
Multidisciplinary Study ◽  
Central Nepal ◽  
Augen Gneiss

A multidisciplinary study was carried out in the Lesser Himalaya (LH), the Kathmandu Crystalline Nappe (KCN) and the Gosainkund Crystalline Nappe (GCN) in central Nepal Himalaya. Two principal deformations are recorded in both the crystalline nappes and the Lesser Himalaya: ductile, syn-MCTor syn-MT metamorphic deformation marked by microstructures (stretching lineation, S-C structures, and isoclinal folding) and post-MCT/or post-MT metamorphic deformation recorded by a major EW-directed Likhu Khola anticline and by NNE-SSW-directed folds. The Upper Lesser Himalayan rocks close to the Main Central Thrust (MCT) record syn-MCT metamorphic conditions at 750 MPa and 566 °C. The rocks of the KCN record P-T condition from 900 to 720 MPa and 700 to 484 °C, while the GCN rocks were equilibrated at upper amphibolite- to granulite-facies conditions from 890 to 583 MPa and 754 to 588 °C. The P-T conditions and field observations exhibit well-preserved inverted metamorphism between the Upper Lesser Himalaya and the Gosainkund Crystalline Nappe. The augen gneisses from the GCN yielding 486±9Ma U-Pb zircon age and the granites of similar age in the KCN bear similar petrographic and geochemical characteristics and suggest a similar magmatic origin although they belong to different tectonic units. The chemical analyses of the Proterozoic Ulleri augen gneiss of the LH and the granites of the KCN fall within the same compositional field, indicating a magmatic origin of these augen gneisses. 40Ar/39Ar datings on muscovite indicate cooling ages younging systematically from south to north: 22 to 14 Ma in the KCN, 16 to 5 Ma in the GCN, and 12 to 6 Ma in the LH. This systematic younging of muscovite ages does not have any correlation with the present elevation, lithology and tectonic unit and is interpreted as a result of the exhumation of the rock units on the Main Himalayan Thrust (MHT) ramp situated to the north of Kathmandu Valley. Both the KCN and the GCN record a late emplacement history, but the KCN was exhumed earlier than the GCN. The two crystalline nappes presently form a single tectonic block, and the combined uplift of the two nappes occurs on a ramp of a major decollement developed in the upper part of the Indian crust.

scholarly journals Lithostratigraphy of the Nawakot Complex (Lesser Himalayan Sequence) from Malekhu area (south-west) to Syabrubensi area (north-east) along the Trishuli River, central Nepal Himalaya

2011 ◽  
Vol 42 ◽  
pp. 65-74
Author(s):  
Santa Man Rai
Keyword(s):  
Amphibolite Facies ◽  
Kathmandu Valley ◽  
Main Central Thrust ◽  
Nepal Himalaya ◽  
North East ◽  
Central Nepal ◽  
South West ◽  
Facies Metamorphism ◽  
Area North ◽  
Stratigraphic Sequences

All formations (Kuncha Formation, Fagfog Quartzite, Dandagoan Phyllite, Nourpul Formation, Dhading Dolomite of the Lower Nawakot Group and Benighat Slate, Malekhu Limestone and Robang Formation of the Upper Nawakot Group) of the Nawakot Complex are well exposed along the Malekhu-Thopal Khola and Galchi - Kaljeri section s, west of the Kathmandu Valley. The Phalangu Khola and Syabrubensi sections, north of the Kathmandu Valley do not show the exposures of all formations (exposures of the Kuncha Formation, Fagfog Quartzite, and Benighat Slate only). The stratigraphic sequences from the Kuncha Formation to Dhading Dolomite (Lower Nawakot Group) along the Malekhu-Thopal Khola section are overturned, showing the younging strata to the deeper sections shown by the sedimentary structures (ripple marks, mudcracks, etc.) and stromatolites. The se overturned sequences could be related to the development of the post Main Central Thrust (MCT)/Mahabharat Thrust (MT) deformational structure (Gorkha - Pokhara anticlinorium, Likhu Khola anticline). The stratigraphic sequences are normal in the formations of the Upper Nawakot Group along the Malekhu-Thopal Khola section. This normal sequence can be also observed along the Galchi - Kaljeri, Phalangu Khola and Syabrubensi sections. In the northern part of the study area along the Likhu Khola, Tadi Khola, Phalangu Khola and Syabrubensi sections, the rocks of the Benighat Slate just below the MCT are highly sheared, deformed, metamorphosed with the development of the garnet and staurolite (medium amphibolite facies metamorphism) due to the movement of the MCT. However, these minerals are not developed in the Robang Formation (immediate below the MT) along the Malekhu-Thopal Khola and Galchi - Kaljeri sections. This formation could be caused by shallow depth metamorphism (green-schist to lower amphibolite facies) along the movement of the MT.

scholarly journals Geology and structure of the main central thrust zone of the annapurna range, central Nepal Himalayas

1982 ◽  
Vol 2 ◽  
pp. 31-50
Author(s):  
Takashi Kano
Keyword(s):  
Thrust Fault ◽  
Main Central Thrust ◽  
The Third ◽  
Tectonic History ◽  
Central Nepal ◽  
Thrust Zone ◽  
Mode Of Occurrence ◽  
Three Stages ◽  
Augen Gneiss

The present paper describes the geology, structure, tectonic history and petrographical feature of lithologic constituents of the region around (MCT) zone. The report area is lithologically divided into four geologic units; the Midland zone, the MCT zone, the himalayan gneiss zone and the Tibetan Tethys zone. The MCT zone is distinguished by the lower augen gneiss zone, (MCT-2) and the upper thrust fault (MCT-1). Three stages of deformations are recognized in the area: the first, the two sets of widespread foldings with striation-like forms, which are comparable to the southwards thrusting of MCT; and the third, latest upwards movement of the Higher Himalayas. Mode of occurrence and petrographical feature of augen gneisses suggest close genetical relations with the movements of MCT and/or the activity of younger turmaline granites.

scholarly journals Distribution of boron in the rocks of central Nepal Himalaya

2003 ◽  
Vol 28 ◽  
Author(s):  
Santa Man Rai
Keyword(s):  
Partial Melting ◽  
Boron Content ◽  
Lesser Himalaya ◽  
Main Central Thrust ◽  
Nepal Himalaya ◽  
Metasedimentary Rocks ◽  
Central Nepal ◽  
Very High

Boron content in the rocks of central Nepal Himalaya depends upon the lithology and the grade of metamorphism. The concentration of boron is abundant (up to 322 ppm) in the metasedimentary rocks of the Lesser Himalaya. There seems to be a rather good correlation between the boron content in the rocks and the grade of metamorphism. The boron content progressively increases from chlorite to garnet isograds, then it systematically decreases in the staurolite±kyanite, kyanite and sillimanite isograds, respectively. This trend may be related to the inverse metamorphism associated with movement along the Main Central Thrust. The Manaslu leucogranite contains very high amount of boron (950 ppm). The enrichment of boron in this rock may be due to the release of boron from the Lesser Himalayan rocks during the partial melting of the Higher Himalayan Crystallines (Tibetan Slab) as a result of the movement along the MCT. Tourmaline from the Manaslu Granite is also highly rich in boron (8460 ppm).

scholarly journals Himalayan and Trans Himalayan granitic rocks in and adjacent to Nepal and their mineral potential

1981 ◽  
Vol 1 (1) ◽  
Author(s):  
A. H. G. Mitchell
Keyword(s):  
Root Zone ◽  
Porphyry Copper ◽  
Tectonic Setting ◽  
Granitic Rocks ◽  
Main Central Thrust ◽  
Southern Tibet ◽  
Late Mesozoic ◽  
The North ◽  
Augen Gneiss ◽  
Host Rocks

Granitic rocks occupying eight distinct tectonic settings can be recognized in the Himalayas and   Transhimalayas.  In the Lower Himalayas geographical belt a few plutons of two-mica granite intrude the lowest unit of the Nawakot Complex or Midland Group. More extensive are sheet- like lies of augen gneiss intrusive within a possibly thrust bounded succession carbonates and graphitic schists beneath the Main Central Thrust to the north. The most abundant granites in the Lower Himalayas are the two- mica cordierite- bearing granite within klippen; minor tin and tungsten mineralization is associated with these plutons, which are of late Cambrian age. Within the Higher Himalayas above the Main Central Thrust, the ‘Central Crystallines’ or Central Gneisses include pegmatites and pegmatitic granites intrusive into gneisses of probable early Proterozoic age; these have same potential for ruby, sapphire, aquamarine and possibly spodumene. Further north within the Higher Himalayan succession a southern belt of anatectic two- mica granites and leucogranites of mid-Tertiary age is favorable for tin, tungsten and uranium mineralization; a northern belt of granites or gneisses is of uncertain age and origin. North of the Indus Suture in the Transhimalayas extensive batholiths of hornblende granodiorite representing the root zone of a late Mesozoic to early Eocene volcanic arc are associated with porphyry copper deposits. Further north in southern Tibet the tectonic, setting for reported granitic bodies of  Tertiary  age  is  uncertain; their location suggests that they could be favorable host rocks for tin, uranium and porphyry molybdenum mineralization.

Paleomagnetism of the Flin Flon – Snow Lake Greenstone Belt, Manitoba and Saskatchewan

1975 ◽  
Vol 12 (8) ◽  
pp. 1272-1290 ◽  
Author(s):  
J. K. Park
Keyword(s):  
Greenstone Belt ◽  
Amphibolite Facies ◽  
Retrograde Metamorphism ◽  
General Direction ◽  
Thermoremanent Magnetization ◽  
Flin Flon ◽  
K 12 ◽  
Very High

The Flin Flon – Snow Lake greenstone belt is of Archean or Aphebian age and has been metamorphosed to greenschist or low amphibolite facies during the Hudsonian orogeny. It contains four rock units — the Amisk Group, the Missi Group, metadiorite and metagabbro bodies, and the Boundary Intrusions. The rocks contain two main magnetizations, an early B magnetization and a later A magnetization. Both magnetizations contain reversals. The A magnetization (43 sites, direction 168°, +73°, k = 17, α95 = 5°, pole 24°N, 095°W) is found in all rock units. It can be divided into three parts (1, 2 and 3) which have the same general direction, but which are significantly different from one another. It is suggested that A1 is a viscous partial thermoremanence (vptrm), and A2 possibly a chemical remanence (crm). Both are considered to have been acquired during uplift (1600–1700 m.y.) following the Hudsonian orogeny. A3 is possibly a crm acquired during late fault movements and appears to be carried by hematite developed during retrograde metamorphism. A3 is considered to be about 1600 m.y. old. The B magnetization (7 sites, 129°, +04°, k = 12, α95 = 18°, pole 20°S, 046°W) occurs in all rock units except the Missi. It is particularly well developed in the Boundary Intrusions where it is considered to be a primary thermoremanent magnetization (trm). In other rock units B is considered to be a vptrm acquired during heating at the time of emplacement of the Boundary Intrusions. The B magnetization is considered to be about 1800 m.y. old. Some enigmatic magnetizations with very high blocking temperatures above 700 °C were observed. Formulas for calculating the coercivities in rocks with more than one magnetization are given.

scholarly journals Weathering and erosional processes within the landslide deposit of Jarlang (Ganesh Himal), central Nepal

1997 ◽  
Vol 15 ◽  
Author(s):  
C. F. Uhlir ◽  
J. M. Schramm
Keyword(s):  
Mass Wasting ◽  
Rock Falls ◽  
Fine Grained ◽  
Himalayan Orogeny ◽  
Initial Event ◽  
Central Nepal ◽  
Main Scarp ◽  
Triggering Factor ◽  
Augen Gneiss ◽  
Landslide Deposit

Within the southern flanks of the Ganesh Himal in central Nepal, an area of complex landslides lies in the Jarlang area, situated at the southeastern slope of the Ankhu Khola valley. Slow rotational rockslide in deeply weathered micaceous quartzites interlayering with mica schists have destabilized the head scarp composed of augen gneiss. It caused rockslides from the main scarp generating big spread-out landslides. The landslides of Jarlang generated a stratified deposit (> 106 m3) of matrix-poor breccias with thin fine grained shear horizons. The initial event for the biggest gully system in central Nepal was a gravitational slump owing to nine, day heavy rainfall in 1954. The recent processes within these colluvial deposits are torrential gully erosion accompanied by successive rotational and translational slides along the gully margins. The high activity within the Jarlang gully system can be explained by reactivation of the old Jarlang landslide's shear horizons. The slide grew from an original width of 300 m to 1.2 km at present, covering an area of 2.68 km2. The total volumetric loss by 1996 is l.46xl08 ml. The triggering factor for rock slides and rock falls generating big spread out landslides and debris slides and slope undercutting is seismic events due to extremely high uplift of the Himalayan Orogeny. The strong influence of human activities on slope stability and mass wasting as proposed in the Himalayan Environmental Degradation Theory can not be validated.

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