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 A preliminary engineering geological study in the northern part of the Taplejung Window, far eastern Lesser Nepal Himalaya

2004 ◽  
Vol 29 ◽  
Author(s):  
T. P. Gautam ◽  
D. R. Sonyok ◽  
B. N. Upreti ◽  
S. M. Rai ◽  
H. Sakai
Keyword(s):  
Hanging Wall ◽  
Agricultural Practices ◽  
Main Central Thrust ◽  
Rock Types ◽  
Valley Slope ◽  
Detailed Surface ◽  
Subsurface Investigation ◽  
Augen Gneiss ◽  
Bottom To Top ◽  
Far Eastern

In the northern part of the Taplejung area, two tectonic units are recognised. These are the Higher Himalayan and Lesser Himalayan Sequences separated by the Main Central Thrust (MCT). The Lesser Himalayan Sequence is exposed in the Taplejung Window represented by Taplejung Formation, Mitlung Augen Gneiss, and Lingkhim Schist from the bottom to top. The main rock types in the Lesser Himalayan Sequence are phyllite, schist, metasandstone, quartzite and augen gneiss. Three Proterozoic granitic bodies are intruded into Taplejung Formation: Tamor River Granite, Amarpur Granite and Kabeli Khola Granite. The rocks of the Higher Himalaya on the hanging wall of the MCT are composed of kyanite-sillimanite bearing banded gneiss, orthogneiss, migmatite, quartzite. Three major landslides in the area, viz., Hangdewa, Hireba, and Paire lie along the valley slope sides of the Tamor River. Stream erosion and incision, presence of highly weathered rocks, surface and subsurface drainage are responsible in activating the landslides. Due to the presence of mainly weathered phyllites, favourable structural orientations and wet cultivation practice in the area have contributed to the development of these landslides.  The Hangdewa and Hireba landslides have endangered the villages in between them and ultimately the Suketar airport. The landslides are gradually destroying more and more areas of cultivated land and property and increased loss of human lives. Excessive anthropogenic interference in the form of development activities like unplanned urbanization, deforestation and unfavorable agricultural practices have greatly aggravated the situation. The intensity of damages amplifies during the late part of monsoon each year. The study suggests that further detailed surface and subsurface investigation of the landslides are needed to prevent further loss of lives and property.

scholarly journals Mineral chemistry (biotite, muscovite, garnet, and plagioclase) in the Kathmandu and Gosainkund regions, central Nepal Himalaya

2004 ◽  
Vol 30 ◽  
Author(s):  
S. M. Rai ◽  
S. Guillot ◽  
B. N. Upreti ◽  
A. Pecher ◽  
P. Le Fort
Keyword(s):  
Granulite Facies ◽  
Mineral Chemistry ◽  
Systematic Variation ◽  
Main Central Thrust ◽  
Metamorphic Evolution ◽  
Nepal Himalaya ◽  
Central Nepal ◽  
Compositional Field ◽  
Southward Extension ◽  
Bottom To Top

The greenschist- to granulite-facies rocks in the Kathmandu and Gosainkund regions are divided into three tectonic units on the basis of structure, lithology, and metamorphism. The Gosainkund Crystalline Nappe (GCN) corresponds to the southward extension of the Higher Himalayan Crystallines (HHC), which thrusts over the Kathmandu Crystalline Nappe (KCN) along the Main Central Thrust (MCT). The GCN and KCN thrust over the Lesser Himalaya (LH) along the MCT and the Mahabharat Thrust (MT), respectively. Systematic traverses with the microprobe of four minerals (i.e. biotite, muscovite, garnet, and plagioclase) from all the three units were carried out to study their chemical variations. Most of the biotite compositions from all units belong to the annite compositional field. There is an inverse relationship between the Ti and the Mg number (Mg2+/ (Mg2++Fe2+) and the latter increases from the top to bottom section of the KCN. The LH biotites resemble the bottom composition of the KCN whereas the GCN biotite compositions are quite scattered. However, the Ti-Mg number trend does not seem to be related directly to the grade of metamorphism. The muscovites from the KCN are rich in FeO while the muscovites from other two units are rich in Al2O3. In the KCN, the almandine and pyrope contents in garnet decrease from bottom to top section, while the grossular and spessartine contents in garnet increase. This trend is consistent with the prograde metamorphic evolution observed in the field. The composition of garnets from the bottom to the top section of the GCN does not show any systematic variation, but in the upper section, where sillimanite appears, the almandine con tent decreases and the spessartine content slightly increases. This variation in composition suggests a polyphase metamorphic evolution. The albite content of plagioclase decreases from the lower to upper section in the KCN while there is not any systematic variation in the GCN. The P-T conditions record the good preservation of inverse metamorphism in the LH below the MCT. The comparison of P-T results between the KCN and the GCN suggests that exhumation of the KCN was followed by the exhumation of the GCN.

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 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).

Assessing Quaternary reactivation of the Main Central thrust zone (central Nepal Himalaya): New thermochronologic data and numerical modeling

Geology ◽  
2009 ◽  
Vol 37 (8) ◽  
pp. 731-734 ◽  
Author(s):  
X. Robert ◽  
P. van der Beek ◽  
J. Braun ◽  
C. Perry ◽  
M. Dubille ◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Main Central Thrust ◽  
Nepal Himalaya ◽  
Central Nepal ◽  
Thrust Zone

scholarly journals Geology of the Kharidhunga-Thokarpa area, Central Nepal, Lesser Himalaya

2001 ◽  
Vol 23 ◽  
Author(s):  
Ranjan Kumar Dahal ◽  
Prakash Chandra Adhikary
Keyword(s):  
Coarse Grained ◽  
Lesser Himalaya ◽  
Granitic Gneiss ◽  
Quaternary Deposits ◽  
Significant Control ◽  
Central Nepal ◽  
Geological Age ◽  
Augen Gneiss ◽  
Bottom To Top ◽  
Channel Deposits

In the Kharidhunga-Thokarpa area, the rocks of Lower Nawakot Group are exposed. The lowermost unit of the study area is the Kuncha Formation. It is composed of a more than 2,500 m thick monotonous sequence of grey to green phyllite, quartzite, and 'gritty' phyllite. Green-grey quartzite is seen in the upper part of the formation. Small (0.5 mm) garnets of brown colour occur in the upper part of the formation. The Fagfog Quartzite has a sharp contact with the underlying Kuncha Formation and consists of fine- to coarse-grained pure white quartzite with thin to very thin bands of grey and green phyllite. The Dandagaon Phyllite follows the Fagfog Quartzite and contains mainly thin bands of grey-green and dark grey phyllite. The Nourpul Formation is separated from the underlying Dandagaon Phyllite by a yellow quartzite band. The Nourpul Formation consists of dark grey carbonaceous slate and phyllite with some intercalations of calcareous phyllite and calcareous quartzite in the upper part. The augen gneiss, granitic gneiss, and banded gneiss are found within the Nourpul Formation mainly in the eastern part of the study area. The Dhading Dolomite overlies the Nourpul Formation and is found mainly around the Kharidhunga area as wavy and massive beds and lenses of dolomite, magnesite, and talc with sporadic quartzite bands. The rock is highly fractured and crystalline. The Pheda Khola and Ghane Khola Faults have a significant control on the landscape of the study area. The Quaternary deposits of the Kharidhunga area are classified into the Balephi, Thumpakhar, Dandapakhar, Bonch, Rolekharka, and Dangdunge Formations, respectively from bottom to top. Of which, the first two formations correspond to debris flow and river channel deposits, whereas the remaining ones represent the deposits of retreating glacier. Generally, the cohesion and plasticity of these sediments increases with their increasing geological age.

scholarly journals Lithostratigraphy and structure of the Dharan–Mulghat area, Lesser Himalayan sequence, eastern Nepal Himalaya

2016 ◽  
Vol 51 ◽  
pp. 77-78
Author(s):  
L. K. Rai ◽  
K. K. Acharya ◽  
M. R. Dhital
Keyword(s):  
Main Central Thrust ◽  
Nepal Himalaya ◽  
Microstructural Study ◽  
Main Boundary Thrust ◽  
Sharp Difference ◽  
Bottom To Top ◽  
Quartz Grains

The Dharan–Mulghat area of the eastern Nepal can be divided into three tectonic units: the Higher Himalayan Crystallines, the Lesser Himalayan Sequence and the Siwaliks from north to south separated by the Main Central Thrust (MCT) and Main Boundary Thrust (MBT), respectively. The Lesser Himalayan Sequence is divided into two groups separated by Chimra Thrust: the Bhedetar Group and the Dada Bajar Group. The Bhedetar Group includes the Raguwa Formation, the Phalametar Quartzite, the Churibas Formation, the Sangure Quartzite, and the Karkichhap Formation from the bottom to top, respectively; overthrusted by the Dada Bajar Group consisting: the Ukhudanda Formation, the Mulghat Formation, the Okhre Formation, and the Patigau Formation, from lower to upper sections, respectively along the Chimra Thrust and the Bhorleni Formation as an individual formation overthrusted by Bhedetar Group along the Chhotimorang Thrust. The Main Central Thrust, the Main Boundary Thrust, the Chimra Thrust and the Chhotimorang Thrust are the major faults in Dharan–Mulghat area. The Leutiphedi Anticline and the Malbase Syncline are the major folds in the study area plunging towards east. The trend/plunge of anticline and syncline are 131o/24o and 096o/09o respectively. The microstructural study in the quartz grains reveals a sharp difference in the history across the MCT; dynamic in the rocks of the Lesser Himalayan Sequences and static in the rocks of the Higher Himalayan Crystallines.

scholarly journals Thin-Skinned Tectonics of the Tansen-Pokhara Section, Central Nepal Himalaya

2015 ◽  
Vol 26 ◽  
pp. 15-28 ◽  
Author(s):  
Lalu Prasad Paudel
Keyword(s):  
Middle Miocene ◽  
Field Survey ◽  
Early Pleistocene ◽  
Tectonic Unit ◽  
Lesser Himalaya ◽  
Duplex Structure ◽  
Main Central Thrust ◽  
Nepal Himalaya ◽  
Central Nepal ◽  
Main Boundary Thrust

Geological field survey and structural analysis were carried out in the Tansen-Pokhara section of central Nepal in an attempt to unravel the thin-skinned tectonic geometry of the Lesser Himalaya. The Lesser Himalaya in the area forms a foreland-propagating duplex structure, each tectonic unit being a horse bounded by imbricate faults. The Upper Main Central Thrust and the Main Boundary Thrust are the roof and floor thrusts, respectively. The Bari Gad-Kali Gandaki Fault is an out-of-sequence fault. The Pindi Khola Fault is an antithetic back-thrust developed on the hangingwall of the Bari Gad-Kali Gandaki Fault, and the Kusma Fault is a splay-off of the Phalebas Thrust. Deformation of the Lesser Himalaya occurred in distinct three phases namely pre-Himalayan, Eohimalayan and Neohimalayan. The duplex structure was formed in the Neohimlayan stage in the period between Middle Miocene and Early Pleistocene. J. Nat. Hist. Mus. Vol. 26, 2012: 15-28

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