Geoiogy Along the Amiko Highway Between Barabise and Kodari (China-Nepal Boardar) Area, Central Nepal Himalaya
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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/285328933 Geology along the Arniko Highway between Barabise and Kodari (China-Nepal Boardar) area, central Nepal Himalaya Article · April 2011 CITATIONS READS 4 601 1 author: Santa Man Rai Tribhuvan University 66 PUBLICATIONS 1,074 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: The subduction and exhumation of the continental lithosphere: their effects on the structure and evolution of the orogens View project Climate change impact on glacial retreat of Langtang Lirung Glacier and Kimjung Glacier View project All content following this page was uploaded by Santa Man Rai on 07 January 2017. The user has requested enhancement of the downloaded file. Jo"mal Qf Ndyal Geological Society, 2011, Wl. 42, PP. 41-50 GeoIogy along the Amiko Highway between Barabise and Kodari (China-Nepal Boardar) area, Central Nepal Himalaya Santa Man Rai Department 4‘ Geology舟i一αand朋Cdmp〃S, 7J砂庇van切訪versi砂 Ghantaghar; Kdthmand均Nとpal ( *Email: SanJaman_mi201 0 @yahoo. com) ABSTRACT The area between Barabise and Kodari in central Nepal along血e Amiko Highway lS geOIogically located into Higher Himalayan Crystallines (HHC) and Lesser Himalayan Sequence (LHS) that is separated by the Main Central T山sut (MCT). The HHC consists of amphibolite facies rooks (Pelitic schist, PSamitic schist, pelitic gneiss and quartzite), While LHS is compri§ed by greenschist to anphibolite facies rocks (Phyllite, Calcaresous phyllite, gameトmica schist, black schist. quartzite and augen gneiss) in uppemost section and ca血onate (doIomite and limestone) with phyllite, and metasandstone in lower section. The MCT in血e area is oriented in E-W direction with about 300 dip due north and S-C struc筒町e PreServed ln 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 hoth HHC and LHS. Metanorphism of inverse grade from biotite at stratigraphically lowemost section of Kuncha Fomation to ganet at the uppemost section having schist and augen gneiss is obvious cIose to the MCT in the section. However,血e Kuncha Fomation contains tiny crystals of gamet in the rocks of greenschist facies. Kyanite and sillimanite isograds are developed in pelitic and psamitic schists, and pelitic schists appeared at the basal pan of HHC above the MCT The transfomation Of ganet to chlorite at the margin and fractures and fomation of chlorite within bulk rocks of the MCT zone and HHC are the indicators of traces of retrograde metamorphism becau§e Of dropping in pressure-temPerature Probably related to post deformation event. Keywords: Le§Ser Himalayan Sequence, MCT zone, Higher Himalayan Crysrallines, Central Nepal Recieved: 28 January 201 l revi§ion accepled: 13 May 201 1 INTRODUCTION been worked out by St6cklin and Bhattarai (1977), St6cklin (1980), Upreti and Rai (2000), Duvadi et al. (2005, Fig. 2) and In central Nepal, the Nawakot Nappe consisting of low- Pradhanaga and Duvadi (2006). Tb the westem and eastem grade metamorphic rocks overlain by medium to high-grade COntinuation of the area were investigated in detail, metamophic rocks of the Kathmandu Nappe was firstly respectively, by Arita et al. (1973), St6cklin and Bhattarai recognized by Hagen (1969). The Nawakot Nappe (1977), Rai (1998, 2001), Dhital et al. (2001), and Maruo et al. COrreSPOnds to Lesser Himalayan Sequence (Nawakot (1973). Complex of St6cklin and Bhattarai 1977) and Kathmandu Nappe is conelated to the Higher Himalayan Crysta11ine GEOLOGICAL SETTING (Kathmandu Complex and undi能鵜ntiated gneiss of St6cklin and Bhattarai 1 977; Kathmandu and Gosainkund Crystalline The study area is divided into two units: Higher nappes (Rai 1998; Rai et al. 1998; Upreti and Le Fort 1999; Himalayan Crystalline§ (HHC) and Lesser Himalayan Rai 2001 )). The Mahabharat ¶1rSut (MT), a major thru§t fault Sequences (LHS) separated by the MCT (Fig. 3). The LHS is SeParateS the Nawakot Complex and血e Kathmandu Complex named as Nawakot Complex (St6cklin and Bhattarai 1 977). and is considered as a southward continuation of the Main Central Thmst (MCT) (St6cklin 1980; Pandey et al. 1995; Johnson et al. 2001). The MCT is the tectonic boundary Higher Himalayan Crysta軸ines and仙e MCT Zone between the Higher Himalayan Crystallines (HHC) and the The rock sequences of HHC and LHS strike in NWW- Lesser Himalayan Sequence (LHS). SEE direction with a dip varying from 150 to 400. The MCT is a maJOr Syn-tO POSt COllisional thrust fault extending The present study focused along the Amiko Highway throughout血e Himalaya (Gansser 1964; Le Fort 1 975; Pecher between Barabise and Kodari villages of central Nepal is 1989). In central Nepal, tWO thrusts (MCT and MC丁I; Arita geoIogically situated in the Lesser Himalayan Sequence and 1983) bound a ductile shear zone (i. e., uPPer Lesser the Higher Himalayan Crystallines (Fig. 1 ), Which has also Himalaya). AIong Dudh Koshi VA11ey, Everest region, the 41 Santa Mbn Rai 青も) 二 事Nl)lA lいo葛」 (判!NA l団i)IA ¥-丁 ヽ- 、 「、…- ∈≡ヨ廿ヽ暗証所用) 一博…自画…叩。刷、園=一冊、伸町子▲ 百両、l 「二コ出帆高時--pl鉦、凧、I霊日朝間、、畑~、 --∴∴ヽ=町 して ー」/、 ¥、¥-く、「、置「〆胴高 田囲うハ、ぐ‖帥uI時-富-ノ川ヾ 麗窮白日小柄,…血 一へ〉〆し葦へl 書書冊十、、小出-剛叩章・ ∴距事:;用理帥 慰惣口演時間一両、-・出、- 田圃五、、年間--、仙当 ・川高点、立川…ぐ機甲}甲、 朝嬉詳)幻11当、、=帖。 同 い、-・同一服l正・一 川口恒h・、川向…吊・・ 富、詳言両面…‖高車、ヽJ用-ぐ∩ト ヽ出自∴ ¥1用吊信用l証宣子¥同…、1 ヽ件 ヽ1」h.1軸.I畑‖ h…、i ¥1了i ヽ1」自主引用捕∴手間小! 、言問¥ ¥、、1両I自広く.周「k喜、物hnl小用上I吊l ヽヽ、l、、。l 仁《- 一 己超 Fig. 1: GeoIogicaI map of Nepal (Upreti and Le Fort 1999) MCT corresponds to the contact between the Greater boundary between two differen=ithoIogies can be Himalayan Crysta11ine gneisses and the upper Lesser considered as the Main Central Th]田St, however, the e鯖ect Himalaya pelitic schists, Whereas the MCTI separates the Of shearing can be seen in the augen gneiss or upper section mylonitic Phaplu augen gneiss from low-grade Lesser Of the LHS and the psamitic or pelitic schists of the HHC Himalayan metasedimentary rocks (Catlos et al. 2002). In the above the MCT. The present study shows tha=he Study area, the MCT zone produces a simple monoclinal OCCurrenCe Of highly mylonitized coarse grained augen StruCture trending E-W and dips about 300N. Thickness of gneiss could be Ulleri type Lesser Himalayan granite. Such the MCTzone is 150m and is divided intoMCTl and MCT Ulleri type augen gneiss can be observed just below the 2 around the鴫topani Village (Pradhananga and Duvadi MCT along Tbdi Khola, Phalangu Khola, Langtang Khola 2006). According to St6cklin and Bhattarai ( 1 977), the MCT north ofShivapuri Range (Rai et al. 1998; Rai 1998, 2001). In PaSSeS at the to:) Of the augen gneiss very cIose to Thtopani fact, the augen gneiss with pelitic schist belongs to the MCT Bazaar, SOuth of Kodari (Fig. 3). Above the MCT two rock ZOne. In the HHC, the rocks are essentially kyanite-gameト units namely I-喜adi Khola Schist on the upper section and biotite bearing pelitic schist to psamitic schist, kyanite-Pelitic Dhad Khola Gneiss on the upper section belonging to the gneiss with subordinate quartzite (Figs. 4a to D・ These rocks Higher Himalayan Crystallines are divided. These two units can be correlated with the Formation I of Tibetan Slab (Le are separated by a thrust. The zone between MCTl and For[ 1975) or Gosainkund Crystalline Nappe (Rai 1998, 2001 ; MCT2 is named as Hadi Khola Schist consisting ofgamet- Rai et a= 998). bioite schist, Calcareous schist with quartzite and gneiss band§. Dhad Khola Gneiss is consisting of porphyroblastic Lesser Hima獲ayan Sequence gneiss, augen gneiss with quartzite and schist (Duvadi et al. According to St6cklin and Bhattarai ( 1977) and St6cklin 2005; Pradhanaga and Duvadi 2006). Marou et al. ( 1 973) have ( 1 980) the rocks along the Amiko Highway between Barabise also mapped the contact (MCT) between the Higher and冊topani belong to Nawakot Complex (Figs. 2 to 4). The Himalayan Crysta11ines (their Himalayan Gneiss Zone) and Nawakot Complex have been subdivided into Lower and the Midland Metasediments Group (Lesser Himalayan Upper Nawakot groups separated by an erosional Sequence) south of Kodari near冊topani Village. Pelitic unconformity (?) (St6cklin and Bhattarai 1977)・ The SChists having few fine-grained kyanite crystals appear on PreSent Study follow the stratography prepared by Stooklin top of the highly sheared augen gneiss (Fig. 3). This Bhattami ( 1977). 42 Geo/ogy a/ong fhe A朋iわHighway between Ba朋bise qnd Ko証すri (αina-N印al Boar加r) aタでa 寄 羊 蹄 」e寄合n寄 」的辛口高所高く部か飢Iや 国師崎山時持 田岨甲南I調細物 田〔〇・帥…時1機・ 日干登壇和雄酔 †田 Fig. 2: GeoIogical map of Sindhupalchok District, Central Nepal (Duvadi et al. 2005) 上ower Ndwa鳥ot Gタの岬 In the type locality, the Kuncha Fomation is overlain by Fagfog Quartzite consisting of coarse to fine grained white The Lower Nawakot Group is the oldest formation quartzite with frequently developed ripple and current perhaps of the entire Lesser Himalaya of Nepal・ Kuncha bedding (St6cklin 1 980). The overlying Dandagoan Phyllite Formation is the base of the group, Whose base is not is comprised by green-gray Phyllite, Which is darker in coIor exposed anywhere. The lower section of the formation than the Kuncha Formation. Thin layers of doIomite and COnSists of a monotonous sequence of flysch-1ike altemating Calc-Phyllite appear first time in this sequence. The Phy11ite, Phy11itic quartzite and phyllitic gritstone. Strikingly, Dandagoan Phyllite passes upward to the Nou呼ul Fomation Carbonate rock is missing except as cementing materials in having a mixed lithoIogy of thinly banded purple slate, SOme Sandstone. The phyllite shows silky luster and Calcareous metasandstone and frequent intercalations of yellowish, blue-gray tO green-grey COIor. The phyllitic thick quartzite. Along the Kodari Highway these formations gritstones contain opal like milky-gray Or bluish quartz, Which are not well represented (Fig.