Manaslu granite

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The Manaslu granite is a Miocene leucogranite in Nepal , of the peak area of the Manaslu ( Nepalese language मनास्लु - 8163 m) and constituting together with a dozen other intrusions to the Leukograniten the high Himalaya is expected.

Geological introduction

Geological overview map of the Himalayas, in black the leuco granites. The Manaslu granite is located in the northwest of Kathmandu .

The collision of the northern passive continental margin of the Indian plate with the active southern continental margin of Eurasia (consisting of the Karakoram in the west and the Lhasa block in Tibet ) began in the Paleocene and has continued to this day. The consequence was the closure of the Tethys , whose last marine sediments along the Indus-Yarlung-Tsangpo suture are exposed and date from the early Eocene . They are 50.5 to 49 million years old. As a result of the collision, crust narrowing (imbrications), metamorphosis and partial melting occurred, combined with folding , shearing and sliding of ceiling systems in a southerly direction over the north Indian continental margin. The constant advancement of India northwards into the Eurasian continent resulted in a doubling of the crust thickness to 70 kilometers both below the Himalayas and below the Karakoram-Lhasa block. The Tibet Plateau was created, the largest high plateau on earth with heights of over 5000 meters.

Drift of the Indian (sub) continent in the course of the Cenozoic

The Himalayan orogen is made up of five more or less parallel lithotectonic belts:

  • the Transhimalayan batholith in the north (red)
  • the Indus-Yarlung-Tsangpo-Sutur zone (green)
  • the Tethyalen High Himalayan sediment sequence (light blue)
  • the metamorphic Greater Himalaya Sequence (orange)
  • the front Himalayas in the south (yellow)

The upper crust of the Tethys Himalaya consists of 10 to 12 kilometers thick, folded and overturned sediments of the Phanerozoic ( Ediacarium to Eocene ) - referred to in English as the Higher Himalayan Sedimentary Series ( HHSS - High Himalayan Sediment Series ). They are cut off in the north by the Indus-Yarlung-Tsangpo-Suture and to the south find their end in the flat shear horizon of the South Tibetan Detachment System (abbreviated STDS - South Tibetan Shear System ) with top to the north as a sense of movement. To the south of this is the Greater Himalayan Sequence ( GHS ) , which is up to 15 kilometers thick - metamorphic rocks of the Barrow type, migmatites and leukogranites. Their stratigraphically deepest metapelites ( Kuncha-Pelit ) are somewhat older than 1830 million and thus come from the Proterozoic . The GHS ends to the south in a 2 to 4 kilometer thick zone with reversed metamorphic isogrades that reach back from the sillimanite-thistle zone to the biotite-chlorite zone. At the base there is a ductile thrust zone with the top to the south as a sense of movement, the Main Central Thrust ( MCT - central main thrust ). The Front Himalaya ( Lesser Himalaya ) lying south in front of it contains rocks from the Indian Plate, including Proterozoic basement and Paleozoic deck sediments of relatively small thickness. The Himalayan orogen ends with the two thrust systems of the Main Boundary Thrust and the Main Frontal Thrust in the northern foreland of Pakistan and India . The lower crust of the Himalayas, which is nowhere exposed, is probably composed of granulite facial shield rocks of India.

The leukogranites of the High Himalayas (English High Himalaya Leucogranites or abbreviated HHL ) form an interrupted belt around 1900 kilometers in length, which extends from northern Pakistan ( Zanskar ) to Bhutan . A dozen Plutone and numerous smaller layer body and sticks overlie the crystalline rocks of Higher Himalayan Crystal Lines ( HHC - high Himalaya crystallin, or also Greater Himalayan Cristallines - GHC or Greater Himalayan Sequence - GHS ) consisting of marbles , calcsilicate rocks, metapelites and eyes gneiss . The plutons intrude below the metasediments of the HHSS, which represent the former, now tectonically displaced sediment cover of the crystalline. The larger leukogranite bodies occupy a structurally uniform position in the upper section of the GHC (in the migmatitic sillimanite alkali feldspar zone) and are always below the STDS. Law and colleagues (2004) seen in the STDS a passively stretching shearing below which a ductile extrusion of the GHC middle crust (Engl. As channelized flow movement Channel Flow ) in combined Couette and Poiseuille flow took place to the south. This channel flow model sees in the GHC a channel-like area inclined slightly to the north, the middle crustal material of which was pressed 80 to 100 kilometers to the south or viscous from the thickened southern edge of the Tibet plateau towards the thinner fold and thrust belt in the north Indian foreland drained.

The contact of the leuco granite with the STDS and the covering sediments of the Triassic and Jurassic is beautifully opened up at the Larkya La pass north of Manaslu.

description

Manaslu (left) and then on the right Ngadi Chuli and Himalchuli

The Manaslu granite is a lenticular body, 5 to a maximum of 10 kilometers thick, a laccolith that slopes gently to the north-northeast. However, it is not a classic diapir , but rather a table-like, strongly inflated warehouse corridor . At its southeast end, it sends an approximately 60-kilometer-long side arm, the Chhokang Arm , to the east, which runs parallel to the Chame Thrust , a dextral ductile shear zone, located within the GHC . On the map, the leuco granite, covering around 400 square kilometers, appears as a rectangle stretched to the southeast, around 30 kilometers long and 13 kilometers wide (with a length / width ratio of 2.3). The summit structure of the 8,163 meter high Manaslu is located at the southeast end of the intrusion and consists entirely of leuco granite.

The intrusion took place in an anticline structure of the Tethyalen metasediments tilted to the north , the base of which is cut off by the STDS. The STDS is dominated by pure shear, but also contains very shallow dipping faults with an offset to the north. With the Phu thrust, it lies over the Manaslu granite and places sediments of the Silurian and Devonian over the sheared contact zone of the leuco granite .

Within the leukogranite pluton there are signs of right-shifting ductile shear (top to the south), which indicates internal deformation of the still hot leucogranite. The intrusion was mainly brought about by penetrating passages that penetrated to a depth of around 12 kilometers at that time, ie up to the brittle-ductile limit. Starting from the corridors, the magma was distributed in storage corridors running concordantly to the foliation, which then expanded ( ballooning ). Below the STDS lie gneisses of the HHC (or GHC), which in turn were pushed onto low-grade slate rocks of the Lesser Himalaya by southward movements along the MCT . Unit I of the GHC (metapelitic unit I of the Neoproterozoic or Haimanta formation ) located below the leukogranite is now generally regarded as the parent rock of the leukogranite due to its geochemical composition and its isotope ratios, but the eye gneiss of unit III must also be taken into account. Seating was in the upper section of the GHC, with magma injected laterally along the planes of anisotropy of the metamorphic foliation.

Physical parameters

Metamorphic and thermobarometric results suggest that the Manaslu granite was exposed to pressures of 0.5-0.6 gigapascals at its base , which corresponds to a depth of 18-21 kilometers. The roof area of ​​the Pluton was under 0.3 to 0.4 GPa, ie under a load of 9 to 13 kilometers. The accompanying temperatures were between 550 and 650 ° C. Experimental work suggests, however, that the maximum pT conditions during the water-undersaturated melting process were likely to have reached 0.8 GPa and 750 ° C.

Mineralogy and Petrology

Manaslu east and main peaks (left) from the southeast. The slight collapse of the leuco granite plate to the right in a northerly direction can be seen.

Manaslu granite is made up of the minerals xenomorphic quartz (31.9 percent by volume), plagioclase (37 percent by volume - An 21 to An 2 ), perthitic alkali feldspar (21 percent by volume), muscovite (7 percent by volume), tourmaline and often also biotite (3 percent by volume ) built up. The biotite is usually converted to chlorite . Tourmaline is very common (up to several percent by volume), but is not counted as part of the actual paragenesis, since it is usually associated with crossing aplitic and pegmatitic passages. Accessories are garnet , monazite and zircon . Rock changes are rare. The planar adjustment of the mica defines an igneous foliation . As rock inclusions, migmatite fragments and mica enclaves are occasionally contained in the leukogranite, other magmatites do not occur. Streaks and so-called ghosts of tourmaline and quartz are also quite common . These are late magmatic to metasomatic circular mineral new formations through boron-containing fluids. Ductile overprints such as in the Chhokang arm have transformed the leuco granite there into eye gneiss.

Geochemical composition

Main elements

The following analyzes by Vidal and colleagues (1982) illustrate the geochemical composition of the main elements of Manaslu granite:

Oxide
wt.%		 Leuco granite Core area
average		 Branch Aplit
SiO 2 73.05 73.64-73.69 73.94 75.04
TiO 2 0.15 0.09-0.10 0.07 0.05
Al 2 O 3 14.59 14.85-14.87 14.76 14.19
Fe 2 O 3 1.19 0.84 - 1.22 0.81 0.67
MnO 0.03 0.03-0.30 0.02 0.04
MgO 0.11 0.11 0.13 0.10
CaO 0.59 0.47 0.46 0.06
Na 2 O 3.63 4.05 4.14 4.38
K 2 O 4.92 4.55 4.48 4.85
P 2 O 5 0.13 0.13
H 2 O + 0.84 0.72

The Manaslu granite is a quartz-depleted, pronounced leucocrates, highly aluminous and predominantly sodium-stressed rock. The muscovite-biotite-leucogranite, more precisely a leuco-adamellite, with Al 2 O 3 = 14.6 percent by weight and a very high Al 2 O 3 / TiO 2 ratio, is extremely peraluminous ( strongly peraluminous or SP ) and very rich in Alkalis (Na 2 O + K 2 O = 8.5 percent by weight). The CaO / Na 2 O ratio is low. Its geochemical composition is similar to the Variscan tin leukogranites of Europe. It emerged from a minimal melt and contains primary tourmaline, muscovite and biotite. The magnesium number is 0.22 and is low. Its high concentration of heat-producing elements points to a collision granite (abbreviated COLG ) of purely crustal origin .

Trace elements

Trace element
ppm		 Leuco granite average Aplit
Ba 415 205 16
Ce 28.14 12.28 3
La 13.9 8.19 1.42
Nd 14.6 4.74 (5.76-15.4) 1.8
Ta 3.2 10.8
Hf 2.2 1.95
Sm 3.3 1.46 (1.69-4.0) 0.6
Gd 3.4 1.58 0.65
Rb 258 286-367 (114-470) 569
Tb 0.7 0.14
Sr 131 75 (41.6-114) 7.52
Yb 0.62 0.64 0.32
Lu 0.083 0.10 0.058
Zr 69 25th 10
Th 5.6 6 (2.89 - 8.83) 0.93
U 8 (3.94-15.9)

In terms of trace elements , Manaslu granodiorite is characterized by high contents of the incompatible elements rubidium , tantalum and cesium , which make it recognizable as a highly differentiated granitoid. The low concentrations of HREE , yttrium , zirconium and hafnium are typical of granites in the collision zones. The Rb / Zr and Ta / Nb ratios are high and clearly distinguish collision granites from other granites.

Isotope ratios

The Manaslu granite is characterized by very high strontium initial ratios ( 87 Sr / 86 Sr) of 0.7400 to 0.7800 (0.7445 - 0.7738). Its ε Sr values ​​are extremely high at + 513, but the ε Nd values, at -12, are very low. The ratio 143 Nd / 144 Nd varies between 0.511894 and 0.511952. The lead ratios are 206 Pb / 204 Pb 18.679 to 18.865, 207 Pb / 204 Pb 15.744 to 15.779 and 208 Pb / 204 Pb 39.231 to 39.337. Its oxygen isotope ratio δ 18 O reaches 12.2 ‰ and is therefore very high.

Petrological facies

Petrologically , the Manaslu granite consists of two types of facies. Around 80 percent is claimed by a two-mica leukogranite, the remaining 20 percent is occupied by a tourmaline-containing leuco granite . Compared to tourmaline leukogranite, the two-mica leukogranite has both a lower Rb / Sr and a lower strontium initial ratio. These low ratio values ​​are, however, quite comparable with the values ​​in the peraluminous metagrauwacke of the GHC, which is why Guillot and Le Fort (1995) consider them as anatectic source rocks.

Regardless of the facies, very fine grain sizes predominate in the southwest section of the Pluton , whereas the center and northeast are coarser-grained, up to a maximum of 10 millimeters. These grain size differences - probably caused by different gating levels in the pluton - can also be correlated with the Rb / Sr, the strontium initial and the Th / U ratio. The center and the north-east (both coarse-grained) show a higher Rb / Sr ratio than the fine-grained south-west. The initial strontium ratio is also increased (> 0.7520), but the Th / U ratio is less than 0.7 and therefore lower. An exception to this is a small area in the southwest, whose strontium initial ratio also exceeds 0.7520. The isotope ratios can show a very high variability even in the meter range, which suggests heterogeneities in the starting material or inhomogeneities in the magma chamber. The pluton may also be composed of countless individual anatectic attacks. The degree of magmatic differentiation that followed was likely to have been low, with monazite and zircon already fractionating very early.

Structures

Manaslu east flank with 3000 meters of leuco granite , seen from Ribum monastery in Lho

The Manaslu granite has a foliation, even if it is often very difficult to see. This is predominantly of magmatic origin and mostly very homogeneous, but can be crossed by muscovite-rich shear bands with the formation of SC geometries. In the vicinity of the Pluton base at the southern end of the massif, the foliation strikes in the mean N 110 and dips at a little more than 40 ° to NNE. In the center of the intrusion it becomes irregular, steepens to 50 ° and strikes mainly N 070 here. At the northern end at Larkya La, the strike direction finally turns north-south and dips between 20 and 50 ° to the east. The associated stretching linear is also very indistinct. At the base they run east-west, in the center northeast-southwest and N 070 on the eastern edge. Their angle of incidence is very flat on the eastern edge, otherwise the angle is usually 40 ° in an easterly or northeastern direction. These results are reflected in AMS data , which show only minor deviations.

Imbrications of alkali feldspar crystals indicate non-coaxial magmatic flow movements . The muscovite shear bands are late magmatic and show a top eastward shear sense.

The deformations progressed further in the solidus area , but are clearly subordinate compared to the igneous structures. At high temperatures above 500 ° C, small and new grains were formed in quartz. At temperatures below 500 ° C, prism bands were formed in quartz and dynamic recrystallization with a simultaneous reduction in grain size occurred. The mica show undulating extinction and kink bands and the feldspars are interspersed with millimeter-thick shear bands filled with quartz, chlorite and clay minerals . Structures of the brittle area are faults covered by quartz and tourmaline , which strike the interior of the massif south-southeast and dip at 70 ° to WSW.

Emergence

It is usually assumed that the Leukogranite of Himalayas by melting pelitic biotite gneiss originated the GHC, in which in addition to the generated friction heat along the MCT additional liquid during the thrust operation could penetrate and thus facilitated the melting process. The thickening of the crust can be assumed as an additional heat source. Another hypothesis, on the contrary, assumes that the leukogranites were formed in a dehydrated state and under pressure relief, brought about by movements on the STDS. Muscovite and possibly also biotite were melted here. As a result, the anatexis occurred immediately after the movements on the STDS and therefore not necessarily synchronized with the thrusts on the MCT. The migmatites are also often viewed as parent rock. Their leucosomes have very similar geochemical compositions, but there are still differences to Manaslu granite, especially with regard to the elements rubidium , strontium , europium and the very heavily depleted fluorine . The Rb / Sr ratio in migmatites, at 0.7 to 1.4, is significantly lower than in leukogranite, which has values ​​from 2.0 to 6.0.

Since the foliation planes in the Manaslu granite are curved in an S-shape, this indicates, in addition to the Chame thrust in the south, a further right-shifting shear zone immediately to the north of the intrusion. There are two spatial models between these two shear systems, which made the rise of the magma possible:

  • as a pull-apart
  • large dimension as a distorting or Fiederspalte (engl. tension gash )

The second model is likely to be more probable due to the foliation conditions in the leuco granite and suggests a main stress running parallel to the longitudinal extent of the intrusion in a northwest-southeast direction.

metamorphosis

The intrusion of the Manaslu granite caused a contact metamorphosis in the cladding rocks of the GHC with a contact aureole almost 100 meters wide. New biotite, muscovite, staurolite and garnet were formed in the pelitic slates of the roof area . In the lower lying calcium silicate gneisses, wollastonite and scapolite were formed . Below the pluton, high-grade parageneses with diopside and alkali feldspar occur in metamorphosed limestone, which indicates temperatures above 500 ° C.

Development over time

For the penetration of the Manaslu granite, two main phases can be distinguished on the basis of Th-Pb dating with a secondary ion microprobe on Monazite according to Harrison and colleagues (1998):

  • the Larkya phase , dated to 22.9 ± 0.6 million years ( Aquitanium )
  • the Bimtang phase , dated 19.3 ± 0.3 million years ago ( Burdigalium ).

Ductile shear movements along the Main Central Thrust and also at the Chame Thrust had already taken place in Aquitanium after the Larkya phase had ended between 22.5 and 21 million years ago, whereas brittle faults on the higher-lying STD only occurred after the Bimtang- Phase began between 19 and 18 million years ago during the Burdigalium and lasted up to 16 million years. In the middle Miocene between 18 and 15 million years (Burdigalium / Langhium period ) the Manaslu granite and its surrounding GHC rocks were exhumed and consequently cooled down very strongly. In the Langhium, between 15 and 13 million years ago, around 350 ° C (muscovite closure temperature) was reached.

The reasons for the cooling lay in the east-west extension of the north-north-east trending Thakkhola Rift north of the STD in the period 14 to 5 million years (late Miocene - Serravallian to Messinian ) and the spreading of the thrusts in the south Lesser Himalayas. The oldest sediments in the Thakkola Trench were dated 11 to 9.6 million years ago in the Tortonian .

Individual evidence

  1. ↑ Zhu, B., Kidd, WSF, Rowley, DB, Currie, BS and Shafique, N .: Age of initiation of the India – Asia collision in the east central Himalaya . In: Journal of Geology . tape 113 , 2005, pp. 265-285 .
  2. ↑ Cottle, JM, Jessup, MJ, Newell, DL, Searle, MP, Law, RD and Horstwood, MSA: Structural insight into the ductile evolution of an orogen-scale detachment: the South Tibetan Detachment System, Dzakaa Chu section, Eastern Himalaya . In: Journal of Structural Geology . tape 291 , 2007, p. 781-797 , doi : 10.1016 / j.jsg.2007.08.007 .
  3. ↑ Jackson, J., McKenzie, D., Priestley, K. and Emmerson, B .: New views on the structure and rheology of the lithosphere . In: Journal of the Geological Society, London . tape 165 , 2008, p. 453-465 .
  4. ↑ Law, RD, Searle, MP and Simpson, RL: Strain, deformation temperatures and vorticity of flow at the top of the Greater Himalayan Slab, Everest Massif, Tibet . In: Journal of the Geological Society, London . tape 161 , 2004, pp. 305-320 .
  5. ↑ Jessup, MJ, Cottle, JM, Searle, MP, Law, RD, Newell, DL, Tracy, RJ and Waters, DJ: PTtD paths of Everest Series schist, Nepal . In: Journal of Metamorphic Geology . tape 26 , 2008, p. 717-739 , doi : 10.1111 / j.1525-1314.2008.00784.x .
  6. ↑ Law, RD, Searle, MP and Godin, L .: Channel Flow, Ductile Extrusion and Exhumation in Continental Collision Zones . In: Geological Society, London, Special Publications . tape 268 , 2006, p. 1-23 .
  7. ↑ Michael P. Searle: Low-angle normal faults in the compressional Himalayan orogen: Evidence from the Annapurna – Dhaulagiri Himalaya, Nepal . In: Geosphere . tape 6 , no. 4 , 2010, p. 296-315 , doi : 10.1130 / GES00549.1 .
  8. ↑ Searle, MP, Cottle, J .M., Streule, MJ and Waters, DJ: Crustal melt granites and migmatites along the Himalaya: Melt source, segregation, transport and granite emplacement mechanisms . In: Transactions of the Royal Society of Edinburgh: Earth Sciences . tape 100 , 2009, p. 1-14 .
  9. ↑ Barbey, P., Brouand, M., Le Fort, P. and Pêcher, A .: Granite-migmatite genetic link: the example of the Manaslu granite and Tibetan Slab migmatites in central Nepal . In: Lithos . tape 38 , 1996, pp. 63-79 .
  10. ^ A b Guillot, S., Pêcher, A., Rochette, P. and Le Fort, P .: The emplacement of the Manaslu granite of central Nepal: field and magnetic susceptibility constraints . In: Treloar, PJ and Searle, MP, Himalayan tectonics (eds.): Geol. Soc. Lond. Spec. Publ. Volume 74 , 1993, pp. 413-428 .
  11. ^ Godin, L .: Tectonic evolution of the Tethyan sedimentary sequence in the Annapurna area, central Nepal Himalaya (doctoral thesis) . Carleton University, Ottawa 1999, pp. 219 .
  12. ↑ Scaillet, B., Pichavant, M. and Roux, J .: Experimental crystallization of leucogranite magmas . In: Journal of Petrology . tape 36 , 1995, pp. 663-705 .
  13. ↑ Le Fort, P., Cuney, M., Deniel, C., France-Lanord, C., Sheppard, SMF, Upreti, BN and Vidal, P .: Crustal generation of the Himalayan leucogranites . In: Tectonophysics . 1987.
  14. ↑ a b Vidal, P., Cocherie, A. and Le Fort, P .: Geochemical investigations of the origin of the Manaslu leucogranite (Himalaya, Nepal) . In: Geochim. Cosmochim. Acta . tape 46 , 1982, pp. 2279-2292 .
  15. ↑ Cuney, M., Le Fort, P. and Wang, ZX: Uranium and thorium geochemistry and mineralogy in the Manaslu leucogranite (Nepal, Himalaya). Proc. Symp. On "Geology of granites and their metallogenic relations" Nanjing Univ, China 1982. Ed .: Xu, K. and Tu, G. Science press, Beijing 1984, p. 853-873 .
  16. ↑ Pearce, JA, Harris, NBW and Tindle, AG: Trace element discrimination diagrams for the tectonic interpretation of granitic rocks . In: Journal of Petrology . tape 25 , 1984, pp. 956-983 .
  17. ↑ Allegre, CJ and Ben Othman, B .: Nd-Sr isotopic relationship in granitoid rocks and continental crust development: a chemical approach to orogenesis . In: Nature . tape 286 , 1980, pp. 335-342 .
  18. ↑ Deniel, C., Vidal, P., Fernandez, A., Le Fort, P. and Peucat, JJ: Isotopic study of the Manaslu granite (Himalaya, Nepal): inferences on the age and source of the Himalayan leucogranites . In: Contributions to Mineralogy and Petrology . tape 96 , 1987, pp. 78-92 .
  19. ↑ Montel, JM: A model for monazite / melt equilibrium and application to the generation of granitic magmas . In: Chemical Geology . tape 110 , 1993, pp. 127-146 .
  20. ↑ P. England, P. Le Fort, P. Molnar and Pêcher, A .: Heat sources for Tertiary metamorphism and anatexis in the Annapurna-Manaslu region (Central Nepal) . In: Journal of Geophysical Research . tape 97 , 1992, pp. 2107-2128 .
  21. ↑ Guillot, S., Le Fort, P., Pêcher, A., Barman, MR and Aprahamian, J .: Contact metamorphism and depth of emplacement of the Manaslu granite (central Nepal). Implications for Himalayan orogenesis. In: Tectonophysics . tape 241 , 1995, pp. 99-119 .
  22. ↑ Colchen, M., Le Fort, P. and Pêcher, A .: Recherches géologiques dans l'Himalaya du Népal. Annapurna, Manaslu, Ganesh. CNRS, Paris 1986, p. 136 .
  23. ^ Harrison, TM et al .: Origin and Episodic Emplacement of the Manaslu Intrusive Complex, Central Himalaya . In: Journal of Petrology . 1998, p. 3-19 . (Digitized version)
  24. ↑ Godin, L., Gleeson, T. and Searle, MP: Locking of southward extrusion in favor of rapid crustal-scale buckling of the Greater Himalayan sequence, Nar valley, central Nepal . In: Law, RD, Searle, MP and Godin, L., Channel Flow, Ductile Extrusion and Exhumation in Continental Collision Zones (Eds.): Geological Society [London] Special Publication . tape 268 , 2006, p. 269-292 .
  25. ↑ Godin, L., Parrish, RR, Brown, RL and Hodges, KV: Crustal thickening leading to exhumation of the Himalayan core of central Nepal: insight from U-Pb geochronology and 40Ar / 39Ar thermochronology . In: Tectonics . tape 20 , 2001, p. 729-747 .
  26. ↑ Michael P. Searle and Laurent Godin: The South Tibetan Detachment and the Manaslu Leucogranite: A Structural Reinterpretation and Restoration of the Annapurna-Manaslu Himalaya, Nepal . In: The Journal of Geology . Vol. 111, 2003, pp. 505-523 , doi : 10.1086 / 376763 .
  27. ↑ Garzione, CN, De Celles, PG, Hodkinson, DG, Ojha, T. and Upreti, BN: East-west extension and Miocene environmental change in the southern Tibetan plateau: Thakkhola graben central Nepal . In: Geological Society of America Bulletin . tape 115 , 2003, p. 3–20 , doi : 10.1130 / 0016-7606 (2003) 115 <0003: EWEAME> 2.0.CO; 2 .