DongXqz408: new new details initial version.

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new new details initial version.

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[[File:Hymalayas 86.15103E 31.99726N.jpg|thumb|right|Satellite image of the Himalayas]]
[[File:Himalaya tectonostratigraphic zones for Wiki.jpg|thumb|right|Spatial arrangement of the Himalayan tectonostratigraphic zones. Modified from N.R. McKenzie et al 2011<ref name="McKenzie 471–483">{{Cite journal|last1=McKenzie|first1=N. Ryan|last2=Hughes|first2=Nigel C.|last3=Myrow|first3=Paul M.|last4=Xiao|first4=Shuhai|last5=Sharma|first5=Mukund|date=2011-12-15|title=Correlation of Precambrian–Cambrian sedimentary successions across northern India and the utility of isotopic signatures of Himalayan lithotectonic zones|journal=Earth and Planetary Science Letters|volume=312|issue=3–4|pages=471–483|doi=10.1016/j.epsl.2011.10.027|bibcode=2011E&PSL.312..471M}}</ref>]]

'''Pre-collisional Himalaya''' is the arrangement of the [[Himalayas|Himalayan]] rock units before [[Orogeny|mountain-building process]]es resulted in the collision of [[Asia]] and [[Indian subcontinent|India]]. The collision began in the [[Cenozoic]] and it is a [[Type locality (geology)|type locality]] of a [[Convergent boundary|continental-continental collision]].<ref name=":0">{{Cite journal|last=Yin|first=An|date=2006|title=Cenozoic tectonic evolution of the Himalayan orogen as constrained by along-strike variation of structural geometry, exhumation history, and foreland sedimentation|journal=Earth-Science Reviews|volume=76|issue=1–2|pages=1–131|doi=10.1016/j.earscirev.2005.05.004|bibcode=2006ESRv...76....1Y}}</ref> The reconstruction of the initial configuration of the rock units and the relationship between them is highly controversial, and major concerns relate to the arrangements of the different rock units in three dimensions. Several models have been advanced to explain the possible arrangements and [[petrogenesis]] of the rock units.

== Major rock units in Himalaya ==
{{Further information|Geology of the Himalayas|Geology of Nepal}}

In the Himalaya, the rock units are conventionally divided into four major sections.<ref name=":2">{{Cite book|title=Central Himalaya Geological Observations of Swiss|last1=Heim|first1=Arnold|last2=Gansser|first2=Augusto|year=1939|pages=1–246}}</ref> From North to South, they are:
* Tethyan Himalayan sequence
* Greater Himalayan crystalline complex
* [[Palaeozoic-Mesozoic Lesser Himalayan Strata|Lesser Himalayan sequence]]
* Sub-Himalayan sequence
The Tethyan Himalayan sequence, Greater Himalayan crystalline complex, and Lesser Himalayan sequence are grouped together as the North Indian sequence due to the overlapping age from [[Proterozoic]] to [[Phanerozoic]].<ref name=":1">{{Cite journal|last=Brookfield|first=M.E|date=1993|title=The Himalayan passive margin from Precambrian to Cretaceous times|journal=Sedimentary Geology|volume=84|issue=1–4|pages=1–35|doi=10.1016/0037-0738(93)90042-4|bibcode=1993SedG...84....1B}}</ref> For Pre-collisional Himalaya, only the North Indian Sequence is of concern as the Sub-Himalayan sequence is a rock unit that was deposited at the same time as the India and Asia collision and the resulting mountain-building process.<ref>{{Cite journal|last1=Schelling|first1=Daniel|last2=Arita|first2=Kazunori|date=1991|title=Thrust tectonics, crustal shortening and the structure of the far-eastern Nepal Himalaya|journal=Tectonics|volume=10|issue=5|pages=851–862|doi=10.1029/91tc01011|bibcode=1991Tecto..10..851S}}</ref>

=== Tethyan Himalayan sequence ===
The Tethyan Himalayan sequence is composed of mainly [[siliciclastic]] and [[Carbonate rock|carbonate sedimentary rocks]] deposited from 1840 Ma to 40 Ma. These are [[Interbedding|inter-bedded]] with [[volcanic rock]]s of [[Paleozoic]] and [[Mesozoic]] age.<ref name=":0" /> This sequence is divided into several sub-units due to the different [[Facies|lithofacies]] present in the sequence. The lithofacies of the rocks are a result of the shift in the [[depositional environment]]. Specific to this sequence, the [[Carboniferous]] to [[Jurassic]] rifting event was the cause of the changing depositional environment. In particular, the rifting event initiated the opening of the [[Tethys Ocean]] during which the [[Cimmerian Plate]] travelled north and moved away from [[Gondwana]].<ref name=":1" /> The boundary and age between the several sub-units are poorly constrained,<ref>{{Cite journal|last1=Yin|first1=An|last2=Harrison|first2=T. Mark|date=2000|title=Geologic Evolution of the Himalayan- Tibetan Orogen|journal=Annual Review of Earth and Planetary Sciences|volume=28|pages=211–280|doi=10.1146/annurev.earth.28.1.211|bibcode=2000AREPS..28..211Y|s2cid=129522844}}</ref> yet the whole sequence is generally considered to have first developed in [[Neoproterozoic]].<ref name=":3">{{Cite journal|last1=Frank|first1=Wolfgang|last2=Grasemann|first2=Bernhard|last3=Guntli|first3=Peter|last4=Miller|first4=Christine|date=1995|title=Geological Map of the Kishtwar- Chamba- Kulu Region (NW Himalayas, India)|journal=Jahrbuch der Geologischen Bundesanstalt|volume=138|pages=299–308|issn=0016-7800}}</ref> The 1840 Ma of the rocks was determined by [[rubidium–strontium dating]] of the Baragoan [[gneiss]],<ref name=":8">{{Cite journal|last1=Miller|first1=C.|last2=Thöni|first2=M.|last3=Frank|first3=W.|last4=Grasemann|first4=B.|last5=Klötzli|first5=U.|last6=Guntli|first6=P.|last7=Draganits|first7=E.|date=2001-05-01|title=The early Palaeozoic magmatic event in the Northwest Himalaya, India: source, tectonic setting and age of emplacement|url=https://www.cambridge.org/core/journals/geological-magazine/article/the-early-palaeozoic-magmatic-event-in-the-northwest-himalaya-india-source-tectonic-setting-and-age-of-emplacement/740A465CBCB3B5DCD03857C17E78E754|journal=Geological Magazine|volume=138|issue=3|pages=237–251|doi=10.1017/S0016756801005283|issn=1469-5081|bibcode=2001GeoM..138..237M|s2cid=131287725|url-access=subscription}}</ref> however some have allocated the gneiss into the Lesser Himalayan Sequence instead.<ref>{{Cite journal|last1=Pandey|first1=A.K.|last2=Virdi|first2=N.S.|date=2003|title=Microstructural and fluid inclusion constraints on the evolution of Jakhri thrust zone in the Satluj valley of NW Himalaya.|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=14870312|journal=Current Science|volume=84|issue=10|pages=1355–1364|url-status=dead|archive-url=https://web.archive.org/web/20161122224513/http://cat.inist.fr/?aModele=afficheN&cpsidt=14870312|archive-date=2016-11-22}}</ref>

=== Greater Himalayan crystalline complex ===
Generally, the Greater Himalayan crystalline complex is a belt of high-grade [[metamorphic rock]]s that extends along the east-trending length of the Himalayan range.<ref name=":4">{{Cite journal|last1=DiPietro|first1=Joseph A.|last2=Pogue|first2=Kevin R.|date=2004|title=Tectonostratigraphic subdivisions of the Himalaya: A view from the west|journal=Tectonics|volume=23|issue=5 |pages=TC5001|doi=10.1029/2003TC001554|bibcode=2004Tecto..23.5001D|s2cid=129138752 }}</ref> It contains [[leucogranite]]s interspersed throughout the entire complex, and they are early to middle [[Miocene]] of age.<ref name=":7">{{Cite journal|last=Le Fort|first=Patrick|date=1975|title=Himalayas: The Collided Range. Present Knowledge of The Continental Arc|journal=American Journal of Science|volume=275-A|pages=1–44}}</ref> The complex is sandwiched by two major faults, with the [[Main Central Thrust]] in the south and the [[South Tibetan Detachment]] to the North. Additionally, the Tethyan Himalayan sequence overlies the complex. The estimated age of the complex ranges from 1800 Ma to 480 Ma, however these ages are poorly constrained.<ref name="McKenzie 471–483" /><ref>{{Cite journal|last1=DeCelles|first1=P. G.|last2=Gehrels|first2=G. E.|last3=Najman|first3=Y.|last4=Martin|first4=A. J.|last5=Carter|first5=A.|last6=Garzanti|first6=E.|date=2004-11-15|title=Detrital geochronology and geochemistry of Cretaceous–Early Miocene strata of Nepal: implications for timing and diachroneity of initial Himalayan orogenesis|journal=Earth and Planetary Science Letters|volume=227|issue=3–4|pages=313–330|doi=10.1016/j.epsl.2004.08.019|bibcode=2004E&PSL.227..313D}}</ref> From bottom to top, the [[Metamorphism|metamorphic grade]] of the complex first increases up section, it is then reversed, with the metamorphic grade decreasing up section. The transition occurs between the middle and top portions of the complex.<ref>{{Cite journal|last1=Hubbard|first1=Mary S.|last2=Harrison|first2=T. Mark|date=1989|title=40Ar/39Ar age constraints on deformation and metamorphism in the main central thrust zone and Tibetan slab, eastern Nepal Himalaya|journal=Tectonics|volume=8|issue=4|pages=865|bibcode=1989Tecto...8..865H|doi=10.1029/TC008i004p00865}}</ref> In addition, inverted metamorphism appears at Central Nepal.<ref>{{Cite journal|last=Arita|first=Kazunori|date=1983|title=Origin of the inverted metamorphism of the lower Himalayas, Central Nepal|journal=Tectonophysics|volume=95|issue=1–2|pages=43–60|doi=10.1016/0040-1951(83)90258-5|bibcode=1983Tectp..95...43A}}</ref>

=== Lesser Himalayan sequence ===
The Lesser Himalayan sequence is characterized by low-grade meta-sedimentary rocks,<ref name=":2" /> metavolcanic rocks and [[Gneiss|augen gneiss]]. The majority of the sequence is marine deposits, however, most of the sequence does not contain any fossils; only in rare instances will a formation contain fossils. Major formations of the sequence include the Tal Formation, Gondwana Strata, Singtali Formation, and Subathu Formation. The entire sequence has an age range of 1870 Ma to 520 Ma.<ref name=":3" /> In North West India, the sequence is overlain by the [[Cambrian]] strata,<ref>{{Cite journal|last1=Brunel|first1=M.|last2=D'Albissin|first2=M. Chaye|last3=Locquin|first3=M.|date=1985|title=The Cambrian Age of Magnesites from E. Nepal as Determined through the Discovery of Paleo Basidiospores|journal=Journal of the Geological Society of India|volume=26|issue=4}}</ref> while in [[Pakistan]], Cambrian or [[Carboniferous]] strata from the Tibetan Himalaya sequence overlays the [[Mesoproterozoic|Mesoproterozic]] strata of the Lower Himalayan sequence.<ref name=":4" />

== Concepts ==
[[File:Reconstruction of Pre-tectonic Himalaya models.png|thumb|Models on the reconstruction of Pre-tectonic Himalaya (curly arrows represents the direction of sedimentation), modified from Yin (2006),<ref name=":0" /> Myrow (2003),<ref name=":6">{{Cite journal|last1=Myrow|first1=P.M.|last2=Hughes|first2=N.C.|last3=Paulsen|first3=T.S.|last4=Williams|first4=I.S.|last5=Parcha|first5=S.K.|last6=Thompson|first6=K.R.|last7=Bowing|first7=S.A.|last8=Peng|first8=S.-C.|last9=Ahluwalia|first9=A.D.|date=2003|title=Integrated tectonostratigraphic analysis of the Himalaya and implications for its tectonic reconstruction|journal=Earth and Planetary Science Letters|volume=212|issue=3–4|pages=433–441|doi=10.1016/S0012-821X(03)00280-2|bibcode=2003E&PSL.212..433M|citeseerx=10.1.1.526.4758}}</ref> DeCelles (2000)<ref name=":5">{{Cite journal|last1=DeCelles|first1=P.G.|last2=Gehrels|first2=G.E.|last3=Quade|first3=J.|last4=LaReau|first4=B.|last5=Spurlin|first5=M.|date=2000|title=Tectonic Implications of U-Pb Zircon Ages of the Himalayan Orogenic Belt in Nepal|journal=Science|volume=288|issue=5465|pages=497–499|doi=10.1126/science.288.5465.497|pmid=10775105|bibcode=2000Sci...288..497D}}</ref>|705x705px]]
The initial configuration of pre-collisional Himalaya can be expressed in the four following models:<ref name=":0" />
* Passive continental margin model
* Crystalline axis model
* Accreted terrane model
* Carboniferous-extension model

=== Passive continental margin model ===
==== Background ====
This model is a single margin model. Here, the North Indian sequence was deposited on a continental margin of northern India that was facing north. The units in the North Indian sequence represents the same set of sediments, but became distinct, since nearshore and offshore conditions changes the characteristics of the rock units during deposition.<ref>{{Cite journal|last1=Corfield|first1=R. I.|last2=Searle|first2=M. P.|date=2000-01-01|title=Crustal shortening estimates across the north Indian continental margin, Ladakh, NW India|url=http://sp.lyellcollection.org/content/170/1/395|journal=Geological Society, London, Special Publications|language=en|volume=170|issue=1|pages=395–410|doi=10.1144/GSL.SP.2000.170.01.21|issn=0305-8719|bibcode=2000GSLSP.170..395C|s2cid=128483822|url-access=subscription}}</ref><ref>{{Cite journal|last1=Frank|first1=W.|last2=Hoinkes|first2=G.|last3=Miller|first3=Christine|last4=Purtscheller|first4=F.|last5=Richter|first5=W.|last6=Thöni|first6=M.|title=Relations between metamorphism and orogeny in a typical section of the Indian Himalayas|journal=Tschermaks Mineralogische und Petrographische Mitteilungen|language=en|volume=20|issue=4|pages=303–332|doi=10.1007/BF01081339|issn=0369-1497|year=1973|bibcode=1973TMPM...20..303F}}</ref>

==== Predictions ====
This model predicts that all three units–namely, the Lesser Himalayan, Greater Himalayan, and Tethyan Himalayan–must have a nearly identical depositional age and depositional setting, and are derived from similar sources. Immediately, primary evidence from [[Detrital zircon geochronology|detrital zircon ages]], [[paleocurrent]] recorded in the units, and animal similarities supports these predictions.<ref name=":6" /> Firstly, the detrital zircon data for the Lesser Himalaya and Tethyan Himalaya sequence yield similar age spectra when similar aged samples were used. Furthermore, when [[samarium–neodymium dating]] of the entire North Indian sequence was made, significant overlap of Nd isotopic signatures between the different rocks units indicates a sharing of similar sources.<ref>{{Cite journal |last1=Whittington|first1=Alan|last2=Foster|first2=Gavin|last3=Harris|first3=Nigel|last4=Vance|first4=Derek|last5=Ayres |first5=Michael|date=1999-07-01|title=Lithostratigraphic correlations in the western Himalaya—An isotopic approach|journal=Geology|language=en|volume=27|issue=7|pages=585–588|doi=10.1130/0091-7613(1999)027<0585:LCITWH>2.3.CO;2|issn=0091-7613 |bibcode=1999Geo....27..585W}}</ref><ref>{{Cite journal|last1=Ahmad|first1=T.|last2=Harris|first2=N.|last3=Bickle|first3=M.|last4=Chapman|first4=H.|last5=Bunbury|first5=J.|last6=Prince|first6=C.|title=Isotopic constraints on the structural relationships between the Lesser Himalayan Series and the High Himalayan Crystalline Series, Garhwal Himalaya|journal=Geological Society of America Bulletin|volume=112|issue=3|pages=467–477|doi=10.1130/0016-7606(2000)112<467:icotsr>2.0.co;2|year=2000|bibcode=2000GSAB..112..467A}}</ref>

Secondly, the paleocurrent data orientated from south-south west to north-north east is common to both Lesser Himalaya and Tethyan Himalaya, more specifically in the Tal Group and Kunzam La Formation, respectively.<ref>{{Cite journal|last=Ganesan|first=T. M.|date=1975-12-01|title=Palaeocurrent Pattern in the Upper Tal Rocks of Nigali, Korgai Synclines (H.P.) & Mussoorie Syncline (U.P.)|url=http://www.geosocindia.org/index.php/jgsi/article/view/63499|journal=Geological Society of India|language=en|volume=16|issue=4|pages=503–507|issn=0974-6889}}</ref> Moreover, the [[lithology]] of the two sequences connotes a [[fluvial]] depositional setting and the lithofacies of the rocks strongly supports the idea that the Lesser Himalaya and Tethyan Himalaya represent nearshore and offshore portions of a continental margin.<ref name=":6" /> Finally, both sequences contain the same [[Cambrian|Early Cambrian]] equatorial [[trilobite]] species, reinforcing the likelihood of the passive continental margin model.<ref>{{Cite book|last1=Hughes|first1=Nigel C.|last2=Jell|first2=Peter A.|date=1999-02-01|title=Biostratigraphy and biogeography of Himalayan Cambrian trilobites|journal=Geological Society of America Special Papers|language=en|volume=328|pages=109–116|doi=10.1130/0-8137-2328-0.109|issn=0072-1077|isbn=978-0-8137-2328-0}}</ref>

Additionally, it is proposed that the [[protolith]] of the Greater Himalaya may have been [[Sedimentary rock|sedimentary]] in nature and correlate with the Lesser and Tethyan Himalayan sequences.<ref name=":7" /> Although precise matching of the ancient stratigraphy of the Greater Himalaya with the other zones is not possible, the Greater Himalayan sequence shares correlative strata with Neoproterozoic to Cambrian age rocks in Tethyan Himalaya. Similar transition from siliciclastic rocks to carbonates occurs in both sequences in strata of similar ages.<ref>{{Cite journal|last1=Garzanti|first1=Eduardo|last2=Casnedi|first2=Raffaele|last3=Jadoul|first3=Flavio|date=1986-07-01|title=Sedimentary evidence of a Cambro-Ordovician orogenic event in the northwestern Himalaya|journal=Sedimentary Geology|volume=48|issue=3|pages=237–265|doi=10.1016/0037-0738(86)90032-1|bibcode=1986SedG...48..237G}}</ref> In spite of the metamorphic grade of Greater Himalaya, the protolith lithology is nevertheless similar to the other zones and possibly shares the same depositional setting.

==== Problems ====
Brookfield opposes the model by explaining that in the Lesser Himalaya, thick and well developed strata, younger than [[Precambrian]] of age, are absent, while it is very well preserved in Tethyan Himalaya.<ref name=":1" /> DeCelles et al. also demonstrated that this model fails to explain the relationship of Greater Himalaya and Lesser Himalaya, along the main central thrust in [[Nepal]].<ref name=":5" /> In addition, Spencer et al. achieved contrasting results in the εNd values, revealing a more negative value in Lesser Himalaya compared to both the Greater Himalaya and Tethyan Himalaya, suggesting different sources amongst the sequences. The latter two have values that resemble the [[Arabian-Nubian Shield|Arabian Shield]] and Eastern [[Antarctica]], which conflict with the [[Indian Shield]] source that composes Lesser Himalaya.<ref name=":9">{{Cite journal|last1=Spencer|first1=Christopher J.|last2=Harris|first2=Ron A.|last3=Sachan|first3=Himanshu Kumar|last4=Saxena|first4=Anubhooti|date=2011-05-25|title=Depositional provenance of the Greater Himalayan Sequence, Garhwal Himalaya, India: Implications for tectonic setting|journal=Journal of Asian Earth Sciences|volume=41|issue=3|pages=344–354|doi=10.1016/j.jseaes.2011.02.001|bibcode=2011JAESc..41..344S}}</ref><ref>{{Cite journal|last1=Imayama|first1=Takeshi|last2=Arita|first2=Kazunori|date=2008-04-28|title=Nd isotopic data reveal the material and tectonic nature of the Main Central Thrust zone in Nepal Himalaya|journal=Tectonophysics|series=Asia out of Tethys: Geochronologic, Tectonic and Sedimentary Records|volume=451|issue=1–4|pages=265–281|doi=10.1016/j.tecto.2007.11.051|bibcode=2008Tectp.451..265I}}</ref>
[[File:Tectonic Evolution of the Passive Continental Margin Model.png|center|thumb|Tectonic evolution of the passive continental margin model|715x715px]]

=== Crystalline axis model ===
==== Background ====
This model posits that the Lesser and Tethyan Himalaya were deposited in distinct basins that are separated by the Greater Himalaya complex.<ref name=":10">{{Cite journal|last=Saxena|first=M.N.|date=1971|title=The Crystalline Axis of the Himalaya: The Indian Shield and Continental Drift|journal=Tectonophysics|volume=12|issue=6|pages=433–447|doi=10.1016/0040-1951(71)90044-8|bibcode=1971Tectp..12..433S}}</ref>

==== Problems ====
Results of the zircon ages and possible protolith lithologies and their corresponding first-order similarities between the rock units from Myrow et al. have generally discredited this model.<ref name=":6" /> To begin with, the Greater Himalaya yields younger detrital zircon ages than that of Lesser and Tethyan Himalaya, which makes it very unlikely for Greater Himalaya to be a topographic high that separates two depositional basins.<ref>{{Cite journal|last1=Parrish|first1=Randall R.|last2=Hodges|first2=V.|date=1996-07-01|title=Isotopic constraints on the age and provenance of the Lesser and Greater Himalayan sequences, Nepalese Himalaya|journal=Geological Society of America Bulletin|language=en|volume=108|issue=7|pages=904–911|doi=10.1130/0016-7606(1996)108<0904:icotaa>2.3.co;2|issn=0016-7606|bibcode=1996GSAB..108..904P}}</ref><ref>{{Cite journal|last1=Aharon|first1=Paul|last2=Schidlowski|first2=Manfred|last3=Singh|first3=Indra B.|date=1987-06-25|title=Chronostratigraphic markers in the end-Precambrian carbon isotope record of the Lesser Himalaya|journal=Nature|language=en|volume=327|issue=6124|pages=699–702|doi=10.1038/327699a0|bibcode=1987Natur.327..699A|s2cid=4354472}}</ref> All the evidence that supports the passive margin model is also problematic for this model, since the strong paleontological, lithological, and sedimentological relationships between Lesser and Tethyan Himalaya basically rejects the connotation that they were once separated. Missing [[Suture (geology)|suture zone]] rocks in the Main Central Thrust also makes it difficult to explain this model.<ref name=":6" />

=== Accreted terrane model ===
==== Background ====
In this model, Lesser and Greater Himalaya were developed in separate areas during Precambrian to Cambrian, and soon after in late Cambrian to [[Ordovician|Early Ordovician]]. Greater Himalaya accreted as an exotic terrane into the Northern India margin and came into contact with Lesser Himalaya. Tethyan Himalaya was later deposited on top of Greater Himalaya as an overlying sequence.<ref name=":5" />

==== Predictions ====
This reconstruction predicts that the Greater Himalaya thrust over Lesser Himalayan rocks during the early Paleozoic. As such. it is able to more successfully explain the age relationship between the strata across the main central thrust.<ref name=":0" /> Other models would require greater slip along the main central thrust during the Cenozoic orogeny to achieve the present stratigraphical arrangement. Deformation produced by Paleozoic tectonics may have been overprinted by the Cenozoic reactivation of the main central thrust, which result in the lack of old suture zone rocks. Moreover, aligned with this model, sediments in northern India have experienced a transition from [[turbidite]]s to syn-collision sediments in Cambrian to Ordovician.<ref>{{Cite book|last1=Pogue|first1=Kevin R.|last2=Hylland|first2=Michael D.|last3=Yeats|first3=Robert S.|last4=Khattak|first4=Wali Ullah|last5=Hussain|first5=Ahmad|date=1999-02-01|title=Stratigraphic and structural framework of Himalayan foothills, northern Pakistan|journal=Geological Society of America Special Papers|language=en|volume=328|pages=257–274|doi=10.1130/0-8137-2328-0.257|issn=0072-1077|isbn=978-0-8137-2328-0}}</ref> Additional evidence with regard to isotopic signatures and detrital zircon ages may also increase the credibility of this model.<ref name=":9" /> Further investigation is required to support more predictions of this model, since metamorphism of the Greater Himalayan strata in the early Paleozoic, and Cambrian to Ordovician syn-tectonic sediments in Tethyan Himalaya, are lacking.<ref name=":5" />

==== Problems ====
This model fails to reconcile with detrital zircon ages, and paleontological evidence with respect to the similarities between Tethyan and Lesser Himalaya. Similar to the crystalline axis model, this model faces the same challenges with respect to the evidence that supports the passive margin model. Trilobite fauna, paleocurrent and lithological similarities would be unlikely if the rock units were formed in separate terranes as explained by Myrow et al.<ref name=":6" /> Earlier predictions<ref name=":5" /> that suggest a thrust/ shortening event in Tethyan Himalaya in the early Paleozoic, and the simultaneous formation of granitic intrusions under the sequence, were also undermined by the apparent rifting isotopic signatures in the granites.<ref name=":8" />
[[File:Accreted Terrane Model.gif|center|thumb|Tectonic Evolution of the Accreted Terrane Model, Grey= Oceanic Plate, Blue= Lesser Himalaya, Pink= Greater Himalaya, Green= Tethyan Himalaya (MBT= [[Main Boundary Thrust]], MCT= [[Main Central Thrust]], STD= [[South Tibetan Detachment]])|635x635px]]

=== Carboniferous-extension model ===
==== Background ====
This model illustrates that in Carboniferous, due to possible [[rift]]ing,<ref name=":1" /> the Lesser and Greater Himalaya were separated by a north-dipping [[Fault (geology)|normal fault]]. In this reconstruction, the former is the footwall and the latter is the hanging wall.

==== Predictions ====
This model explains the apparent missing lower Paleozoic strata in Lesser Himalaya due to footwall uplift and erosion, and provides a possible solution to the age relationship across the main central thrust by the reactivation of this ancient normal fault.<ref name=":0" />

==== Problems ====
Vannay et al. explains that the missing strata in Lesser Himalaya could be a result of glaciation in late Carboniferous.<ref>{{Cite journal|last1=Vannay|first1=Jean-Claude|last2=Steck|first2=Albrecht|date=1995-04-01|title=Tectonic evolution of the High Himalaya in Upper Lahul (NW Himalaya, India)|journal=Tectonics|language=en|volume=14|issue=2|pages=253–263|doi=10.1029/94TC02455|issn=1944-9194|bibcode=1995Tecto..14..253V}}</ref> Similar to the passive margin model, this model also implies that all the zones within the North Indian sequence share the same source; however, the εNd value and detrital zircon ages are currently controversial and may not favor this interpretation.<ref name=":9" /><ref>{{Cite journal|last1=Yoshida|first1=Masaru|last2=Upreti|first2=Bishal N.|date=2006-11-01|title=Neoproterozoic India within East Gondwana: Constraints from recent geochronologic data from Himalaya|journal=Gondwana Research|volume=10|issue=3–4|pages=349–356|doi=10.1016/j.gr.2006.04.011|bibcode=2006GondR..10..349Y}}</ref>[[File:Carboniferous model.jpg|center|thumb|Evolution of the Carboniferous-extension model, modified from Yin (2006).<ref name=":0" /> Age abbreviations: M. Prot- Mesoproterozoic, D- Devonian, C- Carboniferous, P- Permian, K- Cretaceous.|722x722px]]

== Model comparison ==
{| class="wikitable sortable"
!
! colspan="5" |Predictions<ref name=":0" /><ref name=":6" /><ref name=":5" /><ref name=":10" />
|-
!Models
!Same source
!Older Greater Himalaya
!Early Paleozoic tectonics
!Current age relationships along the Main Central Thrust
!Rifting in Carboniferous
|-
|Passive Continental Margin Model
|✔
|'''×'''
|'''×'''
|'''×'''
|'''×'''
|-
|Crystalline Axis Model
|'''×'''
|✔
|'''×'''
|'''×'''
|'''×'''
|-
|Accreted Terrane Model
|'''×'''
|'''×'''
|✔
|✔
|'''×'''
|-
|Carboniferous- extension Model
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== See also ==
{{Portal|Asia|Geology}}
* [[Geology of Nepal]]
* [[Geology of the Himalaya]]
* [[Main Central Thrust]]
* [[South Tibetan Detachment]]

== References ==
{{reflist|30em}}

== Further reading ==
* {{cite journal|last1=DeCelles|first1=P. G.|title=Tectonic Implications of U-Pb Zircon Ages of the Himalayan Orogenic Belt in Nepal|journal=Science|date=2000|volume=288|issue=5465|pages=497–499|doi=10.1126/science.288.5465.497|pmid=10775105|bibcode=2000Sci...288..497D}}
* {{cite journal|last1=Myrow|first1=P. M.|last2=Hughes|first2=N. C.|last3=Paulsen|first3=T. S.|last4=Williams|first4=I. S.|last5=Parcha|first5=S. K.|last6=Thompson|first6=K. R.|last7=Bowring|first7=S. A.|last8=Peng|first8=S.-C.|last9=Ahluwalia|first9=A. D.|title=Integrated tectonostratigraphic analysis of the Himalaya and implications for its tectonic reconstruction|journal=Earth and Planetary Science Letters|date=2003|volume=212|issue=3–4|pages=433–441|doi=10.1016/S0012-821X(03)00280-2|bibcode=2003E&PSL.212..433M|citeseerx=10.1.1.526.4758}}
* {{cite journal|last1=Yin|first1=A.|title=Cenozoic tectonic evolution of the Himalayan orogen as constrained by along-strike variation of structural geometry, exhumation history, and foreland sedimentation|journal=Earth-Science Reviews|date=2006|volume=76|issue=1–2|pages=1–131|doi=10.1016/j.earscirev.2005.05.004|bibcode=2006ESRv...76....1Y}}

[[Category:Geology of the Himalaya]]
[[Category:Cenozoic geology of Asia]]
[[Category:Paleogene Asia]]
[[Category:Neogene Asia]]
[[Category:Cenozoic China]]
[[Category:Geology of India]]
[[Category:Geology of Pakistan]]
[[Category:Geology of Tibet]]

Pre-collisional Himalaya - Revision history

DongXqz408: new new details initial version.