Cenozoic tectonic evolution of the Himalayan orogen as constrained by along-strike variation of ...

123 Pages·2006·3.96 MB·English

Earth-ScienceReviews76(2006)1–131
www.elsevier.com/locate/earscirev
Cenozoic tectonic evolution of the Himalayan orogen as
constrained by along-strike variation of structural geometry,
exhumation history, and foreland sedimentation
An Yin*
DepartmentofEarthandSpaceSciencesandInstituteofGeophysicsandPlanetaryPhysics,UniversityofCalifornia,
LosAngeles,CA90095-1567,UnitedStates
Received26August2003;accepted2May2005
Availableonline8February2006
Abstract
Despitealongresearchhistoryoverthepast150years,thegeometry,kinematics,anddynamicevolutionoftheHimalayan
orogenremainpoorlyunderstood.Thisismainlyduetocontinuedemphasisonthetwo-dimensionalityoftheHimalayanorogenic
architectureandextrapolationofgeologicrelationshipsfromafewwell-studiedbutsmallareastotherestoftheorogen.Confusion
and misconception are also widespread in the Himalayan literature in terms of the geographic, stratigraphic, and structural
divisions.Toclarifytheseissuesandtoprovideanewplatformforthosewhoareinterestedinstudyingthegeologicdevelopment
ofthisspectacularmountainbelt,Isystematicallyreviewtheessentialobservationsrelevanttothealong-strikevariationofthe
HimalayangeologicframeworkanditsroleinCenozoicHimalayanexhumation,metamorphismandforelandsedimentation.A
mainfocusofmysynthesisistoelucidatetheemplacementhistoryofthehigh-gradeGreaterHimalayanCrystallineComplex
(GHC) that occupies the core of the orogen. Because the north-dipping Main Central Thrust (MCT) above and South Tibet
Detachment(STD)belowboundtheGHCinmostpartsoftheHimalaya,itiscriticaltodeterminetherelationshipbetweenthemin
mapandcross-sectionviews.TheexposedmappatterninthecentralHimalaya(i.e.,Nepal)indicatesthattheMCThasaflat-ramp
geometry.Thethrustflatinthesouthcarriesa2–15-km-thickslaboftheGHCovertheLesserHimalayanSequence(LHS)and
createsalargehanging-wallfault-bendfoldcontinuingN100kmsouthoftheMCTrampzone.InthewesternHimalayanorogenat
thelongitude~778E,theMCTexhibitsamajorlateralramp(theMandiramp).Westofthisramp,theMCTplacesthelow-grade
TethyanHimalayanSequence(THS)overthelow-gradeLHS,whereaseastoftheramp,theMCTplacesthehigh-gradeGHCover
thelow-gradeLHS.Thisalong-strikechangeinstratigraphicjuxtapositionandmetamorphicgradeacrosstheMCTindicatesa
westwarddecreaseinitsslipmagnitude,possiblyaresultofawestwarddecreaseintotalcrustalshorteningalongtheHimalayan
orogen.Everywhereexposed,theSTDfollowsroughlythesamestratigraphichorizonatthebaseoftheTHS,exhibitingalong
(N100km)hanging-wallflat.ThisrelationshipsuggeststhattheSTDmayhaveinitiatedalongapreexistinglithologiccontactor
thesubhorizontalbrittle–ductiletransitionzoneinthemiddlecrust.AlthoughtheSTDhastheTHSinitshangingwalleverywhere
intheHimalayanorogen,noTHSfootwallcutoffshavebeenidentified.ThishasmadeslipestimatesoftheSTDexceedingly
* Tel.:[phone];fax:[phone].
E-mail address: [email protected].
0012-8252/$-seefrontmatterD2005ElsevierB.V.Allrightsreserved.
doi:10.1016/j.earscirev.2005.05.004
2 A.Yin/Earth-ScienceReviews76(2006)1–131
difficult.ThesouthernmosttraceoftheSTDeithermergeswiththeMCT(e.g.,inZanskar)orlieswithin1–2kmoftheMCT
frontaltrace(e.g.,inBhutan),suggestingthattheMCTmayjointheSTDintheirup-dipdirectionstothesouth.Thisgeometry,
largelyneglectedbytheexistingmodels,hasimportantimplicationsforthedeformation,exhumation,andsedimentationhistory
oftheentireHimalayanorogen.
D2005Elsevier B.V.All rights reserved.
Keywords: Himalayan orogen; Main Central Thrust; South Tibet Detachment; passive-roof fault; active-roof fault; erosional exhumation
1. Introduction entirety. This may be attributed to the following
factors:
bDistinguishing between myth and science is sub-
(1) Himalayan research is long (over 150 yr, e.g.,
tle,forbothseektounderstandthethingsaroundus.
Hooker, 1854; Godwin-Austen, 1864; Mallet,
The characteristic style of mythic thinking is to
1875; La Touche, 1883; Pilgrim, 1906; Auden,
place special emphasis on a selective conjecture,
1935; Lahiri, 1941) and rich, making its litera-
based typically on the initial observation or recog-
ture nearly intractable. The problem is com-
nition of a phenomenon, which is thereafter given
pounded by the accelerated rate of publication
privileged status over alternate interpretations.Q
on more and more specialized subjects on Hi-
William. R. Dickinson
malayan geology in the past two decades.
(2) The terminology of the Himalayan geology is
The Himalaya is a classic example of an orogen-
often confusing. Its physiographic division is
ic system created by continent–continent collision
commonlyequatedtostructuralandstratigraphic
(e.g., Dewey and Bird, 1970; Dewey and Burke,
divisions.Namesofthesamestratigraphicunits
1973). Its youthfulness and spectacular exposure
and structures vary from place to place across
make the orogen ideal for studying diverse geologic
international borders or even within the same
processes related to mountain building. Its potential
country.
as a guide to decipher the feedback processes be-
(3) There has been a proliferation of kinematic,
tween lithospheric deformation and atmospheric cir-
thermal, and dynamic models for the develop-
culation has motivated intense research in recent
ment of the Himalayan orogen in the past two
years on the history of the Himalayan–Tibetan oro-
decades. Debate is intense and consensus
gen, its role in global climate change, and its inter-
changes rapidly. This has made it especially
action with erosion (e.g., Harrison et al., 1992,
difficult to evaluate the validity of each model
1998a; Molnar et al., 1993; Royden et al., 1997;
or apply them to other mountain belts.
Ramstein et al., 1997; Tapponnier et al., 2001;
Beaumont et al., 2001; Yin et al., 2002). Many The classic reviews of the Himalayan geology by
workers have also used the Himalayan knowledge Wadia(1953),Gansser(1964) andLeFort (1975) laid
to infer the evolution of other mountain belts: the thefoundationforproductivegeologicresearchinthe
Altai system in central Asia (Yang et al., 1992; Qu nextseveraldecadestofollow.However,theirreviews
and Zhang, 1994), the Trans-Hudson orogen and are largely out of date in light of new observations.
Canadian Cordillera in North America (e.g., Nabe- Although several recent reviews on the Himalayan
lek et al., 2001; Norlander et al., 2002), the Cale- geology could potentially overcome the problem,
donides in Greenland (e.g., McClelland and Gilotti, they cover only selected segments of the Himalayan
2003), and the East African–Antarctic orogen in orogen. For example, reviews by LeFort (1996),
Africa and Antarctica (e.g., Jacobs and Thomas, Hodges (2000), Johnson (2002), DeCelles et al.
2004). Despite the broad interests, it has become (2002), and Avouac (2003) emphasize the central Hi-
increasingly daunting for both a beginner and an malayan orogen, while syntheses by Searle et al.
experienced Himalayan geologist to comprehend the (1992), Thakur (1992), Steck (2003), and DiPietro
intricate complexity of the Himalayan geology in its and Pogue (2004) focus exclusively on the western
A.Yin/Earth-ScienceReviews76(2006)1–131 3
Himalayan orogen. Similarly, geologic summaries by marksthenorthernlimitoftheIndo-Gangetic depres-
Acharyya (1980), Singh and Chowdhary (1990), and sion(Fig.1A).ImmediatelytothewestoftheHimala-
Kumar (1997) only cover the geology of the eastern yanrangearetheHinduKushMountains,totheeastthe
Himalayanorogen.Thelackofanupdatedoverviewof Indo-BurmaRanges(commonlyknownastheRongk-
theentireHimalayanorogenmakesitdifficulttoassess lang Range), and to the north the Karakorum Moun-
how theHimalayan deformationhasrespondedtothe tains and the Gangdese Shan (also known as the
well-understoodplateboundaryconditionsanditsim- TranshimalayainHeimandGansser,1939)(Fig.1A).
pactontheoverallIndo-Asiancollisionzoneandevo- The southern politicalboundaryof Tibet (i.e., Xizang
lutionofgreatriversinAsia(e.g.,PatriatandAchache, in Chinese) follows approximately the crest of the
1984; Dewey et al., 1989; Le Pichon et al., 1992; Himalayan range.Thedifferenceinpoliticalandgeo-
Brookfield, 1998; Hallet and Molnar, 2001; Clark et graphic divisions has led to different naming of the
al.,2004). samestructuresintheHimalayanrange(e.g.,theNorth
The present review intends to introduce the Hima- Himalayan Normal Fault versus South Tibet Detach-
layangeologyinitsentirety.Inordertoseparateobser- mentSystem;Burgetal.,1984a;Burchfieletal.,1992).
vationsfrominterpretations,Iapproachthesynthesisin The Himalayan orogen is defined by the Indus–
the following order. First, I define the basic terminol- Tsangpo suture in the north, the left-slip Chaman
ogy commonly used in Himalayan literature and dis- fault in the west, the right-slip Sagaing fault in the
cuss their pitfalls in limiting our ability to understand east, and the Main Frontal Thrust (MFT) in the south
the complexity of the geology. Second, I provide a (Fig. 2A) (LeFort, 1975). Because the MFT links
systematic overview of the Himalayan structural transpressional systems in the Indo-Burma Ranges
framework, metamorphic conditions, exhumation his- (=Rongklang Range) in the east (e.g., Guzman-Spe-
tory, and foreland sedimentation. Third, prominent ziale and Ni, 1996) and the Kirthar-Sulaiman thrust
tectonic hypotheses and quantitative physical models salientsinthewest(e.g.,Schelling,1999)(Fig.2A),the
fortheevolutionoftheHimalayanorogenareoutlined Himalayan orogen defined above extends all the way
andtheirpredictionsareevaluatedinlightoftheavail- fromtheHimalayan range totheArabianSeaandthe
able data.Finally,thecurrentunderstandingofHima- BayofBengal.IconsidertheSillongPlateaubounded
layangeologyisintegratedintoaninternallyconsistent bytheactivesouth-dippingDaukithrustaspartofthe
tectonic model that accounts for both map and cross- broadlydefinedHimalayanorogen,becauseitsbound-
section views of the Himalayan architecture and the ingstructureislinkedwiththetranspressionalsystem
exhumationandsedimentationhistories. intheIndo-BurmanRanges(Fig.2A).
TheHimalayantectonicsystemisabroaderconcept
thantheHimalayanorogen.ItconsistsoftheHimala-
2. Basic terminology yan orogen, the active Himalayan foreland basin
(=Indo-Gangeticdepression),andtheIndusandBengal
2.1. Himalayan range, Himalayan Orogen, and Hi- Fans(Fig.2A).Allofthesefeatureswereproducedby
malayan tectonic system theCenozoicIndo-Asiancollision.
The Indo-Gangetic depression is a broad up-side-
Before embarking on an exhaustive synthesis, it is down bU-shapedQ basin in map view (Fig. 1A). Its
useful to have a clear distinction of the politically, basementdipsatabout2–38fromthePeninsulaHigh-
geographically, structurally, and stratigraphically de- landsoftheIndiancratontowardstheHimalayanoro-
fined Himalaya. Geographically, the Himalayan gen, with the thickness of basin fill increasing
range liesbetweenitseasternandwesternsyntaxisas progressively to about 4–5 km against the Himalayan
represented by the Namche Barwa and Nanga Parbat front(Hayden,1913;Rao,1973;Lyon-CaenandMol-
peaks (Fig. 1A). The northern boundary ofthe Hima- nar, 1985; Raiverman, 2000). The northern boundary
layan range is the east-flowing Yalu Tsangpo ofthedepressionissharplydefined,whereasthesouth-
(Tsangpo—big river in Tibetan) and west-flowing ernboundaryisdiffuseandhighlyirregular.Thesouth-
Indus River (Fig. 1A). The southern boundary of the ern boundary is referred to as the hinge zone in this
HimalayanrangeistheMainFrontalThrust(MFT)that paper,whichseparatestheHimalayanforelandbasinin
4 A.Yin/Earth-ScienceReviews76(2006)1–131
the north from the Peninsula Highlands of the Indian (2) structurally defined MBT hanging wall=litho-
cratoninthesouth.Burbank(1992)notesthattheeast- logically defined Lower Himalaya=topographi-
flowing Ganges drainage system is currently flowing cally defined Lower Himalaya;
about 200 km away from the Himalayan mountain (3) structurally defined MCT hanging wall=litho-
front directly against the hinge zone defined here logicallydefinedHigherHimalaya=topographi-
(Fig. 1A). He attributes this pattern to erosion-domi- cally defined Higher Himalaya;
nated Himalayan development in Plio-Pleistocene (4) structurally defined STD hanging wall=litholo-
times, whichcaused isostaticupliftofboth theHima- gically defined Tethyan Himalaya=topographi-
layanrangeandsouthwardprogradationoflargeallu- cally defined Tethyan Himalaya north of the
vial fans and pushed the river far away from the Himalayan crest.
mountainfront.Basedonsuccessivesouthwardonlap-
pingunconformitiesinthedepression,Lyon-Caenand Theserelationships arebroadly valid inthecentral
Molnar(1985)suggestthatahingeline~200kmfrom HimalayainNepalandtheKumaunregionofeastern-
theHimalayanthrustfronthasmigratedsteadilysouth- mostNWIndia.However,thedefinitionprecludesthe
wardatarateof~15mm/yr(alsoseeAvouac,2003). possibility that individual lithologic units may extend
Raiverman(2000)laterquestionsthemodelandargues across major thrusts, such as the MCT and MBT,
insteadthatthehingezonemayhavemigratedepisod- outside the type locality where these divisions were
icallybothtothenorthandsouthduringtheCenozoic derived.Theinabilityinthepastdecadestorecognize
developmentoftheHimalayanorogen. thislimitationhasledtocircularreasoninginlocating
major Himalayan structures and the lack of apprecia-
2.2. Himalayan divisions
tion of along-strike variation of the Himalayan archi-
tecture(e.g.,Arglesetal.,2003;alsoseediscussionon
In the Himalayan literature, the politically, geo-
this issueby DiPietro andPogue, 2004).
graphically, structurally, and stratigraphically defined
ThedivisionofHeimandGansser(1939)isinfact
Himalayaisoftenassumedtobeinterchangeable(e.g.,
contradictory to many geologic observations. For ex-
LeFort,1975,1996).Thistraditioncanbetracedback
ample, the high-grade Higher Himalayan Crystallines
atleasttotheclassicworkofHeimandGansser(1939),
of Heim and Gansser (1939) are exposed in all three
whobasedontheirexperienceintheKumaunregionof
geographical zones they defined: the Tethyan Hima-
NW India (Fig. 2A), divided the Himalaya into four
laya, Higher Himalaya, and Lower Himalaya (e.g.,
east-trendinggeographicbeltsthatcorrespondexactly
Sto¨cklin, 1980; Scha¨rer et al., 1986; Frank et al.,
to four geologic domains. These geographic and geo-
1995; Fuchs and Linner, 1995; de Sigoyer et al.,
logic zones are assumed continuous along the entire
2000, 2004; Lee et al., 2000; Murphy et al., 2002)
Himalayan orogen (Gansser,1964;LeFort,1975)and
(Fig.2).Conversely,theTethyan andHigherHimala-
include:
yan lithologic units of Heim and Gansser (1939) are
(1) sub-Himalaya (Tertiary strata); also present in the geographically defined Lower and
(2) Lower Himalaya (nonfossiliferous low-grade Higher Himalaya (e.g., Sto¨cklin, 1980; Gansser,
metamorphic rocks; it is also known as the 1983).Furthermore,theTethyanHimalayanSequence
Lesser Himalaya, see LeFort, 1975); of Heim and Gansser (1939) is exposed in both the
(3) HigherHimalaya(crystallinecomplexconsisting MCT hanging wall and footwall in northern Pakistan
ofgneissesandapliticgranites;itisalsoknown (e.g.,Pogueetal.,1992,1999).Attemptstoavoidthe
astheGreaterHimalaya,seeLeFort,1975);and aboveconfusionweremade atlocalscales,forexam-
(4) Tethyan Himalaya (marine, fossiliferous strata). ple in Nepal (Upreti, 1999) and in northern Pakistan
(DiPietro and Pogue, 2004), but there has been no
Heim and Gansser’s (1939) division implies the fol-
systhematiceffortindoingsofortheentireHimalaya.
lowing interchangeable relationships:
(1) structurally defined MBT footwall=lithologi- 2.2.1. Geographic division
cally defined sub-Himalaya=topographically In order to decouple the Heim-Gansser Himalayan
defined sub-Himalaya; divisions from one another, the following geographic
A.Yin/Earth-ScienceReviews76(2006)1–131 pp.5–6
Fig.1.(A)TopographicmapoftheHimalayanorogen.RegionsoutlinedbyyellowlinesarebasementridgesbeneaththeIndo-GangeticdepressionafterRao(1973)andRaiverman(2000).DLS,Delhi–Lahore–Sargodhabasementhigh;DM,Delhi–Muzaffarnagar
ridge;FR,Faizabadridge;MS,Manghyr–Saharsaridge;RGR,Rajmahal–GaroGapridge;RGG,Rajmahal–GaroGap.Rivers:B.R.,BhagirathiRiver;A.R.,AlaknandaRiver;K.R.,KaliRiver.Rifts:K,KongurShanextensionalsystem;TM,TsoMoraririft;PG,
Pulan–GurlaMandhataextensionalsystem;T,Thakkholagraben;L,Longgerift;X,Xiakangjianrift;TY,TangraYumCorift;YG,Yadong–Gururift;CM,Comarift.LineAisthelocationofstratigraphicsectionsoftheIndo-GangeticdepressionshowninFig.3.
Locationsofstratigraphicsectionsbasedondrillholedata:KB,Kangasub-basin,DB,Dehradunsub-basin,SB,Sardasub-basin,GB,GanakBasin,P,Purnea.ThestratigraphicsectionsfromRaiverman(2000)areshowninFig.3.(A)Stratigraphicsectionsbeneath
theIndo-GangeticplainsfromBurbank(1992).(B)TopographicprofilesacrosstheHimalayanorogenusingdatafromGTOPO30.Eachprofileisanaverageofdatafroma4-kmwideswathusinga400mrunningbin.(C)Closeupviewoftopographicexpression
ofwesternHimalayanorogen.Theregionischaracterizedbythepresenceoflargebasinswithlowaspect(i.e.,widthversuslength)ratios.Seepanel(A)forlocation.(D)CloseupviewoftopographicexpressionofcentralHimalayanorogen.Theregionis
characterizedbythepresenceoflargebasinswithlargeaspect(i.e.,widthversuslength)ratios.Seepanel(A)forlocation.(E)CloseupviewoftopographicexpressionofeasternHimalayanorogen.Notethatnoprominentintermontanebasinsarepresentinthis
region.Seepanel(A)forlocation.
pp.7–8 A.Yin/Earth-ScienceReviews76(2006)1–131
(B)
8000 8000 Garhwal 8000 Bhutan ITS Tibetan
Himalaya ITS Tibetan plateau Himalaya North Plateau
6000 6000 HH 6000 Himalaya
HH
4000 4000 4000 LH
2000 prof1 Kirthar thrust belt Chaman fault 2000 prof7 SH LH Karakorum fault 2000 prof13 Shillong Plateau
0 0 0
0 500 0 500 0 500
Horizontal distance (km) Horizontal distance (km) Horizontal distance (km)
68000000 68000000 KHuimmaaluanya HH ITSGaTnibgdeetasen S phlaanteau 68000000 CH,i mAarulanyaHacHhalNHoimrtahlayaITS TPilbaetetaanu
4000 Sulaiman thrust belt Chaman fault 4000 LH 4000 LH
2000 prof2 2000 prof8 SH 2000 prof14 Shillong Plateau SH
0 0 0
0 500 0 500 0 500
Horizontal distance (km) Horizontal distance (km) Horizontal distance (km)
8000 8000 W. Nepal Himalaya ITS Tibetan Plateau 8000 E, Arunachal ITS Tibetan
6000 Hindu Kush 6000 N. Hima 6000 Himalaya Plateau
MMT = ITS HH
meters) 240000000 prof3 Pakistan Himalaya 240000000 prof9 IDnedpor-eGssainognetic SH LH 240000000 prof15 SH LH HH
n ( 0 Horizontal distance (km) 500 0 Horizontal distance (km) 500 0 Horizontal distance (km) 500
o
ati 8000 W. Kashmir 8000 C. Nepal Himalaya ITS Tibetan 8000 Namche North ITS Tibetan
Elev 6000 Himalaya ITS 6000 HH N. Himalaya Plateau 6000 Barwa Himalaya Plateau
4000 Kashmir basin 4000 LH 4000 HH
2000 prof4 2000 prof10 Indo-Gangetic SH 2000 prof16 LH
Depression
0 0 0
0 500 0 500 0 500
Horizontal distance (km) Horizontal distance (km) Horizontal distance (km)
8000 E. Kashmir 8000 E. Nepal Himalaya ITS Tibetan
6000 Himalaya Karakorum Mountains 6000 N. Himalaya Plateau
HH
4000 ITS 4000
prof5 LH
2000 2000 prof11 Indo-Gangetic
Depression
0 0
0 500 0 500
Horizontal distance (km) Horizontal distance (km)
8000 Zanskar 8000 Sikkim ITS Tibetan
6000 Himalaya ITSTibetan Plateau 6000 HimallHaHya NHoimrtahlaya Plateau
4000 HH 4000 LH
2000 prof6 SH LH HLHH,, LHoigwheerr H Hiimmaallaayyaann z zoonnee 2000 prof12 Indo-Gangetic
SH, sub-Himalayan zone Depression
0 0
0 500 0 500
Horizontal distance (km) Horizontal distance (km)
Fig.1(continued).
A.Yin/Earth-ScienceReviews76(2006)1–131 9
Fig.1(continued).
definitions of the Himalayan orogen are adopted. In and Gansser (1939) or the Tibetan Himalaya of
the north–south direction, the Himalayan orogen may LeFort (1975). Following the tradition of Heim and
bedividedintotheNorth Himalaya andSouth Hima- Gansser (1939) and Gansser (1964), the South Hima-
laya partitioned by its high crest line (Table 1). The layaisdividedintoHigher,Lower,andsub-Himalaya
North Himalaya is approximately equivalent to the from north to south (Table 1). I define the southern
geographically defined Tethyan Himalaya of Heim boundary of the Higher Himalaya at the base of the
10 A.Yin/Earth-ScienceReviews76(2006)1–131
Table1
Geographical,stratigraphic,andstructuraldivisionoftheHimalayanrangeandHimalayanorogen
Geographical/Topographic Division in this Paper Litho- and Chrono-stratigraphy Structural Division
Map View: Tibetan Plateau 1. Siwalik Group: Neogene fine- to
coarse-grained continental strata 1. STD hanging wall
Indus River/Yalu Tsangpo (~20 - 2 Ma).
North Himalaya STD
Himalayan Crest 2. Lesser Himalayan Sequence (LHS): 2. MCT hanging wall
Higher Himalaya Metasedimentary and metavolcanic
Base of northernmost strata, augen gneiss (1870-800 Ma). MCT
steep slope
Lower Himalaya 3. MBT hanging wall
3. Greater Himalayan Crystalline
Lowest intermontane valley
Complex (GHC): High-grade MBT
Sub-Himalaya
metamorphic rocks (800-480 Ma).
4. MFT hanging wall
Vertical Division: Upper Himalaya (> 3500 m)
Middle Himalaya (1500-3500 m) 4. Tethyan Himalayan Sequence MFT
Basal Himalaya (50-1500 m) (THS): Late Precambrian to Eocene
5. MFT footwall
(~ 650- 40 Ma) sedimentary sequence
Along-strike Western Himalayan orogen
Division: (west of 81 °E, including Salt Range, locally interlayered wtih volcanic
flows.
Kashmir, Zanskar, Spiti, Himachal
a. Late Prot.-D: pre-rift
Pradesh, Garhwal, and Kumaun)
b. C-J1: syn-rift
Central Himalayan orogen c. J2-K: passive-margin
(8 1 °E - 89 °E, including Nepal, Sikkim, d. Paleocene-Eocene: syn-collision
and south-central Tibet)
5. North Indian Sequence (NIS):
Eastern Himalayan orogen
(east of 89°E, including Bhutan, Phanerozoic cover sequence above
LHS (520 - 20 Ma).
Arunachal Pradesh, and southeast Tibet)
northernmost steepest slope of the southern Himala- Pakistan south of the Indus–Tsangpo suture (=Main
yan range, whereas the boundary between the Lower MantleThrust)asnotedbyDiPietroandPogue(2004)
Himalaya andsub-Himalayaliesalongtheaxisofthe (Fig. 1B).
lowestintermontanevalleyparalleltotherange(Table Alongstrike,theHimalayanorogenmaybedivided
1)(Fig.1B).Althoughtheseboundariesarerelatively into the western (668–818), central (818–898), and
easytodefineonindividualtopographicprofiles(Fig. eastern (898–988) segments (Table 1). The western
1B), in map view they can be discontinuous. This Himalayan orogen covers the following regions that
problem is particularly striking for the boundary be- commonly appear in the literature: Salt Range in
tween the Lower and sub-Himalaya, because most northern Pakistan, Kashmir (also known as the
range-parallel intermontane valleys are discontinuous Jammu–Kashmir State of NW India), Zanskar, Spiti,
in the Pakistan and NW India Himalaya, become Chamba, Himachal Pradesh, Lahul, Garhwal, and
narrower in Nepal, and disappear completely east of Kumaun (also spelled as Kumaon) (Fig. 2A). The
Sikkim (Fig. 1C–E). central Himalayan orogen occupies Nepal, Sikkim,
Elevation of some parts of the Lower Himalaya is and south-central Tibet, whereas the eastern Himala-
in fact higher than some lower parts of the Higher yanorogenincludesBhutan,ArunachalPradeshofNE
Himalaya (Duncan et al., 2003) (Fig. 1B). To avoid India, andsoutheasternTibet (Fig. 2A).
confusion over the traditionally defined Higher, A systematic along-strike change in the Himala-
Lower, and sub-Himalaya, I suggest that the Himala- yan topography is best expressed by the geometrical
yan range may be divided vertically into the Basal variation of the modern intermontane basins in the
(b1500m),Middle(1500–3500m),andUpperHima- South Himalaya. For example, intermontane basins
laya (N3500 m) (Table 1). Following this definition, with north–south widths N80–100 km are present in
the Upper Himalaya is mostly absent in northern northern Pakistan (e.g., Jalalabad and Peshawar
A.Yin/Earth-ScienceReviews76(2006)1–131 11
basins) and Kashmir (Kashmir basin) (Figs. 2A and (1975), the structural units defined here do not have
1C). However, intermontane basins become more unique correlations with individual lithologic units
elongated and narrower (b30–40 km in the north– (e.g., DiPietro and Pogue, 2004). That is, identifying
south width) in the central Himalayan orogen (Fig. anddifferentiatingHimalayanlithologicunitsaloneare
1D) and are completely absent in the eastern Hima- notsufficienttodeterminethelocationofmajorHima-
laya (Fig. 1E). As discussed in Section 7.6, this layan thrusts (cf. Ahmad et al., 2000), because the
variation may be a direct result of an eastward in- faults may cut up and down sections laterally and in
crease in the total crustal shortening along the Hima- their transport directions across major lithological
layan orogen (also see Yin et al., submitted for boundaries.
publication).
2.2.4. Temporal division
2.2.2. Stratigraphic division The history of the Himalayan evolution has been
Stratigraphically, the major lithologic units in the generally divided into two stages: the Eohimalayan
Himalayan orogen consist of the Neogene Siwalik event that occurred during the middle Eocene to Oli-
Group, the Proterozoic Lesser Himalayan Sequence gocene (45–25 Ma) and the Neohimalayan event that
(LHS), the Proterozoic–Ordovician Greater Himala- occurred since the early Miocene (e.g., LeFort, 1996;
yan Crystalline Complex (GHC), and the Proterozoic Hodges,2000).Thisdivisionwasoriginatedfrom the
toEoceneTethyanHimalayanSequence (THS)(Table recognition that several phases of metamorphism oc-
1)(e.g.,LeFort,1996).Amongtheseunits,thedefini- curred duringthedevelopment of theHimalayan oro-
tion and lateral correlation of the Greater Himalayan gen,withtheolderphasestypicallyinducedbycrustal
Crystalline Complex are most problematic. Heim and thickening and expressed by prograde metamorphism
Gansser(1939)originallydefinetheunitashigh-grade andlaterphasesbyunroofingandretrogrademetamor-
metamorphicrocksstructurallybelowthefossiliferous phism (e.g., LeFort, 1975; Brunel and Kienast, 1986;
TethyanHimalayanSequence.Thisdefinitionwasfol- HodgesandSilverber,1988;Searleetal.,1999a).The
lowedbyLeFort(1975)whoreplacedtheGHCbythe essenceofthisdivisionistheimplicitlyassumedsyn-
term bTibetan slabQ and designate it as bhighly meta- chroneity of similar deformation and metamorphic
morphicandtectonizedbasementofthePaleozoicand styles occurring along the entire length of the Hima-
Mesozoic Tethyan sedimentsQ (p. 4, LeFort, 1975). layan orogen. As shown by DiPietro and Pogue
Because the basal parts of the THS in northern (2004), application of this interpretation to the evolu-
Nepal and south-central Tibet also exhibit up to tion of the western Himalayan orogen is problematic,
amphibolite facies metamorphism (e.g., Schenider where the typical bNeohimalayanQ event associated
and Masch, 1993), the Heim and Gansser (1939) withunroofingandretrograde metamorphismiscom-
definition is untenable. In this paper, I regard both pletelyabsent.Becauseofitslimitedapplicationtothe
the Greater Himalayan Crystalline Complex and evolutionofthewholeHimalaya,oneshouldtreatthe
Tethyan Himalayan Sequence as chronostratigraphic above temporal division as a hypothesis rather an
units regardless of their metamorphic grades. This accepted fact.
definition has been implicitly or explicitly adopted
by many workers (e.g., DeCelles et al., 2000; Steck, 2.3. Major Himalayan lithologic units
2003; DiPietro and Pogue, 2004). Another problem
in the Himalayan stratigraphic division is the use of 2.3.1.TethyanHimalayanSequence(THS)(1840Ma–
lithostratigraphy as the basis for defining chronos- 40 Ma; Paleoproterozoic to Eocene)
tratigraphic units. The Tethyan Himalayan Sequence consists of
Proterozoic to Eocene siliciclastic and carbonate sed-
2.2.3. Structural division imentary rocks interbedded with Paleozoic and Me-
ThemajortectonostratigraphicunitsintheHimala- sozoic volcanic rocks (Baud et al., 1984; Garzanti et
yanorogenaredefinedastheMFThangingwall,MBT al., 1986, 1987; Gaetani and Garzanti, 1991; Gar-
hanging wall, MCT hanging wall, and STD hanging zanti, 1993, 1999; Brookfield, 1993; Steck et al.,
wall (Table 1). Unlike Gansser (1964) and LeFort 1993; Critelli and Garzanti, 1994; Liu and Einsele,
12 A.Yin/Earth-ScienceReviews76(2006)1–131
Table2
SelectedstratigraphicsectionsoftheTethyanHimalayanSequence
SE Zanskar Northern Nepal South-central Tibet
Chulung La FM. (Eocene ?) Muding FM. (E. Cret.) Zongshan FM (L. Cret.)
(siltstone, 100 m) (marlstoone, > 40m) (limestone, marl, sandstone, 270 m)
Spanboth FM. (L. Cret.-Pa.) “glauconitic horizon” (E. Cret.) Jiubao FM. (L. Cret.)
(calcarenite, 120-140 m), (arenite, 25 m) (limestone, sandstone, 90-180 m)
Kangi La FM. (L. Cret. ?) Daong FM. (E. Cret.)
(siltstone, shale, sandstone, (shale and sandstone, 400 m) Lengqingre FM. (L. Cret.)
(shale, marl, 210-230 m)
400-600 m) Kagbeni FM. (E. Cret.)
Chikkim FM. (L. Cret. ?) (volcaniclastics, coal, 130 m) Chaqiela FM. (E. Cret.)
(limestone, 90-100 m) Dangardzong Quartzarenite (L. Cret.) (shale, limestone, 160-180 m)
(sandstone, shale, 45 m)
Giumal Sandstone (L. Cret.-Pa./Eo.) Dongshan FM. (E. Cret.)
(sandstone, 200-300 m) Spiti Shale (L. Jr.) (black shale, 500-800 m)
(black shale, 150 m)
Spiti Shale (L. Jurassic-E. Cret.) Xiumo FM. (L. Jr.)
(shale, 30 to >150 m) Dangar FM. (M. Jr.) (limestone, sandstone, 1800 m)
(marlstone, 10 m)
Laptal FM. (no information)
Ferruginous Oolite FM. (M. Jr.) Menbu FM. (L. Jr.)
Kioto Limestone (E. Jurassic) (ironstone, arenite, 7 m) (shale, >500 m)
(dolostone, 400 m) Laptal FM. (M. Jr.) Lalongla FM. (M. Jr.)
Quartzite Series/Alaror FM. (E. Triassic) (marl, arenite, 100-120 m) (limestone, quartzarenite, 740 m)
(sandstone, quartzarenite, 120 m) Kioto Limestone (E.-M. Jr.)
Zozar FM. (L. Triassic) (carbonate, 250-300 m) Niehnieh Hsionla FM. (M. Jr.)
(limestone, 20 m) Zhamure Sandstone (L. Tr.-E. Jr. ?) (oolitic limestone, sandstone, 780 m)
Hans FM. (M. Triassic) (arenite, sandstone, 30 m) Pupuga FM. (E. Jr.)
(marls, limestone, 410 m) Yak Kharka FM. (L. Tr. ?) (siltstone, shale, sandstone, 880 m)
(siltstone, limestone, arenite, 150 m)
Tamba Kurkur FM. (E.-M. Triassic) Zhamure FM. (L. Tr.)
(limestone, shale, 40-100 m) Tarpa FM. (M. Tr.) (shale, sandstone, 140 m)
(siltstone, sandstone, 400-500 m)
Kuling FM. (L. Permian) Derirong/Qulonggongba/Yazhi FM.
(quartz arenite, 30-55 m) Mukut FM. (E. Tr.) (L. Tr., sandstone)
(marl, marly limestone, 200-270 m)
Panjal Traps (Permian) (shale, limestone, 1000 m)
Tamba-Kurkur FM. (E. Tr.)
(volcanics and volcaniclastics, (pelagic limestone, 23-50 m) Kangshare FM. (L. Tr.)
2500 m) (limestone, shale, 99 m)
Ganmachidam FM. (Carb.- E. Permian) Nar-Tsum Spilites (E. Permian)
(sandstone, siltstone, shale; (spilitized tholeiitic basalt, 0-85 m) Qudenggongba FM. (M. Tr.)
no thickness estimates) Puchenpra FM. (E. Permian) (carbonate, shale, 200-400 m)
Po FM. (Carboniferous) (sandstone, arenite, 100-150 m) Tulong FM. (E. Tr.)
(sandstone, limestone, 80-100 m) Atali Quartzarenite (L. Carb.) (limestone, shale, 100-300 m)
Lipak FM. (E. Carb.) (sandstone, 100 m) Baga FM. (L. Permian)
(marly limestone, 50-70 m) Braga FM. (L. Carb. ?) (domostone, marl, 10 m)
(shale, sandstone, diamictite, 120 m)
Muth Quartzite (Devonian)
(massive white quartzite, > 200 m) Bangba FM. (L. Carb.) Shengmi FM. (E. Permian)
(shale, limestone, sandstone, 400 m)
(sandstone, shale, diamictite, 90 m)
Thaple FM. (Ordov.-Silu.)
(conglomerate, > 300 m) Col Noir Shale (L. Carb.) Jiling FM. (L. Carb.)
(shale, sandstone, 160 m) (Quartzarenite, diamictite, 700 m)
unconformity
“Syringothyris beds” (L. Carb.)
Naxing FM. (E. - M. Carb.)
Karsha FM. (M.-L. Camb.) (arenite, shale, sandstone, 65 m)
(shale, marl, sandstone, 60 m)
(dolostone and slate, ~200 m)
Marsyandi FM. (E. Carb.)
Phe FM. (late Protero.-Camb.?) (shale, sandstone, arenite, 400 m) Poqu Group (M.-L. Dev.)
(shale, sandstone, ~ 1500 m) Ice Late/Tilcho Lake FM. (E. Carb.) (shale, quartzarenite, 320 m)
(carbonate, 320 m) Liangquan FM. (E. Dev.)
Tilicho Pass FM. (L. Dev.) (arenite, limestone)
(quartzarenite, carbonate)
Pulu Group (M. - L. Silurian)
Muth FM. (M. - L. Dev.) (quartz arenite, limestone, 50 m)
(carbonate, quartzarenite, mudstone)
Shiqipo FM. (E. Silurian)
Dark Band FM. (E. Silurian-Early Dev.)
(shale, sandstone, limestone, 90 m)
(pelite, limestone, marl)
North Face Quartzite/Gyaru FM. (L. Ordo.) Hongshantou FM. (L. Ordo.)
(quartzite, mudstone) (shale, sandstone, 70 m)
Dhaulagiri Limestone/Nilgiri FM. (M. Ordo.) Jiacun Group (E. - M. Ordo.)
(strongly recrystallized carbonate) (carbonate, 820 m)
Annapurna Yellow FM. (Cambrian ?)
Ruqiecum Group (Cambrian ?)
(Bt+Ms calc schist, psammite)
(marble, banded limestone, 240 m)
Sanctuary FM. (Cambrian ?)
(BT+Ms schist, sandstone)