Neogene Marine Isotopic Evolution and the Erosion of Lesser Himalayan Strata: Implications for Cenozoic Tectonic History ∗ Paul M

Earth and Planetary Science Letters 417 (2015) 142–150

Contents lists available at ScienceDirect

Earth and Planetary Science Letters

www.elsevier.com/locate/epsl

Neogene marine isotopic evolution and the erosion of Lesser Himalayan strata: Implications for Cenozoic tectonic history ∗ Paul M. Myrow a, , Nigel C. Hughes b, Louis A. Derry c, N. Ryan McKenzie d,e, Ganqing Jiang f, A. Alexander G. Webb g, Dhiraj M. Banerjee h, Timothy S. Paulsen i, Birendra P. Singh j a Department of Geology, Colorado College, Colorado Springs, CO 80903, USA b Department of Earth Sciences, University of California, Riverside, CA 92521, USA c Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY 14853, USA d Jackson School of Geosciences, University of Texas, Austin, TX 78713, USA e Department of Geology and Geophysics, Yale University, New Haven, CT 06511, USA f Department of Geosciences, University of Nevada, Las Vegas, NV 89154, USA g Department of Geology & Geophysics, Louisiana State University, LA 70803, USA h Department of Geology, University of Delhi, Delhi, 110007, India i Department of Geology, University of Wisconsin, Oshkosh, WI 54901, USA j Department of Geology, Panjab University, Chandigarh, 160014, 54901, India a r t i c l e i n f o a b s t r a c t

Article history: An extensive, northward deepening blanket of Neoproterozoic and Cambrian sedimentary rocks once Received 30 September 2014 extended from the Himalayan margin far onto the Indian craton. Cambrian deposits of this “upper Lesser Received in revised form 29 January 2015 Himalayan” succession, which include deposits of the “outer” Lesser Himalaya tectonic unit, are enriched Accepted 12 February 2015 in radiogenic 187Os. They make up part of a proximal marine facies belt that extends onto the craton Available online 6 March 2015 and along strike from India to Pakistan. By contrast, age-equivalent facies in the Tethyan Himalaya are Editor: A. Yin more distal in nature. Neoproterozoic to Cambrian strata of the upper Lesser Himalayan succession are Keywords: now missing in much of the Lesser Himalaya, with their erosion exposing older Precambrian Lesser Himalaya Himalayan strata. We suggest that exhumation and weathering of the upper Lesser Himalaya and related tectonics strata caused dramatic changes in the 187Os/188Os and 87Sr/86Sr Neogene record of seawater starting at geochemistry ∼16 Ma. First-order estimates for the volume of upper Himalayan strata, as well as the volume of all isotopes LH rock eroded since this time, and geochemical box modeling, support this idea. Exhumation at 16 Ma Neogene is a fundamental event in the evolution of the Himalayan orogeny and the geochemical evolution of the oceans, and will be a critical part of the construction of future models of Himalayan thrust belt evolution. © 2015 Elsevier B.V. All rights reserved.

1. Introduction the timing of exhumation of lithotectonic zones of the Himalaya (Fig. 1), and debates on the pre-deformational configuration of The uplift and erosional history of the Himalayan orogen had the north Indian margin (e.g., Yin, 2006). Recent studies of the fundamental influence on climate and secular changes in ocean Neoproterozoic–early Paleozoic successions of the ancient northern chemistry (Derry and France-Lanord, 1996; France-Lanord and Indian margin, both along and across the strike of the Himalayan Derry, 1997; Galy et al., 2007). Of key interest are the links be- orogen, provide insights into the stratigraphic, depositional, and tween Neogene uplift and both the erosion of Himalayan bedrock tectonic relationships between these zones; in other words, the and the record of the isotopic variations of Os and Sr in seawa- pre-collisional nature of the margin (Myrow et al., 2003; Hughes ter. Quantification of the erosional history of the Himalayan oro- et al., 2005; Myrow et al., 2006; McQuarrie et al., 2008; Myrow et gen requires restoration of the geology prior to major unroofing. al., 2009, 2010; Long et al., 2011; McKenzie et al., 2011; Webb et This objective, however, has been hampered by uncertainties in al., 2011b; McQuarrie et al., 2013). We comprehensively studied the spatial distribution of late Neoproterozoic–Cambrian successions across the northern Indian * Corresponding author. subcontinent in order to evaluate the uplift and erosion of var- E-mail address: [email protected] (P.M. Myrow). ious potential source rocks during propagation of thrust faults http://dx.doi.org/10.1016/j.epsl.2015.02.016 0012-821X/© 2015 Elsevier B.V. All rights reserved. P.M. Myrow et al. / Earth and Planetary Science Letters 417 (2015) 142–150 143

Fig. 1. (a) Overview Himalayan geologic map. (b) Simplified geological map of the northern Indian Himalaya west of Nepal (modified after Valdiya, 1980; Yin, 2006; Célérier et al., 2009b; Webb et al., 2011b; Webb, 2013). associated with Himalayan deformation. Such eroded rocks may against Cenozoic basin deposits are generically referred to as the include the late Neoproterozoic–Cambrian strata of the Lesser Main Boundary Thrust system (MBT) and uplifted foreland basin Himalaya, some of which are enriched in radiogenic 187Os, par- deposits reside in the hanging wall of the southernmost Frontal ticularly a shale unit in the Tal Group (Singh et al., 1999; Thrust system (FT), which marks the boundary between the thrust Pierson-Wickmann et al., 2000). The spatial and temporal pattern belt and the foreland basin. of erosion and chemical weathering of these strata may have been A prominent ∼500 million year unconformity that separates an important driving factor for secular changes in Neogene seawa- late Paleoproterozoic and older rocks (>1.6Ga) from late Meso- ter 187Os/188Os and 87Sr/86Sr. If so, changes in the isotopic record proterozoic and younger rocks (<1.1Ga) has been recognized of seawater may record significant changes in the thrust belt evo- across the Indian margin (McKenzie et al., 2011, 2013). In the lution of the Himalaya, including tectonic uplift and exhumation Himalaya, this unconformity is generally recognized within the of changing source rocks. Therefore, we explore the feasibility, via LH, and the terms “lower Lesser Himalaya” and “upper Lesser Hi- geochemical modeling, that successive exhumation and weather- malaya” have been applied to the overlying and underlying units ing of two distinct Lesser Himalayan (LH) stratigraphic successions (e.g., Robinson et al., 2001, Richards et al., 2005; Robinson et al., can quantitatively explain the observed trends in Neogene seawa- 2006; McQuarrie et al., 2008; Gehrels et al., 2011 McKenzie et ter 187Os/188Os and 87Sr/86Sr. The proposed exhumation history of al., 2011). However, rocks with ages that are comparable to those the LH proposed here is consistent with foreland basin sedimen- above and below this unconformity have been recognized within tation and detrital zircon records, as well as the marine Os and Sr the GH (cf. Yin et al., 2010; Webb et al., 2011b), demonstrating isotopic evolution. this is not a diagnostic feature of the LH, but occurs more widely. Therefore, we will use the broad terms “upper Lesser Himalayan 2. Geologic background succession” and “lower Lesser Himalayan succession” to refer to strata deposited above and below this unconformity, respectively. Current convention is to divide the Himalaya into lithotectonic Rocks of the upper and lower Lesser Himalayan successions are zones (e.g., Yin, 2006) (Fig. 1). The northernmost of these units, the variably exposed along the orogen. Sedimentary rocks of both age Tethyan Himalaya (TH), is situated in the hanging wall of the South groups are present in the LH of the eastern Himalaya in Bhutan Tibetan Fault System (STFS) and consists of late Neoproterozoic (McQuarrie et al., 2008; Long et al., 2011; McQuarrie et al., 2013) to Eocene sedimentary successions. A central belt of high-grade and Arunachal Pradesh (Tewari, 2001), whereas rocks of the up- metamorphic rocks, the Greater Himalaya (GH), is situated in the per Lesser Himalayan succession are reportedly absent (due to hanging wall of the Main Central Thrust (MCT) (but see Webb et later erosion) throughout the LH of Nepal (Robinson et al., 2001; al., 2011b, 2011a for discussion of various MCT definitions). The DeCelles et al., 2004; Gehrels et al., 2011; Martin et al., 2011). Neo- Lesser Himalaya (LH) is situated in the footwall of the Main Cen- proterozoic and Cambrian rocks are also known along strike south tral Thrust (MCT) and consists mostly of Proterozoic strata with of the Main Central Thrust in Pakistan, within the sub-Himalaya of packages of younger Phanerozoic rocks scattered across the orogen. the Salt Range of Pakistan, and on the Indian craton itself in Ra- A series of thrust faults that place Himalayan bedrock structurally jasthan, south of the Himalayan Frontal Thrust. 144 P.M. Myrow et al. / Earth and Planetary Science Letters 417 (2015) 142–150

Fig. 2. Stratigraphic sections of Neoproterozoic and Cambrian rocks from the Himalayan margin and Indian craton. Data sources in Supplementary Data 1.

West of Nepal, the Tons Thrust divides the Indian LH into “in- Neoproterozoic carbonate, a Cambrian succession with evaporites, ner” (iLH) and “outer” (oLH) zones (Valdiya, 1980; Ahmad et al., and early Cambrian trilobites and brachiopods (Jell and Hughes, 2000)with oLH rocks sitting in the hanging wall of the Tons Thrust 1997). The Krol–Tal belt of the oLH includes a Neoproterozoic and iLH rocks in the footwall (Célérier et al., 2009a, 2009b; Webb glacial diamictite, a thick evaporite-bearing carbonate succession et al., 2011b; Webb, 2013). Presently, strata from only the upper LH (Krol Formation), and a dominantly siliciclastic Cambrian unit (Tal succession have been conﬁrmed in the oLH, most of which range Group) with distinctive phosphatic shale and various shelly fossils from Cryogenian to Cambrian in age (Jiang et al., 2002; Hughes et (Hughes et al., 2005). Lateral continuity of facies along strike is al., 2005; Célérier et al., 2009a; McKenzie et al., 2011). iLH rocks provided by strata exposed in Abbottabad, Pakistan, which have include two main structural units, the Damtha–Deoban duplex and comparable thick carbonate deposits and Cambrian phosphatic the Berinag Thrust sheet. In this region of India, the iLH contains shale (Pogue et al., 1992)with similar fauna (Hughes et al., 2005) strata of both the lower Lesser Himalaya succession and the low- (Fig. 2). In addition, in the eastern Himalaya a likely Neoprotero- ermost part of the upper Lesser Himalayan succession (McKenzie zoic carbonate/siliciclastic suite in the LH of Bhutan and Arunachal et al., 2011). Klippen of GH rock occurs structurally above both iLH Pradesh (Buxa Formation) (Long et al., 2011)represents a pos- and oLH rocks (Célérier et al. 2009a, 2009b; Webb et al., 2011b; sible equivalent to the Krol Formation. Collectively, rocks of this Mandal et al., 2014). proximal facies realm were characterized by periodic episodes of condensed and hypersaline sedimentation, and all are capped un- 3. Continuity of Cambrian strata and depositional systems conformably by Permian or younger deposits. In contrast, Neoproterozoic and Cambrian deposits in the hang- 3.1. Regional lithofacies ing wall of the STFS are thick successions that represent generally more distal marine facies associations, although both facies realms Regional lithofacies relationships for Neoproterozoic and Cam- share a late Neoproterozoic diamictite (Draganits et al., 2008). In brian strata across the TH and LH, as well as cratonic successions, the TH, (1) shale units form the distal equivalents of the prox- demonstrate northward deepening across the northern Indian mar- imal Neoproterozoic Krol Formation carbonate of the LH (Jiang gin. Sedimentological data (references in Supplemental Data 1) et al., 2002), (2) shale of the Phe Formation is age equivalent to from deposits south of the MCT (Fig. 2) suggest that this area com- lower/middle Tal Group shallow water strata (including phosphatic prises a proximal marine facies realm relative to the GH and TH to facies) (Myrow et al., 2003), and (3) Cambrian deltaic sandstone the north. Up to 900 km south of the Himalayan Frontal Thrust of the Parahio Formation are age equivalents of the upper Tal in the Marwar basin of Rajasthan are successions of Neoprotero- Group ﬂuvial sandstone in the LH proximal facies realm (Myrow zoic evaporite-bearing carbonate and Cambrian sandstone (Malone et al., 2003, 2006). Parts of the GH have been precisely corre- et al., 2008; McKenzie et al., 2011). South of the Main Boundary lated with protolith TH rocks of the Cambrian Parahio Formation Thrust (MBT) in the Salt Range of Pakistan is an evaporite-bearing (Myrow et al., 2009). Ordovician and younger Paleozoic strata un- P.M. Myrow et al. / Earth and Planetary Science Letters 417 (2015) 142–150 145

Fig. 3. Comparison of detrital zircon U–Pb age distributions of siliciclastic rocks from major structural units and foreland basin deposits of the Kumaon–Garhwal region of the Indian Himalaya and Neoproterozoic–Cambrian rocks of the Marwar Supergroup of the Indian craton. Neoproterozoic–Cambrian strata in all zones yield similar age distributions, whereas older Paleoproterozoic rocks of the inner Lesser Himalaya distinctly lack grains younger than ∼1.6Ga. No discernable changes in detrital zircon age populations are observed in foreland basin deposits, implying the iLH was not a major contributor of detritus prior to at least 11 Ma. Age data are from Myrow et al. (2003, 2010), Malone et al. (2008), McKenzie et al. (2011), Ravikant et al. (2011), and Webb et al. (2011b). conformably cap successions in the distal facies realm. These can represents erosion of granitic plutons emplaced during the final be used to identify klippe of TH strata exposed atop the LH, rela- assembly of Gondwanaland, including parts of northern India (e.g., tive to Neoproterozoic–Cambrian successions indigenous to the LH, LeFort et al., 1986). A large fraction of bedrock currently exposed which are capped by Permian strata. in the LH has depositional ages that are older than 1.6 Ga and the The stratigraphic data indicate that a contiguous Neoproterozo- stratigraphic influx of abundant zircon grains older 1.6 Ga into syn- ic–Cambrian sedimentary blanket may have extended from the tectonic foreland basin deposits shed from the Himalaya had been craton across the northern Indian margin, and along strike from used to date the initial timing of uplift of the LH (e.g., DeCelles western to eastern syntaxes of the Himalaya. Sedimentological data et al., 1998a). Younger detrital zircon ages (0.5–1.6 Ga) and less and stratigraphic correlation to less deformed successions in Pak- negative εNd values, typical of GH and TH rocks, have also been istan, west of the western syntax where Himalayan deformation is documented from the LH of Bhutan (McQuarrie et al., 2008; Long minimal, show that the Krol–Tal Belt upper Lesser Himalayan suc- et al., 2011; McQuarrie et al., 2013), and the upper LH succes- cession was part of the proximal marine facies realm, and thus sion, lower LH succession, and Indian craton (Myrow et al., 2003; an erosional remnant of the extensive Neoproterozoic–Cambrian McKenzie et al., 2011)(Fig. 3). This indicates, in combination with blanket. Recent structural analysis suggests that a large swath of lithofacies analysis, that rocks of such age extended from craton to rocks in Nepal of the oLH structural unit was removed within the the TH, thus spanning the entire region, including the area where last 5m.y. (Yu et al., in press), further supporting the idea of rocks of the iLH are presently exposed. widespread erosion of upper Lesser Himalayan strata. Distinctive phosphatic and evaporitic strata can be used to correlate proximal- 4. Evidence for ∼16 Ma exhumation of the upper LH succession facies rocks far along strike within the LH. Strata of the proximal- and associated proximal-facies strata facies realm are not known from the TH, which primarily contains more distal marine facies rocks. Recent interpretations suggest the oLH, including the upper LH strata of the Krol–Tal Belt, is a far transported thrust sheet that 3.2. Detrital zircon age distributions of Cambrian strata across the roots along the TH (Célérier et al. 2009a, 2009b). In this case, the northern Indian margin oLH would have been juxtaposed against the lower LH strata of the iLH by the Oligocene with the oLH subsequently overthrust Continuity of sediment transport across the Indian margin is by the MCT. An alternative model suggests that the oLH is a short- confirmed by similarities in detrital zircon age distributions of traveled thrust sheet that was emplaced through footwall accretion Neoproterozoic through Ordovician sandstone units from cratonic, via break-forward in-sequence thrusting of the sole décollemont LH, GH, and TH samples (Myrow et al., 2010; McKenzie et al., of the MCT (Webb et al., 2011b; Webb, 2013). Our stratigraphic 2011; Webb et al., 2011b)(Fig. 3). Samples taken from across data demonstrates that the Krol–Tal Belt of the oLH was part of the ancient northern Indian Himalayan margin show remarkably the upper LH proximal marine facies realm, distinct from the age uniform signatures that include ages from Archean to Ordovician, equivalent, generally more distal, marine facies now exposed in with peaks at ∼2.5 Ga and ∼1.9–1.7Ga, various peaks from ∼1.3 the TH zone. All of these strata were part of a Neoproterozoic– to 0.8 Ga, and a large peak at ∼0.6–0.5Ga(Myrow et al., 2010; Cambrian succession that overlaid the older rocks exposed in the McKenzie et al., 2011; Mandal et al., 2014). The ∼0.5Gapeak LH, and extended south onto the Indian craton and north across 146 P.M. Myrow et al. / Earth and Planetary Science Letters 417 (2015) 142–150 the Tethyan realm. This interpretation is consistent with a prox- takes place at ∼17 Ma, where strata record a shift from sediment imal pre-deformational setting of the oLH (Webb et al., 2011b; sourced from higher-grade GH rocks to low-grade sedimentary Webb, 2013). The similarity in detrital zircon spectra between the sources (mostly carbonate and shale). The shift at ∼17 Ma, coin- upper LH strata of the oLH and TH strata also supports a proxi- ciding with the transition from the lower to the upper Dharamsala mal to distal continuous depositional system (Myrow et al., 2003, Formation of the Himalayan foreland basin deposits, also shows a 2010). significant decrease in detrital white mica content, and a change These data are important for reconstructing the timing of uplift in the mica 40Ar/39Ar thermochronological ages from <60 Ma of LH-associated rocks. The ages of detrital zircon grains from Pa- (most 20–30 Ma) to >60 Ma and ranging into the Proterozoic. The leocene to late Miocene foreland basin deposits have been linked younger micas in the lower Dharamsala Formation reflect rapid up- to a south-directed, break-forward sequence of thrusting within lift and erosion of the GH, which likely occurred during thrusting the Himalaya, and thus to the sequential uplift of specific litho- of the MCT, while the upper Dharamsala Formation micas reflect tectonic zones. The detrital zircon signature of samples from lower erosion of rocks in which the mica cooling ages were not reset Eocene to middle Miocene foreland basin deposits were postulated by Himalayan metamorphism. The latter micas were attributed to to have been derived from the GH and TH, whereas later breach- erosion of Haimanta Group rocks that are of TH affinity (White et ing and erosion of the LH is recorded by upward coarsening, an al., 2002). However, it is more likely that the shift in mica sources influx of abundant >1.6Gadetrital zircon grains (DeCelles et al., reflects erosion through the GH and into oLH rocks of the MCT 1998a), and decreases in εNd values in the upper part of the lower footwall, as their 40Ar/39Ar ages would not likely have been reset Siwalik Group and middle Siwalik Group (Najman et al., 2000; by Himalayan metamorphism. Robinson et al., 2001). Based on our estimates of stratigraphic Deeken et al. (2011) used zircon (U–Th/He) thermochronomet- thickness and estimates of areas of exposed strata, we calcu- ric data to argue for uplift ∼100 km west of the westernmost late that ∼9300 m of Neoproterozoic and younger oLH-age strata exposure of the oLH via active thrusting on faults to the south of (Supplemental Data 2) must have been eroded to expose Pale- the MCT by at least ∼15 Ma, which is supported by data presented oproterozoic rocks, the source of abundant >1.6Gagrains. The herein. Similarly, Bernet et al. (2006) propose LH exhumation in geochronological and geochemical signature of these strata would the Nepali Himalaya around ∼16 Ma. They postulate that uplift have included abundant 0.5 to 1.6 Ga grains and much less neg- and erosion at this time led to widespread cooling, as recorded by ative εNd values (Myrow et al., 2003; Richards et al., 2005; zircon fission track ages, due to movement along the STFS, MCT, McKenzie et al., 2011; Webb et al., 2011b), similar to GH and and the Ramgarh Fault, the latter of which includes iLH-equivalent TH rocks to the north. Detrital zircon U–Pb age data from fore- rocks in its hanging wall. Bernet et al. (2006) do not mention up- land basin deposits in northern India showed no change in prove- per Lesser Himalayan rocks in Nepal, whose pervasive absence we nance from the Eocene Subathu Formation through to lower Siwa- attribute to extensive erosion of the youngest strata. However, such lik Group, which was deposited between 13 and 11 Ma, as based strata would have existed above the older lower Lesser Himalayan on Ravikant et al.’s (2011) data. All of these foreland basin U– rocks of the Ramgarh thrust sheet (Yu et al., in press), and they Pb age distributions are representative of upper Lesser Himalayan would have been the first rocks to erode during uplift at 16 Ma, sources, which imply that the lower Lesser Himalaya was not sig- assuming that the younger strata were in the leading edge of the nificantly exposed prior to 11 Ma. thrust. This may explain why the detrital zircon distributions in the It appears that some amount of upper Lesser Himalayan strata Nepalese foreland basin do not show a pronounced shift to older was removed prior to the Neogene, based on stratigraphic and grains until ∼11 Ma (cf. DeCelles et al., 1998a, 2004). Although structural relationships of small, isolated outcrops of Cretaceous spatial and temporal patterns of uplift along the length of the Hi- and Paleocene–Eocene rocks that rest on Precambrian strata in malaya at this time were potentially nonuniform, evidence points both the iLH and oLH zones (e.g., Webb et al., 2011b). These are, to a general shift in the locus of thrusting, which had direct effects however, difficult to assess due to poor exposure, and the possibil- on the provenance record of the foreland basin. ity exists that in some cases the contacts are in fact faulted. There are no reported orogenic events from the late Paleozoic through 5. Implication for geochemical evolution of Neogene Cretaceous in the Himalayan region that may have caused sub- paleoseawater stantial uplift and erosion of upper Lesser Himalayan rocks prior to Himalayan uplift, although some erosion may have taken place Here, we present a combined tectonic–geochemical model that without uplift. Thus, the degree of erosion prior to Himalayan up- links earlier uplift of the LH to the Neogene paleoseawater record lift is difficult to quantify, but our goal is to provide first-order of 187Os/188Os and 87Sr/86Sr (Ravizza, 1993; Oslick et al., 1994; approximations of volumes of eroded strata and the effects of this Peucker-Ehrenbrink et al., 1995; and Reusch et al., 1998). The erosion. 187Os/188Os record shows a period of stability from about 29 Ma During Himalayan deformation, erosion of lower Lesser Hi- to 16 Ma (Fig. 4) followed by a monotonic rise starting at ap- malaya strata of the iLH would have began after erosion of the proximately 16 Ma. The initiation of this dramatic rise in os- thick Neoproterozoic to Cambrian blanket of upper Lesser Hi- mium isotopic ratios closely matches a sharp decrease in the malaya strata, so the stratigraphic appearance of abundant zir- rate of rise of the marine 87Sr/86Sr isotopic signal (Oslick et con grains older than 1.6 Ga in the Siwalik Group records the al., 1994). This record requires a change in the sources of Os erosional breaching of enough lower Lesser Himalayan Paleopro- and Sr to the oceans. Multiple workers have suggested that ero- terozoic (2.5–1.6 Ga) rocks to provide abundant grains of this sion of organic-rich sedimentary rock in the Himalaya led to the age. Using geologic map and stratigraphic data, we estimate that dramatic rise in Os isotopic values (e.g., Pegram et al., 1992; ∼930 000 km3 (±300 000 km3) of upper Lesser Himalayan strata Ravizza, 1993). Links were specifically made to black shale in was removed from the LH (Supplementary Data 2). the early Cambrian Tal Group of the upper Lesser Himalayan Recent studies in the Himachal Himalaya (White et al., 2002; succession, which is greatly enriched in radiogenic Os (Singh Najman et al., 2009)also posit unroofing of a younger succes- et al., 1999; Pierson-Wickmann et al., 2000), but the puta- sion starting around 17 Ma, prior to erosional exposure of the tive discrepancy between the timing of exposure of Tal Group older rocks of the lower Lesser Himalayan succession at 11 Ma. strata and the increase in 187Os/188Os of seawater led some In particular, they demonstrate that a fundamental shift in petro- workers to question the relationship between radiogenic sources logic and thermochronological character of foreland basin deposits and changes in marine Os isotope ratios. Based on discussions P.M. Myrow et al. / Earth and Planetary Science Letters 417 (2015) 142–150 147

Fig. 4. Osmium and strontium isotope evolution of the Neogene ocean. Both show a significant break in slope near 16 Ma. From 28 to 19 Ma the 187Os/188Os data can be fit − with a zero-slope line with 187Os/188Os = 0.7337. From 16 to 1 Ma the Os data can be fit with a constant slope = 0.01329 Ma 1. The strontium isotope data can similarly − − − − be fit with two linear segments, from 22.2 to 15.8 (dR/dt = 6.86 × 10 5 Ma 1) and from 15.5 to 9.2 Ma (dR/dt = 2.67 × 10 5 Ma 1). Data sources: Ravizza (1993), Oslick et al. (1994), Peucker-Ehrenbrink et al. (1995), and Reusch et al. (1998). above, we postulate that initial uplift and exhumation of up- Ar ages of the youngest detrital white micas (White et al., 2002; per Lesser Himalayan strata (possibly the oLH) took place at Najman et al., 2009). ∼16 Ma, and that it is recorded in marked inflections in the marine Os and Sr records at that time. Decreased erosion of 5.2. Geochemical model for oLH weathering and Neogene 187Os/188Os the GH and increased erosion of younger oLH strata could have and 87Sr/86Sr plausibly driven the observed changes in the Os and Sr paleoseawater curves beginning near 16 Ma, because radiogenic Os Assuming initiation of exhumation of the younger Lesser Hi- is concentrated in organic rich shale that accumulated in proxi- malayan succession at ∼16 Ma, and erosion of the highest strati- mal parts of the Neoproterozoic and Cambrian margin (e.g., Singh graphic deposits we constructed paired geochemical box models et al., 1999), and radiogenic Sr is concentrated in the high- to test the effects of erosion and weathering of oLH and asso- grade rocks of the GH (France-Lanord et al., 1993; Ahmad et al., ciated strata on the Os and Sr isotopic evolution of the Miocene 2000). oceans. The approach is a forward model (Supplementary Data 3) Exhumation rates in the Himalaya varied both spatially and that can test the consequences of assumptions about the tempo- temporally over the Cenozoic, but most estimates are less than ral evolution fluxes of Os and Sr. We seek to evaluate whether the 2 mm/yr (White et al., 2002; Najman et al., 2009; Deeken et al., observed isotopic evolution curves for Os and Sr in paleoseawater 2011). An average rate of 1.9 mm/yr would be required to unroof are quantitatively consistent with our inferences about the expo- the estimated 9300 m of younger upper Lesser Himalayan strata sure history of LH rocks, but do not imply that we can know those over the interval of ∼5 million years (from 16 to 11 Ma) required fluxes with certainty. For Os (Fig. 5), we made a first-order esti- to expose enough of the older lower Lesser Himalayan succession mate of the volume of eroded lower Tal Group black shale using to provide its detrital signal to the foreland basin. In addition, an area calculation of eroded Tal strata (Supplementary Data 2), analysis of Fe/Mn nodules (Chesley et al., 2000)from palaeosols and by assuming a uniform thickness of 150 m (supported by the in the foreland of the Ganges and Indus rivers, in an attempt to notable lateral continuity of Cambrian lithofacies and unit thick- reconstruct the isotopic composition of past river fluxes, reveals nesses along the Indian margin, Myrow et al., 2006) (Fig. 2). We increased radiogenic Os in the Ganges foreland by ∼15 Ma, which provide two minimum (2900 km3, 3600 km3) and one maximum is consistent with our proposed estimate for initial oLH exhuma- estimates (17 990 km3) respectively (Supplementary Data 2), and tion near 16 Ma. these can be significant, given that the release of Os from a unit Exhumation of the oLH at ∼16 Ma would have resulted from volume of black shale is 1000 times greater than that of typical southward fault propagation from the MCT to thrust faults to the granitoids (Peucker-Ehrenbrink and Blum, 1998). The major sources south, e.g., the Tons Thrust, Berinag Thrust, and/or MBT. Structural of uncertainty in calculating the potential impact of the erosion of data from Nepal support southward propagation at ∼15 Ma (Searle the Tal are 1) the volume eroded, and 2) the dissolved yield of and Godin, 2003), including initiation of the emplacement of the Os associated with this denudation. If the eroded volume is close Ramgarh–Munsari Thrust sheet (DeCelles et al., 1998b). In addition, to our upper estimate, then a yield of 43% is sufficient to drive 187 188 ductile shearing and high temperature metamorphism along the all of the observed increase in ( Os/ Os)sw during the interval MCT is thought to have ceased shortly after ∼18 Ma (Searle and from 16 to 11 Ma. If the eroded volume is close to our lower limit Godin, 2003). Cooling of leucogranite bodies at ∼16 Ma (Horton (2900 km3), the Tal can account for at most about half of the ob- 187 188 and Leech, 2013)along the MCT was linked to cessation of move- served rise in ( Os/ Os)sw during that interval, which in itself ment and southward propagation of the thrust belt (Jessup et al., is a significant statement. 2006). Finally, foreland basin deposits show a dramatic decrease in Our Os model focuses on the lower Cambrian shale due to ex- Himalayan exhumation rates at ∼17 Ma, as shown by a shift in isting constraints on the stratigraphic thickness and lateral extent lag times between the depositional ages of samples and the Ar– of a particular Tal Group unit. However, additional potential 187Os 148 P.M. Myrow et al. / Earth and Planetary Science Letters 417 (2015) 142–150

Fig. 5. Osmium isotope evolution of the Neogene ocean from 28 to 11 Ma. Model Fig. 6. Strontium isotope evolution of the Neogene ocean from 23 to 10 Ma. The curve presents steady state solution from 28 to 16 Ma. From 16 to 11 Ma, model curve is initialized with an “excess flux” of radiogenic Sr from Himalayan 87 86 = an additional radiogenic flux with Tal-like characteristics (187Os/188Os)16 = 2.95, rivers with Sr/ Sr 0.715 at 24 Ma. From 24 to 16 Ma the Himalayan Sr flux − − × −7 −1 187Re/188Os = 185 that grows at a rate of 1.95 × 10 6 yr 1 is added. The time- grows at a rate of 1.3 10 yr , while its isotopic composition evolves at a rate of × −9 −1 × −7 −1 integrated flux of this source from 16 to 11 Ma is 2.4 × 107 kg, compared to an 1.2 10 yr . From 16 to 10 Ma, the flux grows at 1.1 10 yr while the rate 87 86 − × −9 −1 estimated initial Os content of the Tal = 5.7 × 107 kg. The modeled isotopic growth of change of the Sr/ Sr of Himalayan rivers is 0.8 10 yr . Other inputs, − rate = 0.0125 Ma 1, consistent with a least squares fit to the data from 16 to including the world’s rivers, hydrothermal, and diagenetic fluxes, are held constant 11 Ma. Paleoseawater 187Os/188Os continues to grow at a near constant rate from (see Supplementary Data 3 for details). Modeled Himalayan river isotopic ratios are 11 to 1 Ma, but the unroofing of the lower Lesser Himalaya implies that Himalayan consistent with data from Neogene paleoriver archives from the Himalayan foreland. × sources became notably more radiogenic after that time, necessitating a correspond- Linear fits to the model output from 23 to 16 and from 16 to 10 Ma are 6.1 −6 −1 × −6 −1 ing decrease in the rate of flux growth to satisfy the observations. Data sources as 10 yr and 2.7 10 yr respectively, consistent with data from ODP 747A in Fig. 4. (Oslick et al., 1994).

87 86 source rocks are known from the LH, which could have contributed mentary Data 3 for model details). The Sr/ Sr of the Ganges– radiogenic Os to the ocean at any time from 16 Ma to the present. Brahmaputra declined slightly from 16 to ∼11 Ma, and then began Prominent Neoproterozoic age black shale enriched in 187Os un- to increase dramatically (Derry and France-Lanord, 1996), consis- derlay the Tal Group in the oLH (Singh et al., 1999). Older lower tent with exhumation of the oLH beginning ∼16 Ma and the iLH Lesser Himalayan organic-rich shale units and carbonate rocks with ∼11 Ma. The model results for Os and Sr are fully consistent, abundant and even more radiogenic Os (187Os/188Os = 7to21) and demonstrate that there is a plausible link between ama- are present in the Nepal LH (Chesley et al., 2000), and repre- jor shift in Himalaya bedrock exhumation at ∼16 Ma and the sent additional sources of radiogenic Os from the LH that con- evolution of Os and Sr in the Neogene oceans. The combina- 187 188 tributed to the rise of ( Os/ Os)sw after they were unroofed tion of our model calculation, and our inferred initiation of ero- near 11 Ma. The detailed erosional history of LH strata is not sion of the Tal Group and related strata beginning near 16 Ma, known, but paleoriver archives from the Himalayan foreland record explain the ∼5m.y.offset between the shift in the marine Os 187 188 and Sr isotopic records at ∼16 Ma and the influx of older LH ( Os/ Os)river ≈ 2.0by 16 Ma (Chesley et al., 2000), clearly in- dicating the presence of an anomalously radiogenic source. The source materials at ∼11 Ma in Nepal (DeCelles et al., 1998a; model illustrates that a volumetrically minor oLH source driven Chesley et al., 2000). by a plausible tectonic history can generate a quantitatively sig- Various geochemical, mineralogical, and sedimentological in- nificant flux of radiogenic Os beginning ∼16 Ma, and is consistent dices that reflect intensity of chemical weathering and erosional with unroofing of the iLH near 11 Ma. The estimates above are flux of sediment, derived from cores in three oceans adjacent to a first-order attempt at such an analysis, and set the stage for the Himalayan system, provide independent evidence for an abrupt future studies based on more refined stratigraphic, tectonic, and change in the nature and intensity of weathering processes at ∼ geochemical data. 16 Ma (Clift et al., 2008). Changes in Himalayan orography asso- The impact of enhanced erosion and weathering of oLH strata ciated with southward shifting of the locus of thrusting at 16 Ma on the Sr isotopic flux from the Himalaya would have promoted could have led to these changes through a number of different a significant decline in the mean 87Sr/86Sr of Himalayan rivers, processes, including exposure of new source materials for both 87 86 weathering and erosion, spatial and temporal changes in precipi- consistent with the observed evolution of ( Sr/ Sr)sw that shows amarked decrease in slope at 16 Ma. While GH rocks above the tation patterns, and associated changes in the locus of erosion. MCT have 87Sr/86Sr near 0.74–0.76 (France-Lanord et al., 1993), oLH carbonate strata (the dominant oLH source of dissolved Sr) are 6. Implications for thrust belt evolution and oLH emplacement much less radiogenic and range from 0.709 to 0.714 (Singh et al., in northern Indian 1998). Exhumation rates of more radiogenic GH slowed at approx- imately 17 Ma (Najman et al., 2009). An increase in the relative Our results may have important implications for recent mod- contribution of oLH weathering sources of Sr is capable of low- els of the tectonic evolution of the north Indian Himalaya. Existing ering the mean river 87Sr/86Sr sufficiently to produce the observed models show a variety of timing scenarios for uplift and erosion decrease in the rate of growth of the marine 87Sr/86Sr from ∼6.8 × of the oLH, including the Tal Group. These range early collisional − − − − 10 5 Ma 1 to ∼2.7 × 10 5 Ma 1 after 16 Ma (Fig. 6, see Supple- shortening immediately following ∼50 Ma to as late as ∼5Ma. P.M. Myrow et al. / Earth and Planetary Science Letters 417 (2015) 142–150 149

The early balancing effort by Srivastava and Mitra (1994) shows thrust belt. Given the potential influence of this shift on global Himalayan development as a function of deformation of a single ocean chemistry for the rest of the Cenozoic, it should be a critical layer-cake stratigraphy, such that Tal-equivalent rocks near the top component of future models regarding Himalayan system evolu- of this stratigraphy were uplifted and eroded semi-continuously tion. throughout all Himalayan shortening. Célérier et al. (2009a, 2009b) shows the oLH as the southernmost toe of the Tethyan fold- Acknowledgements thrust belt, with uplift and erosion of the unit in the Eocene and Oligocene. Similarly, Ahmad et al. (2000) suggests that the oLH We gratefully acknowledge the input from three excellent was the dominant exposed part of the eroding orogenic wedge at anonymous reviewers, and the guidance provided by editor An Yin. ∼30 Ma; thus, initial erosion of the oLH would precede 30 Ma. This research was supported by NSF grant EAR-1124518 to PMM Webb and co-workers show stratigraphic connection between the and EAR-1124303 to NCH. NRM was supported by a UT Austin oLH and Tethyan rocks to the north, but restrict initial uplift of the Jackson Postdoctoral Fellowship and a Yale Flint Postdoctoral Fel- oLH rocks to ∼14 Ma and initial erosion of these rocks to ∼5Ma lowship. (Webb et al., 2011b; Webb, 2013). Stasis in the Eocene to early Miocene 187Os/188Os seawater Appendix A. Supplementary material record (Fig. 4), followed by a shift to increasing values at ∼16 Ma, is consistent with many lines of evidence to suggest transfer of Supplementary material related to this article can be found on- movement from the MCT to faults further south (e.g., Tons Thrust) line at http://dx.doi.org/10.1016/j.epsl.2015.02.016. to cause onset of weathering of Os-rich rock. Thus, oLH erosion did not start prior to the Miocene (cf. Srivastava and Mitra, 1994; References Ahmad et al., 2000; Célérier et al., 2009b), nor was it so late as the Miocene–Pliocene transition (cf. Webb, 2013). Our model, calling Ahmad, T., Harris, N., Bickle, M., Chapman, H., Bunbury, J., Prince, C., 2000. Isotopic for a tectonic shift and onset of weathering at 16 Ma is supported constraints on the structural relationships between the Lesser Himalayan Se- ries and the High Himalaya Crystalline Series, Garhwal Himalaya. Geol. Soc. Am. by apatite fission track and zircon (U–TH)/He data that indicate up- Bull. 112, 467–477. lift of the LH on a system of thrusts south of the MCT, no later than Bernet, M., van der Beek, P., Pik, R., Huyghe, P., Mugnier, J.-L., Labrin, E., Szulc, A., ∼15 Ma (Deeken et al., 2011). As mentioned earlier, an 11 Ma shift 2006. Miocene to Recent exhumation of the central Himalaya determined from in provenance likely represents onset of exposure of older lower combined detrital zircon fission-track and U/Pb analysis of Siwalik sediments, western Nepal. Basin Res. 18, 393–412. Lesser Himalayan strata following erosion through the younger up- Célérier, J., Harrison, T.M., Webb, A.A., Yin, A., 2009a. The Kumaun and Gar- per Lesser Himalayan strata in the LH zone. whal Lesser Himalaya, India. Part 1: Structure and stratigraphy. Geol. Soc. Am. If correct, the near-synchronous changes in the Neogene 187Os/ Bull. 121, 1281–1297. 188Os and 87Sr/86Sr record of seawater, and the linked tectonic–ge- Célérier, J., Harrison, T.M., Beyssac, O., Herman, F., Dunlap, W.J., Webb, A.A.G., 2009b. ochemical model described herein to explain these changes, at The Kumaon and Garwhal Lesser Himalaya, India: Part 2. Thermal and deformation histories. Geol. Soc. Am. Bull. 121, 1281–1297. 16 Ma would provide the timing of uplift that could be incorpo- Chesley, J.T., Quade, J., Ruiz, J., 2000. The Os and Sr isotopic record of Himalayan rated into future models and tested using various thermochrono- paleorivers: Himalayan tectonics and influence on ocean chemistry. Earth Planet. metric techniques. Sci. Lett. 179, 115–124. Clift, P.D., Hodges, K.V., Heslop, D., Hannigan, R., Long, H.V., Calves, G., 2008. Cor- relation of Himalayan exhumation rates with monsoon intensity. Nat. Geosci. 1, 7. Conclusions 875–880. DeCelles, P.G., Gehrels, G.E., Najman, Y., Martin, A.J., Carter, A., Garzanti, E., Our stratigraphic and geochemical data have important implica- 2004. Detrital geochronology and geochemistry of Cretaceous–Early Miocene tions for the inferred uplift and erosional history of the Himalaya, strata of Nepal: implications for timing and diachroneity of initial Himalayan including a potential explanation for marked secular changes in orogenesis. Earth Planet. Sci. Lett. 227, 313–330. http://dx.doi.org/10.1016/ j.epsl.2004.08.019. the isotopic geochemistry of the oceans. Lithostratigraphic and DeCelles, P.G., Gehrels, G.E., Quade, J., Ojha, T.P., 1998a. Eocene–early Miocene fore- paleoenvironmental reconstructions indicate that Neoproterozoic land basin development and the history of Himalayan thrusting, western and to Cambrian strata formed a northward-deepening succession of central Nepal. Tectonics 37, 741–765. strata that extended from the craton to the Tethyan Himalaya to DeCelles, P.G., Gehrels, G.E., Quade, J., Ojha, T.P., Kapp, T.A., Upreti, B.N., 1998b. Neo- gene foreland basin deposits, erosional unroofing, and the kinematic history of the north. A proximal marine facies belt, which includes fossilifer- the Himalayan fold-thrust belt, western Nepal. Geol. Soc. Am. Bull. 110, 2–21. ous phosphatic shale and evaporite, is extensively exposed south of Deeken, A., Thiede, R.C., Sobel, E.R., Hourigan, J.K., Strecker, M.R., 2011. Exhumational the Main Central Thrust well onto the craton, and along strike from variability within the Himalaya of northwest India. Earth Planet. Sci. Lett. 305, north-central India to Pakistan. More distal deposits of the Tethyan 103–114. belt consist of deltaic to shelf deposits. These Neoproterozoic to Derry, L.A., France-Lanord, C., 1996. Neogene Himalayan weathering history and river 87Sr/86Sr: impact on the marine Sr record. Earth Planet. Sci. Lett. 142, Cambrian strata present in the Lesser Himalaya (LH) were presum- 59–74. ably eroded during uplift of the Himalaya during Cenozoic collision Draganits, E., Schlaf, J., Grasemann, B., Argles, T., 2008. Giant submarine landslide of India with Asia. We postulate that unroofing of these cover rocks grooves in the Neoproterozoic/Lower Cambrian Phe Formation, northwest Hi- along the Himalayan front began at ∼16 Ma, and would have re- malaya: mechanisms of formation and palaeogeographic implications. Sediment. Geol. 205, 126–141. quired an average exhumation rate of 1.9 mm/yr, consistent with France-Lanord, C., Derry, L.A., 1997. Organic carbon burial forcing of the carbon cycle published estimates of Cenozoic Himalayan denudation rates. First- from Himalayan erosion. Nature 390, 65–67. order, geochemical modeling of the effects of erosion of the strata France-Lanord, C., Derry, L., Michard, L.A., 1993. Evolution of the Himalaya since in this succession, and erosion patterns in general, indicate that Miocene Time: isotopic and sedimentological evidence from the Bengal Fan. In: these changes were likely responsible, in part, for secular changes Treloar, P.J., Searle, M.P. (Eds.), Himalayan Tectonics. In: Geol. Soc. (Lond.) Spec. 187 188 87 86 Publ., vol. 74, pp. 605–622. in the Neogene Os/ Os and Sr/ Sr record of seawater. This Galy, V., France-Lanord, C., Beyssac, O., Faure, P., Kudrass, H., Palhol, F., 2007. Efficient has major implications for models concerned with global silicate organic carbon burial in the Bengal fan sustained by the Himalayan erosional weathering and CO2 consumption during the Cenozoic (e.g., Torres system. Nature 450, 407–411. et al., 2014). Gehrels, G., Kapp, P., DeCelles, P., Pullen, A., Blakey, R., Weislogel, A., Ding, L., Guynn, J., Martin, A., McQuarrie, N., Yin, A., 2011. Detrital zircon geochronology of pre- Furthermore, exhumation at 16 Ma was part of a significant Tertiary strata in the Tibetan–Himalayan orogen. Tectonics 30, TC5016. tectonic shift in the evolution of the Himalayan orogeny, which Horton, F., Leech, M.L., 2013. Age and origin of granites in the Karakoram shear zone resulted from a southward advance in the position of the active and Greater Himalaya Sequence, NW India. Lithosphere 5, 300–320. 150 P.M. Myrow et al. / Earth and Planetary Science Letters 417 (2015) 142–150

Hughes, N.C., Peng, S.-C., Bhargava, O.N., Ahluwalia, A.D., Walia, A., Myrow, P.M., Par- Peucker-Ehrenbrink, B., Blum, J.D., 1998. Re–Os isotope systematics and weather- cha, S.K., 2005. The Cambrian biostratigraphy of the Tal Group, Lesser Himalaya, ing of Precambrian crustal rocks: implications for the marine Os isotope record. India, and early Tsanglangpuan (late early Cambrian) trilobites from the Nigali Geochim. Cosmochim. Acta 62, 3193–3203. Dhar syncline. Geol. Mag. 142, 57–80. Peucker-Ehrenbrink, B., Ravizza, G., Hofmann, A.W., 1995. The marine 187Os/186Os Jell, P.A., Hughes, N.C., 1997. Himalayan Cambrian trilobites. Spec. Pap. Palaeon- record of the past 80 million years. Earth Planet. Sci. Lett. 130, 155–167. tol. 58, 1–113. Pierson-Wickmann, A.-C., Reisberg, L., France-Lanord, C., 2000. The Os isotopic com- Jessup, M.J., Law, R.D., Searle, M.P., Hubbard, M.S., 2006. Structural evolution and position of Himalayan river bedloads and bedrocks: importance of black shales. vorticity of flow during extrusion and exhumation of the Greater Himalayan Earth Planet. Sci. Lett. 176, 203–218. Slab, Mount Everest Massif, Tibet/Nepal: implication for orogen-scale flow par- Pogue, K.R., Wardlaw, B.R., Harris, A.G., Hussain, A., 1992. Paleozoic and Mesozoic titioning. In: Law, R.D., Searle, M.P., Godin, L. (Eds.), Channel Flow, Extrusion, and stratigraphy of the Peshawar basin, Pakistan: correlations and implications. Geol. Exhumation in Continental Collision Zones. In: Geol. Soc. London Spec. Papers, Soc. Am. Bull. 104, 915–927. vol. 268, pp. 379–414. Ravikant, V., Wu, F.-Y., Ji, W.-Q., 2011. U–Pb and Hf isotopic constraints of detrital Jiang, G., Christie-Blick, N., Kaufman, A.J., Banerjee, D.M., Rai, V., 2002. Sequence zircons from the Himalayan foreland Subathu sub-basin on the Tertiary palaeo- stratigraphy of the Neoproterozoic Infra Krol Formation and Krol Group, Lesser geography of the Himalaya. Earth Planet. Sci. Lett. 304, 356–368. Himalaya, India. J. Sediment. Res. 72, 524–542. Ravizza, G., 1993. Variations of the 187Os/186Os ratio of seawater over the past LeFort, P., Debon, F., Pecher, A., Sonet, J., Vidal, P., 1986. The 500 Ma magmatic event 28 million years as inferred from metalliferous carbonates. Earth Planet. Sci. in Alpine southern Asia, a thermal episode at Gondwana scale. Sci. Terre, Inform. Lett. 118, 335–348. Geol. 47, 191–209. Reusch, D.N., Ravizza, G., Maasch, K.A., Wright, J.D., 1998. Miocene seawater Long, S., McQuarrie, N., Tobgay, T., Rose, C., Gehrels, G., Grujic, D., 2011. Tectonos- 187Os/188Os ratios inferred from metalliferous carbonates. Earth Planet. Sci. tratigraphy of the Lesser Himalaya of Bhutan: implications for the along-strike Lett. 160, 163–178. stratigraphic continuity of the northern Indian margin. Geol. Soc. Am. Bull. 123, Richards, A., Argles, T., Harris, N., Parrish, R.R., Ahmad, T., Darbyshire, F., Draganits, 1406–1426. E., 2005. Himalayan architecture constrained by isotopic markers from clastic Malone, S.J., Meert, J.G., Banerjee, D.M., Pandit, M.K., Tamrat, E., Kamenov, G.D., Prad- sediments. Earth Planet. Sci. Lett. 236, 773–796. han, V.R., Sohl, L.E., 2008. Paleomagnetism and detrital zircon geochronology of Robinson, D.M., DeCelles, P.G., Copeland, P., 2006. Tectonic evolution of the Hi- the upper Vindhyan sequence, Son Valley and Rajasthan, India: a ca. 1000 Ma malayan thrust belt in western Nepal: implications for channel flow models. closure age for the Purana basins? Precambrian Res. 164, 137–159. Geol. Soc. Am. Bull. 192, 865–885. Mandal, S., Robinson, D.M., Khanal, S., Das, O., 2014. Redefining the tectonostrati- Robinson, D.M., DeCelles, P.G., Patchett, P.J., Garzione, C.N., 2001. The kinematic his- graphic and structural architecture of the Almora klippe and the Rangarh– tory of the Nepalese Himalaya interpreted from Nd isotopes. Earth Planet. Sci. Munsiari Thrust sheet in NW India. In: Mukherjee, S., Carosi, R., van der Beek, Lett. 192, 507–521. http://dx.doi.org/10.1016/S0012-821X(01)00451-4. P.A., Mukherjee, B.K., Robinson, D.M. (Eds.), Tectonics of the Himalaya. In: Geol. Searle, M.P., Godin, L., 2003. The South Tibetan detachment and the Manaslu Soc. (Lond.) Spec. Publ., vol. 412. leucogranite: a structural reinterpretation and restoration of the Annapurna- Martin, A.J., Burgy, K.D., Kaufman, A.J., Gehrels, G.E., 2011. Stratigraphic and tectonic Manaslu Himalaya, Nepal. J. Geol. 111, 505–523. implications of field and isotopic constraints on depositional ages of Proterozoic Singh, S.K., Trivedi, J.R., Pande, K., Ramesh, R., Krishnaswami, S., 1998. Chemical Lesser Himalayan rocks in central Nepal. Precambrian Res. 185, 1–17. and strontium, oxygen, and carbon isotopic compositions of carbonates from McKenzie, N.R., Hughes, N.C., Myrow, P.M., Xiao, S., Sharma, M., 2011. Correlation of the Lesser Himalaya: implications to the strontium isotope composition of the Precambrian–Cambrian sedimentary successions across northern India and the source waters of the Ganga, Ghaghara, and the Indus rivers. Geochim. Cos- utility of isotopic signatures of Himalayan lithotectonic zones. Earth Planet. Sci. mochim. Acta 62, 743–755. Lett. 312, 471–483. Singh, S.K., Trivedi, J.R., Krishnaswami, S., 1999. Re–Os isotope systematics in black McKenzie, N.R., Hughes, N., Myrow, P.M., Banerjee, D.M., Deb, M., Planavsky, N.J., shales from the Lesser Himalaya: their chronology and role in the 187Os/188Os 2013. New age constraints on the Aravalli–Delhi successions of India and their evolution of seawater. Geochim. Cosmochim. Acta 63, 2381–2392. implications. Precambrian Res. 238, 120–128. Srivastava, P., Mitra, G., 1994. Thrust geometries and deep structure of the outer and McQuarrie, N., Long, S.P., Tobgay, T., Nesbit, J.N., Gehrels, G., Ducea, M.N., 2013. Doc- lesser Himalaya, Kumaon and Garhwal (India): implications for evolution of the umenting basin scale, geometry and provenance through detrital geochemical Himalayan fold-and-thrust belt. Tectonics 13, 89–109. http://dx.doi.org/10.1029/ data: lessons from the Neoproterozoic to Ordovician Lesser, Greater, and Tethyan 93TC01130. Himalayan strata of Bhutan. Gondwana Res. 23, 1491–1510. Tewari, V.C., 2001. Discovery and sedimentology of microstromatolites from McQuarrie, N., Robinson, D., Long, S., Tobgay, T., Grujic, D., Gehrels, G., Ducea, M., Menga limestone (Neoproterozoic/Vendian). Upper Subansiri district, Arunachal 2008. Preliminary stratigraphic and structural architecture of Bhutan: implica- pradesh, Northeastern Himalaya, India. Curr. Sci. 80, 1440–1444. tions for the along strike architecture of the Himalayan system. Earth Planet. Torres, M.A., West, A.J., Li, G., 2014. Sulphide oxidation and carbonate dissolution as Sci. Lett. 272, 105–117. Myrow, P.M., Hughes, N.C., Goodge, J.W., Fanning, C.M., Williams, I.S., Peng, S.-C., a source of CO2 over geological timescales. Nature 507, 346–349. Bhargava, O.N., Tangri, S.K., Parcha, S.K., Pogue, K.R., 2010. Extraordinary trans- Valdiya, K.S., 1980. Geology of Kumaun Lesser Himalaya. Wadia Institute of Hi- port and mixing of sediment across Himalayan central Gondwanaland during malayan Geology, Dehradun. 291 p. the Cambrian–Ordovician. Geol. Soc. Am. Bull. 122, 1660–1670. Webb, A.A.G., 2013. Preliminary balanced palinspastic reconstruction of Cenozoic Myrow, P.M., Hughes, N.C., Paulsen, T., Williams, I., Parcha, S.K., Thompson, K.R., deformation across the Himachal Himalaya (northwestern India). Geosphere 9, Bowring, S.A., Peng, S.-C., Ahluwalia, A.D., 2003. Integrated tectonostratigraphic 572–587. reconstruction of the Himalaya and implications for its tectonic reconstruction. Webb, A.A.G., Schmidtt, A.K., He, D., Weigland, E.L., 2011a. Structural and geochrono- Earth Planet. Sci. Lett. 212, 433–441. logical evidence for the leading edge of the Greater Himalayan Crystalline com- Myrow, P.M., Hughes, N.C., Searle, M.P., Fanning, C.M., Peng, S.-C., Parcha, S.K., 2009. plex in the central Nepal Himalaya. Earth Planet. Sci. Lett. 304, 483–495. Stratigraphic correlation of Cambrian–Ordovician deposits along the Himalaya: Webb, A.A.G., Yin, A., Harrison, T.M., Célérier, J., Gehrels, G.E., Manning, C.E., Grove, implications for the age and nature of rocks in the Mt. Everest region. Geol. Soc. M., 2011b. Cenozoic tectonic history of the Himachal Himalaya (NW India) and Am. Bull. 121, 323–332. its constraints on the formation mechanism of the Himalayan orogen. Geo- Myrow, P.M., Snell, K., Hughes, N.C., Paulsen, T., Heim, N.A., Parcha, S.K., 2006. Cam- sphere 7, 1013–1061. brian depositional history of the Zanskar Valley region of Indian Himalaya: White, N.M., Pringle, M., Garzanti, E., Bickle, M., Najman, Y., Chapman, H., Friend, P., tectonic implications. J. Sediment. Res. 76, 364–381. 2002. Constraints on the exhumation and erosion of the High Himalayan Slab, Najman, Y., Bickle, M., Chapman, H., 2000. Early Himalayan exhumation: isotopic NW India, from foreland basin deposits. Earth Planet. Sci. Lett. 195, 29–44. constraints from the Indian foreland basin. Terra Nova 12, 28–34. Yin, A., 2006. Cenozoic tectonic evolution of the Himalayan orogen as constrained by Najman, Y., Bickle, M., Garzanti, E., Pringle, M., Barfod, D., Brozovic, N., Burbank, D., along-strike variation in structural geometry, exhumation history, and foreland Ando, S., 2009. Reconstructing the exhumation history of the Lesser Himalaya, sedimentation. Earth-Sci. Rev. 76, 1–131. northwest India, from a multitechnique provenance study of the foreland basin Yin, A., Dubey, C.S., Kelty, T.K., Webb, A.A.G., Harrison, T.M., Chou, C.Y., Célérier, Siwalik Group. Tectonics 28, 15. J., 2010. Geologic correlation of the Himalayan orogen and Indian craton: Part Oslick, J.S., Miller, K.G., Feigenson, M.D., Wright, J.D., 1994. Oligocene–Miocene 2. Structural geology, geochronology, and tectonic evolution of the Eastern Hi- strontium isotopes: stratigraphic revisions and correlations to an inferred malaya. Geol. Soc. Am. Bull. 122, 360–395. glacioeustatic record. Paleoceanography 9, 427–443. Yu, H., Webb, A.A.G., He, D., in press. Extrusion vs. duplexing models of Himalayan Pegram, W.J., Krishnaswami, S., Ravizza, G.E., Turekian, K.K., 1992. The record of sea mountain building 1: discovery of the Pabbar thrust confirms duplex-dominated water 187Os/186Os variation through the Cenozoic. Earth Planet. Sci. Lett. 113, growth of the northwestern Indian Himalaya since Mid-Miocene. Tectonics. 569–576. http://dx.doi.org/10.1002/2014TC003589.