EARTH-01687; No of Pages 28 Earth-Science Reviews xxx (2011) xxx–xxx Contents lists available at ScienceDirect Earth-Science Reviews journal homepage: www.elsevier.com/locate/earscirev Constraints to the timing of India–Eurasia collision; a re-evaluation of evidence from the Indus Basin sedimentary rocks of the Indus–Tsangpo Suture Zone, Ladakh, India Alexandra L. Henderson a, Yani Najman a,⁎, Randall Parrish b, Darren F. Mark c, Gavin L. Foster d a Lancaster Environment Centre, Lancaster University, Lancashire, LA1 3YQ, UK b NERC Isotope Geosciences Laboratory, Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG, UK c SUERC, Scottish Enterprise Technology Park, Rankine Avenue, East Kilbride, Glasgow, G75 OQF, UK d National Oceanography Centre Southampton, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH, UK article info abstract Article history: Deposited within the Indus–Tsangpo suture zone, the Cenozoic Indus Basin sedimentary rocks have been Received 4 March 2010 interpreted to hold evidence that may constrain the timing of India–Eurasia collision, a conclusion challenged Accepted 16 February 2011 by data presented here. The Eurasian derived 50.8–51 Ma Chogdo Formation was previously considered to Available online xxxx overlie Indian Plate marine sedimentary rocks in sedimentary contact, thus constraining the timing of collision as having occurred by this time. Using isotopic analysis (U–Pb dating on detrital zircons, Ar–Ar dating Keywords: on detrital white mica, Sm–Nd analyses on detrital apatite), sandstone and conglomerate petrography, Himalaya India–Asia collision mudstone geochemistry, facies analysis and geological mapping to characterize and correlate the formations Indus–Tsangpo suture zone of the Indus Basin Sedimentary rocks, we review the nature of these contacts and the identification and Indus molasse correlation of the formations. Our results reveal that previously interpreted stratigraphic contacts identifying Chogdo Formation unconformably overlying Indian plate sedimentary rocks are incorrect. Rather, we suggest that the inaccuracy of previous interpretations is most likely a result of Formation misidentification and thus cannot be used to constrain the timing of India–Asia collision. © 2011 Elsevier B.V. All rights reserved. Contents 1. Introduction ............................................................... 0 2. Regional geology ............................................................. 0 3. The Indus Basin sedimentary rocks: previous and current work ....................................... 0 4. Field area 1: The Lato–Upshi section ................................................... 0 4.1. Stratigraphy and structure ..................................................... 0 4.1.1. The Miru Formation.................................................... 0 4.1.2. Gonmaru La Formation .................................................. 0 4.1.3. Artsa Formation ..................................................... 0 4.1.4. Umlung Formation .................................................... 0 4.1.5. Upshi Formation ..................................................... 0 4.1.6. Rong Formation...................................................... 0 4.1.7. Lato Formation ...................................................... 0 4.2. Geochemical characteristics of the Formations............................................ 0 4.2.1. Mudstone geochemistry .................................................. 0 4.2.2. Sandstone petrography .................................................. 0 4.2.3. Conglomerate clast counts................................................. 0 4.2.4. 206Pb/238U dating of detrital zircons ............................................ 0 4.2.5. 40Ar/39Ar dating of detrital white micas .......................................... 0 4.2.6. Sm–Nd of detrital apatites................................................. 0 ⁎ Corresponding author. Tel.: +44 1524 593898, +64 (0)21 261 9573 (currently). E-mail address: [email protected] (Y. Najman). 0012-8252/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.earscirev.2011.02.006 Please cite this article as: Henderson, A.L., et al., Constraints to the timing of India–Eurasia collision; a re-evaluation of evidence from the Indus Basin sedimentary rocks of the Indus–Tsangpo Suture Zone, Ladakh, India, Earth-Sci. Rev. (2011), doi:10.1016/j.earscirev.2011.02.006 2 A.L. Henderson et al. / Earth-Science Reviews xxx (2011) xxx–xxx 4.3. Detrital provenance ........................................................ 0 4.3.1. Provenance of the Indus Basin sedimentary rock formations ................................. 0 4.3.2. Provenance of the Lato Formation ............................................. 0 4.4. IBSR stratigraphic correlation .................................................... 0 4.4.1. Correlation of the Miru Formation with the Tar Group in the Zanskar Gorge ......................... 0 4.4.2. Correlation of the Gonmaru La, Artsa, Umlung, Upshi and Rong Formations with Indus Group rocks of the Zanskar Gorge .... 0 4.5. Examining evidence for India–Eurasia collision from the Upshi–Lato section (Table 2) ......................... 0 4.6. Suggested paleodepositional environment reconstruction for the IBSR................................. 0 5. Field area 2: The Chilling–Sumda section, Zanskar Gorge .......................................... 0 5.1. Stratigraphy and structure ..................................................... 0 5.1.1. Jurutze Formation ..................................................... 0 5.1.2. Lower Chilling Formation ................................................. 0 5.1.3. Upper Chilling Formation ................................................. 0 5.1.4. Chilling ophiolitic mélange................................................. 0 5.2. Compositional characterization of the Chilling Formation ....................................... 0 5.2.1. Mudstone geochemistry .................................................. 0 5.2.2. Sandstone petrography .................................................. 0 5.2.3. Conglomerate clast counts ................................................. 0 5.2.4. U–Pb ages of detrital zircons ................................................ 0 5.3. Provenance of the Chilling Formation ................................................ 0 5.4. Correlation of the Chilling Formation ................................................ 0 5.5. Examining evidence for India–Eurasia collision at the Chilling–Sumda section . ............................ 0 6. Summary and conclusions......................................................... 0 Acknowledgements .............................................................. 0 References .................................................................. 0 1. Introduction of India–Eurasia collision. The nature of the IBSR has been examined by several authors; (e.g. van Haver, 1984; Garzanti et al., 1987; Searle It has been widely demonstrated that the evolution of the et al., 1990; Sinclair and Jaffey, 2001; Clift et al., 2002; Henderson Himalaya has influenced many external factors including oceanic et al., 2010b); with all work agreeing that sediments were dominantly geochemistry (e.g. Richter et al., 1992), atmospheric circulation and sourced from the Eurasian margin, and deposited south of the global climate during the Cenozoic (e.g. Raymo and Ruddiman, 1992). Kohistan Ladakh Batholith between Early to ~Mid Cenozoic times, In order to assess the extent to which these have been caused by thus spanning the most commonly quoted age of collision of around mountain building processes it is necessary to understand Himalayan 50–55 Ma. The stratigraphy appears to provide an excellent record of orogenic events, in particular the timing of India–Eurasia continental erosion that occurred during Indian–Eurasia collision. Previous collision. However, despite the importance for constraining the timing studies of the IBSR constrained the time of India–Eurasia collision of collision, the date of initial collision is still disputed; the general using the time of cessation of marine facies (Searle et al., 1990), first consensus places it around 50–55 Ma (e.g. Powell and Conaghan, arrival of Eurasian detritus on the Indian plate (Clift et al., 2001, 2002) 1973; Tonarini et al., 1993; de Sigoyer et al., 2000; Clift et al., 2002; and/or earliest record of mixed Indian and Eurasian detritus in Leech et al., 2005), with more extreme estimations ranging from the sedimentary rocks (Clift et al., 2002; Wu et al., 2007; Henderson 34 Ma to ~70 Ma (e.g. Ding et al., 2005; Yin, 2006; Aitchison et al., et al., 2010b). In this paper, we re-examine the evidence at key 2007). Part of this discrepancy is due to different definitions of locations, and introduce new data from the IBSR to re-assess collision and the variety of approaches to measuring it (e.g. Rowley, constraints to the timing of India–Eurasia collision. In contrast to 1996). Examples of current methods used for constraining the timing previous work, we conclude that Eurasian derived sediments of 51 Ma of collision include dating of the ultra-high pressure eclogites which do not stratigraphically overlie Indian plate rocks, and thus cannot be represent continental subduction (Tonarini et al., 1993; Leech et al., used to constrain the time of collision in the manner previously 2005; Parrish et al., 2006), earliest evidence of similar terrestrial proposed. faunas found on both Indian and