Earth-Science Reviews 160 (2016) 264–299 Contents lists available at ScienceDirect Earth-Science Reviews journal homepage: www.elsevier.com/locate/earscirev Invited review The timing of India-Asia collision onset – Facts, theories, controversies Xiumian Hu a,⁎,EduardoGarzantib,⁎, Jiangang Wang c, Wentao Huang d,WeiAna, Alex Webb e a State Key Laboratory of Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China b Laboratory for Provenance Studies, Department of Earth and Environmental Sciences, Università di Milano-Bicocca, 20126 Milano, Italy c Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China d Department of Geosciences, University of Arizona, Tucson, AZ, 85721, USA e School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK article info abstract Article history: The timing of initial collision between India and Asia has remained controversial for half a century. This paper at- Received 30 December 2015 tempts to review this crucial and hotly debated argument, describing first the different methods used to constrain Received in revised form 26 July 2016 the age of collision and discussing next the rationale, results, inferences and problems associated with each. We Accepted 26 July 2016 conclude that stratigraphy represents the best direct way to unravel collision chronology. Other methods focus- Available online 29 July 2016 ing on the magmatic, metamorphic or paleomagnetic record provide additional fundamental constraints, but cannot provide a robust direct estimate of collision onset. Keywords: Continental collision Initial collision in the central-eastern Himalaya is dated directly at the middle Paleocene (59 ± 1 Ma) by the India-Asia collision chronology abrupt change in sediment provenance recorded in trench settings. The quasi-synchronous unconformities doc- Himalayan Orogeny umented along both Tethyan passive margin of India and active margin of Asia from Tibet to Zanskar-Ladakh con- Indus-Yarlung suture zone firm that orogeny was underway at the close of the Paleocene (56 Ma), well before the disappearance of marine Ophiolite obduction seaways in the Himalaya during the early-middle Eocene (50–45 Ma). Sedimentary evolution and provenance Paleogeography of eastern Tethys changes in marine to fluvio-deltaic successions are recorded synchronously within error from the western to Paleocene the central-eastern Himalaya, failing to provide conclusive evidence for diachronous collision. Tibet These coherent observations are hard to reconcile with three widely cited hypotheses invoking either Paleogene arc-continent collision or Late Cretaceous ophiolite obduction, or the protracted existence of a Greater India Basin, which are all not favored after discussing the geological evidence critically point by point. A scenario no more complex than the one involving solely the passive continental margin of India and the active continental margin of Asia is needed to explain the geological evolution of the nascent Himalaya. The collision between the Tethys Himalaya and the Transhimalayan arc-trench system does represent the collision between India and Asia. Because the Yarlung Zangbo Ophiolite is the forearc basement of the Asian active margin, its obduction onto India could not have preceded the initial closure of Neo-Tethys. Ophiolite obduction began when collision began, in the middle Paleocene. © 2016 Elsevier B.V. All rights reserved. Contents 1. Introduction.............................................................. 265 1.1. Halfcenturyofinconclusivedebate................................................. 266 1.2. Definitionofcollisiononset.................................................... 267 2. GeologicoutlineoftheHimalayaandsouthernTibet............................................ 267 2.1. Tectonicunits.......................................................... 267 2.2. UpperCretaceous-Paleogenestratigraphy.............................................. 270 2.2.1. SouthernTethysHimalayainTibet............................................. 270 2.2.2. NorthernTethysHimalayainTibet............................................. 270 2.2.3. Xigazeforearcbasin................................................... 273 3. Methodsusedtoconstraincollisiononset................................................. 274 3.1. Stratigraphyandsedimentology.................................................. 274 ⁎ Corresponding authors. E-mail addresses: [email protected] (X. Hu), [email protected] (E. Garzanti). http://dx.doi.org/10.1016/j.earscirev.2016.07.014 0012-8252/© 2016 Elsevier B.V. All rights reserved. X. Hu et al. / Earth-Science Reviews 160 (2016) 264–299 265 3.1.1. Provenancechanges................................................... 274 3.1.2. Cessationofmarinesedimentation............................................ 275 3.1.3. Intermontanesedimentationalongthesuturezone..................................... 276 3.1.4. Unconformitiesandabruptsedimentarychanges...................................... 276 3.1.5. Tectoniccharacterofsedimentarybasins.......................................... 277 3.2. Paleomagneticconstraints.................................................... 277 3.2.1. Paleolatitudeoverlap................................................... 277 3.2.2. Convergencerate.................................................... 279 3.2.3. Remagnetization..................................................... 279 3.3. Othermethodsusedtoconstraincollisiononset........................................... 279 3.3.1. Faunalmigration..................................................... 279 3.3.2. Ultra-highpressuremetamorphism............................................ 280 3.3.3. Magmatism....................................................... 280 3.3.4. Continentaldeformation................................................. 281 4. ThePaleogenearc-continentcollisionhypothesis............................................. 283 4.1. TheZedongterrane:remnantofanintra-oceanicarc?........................................ 283 4.1.1. Evidenceinfavor.................................................... 283 4.1.2. Evidenceagainst..................................................... 283 4.1.3. Conclusion....................................................... 283 4.2. TheDazhuquterrane:partofanintra-oceanicsubductionsystem?.................................. 283 4.2.1. AtwhichpaleolatitudedidtheYarlungZangboOphioliteform?............................... 283 4.2.2. StratigraphyoftheChongduiFormation.......................................... 283 4.2.3. RelationbetweentheChongduiandNgamringformations.................................. 284 4.2.4. Conclusion....................................................... 285 4.3. TheLiuquConglomerate:recordofarc-continentalcollision?..................................... 287 4.3.1. Faciesandcomposition.................................................. 287 4.3.2. Depositionalage..................................................... 287 4.3.3. IsAsian-deriveddetritusindeedabsent?.......................................... 287 4.3.4. Conclusion....................................................... 288 4.4. ThePaleogenearc-continentcollisionhypothesisrejected...................................... 288 5. TheGreaterIndiaBasinhypothesis.................................................... 288 5.1. Geologicalevidence,infavororagainst?.............................................. 288 5.2. Where should we look for a “cryptic” suture?............................................ 288 5.3. TheGreaterIndiaBasinhypothesisrejected............................................. 289 6. TheLateCretaceousophioliteobductionhypothesis............................................ 289 6.1. DebateonophioliteobductioninthewesternHimalaya....................................... 289 6.2. DebateonophioliteobductioninthecentralandeasternHimalaya.................................. 289 6.3. TheLateCretaceousophioliteobductionhypothesisrejected..................................... 289 7. Discussion............................................................... 290 7.1. TimingofIndia-Asiacollisiononset................................................ 290 7.2. DiachroneityofIndia-Asiacollisiononset.............................................. 291 7.3. Assessmentofmethodsusedtoconstraincollisiononset....................................... 292 8. Conclusionandperspectives....................................................... 293 Acknowledgements............................................................. 294 AppendixA. Supplementarydata...................................................... 294 References................................................................. 294 “There is something fascinating about science. One gets such wholesale shortening, to unravel the subsequent tectonic evolution as well as the returns of conjecture out of such a trifling investment of fact.” uplift mechanism of the Qinghai-Tibet Plateau, to understand the mi- [Mark Twain, 1883, Life on the Mississippi, ch. 17] gration and evolution of faunas (Bossuyt and Milinkovitch, 2001)orto test the potential link between orogenic growth, global cooling and in- tensification of the Asian monsoon (Raymo and Ruddiman, 1992; An 1. Introduction et al., 2001). It is customary in the literature to assign a variety of ages to the Continental collision, perhaps the most spectacular result of plate India-Asia collision, ranging rather freely from as old as the Late Creta- tectonics, generates