Journal of Palaeogeography 2015, 4(1): 85-98 DOI: 10.3724/SP.J.1261.2015.00069 Geochemistry and sedimentary environments Provenance and drainage system of the Early Cretaceous volcanic detritus in the Himalaya as constrained by detrital zircon geochronology Xiu-Mian Hu1, *, Eduardo Garzanti2, Wei An1 1. State Key Laboratory of Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210029, China 2. Department of Earth and Environmental Sciences, Università di Milano‑Bicocca, Milano 20126, Italy Abstract The age range of the major intra-plate volcanic event that affected the northern Indian margin in the Early Cretaceous is here defined precisely by detrital zircon geochronol- ogy. U–Pb ages of Early Cretaceous detrital zircons found in the Cretaceous to the Paleocene sandstones cluster mainly between 142 Ma and 123 Ma in the northern Tethys Himalayan unit, and between 140 Ma and 116 Ma in the southern Tethys Himalayan unit. The youngest and oldest detrital zircons within this group indicate that volcanism in the source areas started in the latest Jurassic and ended by the early Albian. Stratigraphic data indicate that volcaniclastic sedimentation began significantly earlier in southern Tibet (Tithonian) than in Nepal (Valangin- ian), and considerably later in Spiti and Zanskar (Aptian/Albian) to the west. This apparent westward migration of magmatism was explained with progressive westward propagation of extensional/transtensional tectonic activity and development of fractures cutting deeply across the Indian continental margin crust. However, detrital zircon geochronology provides no indi- cation of heterochroneity in magmatic activity in the source areas from east to west, and thus lends little support to such a scenario. Westward migration of volcaniclastic sedimentation may thus reflect instead the westward progradation of major drainage systems supplying vol- canic detritus sourced from the same volcanic centers in the east. Development of multiple radial drainage away from the domal surface uplift associated with magmatic upwelling, as observed for most large igneous provinces around the world, may also explain why U–Pb ages of detrital zircons tend to cluster around 133–132 Ma (the age of the Comei igneous province) in Tethys Himalayan units, but around 118–117 Ma (the age of the Rajmahal igneous province) in Lesser Himalayan units. Key words northern Indian margin, Cretaceous Himalayan Orogen, volcaniclastic detri- tus, drainage system, zircon geochronology, palaeogeography 1 Introduction* event affected the entire northern India passive margin facing Neotethys, as long documented by studies of vol‑ In the Early Cretaceous, a major intra‑plate volcanic canic and volcaniclastic rocks exposed in various regions of the Himalayan orogeny (Figure 1). Lower Cretaceous * Corresponding author. E‑mail: [email protected]. volcaniclastic sandstones have been deposited all along Received: 2014-06-27 Accepted: 2014-10-17 the Tethys Himalayan domain, from the Zanskar Range 86 JOURNAL OF PALAEOGEOGRAPHY Jan. 2015 (Baud et al., 1984; Garzanti, 1991, 1993a) to Spiti, Ne‑ Trachyte; Sakai, 1983; Sakai et al., 1992) and in the Tethys pal (Bordet et al., 1971; Garzanti and Pagni Frette, 1991; Himalaya of southeastern Tibet (Sangxiu Formation; Zhu Gibling et al., 1994; Garzanti, 1999) and southern Tibet et al., 2009; Qiu et al., 2010; Xia et al., 2014). Mafic pro‑ (Jadoul et al., 1998; Hu et al., 2008, 2010; Figure 2). Geo‑ toliths of late Early Cretaceous age have been recognized chemical analyses of basaltic grains and detrital Cr‑spinels even in Lesser Himalayan eclogites of Nepal (Groppo et from these sandstones point to the alkaline character of the al., 2007). All of these volcanic rocks are generally con‑ volcanism, consistent with a “within‑plate” tectonic set‑ sidered as belonging to the Rajmahal-Sylhet flood-basalt ting (Dürr and Gibling, 1994; Zhu et al., 2004; Hu et al., igneous province of the northeastern Indian subcontinent 2010, 2014). Lower Cretaceous volcanic rocks have never (Baksi, 1995; Kent et al., 2002) and/or to the Comei large been reported so far in the western Himalaya, but are well igneous province (Zhu et al., 2009). known to occur in the Lesser Himalaya of Nepal (Aulis This article provides new U-Pb ages of zircon grains a Places and references for detrital zircon samples 36°N Karakoram Fault (1) Duoping, this study (2) Tianba, this study Ladakh (3) Saga, Wang et al., 2011 (4) Gangjiu, Zhang et al., 2014 Kashmir GCT Tibet Zanskar (5) Babazhadong, Du et al., 2015 (7) 34° , China (6) Chuangde, Cai et al., 2011 (7) Zanskar, Clift et al., 2014 (8) Zhepure Mt., Hu et al., 2010 32° (9) Gamba, Garzanti and Hu, 2014 Spiti (10) Gucuo, Hu et al., 2010 74° (11) Selong, Zhu et al., 2011 STDZ (12) Mustang, Gehrels et al., 2011 0 100 200 km Kailas (13) Tansen, Gehrels et al., 2011 Dajin Gangdese batholith Figure 1b Linzizong volcanic 30° successions (5) Zhongba Xigaze forearc Lhasa (4) 78° MCT (1) Xigaze Indus–Yarlung Saga suture zone MFT (11) (3) GCT (6) (12) Gyangze Tethyan Himalaya (10) (8) (2) Tingri (9) 28° Qomolangma Gamba STDZ Greater Himalaya (13) MBT Paleozoic–Mesozoic Kathmandu MCT Lesser Himalaya strata 82° Sub-Himalaya Thrust Nepal Leucogranite Normal fault 86° 90° E India Dazuka Zongzhuo Xigaze Xiukang b 0 30 60 km 3 1 E1–2 Paleogene K2 K -mlg Ophiolites Leucogranite E N conglomerate mélange forearc X mélange Oph Liuqu Weimei, Rilang, Langjiexue Gangdese E2–3 K Cretaceous K1 and Jiabula T P Permian 30°N Mt. Lopu conglomerate Formations Group arc (5) (4) E3N1 Lhasa Zhongba P Lhasa Block (1) 2 K K (3) Saga GCT 2 Ngamring E Oph X-mlg Xigaze T Oph T ZGT E2–3 ZGT E2–3 29° (12) (10) (6) E1–2 K2 K2 Yamzho Yum L. GKT Gyangze K K1 (2) (11) K2 K1 (8) NTH STH E1–2 Tingri GKT Kangmar GH (9) Comei STDZ MCT Gamba STDZ K LH Nyalam E1–2 28° Normal fault Strike-slip fault Thrust Mt. Qomolangma K 84° 86° 88° 90°E Figure 1 a-Geological map of the Himalayan belt; b-Simplified geological map of the southeastern Tibet. Locations of sandstone samples considered for detrital‑zircon geochronology are shown. GCT = Great Counter Thrust; ZGT = Zhongba-Gyangze Thrust; GKT = Gyirong-Kangmar Thrust; STDZ = South Tibetan Detachment Zone; MCT = Main Central Thrust; MBT = Main Boundary Thrust; MFT = Main Frontal Thrust; NTH = Northern Tethyan Himalaya; STH = Southern Tethyan Himalaya; GH = Greater Himalaya; LH = Lesser Himalaya. Xiu‑Mian Hu et al.: Provenance and drainage system of the Early Cretaceous volcanic detritus in the Himalaya as constrained by detrital Vol. 4 No. 1 zircon geochronology 87 from Lower Cretaceous volcaniclastic sandstones of the al., 2003; Najman et al., 2010; Hu et al., 2012). northern Tethyan Himalaya in southern Tibet, and a com‑ The Himalayan belt, south of the Indus‑Yarlung suture pilation of the available geochronological and isotopic zone, is traditionally subdivided into the Tethyan, Greater data on detrital zircons from Cretaceous-Paleocene sand‑ and Lesser Himalayan domains (Figure 1; Gansser, 1964). stones of the northern Indian margin, including the Lesser In southern Tibet, the Tethyan Himalaya is divided into and Tethys Himalaya. Based on the abundant and precise a northern zone and a southern zone, separated by the radiometric ages available for detrital zircons ultimately Gyirong-Kangmar Thrust (Ratschbacher et al., 1994). produced during the Early Cretaceous magmatic event, The northern zone (Gyangze-Saga areas) represents the the age range of volcanic activity can be accurately con‑ continental slope and rise, chiefly consisting of deep-water strained. We also discuss the palaeogeographic signifi‑ sediments of the Mesozoic (Hu et al., 2008). The southern cance of the Early Cretaceous volcanism, and the differ‑ zone (Tingri-Gamba areas) represents a more proximal ences observed in the age distribution of detrital zircons in part of the Indian passive margin, mostly characterized by different regions and tectonic domains of the Himalayan shelfal carbonates and terrigenous sedimentary rocks of belt. The standardized time scale and web of correlation the Paleozoic to the Paleogene (Willems et al., 1996; Hu between relative biostratigraphic and absolute radiometric et al., 2012; Sciunnach and Garzanti, 2012). ages is after Ogg et al. (2012). The Greater Himalaya, south of the southern Tibetan Detachment Zone, largely consists of Proterozoic meta‑ 2 Geological setting sedimentary protoliths intruded by crustal melts during the Cambrian to the Ordovician (DeCelles et al., 2000). During the Jurassic, the northern passive margin of In‑ Deformed at medium‑ to high‑grade metamorphism as a dia was situated at intermediate latitudes in the southern consequence of collision, these rocks were thrust onto the hemisphere, separated from Asia in the north by a several Lesser Himalaya along the Main Central Thrust in the earli‑ thousand km‑wide Neotethys Ocean (Klootwijk, 1984; est Miocene (Hodges, 2000; Yin, 2006). The Lesser Hima‑ Patzelt et al., 1996; van Hinsbergen et al., 2011). In the laya includes a high‑grade metamorphic basement and a Cretaceous, India rifted away from the rest of Gondwana 8-10 km‑thick low‑grade metasedimentary succession of (Norton and Sclater, 1979; Zhu et al., 2009), and drifted the Upper Paleoproterozoic to the upper Lower Cambrian, rapidly northwards until it collided with the Lhasa Block dominated by siliciclastic protoliths in the lower part and in the Paleogene to form the Himalayan Orogen (Guillot et containing carbonates in the upper part; the Upper Paleo‑ Southern Tethyan Himalaya Northern Tethyan Himalaya Age Period/ Lesser W E (Ma) Epoch Himalaya Zanskar Zanda Thakkhola Tingri-Gamba Tianba Gyangze Paleocene Amile Stumpata Jidula 65 100 Gamba- 99.6 Aulis Trachyte Chikkim/ Gyabula Fatu La Bolinxiala Muding cunkou Gyabula Alb. 110 Taltung 112.0 Pingdon La Apt. 120 Gajiejie Kagbeni Tianba Rilang Giumal 125.0 Wölong Early Cretaceous Early Bar. 130 130.0 Haut.