hu-B35124.1 2nd pages / 1 of 14 Initial growth of the Northern Lhasaplano in the early Late Cretaceous Initial growth of the Northern Lhasaplano, Tibetan Plateau in the early Late Cretaceous (ca. 92 Ma) Wen Lai1, Xiumian Hu1,†, Eduardo Garzanti2, Gaoyuan Sun1,3, Carmala N. Garzione4, Marcelle BouDagher Fadel5, and Anlin Ma1 1State Key Laboratory of Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China 2Department of Earth and Environmental Sciences, Università di Milano-Bicocca, Milano 20126, Italy 3College of Oceanography, Hohai University, Nanjing 210098, China 4Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York 14627, USA 5Department of Geological Sciences, University College London, London WC1E6BT, UK ABSTRACT INTRODUCTION Stable isotopes in lacustrine carbonates suggest that the basins surrounding the Gangdese Moun­ Constraining the growth of the Tibetan The Tibetan Plateau, with an average ele­ tains in the southern Lhasa terrane had reached Plateau in time and space is critical for test- vation of ~5000 m, is the world’s highest and an elevation >4500 m since India­Asia collision ing geodynamic models and climatic changes widest orogenic plateau, and exerts a major in­ (Ding et al., 2014). Low­temperature thermo­ at the regional and global scale. The Lhasa fluence on the Asian monsoon, global climate chronology reveal that the central and northern block is a key region for unraveling the early change, and regional distribution of living spe­ Lhasa terranes experienced rapid to moderate history of the Tibetan Plateau. Distinct from cies (Raymo and Ruddiman, 1992; Molnar et al., cooling and exhumation between 85 and 45 Ma the underlying shallow-marine limestones, 1993; An et al., 2001; Dupont­Nivet et al., 2007; (Hetzel et al., 2011; Rohrmann et al., 2012). the Jingzhushan and Daxiong formations Deng et al., 2011). Constraining the surface­up­ These studies shed light on the evolution of the consist of conglomerate and sandstone de- lift history of the Tibetan Plateau is critical for Tibetan Plateau, but do not establish when and posited in alluvial-fan and braided-river sys- understanding the geodynamic mechanisms that where the ancient plateau was initially uplifted. tems. Both units were deposited at ca. 92 Ma, build orogenic plateaus, as well as the plateau’s The aim of the present study is to corroborate as constrained by interbedded tuff layers, influence on regional and global climate (Chung or falsify the early growth of a “Lhasaplano,” detrital zircons, and micropaleontological et al., 1998; Rowley and Currie, 2006; Wang following the Qiangtang­Lhasa collision but pre­ data. Provenance and paleocurrent analy- et al., 2008; 2014; Xu et al., 2015). The spec­ dating the India­Asia collision. To this goal we ses indicate that both units were derived tacular angular unconformity separating folded investigated the spatial distribution, depositional from the same elevated source area located Mesozoic strata of the Lhasa block (Fig. 1A) age, and paleogeographic setting of non­marine in the central-northern Lhasa block. These from the overlying, weakly deformed 60–52 Ma Late Cretaceous strata in the Lhasa block. We two parallel belts of coeval conglomerates Linzizong volcanic succession (Pan et al., 2004; carried out detailed multi­technique sedimento­ record a major change in paleogeography of Zhu et al., 2015), led to the inference of an logical and provenance analysis based on gravel the source region from a shallow seaway to Andean­style orogenic episode associated with composition, sandstone petrology, paleocurrent a continental highland, implying initial topo- the Gangdese arc (England and Searle, 1986). directions, detrital zircon U­Pb ages and Hf iso­ graphic growth of an area over 160,000 km2, Structural restorations suggest that >50% crustal topes to provide evidence for erosion of the cen­ named here the Northern Lhasaplano. The shortening of the Lhasa block took place during tral and northern Lhasa terranes, and resolve the early Late Cretaceous topographic growth the Cretaceous (Murphy et al., 1997; Kapp et al., timing and spatial distribution of surface uplift. of the Northern Lhasaplano was associated 2007a; Volkmer et al., 2007), leading to the hy­ with the demise of Tethyan seaways, thrust- pothesis that a “Lhasaplano,” a narrow high­ele­ GEOLOGICAL BACKGROUND belt development, and crustal thickening. vation plateau similar in size to the modern An­ The same paleogeographic and paleotectonic dean Plateau (Altiplano), developed before the The Tibetan Plateau formed by the progres­ changes were recorded earlier in the North- India­Asia collision (Kapp et al., 2005). Wang sive accretion of a series of microcontinents ern Lhasaplano than in the Southern Lhasa- et al. (2008) argued in favor of a proto­Tibetan (Fig. 1A), including the Lhasa block in the plano, indicating progressive topographic plateau and provided stratigraphic and thermo­ south and the Qiangtang block to the north, growth from north to south across the Ban- chronological evidence of surface uplift of the welded along the Bangong­Nujiang suture zone gong-Nujiang suture and Lhasa block dur- Lhasa and southern Qiangtang terranes before (BNSZ). The Lhasa block (Fig. 1A) can be ing the Cretaceous. Similar to the Central 40 Ma. Such a scenario has led to new important subdivided into southern, central, and northern Andean Plateau, the Northern Lhasaplano questions: if an ancient plateau existed before the terranes, separated by the Shiquanhe­Nam Co developed by plate convergence above the India­Asia collision, then how did it form, and Mélange zone (SNMZ) and by the Luobadui­ oceanic Neo-Tethyan subduction zone before when and where did it start to grow? Milashan Fault (LMF), respectively (Zhu et al., the onset of the India-Asia collision. Most previous reconstructions of Tibetan Pla­ 2011b). The southern Lhasa terrane (Fig. 1B) teau growth have focused on paleoelevation es­ is characterized by Late Triassic to Paleogene †Corresponding author: huxm@ nju .edu.cn. timates and low­temperature thermochronology. Gangdese plutonic and Paleogene Linzizong GSA Bulletin; Month/Month 2019; v. 131; no. X/X; p. 1–14; https://doi.org/10.1130/B35124.1; 10 figures; Data Repository item 2019138.; published online XX Month 2016. For permission to copy, contact [email protected] Geological Society of America Bulletin, v. 1XX, no. XX/XX 1 © 2019 Geological Society of America hu-B35124.1 2nd pages / 2 of 14 Wen Lai et al. 75°E ( (( 95° E 100° E 105°E Legend Middle Cretaceous A Shexing Fm. Upper Cretaceous Mélange or Ophiolite Jingzhushan Fm. Upper Cretaceous Amdo granite 40°N Daxiong Fm. TARIM Linzizong Cretaceous granite Tv QAIDAM volcanic rocks KUNLUN Cretaceous-Tertiary Cenozoic S K-Tg ONGPAN-G ANZI Gangdese granite non-marine strata e1 JSSZ Lower Cretaceous Q Quaternary 0 QIANG & volcanic rocks 7 TANG Fig.1b Central BNSZ SGAT Strike-skip GT L Paleozoic has a GST fault Southe GLT Northern Lhasa 30°N rn Lhas SNMZ 0%7 LMF Jurassic Thrust MF T a T HFT IYSZ GCT Lower Cretaceous Section locality Kcv, Duoni, Langshan Previous literature HIMALAYAS NP XFB Xigaze forearc basin Co Lake B 80eE 82eE 84eE 86eE 88eE 9eE 92eE Rutog Southern Qiangtang Block K- Bang ong T Shiqu -Nuj g an iang S he uture Zone 32eN Gaize Qiagui Co Zhaxi Wuru Co Amdo K- Co SGAT Tg SE-N05 Daze Co GS SE-N02 T iling Co Nima S Biru SE-N04 SE-N01 SE-N03 Nagqu Tv ba GLT Du Baingoin Indu Coqen Zari s Nam Co -Ya K-Tg GLT rlun SE-S02 g ST Tangra m Co Sut ET Yum Co Na e u 01 30 N re Z Tv SE-S on g e -T K-Tg Tv K Linzhou 0 200km K-Tg Lhasa Xigaze Figure 1. (A) Tectonic map of the Tibetan Plateau (modified after Zhu et al., 2011b and Wang et al., 2014). (B) Sketch geological map of the Lhasa block (modified after Pan et al., 2004 and Kapp et al., 2003). Previously studied sites of the Daxiong Formation in the Coqen basin (Sun et al., 2015a) and of the Jingzhushan Formation near Rutog (Li et al., 2014a) are shown. JSSZ—Jinsha suture zone; SNMZ—Shiquan River-Nam Co Mélange zone; LMF—Luobadui-Milashan Fault; SGAT—Shiquanhe-Gaize-Amdo thrust; GST—Gaize-Siling Co thrust; GLT—Gugu La thrust; ST—Shibaluo thrust; ET—Emei La thrust; MCT—Main Central thrust; MBT—Main Boundary thrust; THFT—Tethyan Himalaya fold-thrust belt; GCT—Great counter thrust; IYSZ—Indus-Yarlung Zangbo Suture zone; BNSZ—Bangong-Nujiang suture zone; GT—Gangdese thrust. volcanic rocks yielding zircons with εHf(t) >10 The northern Lhasa terrane (Fig. 1B) comprises The Qiangtang block, bounded to the south (Chu et al., 2006; Ji et al., 2009; Zhu et al., >4 km of Late Jurassic to Early Cretaceous by the BNSZ and to the north by the Jinsha su­ 2011b, 2015). Along the southern margin of marginal­ marine and deltaic strata (XZBGM, ture, is divided into the northern and southern the Gangdese magmatic arc, thick deep­water 1993), overlain by continental deposits of the Qiangtang terranes by an axial metamorphic belt turbidites were deposited in the Xigaze forearc Late Cretaceous Jingzhushan Formation (Kapp including Triassic blueschist­bearing mélange basin during Albian to Santonian (An et al., et al., 2007b; Zhang et al., 2011). Cretaceous (Pullen et al., 2008). In the southern Qiangtang 2014; Orme and Laskowski, 2016). The cen­ plutonic and volcanic rocks also occur (Zhu terrane, Cambrian metasedimentary rocks in­ tral Lhasa terrane (Fig. 1B) includes Precam­ et al., 2011b). truded by Ordovician granites lie in tectonic con­ brian crystalline basement (Pan et al., 2004), The BNSZ, traced for ≥1200 km from east to tact with Carboniferous–Jurassic strata (Pullen very low­grade Carboniferous metasediments, west between the Lhasa and Qiangtang blocks in et al., 2011).