Constraints on the early uplift history of the Tibetan Plateau

Abstract

The surface uplift history of the Tibetan Plateau and Himalaya is among the most interesting topics in geosciences because of its effect on regional and global climate during Cenozoic time, its influence on monsoon intensity, and its reflection of the dynamics of continental plateaus. Models of plateau growth vary in time, from pre-India-Asia collision (e.g., approximately 100 Ma ago) to gradual uplift after the India-Asia collision (e.g., approximately 55 Ma ago) and to more recent abrupt uplift (<7 Ma ago), and vary in space, from northward stepwise growth of topography to simultaneous surface uplift across the plateau. Here, we improve that understanding by presenting geologic and geophysical data from north-central Tibet, including magnetostratigraphy, sedimentology, paleocurrent measurements, and (40)Ar/(39)Ar and fission-track studies, to show that the central plateau was elevated by 40 Ma ago. Regions south and north of the central plateau gained elevation significantly later. During Eocene time, the northern boundary of the protoplateau was in the region of the Tanggula Shan. Elevation gain started in pre-Eocene time in the Lhasa and Qiangtang terranes and expanded throughout the Neogene toward its present southern and northern margins in the Himalaya and Qilian Shan.

Fig. 1.

A simplified tectonic map of the Tibetan Plateau and Himalaya that shows the major tectonic blocks, suture zones, large faults, and basins discussed in the text. JB, Jiuquan basin; QB, Qaidam basin; GBC, Gangrinboche conglomerates; GCT, great counter thrust; GT, Gangdese thrust; NKLF, north Kunlun fault; SKLF, south Kunlun fault; ATF, Altyn Tagh fault; XF, Xianshui River fault; TTS, Tanggula thrust system; JF, Jingsha fault; BNS, Bangong–Nujiang suture zone; YZS, Yarlung Tsangpo suture zone; MBT, main boundary thrust. Small circles with numbers represent sites for Ar/Ar dating: 1–3, sites studied in ref. ; 4, sites at which samples of K-rich lavas in the Zhuerkenwula mountain area (west of longitude 91°30′E; see Figs. 3 and 4 a and c) were collected for Ar/Ar dating; 5, HXB volcanic sites (see Fig. 4 b and c). Labeled boxes (with letters) represent areas at which previous studies for paleoelevation, sedimentology, and magnetostratigraphy of Cenozoic sections were conducted: L, Lunpola (20); FS, Fenghuo Shan (18); N (13, 17); J (43); P (44); Z (see SI Fig. 12 in SI Appendix). WS, FS, and TS represent the Wulanwula, Fenghuoshan, and Tongtianhe sections, respectively, shown in Fig. 2. The large box in the center shows the location of the map shown in Fig. 3.

Fig. 2.

Lithologic and magnetochronostratigraphic correlations of measured sections in the Tongtianhe, Fenghuoshan, and Wulanwula subbasins of the HXB. Magnetochronostratigraphy of the Fenghuoshan subbasin is from ref. . Paleocurrent directions indicate westerly and southerly provenances in the Eocene and most of the Oligocene and northerly provenance in the latest Oligocene. The star in the Fenghuoshan section indicates the carbonate sampling site discussed in ref. .

Fig. 3.

Simplified geologic map of the Hoh Xil region (boxed area in Fig. 1) based on 1:250,000-scale regional geologic mapping, showing the distribution of tectonically disrupted strata of the HXB and structural features. Note that the Jinsha River suture zone (JS, dashed red line) that separates Qiangtang and Songpan-Ganzi terrane is covered in this region. The dashed black line indicates the Qinghai-Tibet highway. TTS, Tanggula thrust system; SKLF, south Kunlun fault; A–B, location of the cross section on the lower left of the figure, which shows significant upper-crustal shortening in the Hoh Xil region. Paleogene volcanic fields of the Zhuerkenwula area are located in the western part of the region shown.

Fig. 4.

⁴⁰Ar/³⁹Ar plateau ages from this study. (a) Zhuerkenwula mountains, which is the largest Cenozoic volcanic province in the northern Tibetan-Kunlun region (≈2,500 km²). The K-rich lavas in this province were previously considered to be <20 Ma old. (b) Plateau ages from the Hoh Xil region. (c) Distributions of radiometric dates of K-rich lavas from the Qiangtang, Hoh Xil, and Kunlun belts (>200 dates collected, mainly from refs. and 60).

Fig. 5.

Generalized geological correlation across the Tibetan Plateau and Himalayan terrane, showing the timing for disappearance of marine strata in the Himalayan, Lhasa, and Qiangtang terranes. The initial age of the Siwalik foreland basin is according to ref. . PQF, marine Pengqu Formation (44); GBC, Gangrinboche conglomerate; JCLF, Jiachala Formation of turbidites (43); HPCMS, Himalayan passive continental margin strata; LZZG, Lingzizhong group volcanics; SXF, shallow marine Sexing Formation (59); TKNF, marine member of the Takena Formation; JZSF, Jingzhushan Formation redbeds; LSF, marine Lang Shan Formation; ABSF, Abushan Formation redbeds; WDLG, continental WG; FHSG-YXCG, FG and YG redbeds; +K, K-rich lava; MCT, main central thrust; YZS, Yarlung Tsangpo suture zone; BNS, Bangong–Nujiang suture zone; TTS, Tanggula thrust system. Solid wavy line, nonconformity; dot–dash line, boundary between marine and continental sediments.

Fig. 6.

Schematic paleogeographic cross sections of the Himalaya and Tibetan Plateau, showing our proposed surface-uplift history for the Tibetan Plateau, in which the plateau grows northward and southward from an elevated proto-Tibetan Plateau (Lhasa and Qiangtang terranes) beginning in the Late Paleogene. MBT, main boundary thrust; GCT, great counter thrust; LZZG, Lingzizhong group volcanics; WDLG, continental Wudaoliang Group; TTS, Tanggula thrust system; NKLF, north Kunlun fault; NQF, north Qilian Mountain fault; GBC, Gangrinboche conglomerates; YZS, Yarlung Tsangpo suture zone; BNS, Bangong–Nujiang suture zone; JS, Jinsha River suture zone; MCT, main central thrust; SL, sea level; GT, Gangdese thrust; GST, Gaize–Siling Tso thrust; LB, Lunpola basin; SGAT, Shiquanhe–Gaize–Amdo thrust; SQF, the south Qilian Mountain fault; SB, Siwalik foreland basin; MFT, main frontal thrust. The Yaluzangbu River has been fixed as a reference point. See the A–B line in Fig. 1 for the position of the 0-Ma cross-section line.