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Active Uplift of Southern Tibet Revealed

Michael Taylor*, Dept. of Geology, University of Kansas, Lawrence, Kansas 66045, USA; Adam Forte, Dept. of Geology and Geophysics,
Louisiana State University, Baton Rouge, Louisiana 70803, USA; Andrew Laskowski, Dept. of Earth Sciences, Montana State University,
Bozeman, Montana 59717, USA; Lin Ding, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China

ABSTRACT of the Yarlung River are superimposed upon at depth at geodetic and millennial time
North of the Himalayas is the Tibetan the internally drained portion of the Tibetan scales (18–22 cm/yr) (Ader et al., 2012; Lavé
plateau—the largest physiographic feature plateau, which by area is the plateau’s larg- and Avouac, 2000). However, disagreement
on Earth related to intercontinental colli- est surficial feature, forming a long wave- exists on whether the downdip geometry of
sion. Here, we study the rugged Gangdese length depression encompassing ~600,000 the MHT is planar, involves crustal ramps
Range along the southern drainage divide km (Fielding et al., 1994) (Fig. 4). Given beneath the high-relief topographic steps
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of the Tibetan plateau using a synthesis of such vastness, the question of how the (e.g., Whipple et al., 2016; Ghoshal et al.,
geologic, thermochronologic, and interseis- internally drained Tibetan plateau formed is 2020), or if surface breaking splay faults
mic geodetic observations that reveal that a matter of pressing interest, although accommodate a significant portion of India-
southern Tibet’s Gangdese Range is under- research to-date has been unable to deter- Asia convergence (e.g., Murphy et al., 2013).
going active surface uplift at present-day mine a conclusive cause (Sobel et al., 2003; Seismic imaging is consistent with a low-
rates rivaling the Himalaya. Uplift has Horton et al., 2002; Kapp and DeCelles, angle (10–20°) north-dipping décollement
likely been sustained since the early 2019). In the following, we present prelimi- for the MHT, with its northward extent
Miocene, and we hypothesize that surface nary results of ongoing work along the occurring below the main Himalayan peaks
uplift of the Gangdese Mountains led to the southern drainage divide of the Tibetan pla- at ~50 km depth (Makovsky and Klemperer,
development of Tibet’s internally drained teau, which coincides with the Gangdese 1999). North of the main Himalayan peaks
plateau, as well as potentially reversed the Range. Compilations of low-temperature are the northern Himalayan gneiss domes,
course of the paleo Yarlung River, in tan- thermochronology, global positioning sys- which are exposed between the South
dem with exhumation of the Himalayan tem (GPS), and terrain analysis reveal that Tibetan fault system in the south and the
gneiss domes. We suggest the data are con- the Gangdese Range has experienced recent Indus-Yarlung suture (IYS) zone to the
sistent with active thrust duplexing, bal- surface uplift and is likely active today. This north (Figs. 2 and 3). The gneiss domes are
anced by upper crustal extension, effec- critical new observation sheds light on the cored by variably deformed orthogneiss and
tively extending the active décollement style of active shortening across the India- locally are intruded by leucogranites,
between the underthrusting Indian plate Asia collision zone, with implications for emplaced between 37 and 34 Ma (e.g., Lee
and the Eurasian upper plate more than 200 large-scale drainage reorganizations for et al., 2000; Larson et al., 2010). The gneiss
km north of the High Himalayas. the Himalayas and Tibetan plateau. We domes are juxtaposed against Tethyan sedi-
begin with the neotectonic setting for the mentary rocks in the hanging wall, with
INTRODUCTION Himalayan-Tibetan orogen, followed by a rapid cooling regionally initiating by 12 ± 4
The Himalayan-Tibetan orogen hosts the discussion of potentially active structures, Ma (Lee et al., 2004) (Figs. 2 and 3).
tallest and largest area of high topography, which suggest the Gangdese as a potential The remainder of active convergence is
and thickest crust, on Earth, representing a candidate to explain recent fluvial reorgani- accommodated throughout the Tibetan pla-
dramatic expression of crustal shortening zations across southern Tibet. teau by north-striking normal faults and
(Fielding et al., 1994) (Figs. 1–4). A topo- generally northeast- and northwest-striking
graphic swath profile between longitudes THE INDIA-ASIA COLLISION ZONE strike-slip structures (e.g., Taylor and Yin,
85–90°E (Figs. 1–4) illustrates from south AND THE GANGDESE RANGE 2009). The geometry and kinematics of
to north the flat Indo-Gangetic plain, the The India-Asia collision zone presently active structures accommodating east-west
foothills of the sub-Himalaya, the extreme absorbs ~4 cm/yr of geodetic convergence extension across southern Tibet and fault
relief of the High Himalayas, the broad east- as India moves in the N20E direction rela- scarps are consistent with recent seismo-
west topographic trough of the Yarlung tive to stable Eurasia (Zhang et al., 2004). genic activity (Taylor and Yin, 2009). Since
River valley, and the high crest of the Most agree that the Main Himalayan Thrust the onset of extension may date when the
Gangdese Range with its gentle north-facing (MHT) and its updip imbricate fault splays Tibetan plateau attained its maximum ele-
slope. Regionally, geomorphic features north accommodate the majority of convergence vation, this timing has been determined

GSA Today, v. 31, https://doi.org/10.1130/GSATG487A.1.

*Corresponding author: mht@ku.edu

4 GSA Today | August 2021