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Abstract

A line-length balanced palinspastic reconstruction across the Himachal Himalaya is presented, highlighting different phases of Himalayan tectonic development: Eocene shortening of the north Indian margin, Early-Middle Miocene emplacement of the crystalline core, and subsequent growth of the range by underplating. The total preserved shortening is 518 km (72%). The reconstruction demonstrates geometric feasibility of crystalline core emplacement via tectonic wedging, i.e., between a southdirected thrust (the Main Central thrust) and a north-directed backthrust (the South Tibet detachment). Crystalline core exposure between these faults occurs ca. 5 Ma in the reconstruction; initial exposure of these crystalline rocks ca. 11 Ma probably occurred in the hinterland within core complexes accommodating east-west extension. After Early-Middle Miocene crystalline core emplacement, ongoing orogenic growth is dominated by underplating processes. Outof-sequence faulting accomplishes <5% of this shortening; frontal accretion of foreland rocks occurs, but the resulting imbricate fan is largely eroded away. Over the past 3-5 m.y., an antiformal stack of mid-crustal horses and a hinterland-dipping duplex of upper crustal horses develop simultaneously. Minimum total shortening across the western Himalaya (from undeformed foreland to the India-Asia suture) is estimated by adding the new results and results from prior work to the north; an estimate of ~703-773 km of assessed shortening is calculated. However, because large portions of the regional deformation remain unassessed, estimates of ~900-1100 km may more accurately refl ect the minimum preserved shortening here. This range is comparable to the ~1350 km of shortening estimated by plate circuit reconstructions for this region. Apparent mismatch between geologic and plate circuit shortening estimates has recently instigated the new Greater India Basin hypothesis for two Cenozoic collisions along Asia's southern margin, but the new results suggest that this mismatch may not exist.

The Influence of Foreland Structures on Hinterland Cooling: Evaluating the Drivers of Exhumation in the Eastern Bhutan Himalaya

“…This link between foreland structures and hinterland ramps can be exploited to create a series of testable cross-section geometries ( Figure 6) that all match the geology at the surface but provide different subsurface geometries and thus different uplift histories. In particular, active uplift in the hinterland of the Himalayan fold-thrust belt has been proposed to be a function of an active duplex (Adams et al, 2013(Adams et al, , 2016Landry et al, 2016;Webb et al, 2011Webb et al, , 2013, out-of-sequence thrusting (Adlakha et al, 2013;Wobus et al, 2003Wobus et al, , 2006, and an active ramp in the décollement (Bollinger et al, 2006;Gilmore et al, 2018;Herman et al, 2010;Long et al, 2012;Robert et al, 2011). These different driving mechanisms predict different uplift, exhumation, and topographic evolutions, which can be directly compared to measured thermochronometers and modern topography.…”

Tracking the Growth of the Himalayan Fold‐and‐Thrust Belt From Lower Miocene Foreland Basin Strata: Dumri Formation, Western Nepal

“…The Neohimalayan "event" is generally associated with south vergent thrusting along the MCT and synchronous tectonic burial of Lesser Himalayan sedimentary rocks. Subsequent slip along the Ramgarh thrust ( Figure 2), growth of the Lesser Himalayan duplex, and imbrication of the MBT system created the major structures observed today within the Lesser Himalayan zone, as well as tilting and folding of the overlying Greater Himalayan rocks (Bhattacharyya & Mitra, 2009;DeCelles et al, 2001DeCelles et al, , 2016Long et al, 2011;Robinson & Martin, 2014;Robinson et al, 2006;Webb, 2013). The most recent phase of shortening has involved the propagation of the thrust front into the foredeep depozone of the mid-Miocene to Pliocene Siwalik Group along faults of the Main Frontal Thrust system (Molnar, 1984;Mugnier et al, 1999), coeval with roughly east-west extension in rocks north of the STDS (Colchen, 1999;Garzione et al, 2003;Hurtado et al, 2001).…”

Millennial and centennial variations in zircon U‐Pb ages in the quaternary indus submarine canyon

“…They structurally overlie higher grade metamorphic rocks and associated leucogranites of Miocene age that comprise the Greater Himalaya, which is well-documented to have begun its exhumation in the Early Miocene, partly through the process of motion on the Main Central Thrust (Catlos et al, 2001;Hodges & Silverberg, 1988;Searle, Law, Jessup, & Simpson, 2006). Final exhumation of the Greater Himalaya may have taken place rather later, possibly in the last five million years (Webb, 2013). These high-grade metamorphic rocks are thrust on top of the Lesser Himalaya, which also comprises slices of the Indian plate but has generally been less strongly metamorphosed and experienced uplift and exhumation more recently (Bollinger et al, 2004;Huyghe, Galy, Mugnier, & France-Lanord, 2001).…”