SALT CONTROL ON THRUST GEOMETRY, STRUCTURAL STYLE AND GRAVITATIONAL COLLAPSE ALONG THE HIMALAYAN MOUNTAIN FRONT IN THE SALT RANGE OF NORTHERN PAKISTAN

Among the foreland belts of the Andean mountain system, the Eastern Cordillera of Colombia (EC) represents a unique example of an isolated, bi-vergent mountain belt. In contrast, to block tectonics of broken foreland basins, it displays a ductile deformation style which involves two mountain fronts with a structural relief of the order of 10 km. Internal parts of the EC have been shortened by buckling at high and a homogeneously strained basement at deeper structural levels. These deformation patterns likely attest to conditions of a thermally weakened backarc setting. Two opposed scenarios have been postulated for its surface uplift and consequent exhumation: 1) an E-migrating deformation front and the formation of progressively forward breaking faults; and 2) the pop-up of a weak crustal welt enclosed by strong foreland blocks. In this latter setting, a synchronous early formation of marginal mountain fronts and a late-stage surface uplift of a central domain may be anticipated. These two constellations compare, in terms of a contrasting model setup, to a foreland migrating orogenic wedge or a relatively stable, doubly vergent wedge formed above a structural discontinuity or rheologic boundaries that acted as sites for the nucleation of the marginal faults.In this contribution, we opt to examine the &#8220;boundary&#8221; conditions for the development of a doubly vergent wedge formed at the tip line of a rigid tapering backstop, that simulates a rigid foreland block. With respect to the shape of this backstop, we examine the effects of tip angles less than the angle of internal friction (<30&#176;) and find, that at a low tip angle of 10&#176; the pop-up evolves above a forward-breaking principal kink-band with the synchronous formation of a sequence of conjugate back-kinks that cut into the sand pack, as it is pushed toward the backstop. At a moderate tip angle of 20o the forward-breaking kink-band is slightly steeper than the backstop and gives rise to a frontal fold with an overturned limb. This latter geometrical configuration loosely compares to the structural relations of a structural section through the high plains of Bogot&#225;, where the eastern mountain front defines a strongly deformed antiform, that is juxtaposed against an undeformed margin of the adjacent Guyana shield.

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Lower Tertiary planktonic biostratigraphy of the Salt Range, Northern Pakistan

Neues Jahrbuch für Geologie und Paläontologie - Monatshefte ◽

10.1127/njgpm/2000/2000/721 ◽

2000 ◽

Vol 2000 (12) ◽

pp. 721-747 ◽

Cited By ~ 2

Author(s):

Jamil Afzal ◽

Aftab A. Butt

Keyword(s):

Northern Pakistan ◽

Lower Tertiary ◽

Salt Range

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Biostratigraphy, microfacies and sequence stratigraphic analysis of the Chorgali Formation, Central Salt Range, northern Pakistan

Solid Earth Sciences ◽

10.1016/j.sesci.2021.11.003 ◽

2021 ◽

Author(s):

Kamran Mirza ◽

Nosheen Akhter ◽

Ayesha Ejaz ◽

Syeda Fakiha Ali Zaidi

Keyword(s):

Northern Pakistan ◽

Sequence Stratigraphic ◽

Stratigraphic Analysis ◽

Salt Range

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Structural Style--Brooks Range Mountain Front, Alaska: ABSTRACT

AAPG Bulletin ◽

10.1306/ad4625ce-16f7-11d7-8645000102c1865d ◽

1985 ◽

Vol 69 ◽

Author(s):

R. C. Crane, C. G. Mull

Keyword(s):

Brooks Range ◽

Structural Style ◽

Mountain Front

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Structural style of the NW Zagros Mountains and the role of basement thrusting for its Mountain Front Flexure, Kurdistan Region of Iraq

Journal of Structural Geology ◽

10.1016/j.jsg.2020.104206 ◽

2020 ◽

Vol 141 ◽

pp. 104206

Author(s):

Mjahid Zebari ◽

Philipp Balling ◽

Christoph Grützner ◽

Payman Navabpour ◽

Jan Witte ◽

...

Keyword(s):

Kurdistan Region ◽

Zagros Mountains ◽

Structural Style ◽

Mountain Front

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Biostratigraphy of Chorgali Formation, Bochal and Pir Makhdum Jahanian area, Central and Eastern Salt Range, Northern Pakistan

10.5176/2251-3353_geos13.54 ◽

2013 ◽

Author(s):

Shahid Jamil Sameeni ◽

Hafiz Muhammad Siddique ◽

Rabia Imtiaz ◽

Sara Sikandar ◽

Ali Aftab ◽

...

Keyword(s):

Northern Pakistan ◽

Salt Range

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Investigating lateral variations in the kinematics of active deformation along the Western Kunlun mountain front (Xinjiang, China): structural and morphological analysis of the Hotan anticline

10.5194/egusphere-egu2020-10132 ◽

2020 ◽

Author(s):

Christelle Guilbaud ◽

Martine Simoes ◽

Laurie Barrier ◽

Jérôme Van der Woerd ◽

Guillaume Baby ◽

...

Keyword(s):

Morphological Analysis ◽

Mountain Range ◽

Thrust Sheet ◽

Active Deformation ◽

Fluvial Terraces ◽

Structural Style ◽

Western Kunlun ◽

Mountain Front ◽

Surface Geology ◽

Lateral Variations

The Western Kunlun Range is a mountain range located at the northwestern boundary of the Tibetan Plateau, facing the Tarim Basin. Our previous combined structural and morphological investigations of the mountain front, nearby the city of Pishan where a Mw 6.4 earthquake occurred in 2015, revealed the existence of a duplex uplifting Cenozoic strata, in which only the most frontal blind ramp is presently active and slips at a probable rate of 2 to 2.5 mm/yr. Located ~100 km further east along the mountain front, the Hotan anticline seems to present a different structure from surface geology, as older strata from Mesozoic and Paleozoic outcrop. Additionally, some authors proposed that the deformation would be here accommodated by a large blind basement thrust sheet, in clear contrast with the duplexes documented further west.To further document potential lateral variations in the structural style and how they may affect the kinematics of active deformation along the mountain front of the Western Kunlun, we carry out a structural and morphological analysis of the Hotan anticline. We build structural cross-sections based on seismic reflection profiles, and calculate the incremental uplift recorded by dated fluvial terraces to quantify shortening rates over the last ~300 kyr. Our analysis reveals that a duplex structure, located below the basement thrust sheet, presently accommodates active deformation at a rate of 0.5 to 2.5 mm/yr, with a preferred rate of ~1.6 to 2.3 mm/yr. In more detail, uplifted terraces reveal that all ramps of the duplex are active in the case of the Hotan anticline, while only the most frontal ramp is documented as active in the case of the Pishan anticline further west. These results indicate that the style and rate of active shortening are rather homogeneous all along the mountain front, in contrast with the first impression provided by surface geology. Moreover, the discrepancy between surface geology and active morphology reveals progressive structural changes over geological times, from a blind basement ramp to duplexes. However, in the details, active deformation still remains segmented as its partitioning on the various ramps of the duplexes is variable along strike.

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Stability of the gravel-sand transition of the Ganga Plains recorded in Siwalik stratigraphy; implications for extreme floods

10.5194/egusphere-egu2020-675 ◽

2020 ◽

Author(s):

Laura Quick ◽

Hugh Sinclair ◽

Mikael Attal ◽

Rajiv Sinha ◽

Rohtash Kumar

Keyword(s):

Depositional Environments ◽

Gangetic Plain ◽

Extreme Floods ◽

Close Proximity ◽

Mountain Front ◽

Himalayan Mountain ◽

Siwalik Group ◽

Indo Gangetic Plain ◽

Stable Feature

Many rivers of the Indo-Gangetic Plain are prone to abrupt switching of channel courses causing devastating floods over some of the world&#8217;s poorest and most densely populated regions. Recent work has identified the gravel-sand transition as an avulsion node for the channels; notably the avulsion of the Kosi River in 2008 occurred in close proximity to its gravel-sand transition. The gravel-sand transition is a geomorphic feature observed within all major mountain-fed, and smaller foothill-fed Himalayan rivers ranging from 10 to 20 km downstream from the mountain front. It is characterised by an abrupt downstream reduction in grain size from gravel to sand and is often associated with a break in channel gradient, which suggests it is a relatively stable feature over the last few thousands of years.However, new subsurface data from the Kosi mega-fan in eastern Nepal reveals 10-20 Ka gravels located ~50 km downstream from the current gravel-sand transition. The implication is that this key geomorphic boundary can periodically prograde considerably further into the Ganga Plains. A greater long-term (>106 yrs) understanding of the controls on the gravel-sand transition is achieved by studying the stratigraphic record of the Miocene Siwalik Group, which is exhumed as a series of thrusted fault blocks at the Himalayan mountain front. The Siwalik succession is divided into three lithofacies units that coarsens upwards from siltstones and sandstones to coarse conglomerates. The units are termed the Lower, Middle and Upper Siwaliks respectively and reflect the current depositional environments found on the Ganga Plains. The gravel-sand transition is recorded as the contact between the Middle and Upper Siwaliks. Significant gravel pulses have been identified directly below the Middle to Upper Siwalik contact and suggests that the gravel-sand transition is indeed mobile and can episodically prograde far into the plains. Sedimentological characteristics of the gravel pulses and sediment entrainment calculations suggest that extreme events (e.g. enhanced monsoon, earthquakes and GLOFS) can force gravel far into the Ganga Plains, impacting the position the gravel-sand transition. These episodes of distant gravel progradation must represent extreme floods from which the sedimentological system must take many years to recover. Such events are beyond the historic timescales of human narrative, and hence have not been recognised as a risk to the populations of the plains.

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