NW Segment Research Articles

First tectonic-geomorphology study along the Longmu–Gozha Co fault system, Western Tibet

The Longmu–Gozha Co left-lateral strike-slip fault system (LGCF) is located in remote western Tibet, forming a triple junction with both the Altyn Tagh fault (ATF) and the Karakorum fault (KF), the two major strike-slip faults in the region. The Ashikule, Gozha Co and Longmu Co faults are clear and distinct left-stepping en-echelon faults, together forming the LGCF system. Although poorly documented, quantifying its activity remains a key problem to understand the kinematics and the tectonic history of the westernmost Tibetan Plateau. Indeed, the Karakax fault (NW segment of the ATF), LGCF and KF together control the tectonics of western Tibet which itself controls the extrusion of Tibet towards the east, with the LGCF acting as a natural boundary for eastward motion of the Tibetan Plateau due to India's northward impingement. The LGCF system shows clear and impressive morphological indications of left-lateral active shear, that we quantify using field measurements (terrestrial LIDAR) along with 10Be surface-exposure dating. Our data suggest a slip-rate <3mm/yr, consistent with geodetic and block model studies. While it is on the order of the Karakax fault slip-rate (~2mm/yr), it is smaller than those along the ATF and KF (>9 and >8mm/yr, respectively), yielding a few mm/yr of extension accommodated most likely in the Ashikule graben and surroundings, located between the ATF and Karakax faults. Numerous evidences of recent tectonic-related events are present in the vicinity, such as the 1951 volcanic eruption as well as the 2008 and 2014 Ms7.3 Yutian earthquakes, attesting of its high activity. In addition, the LGCF's en-echelon geometry and identical direction with the ATF, as well as smaller geological offsets and lower slip-rate compared to those on the surrounding faults, suggest that this segment of the ATF may be the most recent.

The influence of pre-existing structure on the growth of syn-sedimentary normal faults in a deltaic setting, Niger Delta

Three dimensional seismic-reflection data from the western Niger Delta were used to investigate the segmentation and linkage of a syn-sedimentary normal fault array and to estimate the influence of a pre-existing normal fault on the geometry and growth of younger faults. The nucleation, growth and linkage of a regional (seaward-dipping) deltaic fault system were analyzed on reflectivity time-/horizon slices and vertical seismic sections. In the deep subsurface, a master fault that consists of two segments (northwestern, NW, and southeastern, SE) grew through time into a single fault by lateral tip propagation reaching a final length of about 15 km. After attaining this length, displacement along the fault system developed non-uniformly through time. The analysis of the hanging-wall sediments of the deep-seated master fault shows two different processes of vertical linkage above the NW and SE segment. The SE segment links vertically to several younger faults contemporaneously with displacement accumulation on the master fault; in contrast, fault linkage above the NW segment occurred only after an interval of master-fault inactivity connecting the deep-seated structure upwards to a single syn-sedimentary normal fault. The observed differences in fault development suggest that although multi-segment deltaic faults form single fault systems after segment linkage, individual pre-linkage characteristics can be preserved, supporting a possibly diverse upward growth and connection to younger faults in the overburden. The geological interpretations presented highlight the influence of large deep-rooted structures on the development, location and geometry of shallow deltaic faults, documenting the influence of an older structural grain on delta tectonics.

Paleoseismological and morphological evidence of slip rate variations along the North Tabriz fault (NW Iran)

Northwest Iran is characterized by a high level of historical and instrumental seismicity related to the ongoing convergence between the Arabian and Eurasian plates. In this region, the main right-lateral strike-slip fault known as the North Tabriz fault (NTF) forms the central portion of a large crustal fault system called the Tabriz fault system (TFS). The NTF is a major seismic source along which at least three strong and destructive earthquakes have occurred since 858AD. The two most recent destructive seismic events occurred in 1721AD and 1780AD, rupturing the SE and NW fault segments, respectively. This paper reports paleoseismological and quantitative geomorphologic investigations on the SE segment of the NTF, between the cities of Bostanabad and Tabriz. These observations help to improve our understanding of the seismic hazard for Tabriz city and its surrounding areas. Our field investigations revealed evidence of successive faulting events since the Late Quaternary. Paleoseismic investigations indicate that since 33.5kyr, the SE segment of the NTF has experienced at least three major (M>7.5) seismic events, including the 1721AD earthquake (M=7.6–7.7). Along the NW segment of the fault, however, our results suggest that the amount of strong (M~7.5) seismic events during the same period is significantly greater than along the SE segment. One possible explanation of such a difference in seismic activity is that the Late Quaternary–Holocene coseismic slip rate is decreasing along the NTF from the northwest to the southeast. This explanation contradicts the former hypothesis of a constant slip rate along the whole length of the NTF. In addition, more distributed deformation along several parallel fault branches, in a wider fault zone of the SE segment of the NTF may be considered as additional evidence for the estimation of lower rate of deformation along the fault segment. Such a slip distribution pattern can explain the existence of smaller (~300m) Pliocene–Quaternary cumulative dextral offsets along the SE fault segment than the measured cumulative offsets along the NW segment (~800m) of the NTF.

Structural evidence for superposition of transtension on transpression in the Zagros collision zone: Main Recent Fault, Piranshahr area, NW Iran

The Main Recent Fault of the Zagros Orogen is an active major dextral strike-slip fault along the Zagros collision zone, generated by oblique continent–continent collision of the Arabian plate with Iranian micro-continent. Two different fault styles are observed along the Piranshahr fault segment of the Main Recent Fault in NW Iran. The first style is a SW-dipping oblique reverse fault with dextral strike-slip displacement and the second style consists of cross-cutting NE-dipping, oblique normal fault dipping to the NE with the same dextral strike-slip displacement. A fault propagation anticline is generated SW of the oblique reverse fault. An active pull-apart basin has been produced to the NE of the Piranshahr oblique normal fault and is associated with other sub-parallel NE-dipping normal faults cutting the reverse oblique fault. Another cross-cutting set of NE–SW trending normal faults are also exist in the pull-apart area. We conclude that the NE verging major dextral oblique reverse fault initiated as a SW verging thrust system due to dextral transpression tectonic of the Zagros collision zone and later it has been overprinted by the NE-dipping oblique normal fault producing dextral strike-slip displacement reflecting progressive change of transpression into transtension in the collision zone. The active Piranshahr pull-apart basin has been generated due to a releasing damage zone along the NW segment of the Main Recent Fault in this area at an overlap of Piranshahr oblique normal fault segment of the Main Recent Fault and the Serow fault, the continuation of the Main Recent Fault to the N.

Effect of Dopants on Epitaxial Growth of Silicon Nanowires

We investigated the effects of dopants on epitaxial growth of Si NWs, with an emphasis on synthesizing vertical epitaxial Si NW arrays on Si (111) substrates. We found that addition of boron with a B:Si feed-in atomic ratio greater than 1:1000 improved the percentage of Si NWs grown along the vertical &lt;111&gt; direction to more than 90%, compared to 38% for i-Si NWs. We also demonstrated a stemmed growth strategy and achieved a 93% percentage of i-Si NW segments along the vertical &lt;111&gt; direction on Si substrates. In summary, our study opens up potential for using chemical synthesized vertical Si NW arrays integrated on Si substrates for large-scale applications.

TECTONO‐STRATIGRAPHIC EVOLUTION OF THE NW SEGMENT OF THE ZAGROS FOLD‐THRUST BELT, KURDISTAN, NE IRAQ

The Kurdistan (NW) segment of the Zagros fold‐thrust belt, located in the Kurdistan Region of NE Iraq, forms the external part of the Zagros orogen and is bounded by the Zagros suture to the NE. To the SW is the Arabian Plate into which the deformation front has migrated progressively, beginning in the Late Cretaceous and culminating in the Tertiary. Regional compression resulted in obduction of the Mawat ophiolites and emplacement of the Avroman and Qulqula nappes onto the continental margin, and the formation of the Kurdistan foreland basin. In this paper, structural, stratigraphic and palaeontological data together with new field observations are used to investigate the tectono‐stratigraphic evolution of this basin, and to study the propagation of the deformation front from the Zagros Imbricate Zone in the NE towards the Mesopotamian foredeep in the SW. Six unconformities within the Kurdistan foreland basin succession are recognized: Turonian (base‐AP9; 92 Ma); Danian (base‐AP10; 65 Ma); Paleocene–Eocene (intra‐AP10; 55 Ma); late Eocene (top‐AP10; 34 Ma); middle‐upper Miocene (a local unconformity; intra‐AP11; 12 Ma); and Pleistocene. These unconformities can be divided into two groups; obduction‐related (Turonian, Danian, and Paleocene‐Eocene); and collision‐related (late Eocene, middle‐upper Miocene, and Pleistocene).The geographical position of the unconformities is used to determine the rate of propagation of the deformation front, which is estimated at ca. 3 mm/yr. This is in agreement with previous studies which suggested a NW‐ward decrease in the propagation rate. The rate was most rapid (2.95 mm/yr) in the Low Zagros Fold‐Thrust Zone and slower (2.06 mm/yr) in the High Zagros Fold‐Thrust Zone. The more rapid propagation rate in the former area may be attributed to the presence there of the Miocene Lower Fars Formation which acted as a shallow décollement surface.Within the Zagros fold‐thrust belt, the intensity of deformation decreases towards the foreland (SW). Deformation in the High Zagros Fold‐Thrust Zone is characterized by thrust imbricates and high amplitude fault‐propagation folds at the surface separated by narrow synclines. However, the Low Zagros Fold‐Thrust Zone (Simply Folded Belt) is characterised by detachments and low amplitude fault propagation folds separated by broad synclines. In the foredeep area, folds are confined to the subsurface. Deeply buried Jurassic units, together with Upper Cretaceous – Paleocene siliciclastics, and the evaporite‐dominated Lower Fars Formation may have acted as décollement surfaces in the NW segment of the Zagros fold‐thrust belt, and controlled the structural geometry and evolution of the area.

Structure and stratigraphy of the Teplá–Barrandian Neoproterozoic, Bohemian Massif: A new plate-tectonic reinterpretation

The Teplá–Barrandian unit (TBU) of the Bohemian Massif exposes a section across the once extensive Avalonian–Cadomian belt, which bordered the northern active margin of Gondwana during late Neoproterozoic. This paper synthesizes the state-of-the-art knowledge on the Cadomian basement of the TBU to redefine its principal component units, to revise an outdated stratigraphic scheme, and to interpret this scheme in terms of a recent plate-tectonic model for the Cadomian orogeny in the Bohemian Massif. The main emphasis of this paper is on an area between two newly defined fronts of the Variscan pervasive deformation to the NW and SE of the Barrandian Lower Paleozoic overlap successions. This area has escaped the pervasive Variscan (late Devonian to early Carboniferous) ductile reworking and a section through the Cadomian orogen is here superbly preserved. The NW segment of the TBU consists of three juxtaposed allochthonous belts of unknown stratigraphic relation (the Kralovice–Rakovník, Radnice–Kralupy, and Zbiroh–Šárka belts), differing in lithology, complex internal strain patterns, and containing sedimentary and tectonic mélanges with blocks of diverse ocean floor (meta-)basalts. We summarize these three belts under a new term the Blovice complex, which we believe represents a part of an accretionary wedge of the Cadomian orogen. The SE segment of the TBU exposes the narrow Pičín belt, which is probably a continuation of the Blovice complex from beneath the Barrandian Lower Paleozoic, and a volcanic arc sequence (the Davle Group). Their stratigraphic relation is unknown. Flysch units (the Štěchovice Group and Svrchnice Formation) overlay the arc volcanics, and both units contain material derived from volcanic arc. The former was also sourced from the NW segment, whereas the latter contains an increased amount of passive margin continental material. In contrast to the Blovice complex, the flysch experienced only weak Cadomian deformation. The new lithotectonic zonation fits the following tectonic scenario for the Cadomian evolution of the TBU well. The S- to SE-directed Cadomian subduction beneath the TBU led to the involvement of turbidites, chaotic deposits, and 605 ± 39 Ma ocean floor in the accretionary wedge represented by the Blovice complex. The accretionary wedge formation mostly overlapped temporally with the growth of the volcanic arc (the Davle Group) at ~ 620–560 Ma. Upon cessation of the arc igneous activity, the rear of the wedge and some elevated portions of the arc were eroded to supply the deep-water flysch sequences of the Štěchovice Group, whereas the comparable Svrchnice Formation (~ 560 to < 544 Ma) was deposited in a southeasterly remnant basin close to the continental margin. The Cadomian orogeny in the TBU was terminated at ~ 550–540 Ma by slab breakoff, by final attachment of the most outboard ~ 540 Ma oceanic crust, and by intrusion of ~ 544–524 Ma boninite dikes marking the transition from the destructive to transform margin during the early/middle Cambrian.

Seismic Velocity Structure and Improved Seismic Image of the Southern Depression of the Tainan Basin from Pre-Stack Depth Migration

In this paper, a velocity model of the Southern Depression of the Tainan Basin is obtained along with its migrated image from an iterative pre-stack depth migration approach. The Cenozoic strata are uniformly layered with velocities varying from similar to 1.8 to similar to 3.6 km s(-1) However, the general velocity is slightly lower in the NW segment than the SE. Both fractures and burial depth might be the controls of their seismic velocities. There is an unconformable contact between the Cenozoic and underlying Mesozoic strata with an abrupt velocity jump from similar to 3.2 to similar to 4.3 km s(-1). The Mesozoic strata are recognized with acoustically distinct reflection patterns (chaotic, deformed and discontinuous) and complex internal structures (uplift, folds and faults). Their interval velocities range from similar to 4.3 to similar to 4.7 km s(-1) within a depth from similar to 3.5 down to similar to 12.5 km, and the maximum depositional thickness reaches up to 6.5 km. Multiple tectonic events such as collision, subsidence and uplift might be responsible for the complexity of the Mesozoic strata.

Toward Nanowire Electronics

This paper discusses the electronic transport properties of nanowire field-effect transistors (NW-FETs). Four different device concepts are studied in detail: Schottky-barrier NW-FETs with metallic source and drain contacts, conventional-type NW-FETs with doped NW segments as source and drain electrodes, and, finally, two new concepts that enable steep turn-on characteristics, namely, NW impact ionization FETs and tunnel NW-FETs. As it turns out, NW-FETs are, to a large extent, determined by the device geometry, the dimensionality of the electronic transport, and the way of making contacts to the NW. Analytical as well as simulation results are compared with experimental data to explain the various factors impacting the electronic transport in NW-FETs.

Influence of oblique basement strike–slip faults on the Mesozoic evolution of the south‐eastern segment of the Mid‐Polish Trough

ABSTRACTA series of analogue models are used to demonstrate how the multistage development of the Mid‐Polish Trough (MPT) could have been influenced by oblique basement strike–slip faults. Based on reinterpretation of palaeothickness, facies maps and published syntheses of the basin development, the following successive stages in the Mesozoic history of the south eastern part of the MPT were simulated in the models: (1) Oblique extension of the NW segment of the MPT connected with sinistral movement along the Holy Cross Fault (HCF, Early Triassic–latest Early Jurassic). (2) Oblique extension of both NW and SE segment of the MPT, parallel to the HCF (latest Early and Middle Jurassic). (3) Oblique extension of the SE segment of the MPT and much lesser extension of its NW segment connected with dextral movement along the HCF (Early Oxfordian–latest Early Kimmeridgian). (4) Oblique extension of the SE segment of the MPT and much lesser extension of its NW segment connected with dextral movement along the Zawiercie Fault (ZF, latest Early Kimmeridgian–Early Albian). (5) Oblique inversion of the NW segment of the MPT connected with dextral movement along the HCF (Early Albian–latest Cretaceous). (6) Oblique inversion of the SE segment of the MPT along the W–E direction (latest Cretaceous–Palaeogene). The different sense of movements of these two basement strike–slip faults (HCF and ZF) resulted in distinct segmentation of the basin and its SW margin by successive systems of extensional en‐echelon faults. The overall structure of this margin is controlled by the interference of the border normal faults with the en‐echelon fault systems related to successive stages of movement along the oblique strike–slip faults. This type of en‐echelon fault system is absent in the opposite NE‐margin of the basin, which was not affected by oblique strike–slip faults. The NE‐margin of the basin is outlined by a typical, steep and distinctly marked rift margin fault zone, dominated by normal and dip–slip/strike–slip faults parallel to its axis. Within the more extended segment of the basin, extensive intra‐rift faults and relay ramps develop, which produce topographic highs running across the basin. The change in the extension direction to less oblique relative to the basin axis resulted in restructuring of the fault systems. This change caused shifting of the basin depocentre to this margin. Diachronous inversion of the different segments of the basin in connection with movement along one of the oblique basement strike–slip faults resulted in formation of a pull‐apart sub‐basin in the uninverted SE‐segment of the basin. The results of the analogue models presented here inspire an overall kinematic model for the southeastern segment of the MPT as they provide a good explanation of the observed structures and the changes in the facies and palaeothickness patterns.

From partial to full strain partitioning along the Indo-Burmese hyper-oblique subduction

The Andaman–Nicobar Trench and its onshore prolongation—the Indo-Burmese wedge—is the least studied segment of the India–Australia subduction. New offshore geological and geophysical data have recently been collected along the Burma scarp during a marine survey conducted with the R/V Marion Dufresne (Andaman Cruise). Swath bathymetric mapping combined with shallow and deep seismic show that the dominant active tectonics is dextral strike-slip faulting accompanied by various amounts of shortening. The southern portion of the Burma scarp is transpressive (north Andaman Islands), the central portion is pure strike-slip on NNE-oriented segments (southern Myanmar), the northern portion shows sedimentary wedge growth along NW segments, both onshore and offshore (Arakan Yoma prism). Further north, the wedge bends to the west, while dextral shear faults more or less parallel to the Sagaing Fault develop within the internal part of the wedge and elongated NS folds form in its external part, abutting onto the Shillong Plateau. We propose a simple kinematic model involving evolution from partial to full partitioning from south to north along the West Burma Scarp (WBS), and we test it quantitatively using the most recent geodetic results. In the south, half of the 3.5 cm/year of India motion is taken at the trench itself, the other half being accommodated onto a single shear fault, the Sagaing Fault in Myanmar. In the north, where the Bangladesh fold system developed, dextral strike-slip faults are activated within the Arakan Yoma belt and at the accretionary prism–backstop contact, resulting in full partitioning there. Faults accommodating the oblique component of motion of India are progressively migrating in space from far field faults (Andaman–Sagaing) to near trench faults (Arakan Yoma belt and trench itself), the Burma sliver being “buttressed” by the Eastern Himalayas. This kinematic extends back to 4 Ma, which is the time of initiation of the last pulse of oceanic accretion in the Andaman Basin.

Extensional geometry of the Mid Norwegian Margin before Early Tertiary continental breakup

Interpretation of reflection seismic data integrated with existing crustal models provide an interpretation of the deeply buried Mesozoic extensional geometry of the Vøring and Møre margins in the Norwegian Sea. Whereas Late Paleozoic to Triassic basins are limited by high angle normal faults with NW and SE dips, the Late Jurassic–Early Cretaceous Vøring and Møre basins are characterised by low-angle normal faults that dip towards the NW. Between the Vøring and Møre basins, at the SE end of the Jan Mayen Fracture Zone, a synthetic transfer zone is interpreted. Geometrical models based on basin and fault geometries show that the rift system detached near the upper crust–lower crust transition in the study area. This rift system accommodated between 110 and 140 km of post-Early Jurassic extension according to the geometry of the present-day pre-Cretaceous upper crust. A simple geometrical forward model suggests that a substantial part of this stretching occurred during the Late Cretaceous–Paleocene, thinning the central and NW segments of the Late Jurassic–Early Cretaceous rift.

A detailed slip model for the 1995, October 1, Dinar, Turkey, earthquake determined from inversion of teleseismicPandSHwaveforms

Summary Teleseismically recorded P and SH waveforms of the 1995, October 1 Dinar, Turkey, earthquake are inverted to find detailed coseismic slip distribution on the ruptured part of the Dinar-Civril fault. For this purpose a linear finite-fault inversion procedure with time window approach is used to allow variable rise time and rupture velocity on the model fault. The source is represented by a 24 × 21 km rectangle fault plane, which is divided into 56 equal size subfaults. The strike and the dip of the fault plane are assumed as determined by a previous study. The amount of slip and the rake angle on each subfault is retrieved through fitting the observed and synthetic seismograms in a least-squares sense. The previous inversion studies indicated that the earthquake was associated with two subevents, with a 6 s time lag of the NW subevent. Therefore, the model fault plane is also divided into two separate equal-area segments, the SE and the NW segments, to delay the rupture propagation over the NW segment. We tried several models to fix the delay time and hypocentral depth and to explain the waveforms. The smallest misfit error resulted from a model with 5 s delay time and 7.5 km hypocentral depth. The preferred solution suggests that the earthquake is associated with breaking of two asperities and the coseismic slip occurred mostly above the depth of 10 km. The smaller asperity is located to the SE just beneath Dinar town with peak slip of 26 cm while the larger one is located to the NW with peak slip of 41 cm. The observed surface rupture coincides with the location of the smaller asperity. The seismic moment for our slip model is 2.8 × 1018 N m. The modelling yields an average rake angle of −102° and almost no difference between the average rake angles of the two asperities.

Magmatism in North-Delhi Fold Belt, NW India: Evidence for Pre-Rodinia Tectonics

The Paleo-Mesoproterozoic Lesser Himalayan Crystalline Sequence (LHCS) of the Himalayan orogen is critical in the understanding of pre-Himalayan tectonics in relation to the supercontinent Columbia. The LHCS is considered as the Paleoproterozoic northern boundary of the Indian Continental Block (ICB). Geological and geochemical studies of the LHCS have provided contrasting interpretations for its tectonic evolution, leading to a lack of consensus. This contribution reviews all the existing hypotheses for the Columbia assembly focusing on the nature of the northern margin of the ICB and address the inconsistencies regarding tectonic evolution of the LHCS. Petrological, geochemical, and geochronological observations of the LHCS from NW, Central and Eastern segments of the Himalaya suggest that the rocks witnessed a tectonic cycle of Paleoproterozoic oceanic subduction, rifting, and syn-collisional events, which is similar to the tectonic cycle experienced by the Paleoproterozoic rocks of the Eastern Cathaysia Block of South China. Integrating the signatures of these two domains yields a divergent double sided subduction tectonic scenario for their tectonic evolution. This work identified a three-stage tectonic evolution along the Eastern Cathaysia Block and northern boundary of ICB: First stage- Neoarchean oceanic subduction and arc magmatism beneath the Eastern Cathaysia Block; Second stage: c. 1950 Ma divergent double subduction, corresponding to slab-rollback/break off of the oceanic crust and asthenospheric upwelling beneath the Eastern Cathaysia Block, with synchronous subduction of the oceanic plate and formation of the LHCS magmatic belt along the ICB; Third stage: c. 1900 ̶ 1800 Ma soft collision between both domains, forming syn-collisional granites, which is synchronous with back-arc rifting and formation of anorogenic granites in both domains.

Aftershock sequence of the 1994, Mw 6.8, Liwa Earthquake (Indonesia): Seismic Rupture process in a volcanic arc

We present the aftershock activity following the February 15, 1994, Mw 6.8 earthquake which was strongly felt in southern Sumatra, Indonesia, near the Great Sumatran Fault (GSF). At this place, the slip rate is supposed to be low; neverthless, three M&gt;6 events occurred along this segment during this century. No significant instrumental microseismicity has ever been recorded there. We use data from both the regional Indonesian network and a local seismic array operating 11 days after the mainshock during one month. Aftershocks mostly locate in a broad zone of 55 × 20 km² near two active NW‐trending strike‐slip segments of the GSF separated by a recent caldera, Suwoh. During the experiment, the NW segment (from Suwoh up to 15 km SE of the Ranau lake caldera, an old right‐stepover pull‐apart) was very active. As first suggested by the aftershock distribution and the lack of coseismic rupture at the surface, the 20 focal mechanisms determined provide evidence for various post‐seismic stress adjustments on secondary faults located in the Ranau‐Suwoh paleo‐pull‐apart graben. Less than 20% of the aftershocks are directly linked to the main rupture, a nearly pure right‐lateral strike‐slip faulting reaching 25 km depth. A narrow seismic gap underlines the active volcanic area of Suwoh. We conclude that the rupture process along the GSF is controlled both by volcanism and structures, and that the volcanic activity affects the mechanical properties of the crust only in a narrow zone.

EVIDENCE FOR VERTICAL MOVEMENS IN THE SOUTHERN PART OF THE ZAGROS GEOSYNCLINE, IRAN

Detaile dgeological field investigations in the SE Zagros Mountains reveal that this portion of the Zagros was formed by epeirogenic vertical uplifyt. This vertical movement probably started in the Early Paleozoic and continued through geologic time, as shown by disconformities and dominantly shallow‐water sedimentary rocks. Movements of Infra‐Cambrian salt may have contributed to this vertical uplift to produced box‐type folds which are geometrically and genetically different from folds in the NW segment of the Zagros geosyncline. Three late stage of vertical uplift with different magnitudes were measured and studied. Terraces along the mehran River, elevated alluvial cones, and elevated ancient shorelines are among the most spectacular features supporting the vertical uplift of this region.

VARIATIONS IN TECTONIC STYLES IN THE ZAGROS GEOSYNCLINE AND THEIR RELATION TO THE DIAPIRISM OF SALT IN SOUTHERN IRAN

A study of the surface and subsurface geology of the Zagros mountain belt reveals that, from the viewpoint of tectonic fabrics and the cause of diastrophism, the Zagros geosyncline can be divided into NW and SE segments. The NW segment was formed by orogenic compression and the SE segment primarily by epeirogenic uplifts. Movements of Infra‐Cambrian (Hormuz) salt at the base of the sedimentary column in the SE Zagros contributed to the epeirogenesis. Faults in the SE Zagros are of a normal type, whereas in the NW Zagros they are dominantly thrust. Seismic data indicate that movement of salt is the cause of many of the earthquake shocks in the SE Zagros.Hydrocarbons in the SSE Zagros either escaped through fractures within exposed reservoirs or migrated while epeirogeny was proceeding to be trapped in the western flank of the Oman high in the extreme SE portion of the Zagros belt.