Positive Flower Structure Research Articles

Strike-slip fault network of the Huangshi structure, SW Qaidam Basin: Insights from surface fractures and seismic data

The Huangshi structure, as one of the NWW-trending S-shaped structures in the southwestern Qaidam Basin, holds important implications for unraveling the regional structural pattern. There are four dominant sets of surface strike-slip fractures at the core of the Huangshi structure. The fractures with orientations of N28°E, N47°E and N65°E correlate well with conjugate Riedel shears (R′), tension fractures (T) and Riedel shears (R) in the Riedel shear model, respectively. Two conjugate strike-slip fracture sets occur at the surface of the Hongpan structure (secondary to the Huangshi structure) and the southwestern part of the Huangshi structure. In seismic sections, the Huangshi structure is present as a positive flower or Y-shaped structure governed by steeply dipping faults, whereas Hongpan and Xiaoshaping structures, located symmetrically to the Huangshi structure, are thrust-controlled anticlines. The Riedel shear pattern of surface strike-slip fractures, the positive flower or Y-shaped structure in seismic sections and the NW-trending secondary compressional anticlines consistently demonstrate that the Huangshi structure is dominated by left-lateral strike-slip faults which comprise a strike-slip fault network. Considering the similar S-shaped configuration and NWW trend of structures across the southwestern Qaidam Basin, it can be further speculated that these structures are also predominantly of left-lateral strike-slip types.

Postcollisional cooling history of the Eastern and Southern Alps and its linkage to Adria indentation

Indentation of rigid blocks into rheologically weak orogens is generally associated with spatiotemporally variable vertical and lateral block extrusion. The European Eastern and Southern Alps are a prime example of microplate indentation, where most of the deformation was accommodated north of the crustal indenter within the Tauern Window. However, outside of this window only the broad late-stage exhumation pattern of the indented units as well as of the indenter itself is known. In this study we refine the exhumational pattern with new (U–Th–Sm)/He and fission-track thermochronology data on apatite from the Karawanken Mountains adjacent to the eastern Periadriatic fault and from the central-eastern Southern Alps. Apatite (U–Th–Sm)/He ages from the Karawanken Mountains range between 12 and 5 Ma and indicate an episode of fault-related exhumation leading to the formation of a positive flower structure and an associated peripheral foreland basin. In the Southern Alps, apatite (U–Th–Sm)/He and fission-track data combined with previous data also indicate a pulse of mainly Late Miocene exhumation, which was maximized along thrust systems, with highly differential amounts of displacement along individual structures. Our data contribute to mounting evidence for widespread Late Miocene tectonic activity, which followed a phase of major exhumation during strain localization in the Tauern Window. We attribute this exhumational phase and more distributed deformation during Adriatic indentation to a major change in boundary conditions operating on the orogen, likely due to a shift from a decoupled to a coupled system, possibly enhanced by a shift in convergence direction.

Cenozoic tilting history of the south slope of the Altyn Tagh as revealed by seismic profiling: Implications for the kinematics of the Altyn Tagh fault bounding the northern margin of the Tibetan Plateau

The Altyn Tagh fault (ATF) plays a significant role in the northward growth of the Tibetan Plateau, but its Cenozoic kinematics and related structural response in adjacent basins remain debated. In this study, we identified a transition zone between the ATF and the Qaidam Basin interior and termed it the Altyn Slope, based on a dense network of two- and three-dimensional seismic reflection profiles and isopach maps. Tilted by a series of E-W–trending transpressional faults that constitute the positive flower structure of the ATF, the present Altyn Slope is characterized by a southeast-dipping slope with its undulating southeastern boundary with peaks coincidentally located at the major anticlinal belts in the basin. We propose a method for restoring the Cenozoic tilting history of the Altyn Slope during different time periods by identifying growth-strata geometry from the recent isopach maps. The results show that the Altyn Slope began to form in the late Eocene (ca. 40 Ma) and continued to expand until the mid-Miocene (ca. 15 Ma) albeit with a temporally developing shape. However, the Altyn Slope shrank toward the ATF and underwent significant NE-SW–directed folding since the mid-Miocene (ca. 15 Ma), resulting in formation of undulations of its southeastern boundary. We thus infer that the left-slip motion on the ATF is divided into two distinct stages: during the first stage, ca. 40–15 Ma, the ATF was activated with slow slip rate, and most transpressional stress was converted to vertical strain, raising the Altyn Slope instead of producing strike-slip motion. During the second stage, since ca. 15 Ma, faster sinistral strike-slip motion on the ATF took place, releasing the stress beneath the Altyn Slope and inducing intense NE-SW–directed shortening within the Northern Tibetan Plateau.

Tan-Lu fault system and its significance in oil accumulation in the central Liaodong Bay subbasin, Bohai Bay Basin, China

The Tan-Lu fault system in the central Liaodong Bay subbasin, Bohai Bay Basin, has complex structural characteristics, and its tectonism during the Cenozoic is an important factor in oil accumulation. Three-dimensional seismic data were used to document the structural features and evolution of the system. Variations in source rock occurrence, oil catchment area, and faulting intensity were comprehensively evaluated to discuss the heterogeneity of oil occurrence along the system. Detailed analysis of the seismic data indicates a right-lateral slip for the Tan-Lu fault system. Transpression and transtension occur on two branches of the Tan-Lu fault with different orientations, indicating a likely slip azimuth that is between the two orientations, i.e., 30°–35°. The strike-slip began at the middle stage of deposition of the Shahejie Formation and reached its climax during deposition of the first and second members of the Dongying Formation. To date, the slip is still continuing. In the transpressional system, the lower strata on opposite sides of the strike-slip fault were shortened and folded, whereby the upper strata were stretched and normal faulted. As a result, a negative flower structure developed immediately above a positive flower structure. Strain distribution in this system is similar to that in a classic fold. Moderate tectonic deformation could enlarge the oil catchment area, benefiting oil accumulation. Weak or intense deformation is unfavorable for commercial oil accumulation because of a small oil catchment area and poor oil preservation, respectively.

Transpression and juxtaposition of middle crust over upper crust forming a crustal scale flower structure: Insight from structural, fabric, and kinematic studies from the Rengali Province, eastern India

Deformational, metamorphic, monazite age and fabric data from Rengali Province, eastern India converge towards a multi-scale transpressional deformational episode at ca. 498–521 Ma which is linked with the latest phase of tectonic processes operative at proto-India-Antarctica join. Detailed sector wise study on mutual overprinting relationships of macro-to microstructural elements suggest that deformation was regionally partitioned into fold-thrust dominated shortening zones alternating with zones of dominant transcurrent deformation bounded between the thrust sense Barkot Shear Zone in the north and the dextral Kerajang Fault Zone in the south. The strain partitioned zones are further restricted between two regional transverse shear zones, the sinistral Riamol Shear Zone in the west and the dextral Akul Fault Zone in the east which are interpreted as synthetic R and antithetic R' Riedel shear plane, respectively. The overall structural disposition has been interpreted as a positive flower structure bounded between the longitudinal and transverse faults with vertical extrusion and symmetric juxtaposition of mid-crustal amphibolite grade basement gneisses over low-grade upper crustal rocks emanating from the central axis of the transpressional belt.

Transpressional structures and hydrocarbon potential along the Romanche Fracture Zone: a review

Abstract The Romanche Fracture Zone was originally a corridor of Aptian-age dextral transtensional rifting along the Equatorial Atlantic margins. Late Albian plate tectonic compression occurred due to a change in plate vectors, when the African and South American continents were still in contact across a 500 km-long section of the Romanche Fracture Zone. This dextral compression produced reactivation of the rift faults to produce asymmetric landward-vergent anticlines and thrusts that trend ENE to NE. Fold-axial planes dip seaward, parallel to the rift faults. Minor asymmetric anticlines were developed on the long seaward-dipping fold limbs and these have subvertical axial planes. The asymmetry of the minor folds is due to the southward stratal dip having been oblique to the horizontal maximum principal stress during the Albian inversion. The folds on the African margin were subsequently tightened by compression in Santonian and Oligo-Miocene times. Aptian-age ENE strike-slip faults were reactivated during the compression phases to produce broad positive flower structures up to 30 km wide that formed topographical ridges along the original strike-slip faults. The intervening and broader flat-bottomed synclines do not appear to be associated with rift faults. The folding and thrust faulting created seabed relief of 1–2 km at the end of the Albian; evidenced by the amount of subsequent erosion that removed the better-quality reservoirs in the upper Albian sequence from the major fold crests. Consequently, there has been a significant number of failed oil exploration wells drilled along the fold crests. The fold ridges would have diverted turbidite channels in the onlapping Cenomanian–Campanian sequence and these will be preferentially located on the landward side of the anticlinal crests. Late Cretaceous stratigraphic and structural traps located between the major anticlines have not yet been explored for hydrocarbons along the Romanche Fracture Zone margins.

Late Cretaceous Transpressional Fault System: A Case Study of the Yishu Fault Belt, Shandong Province, Eastern China

AbstractOn the basis of field observations of the structures of three profiles from the Linshu region, deformation characteristics and the tectonic background of the Yishu fault belt in the Late Cretaceous–Early Cenozoic have been discussed in detail. Three structural profiles, whose deformations consist mainly of earlier transpressional faults and later normal faults, were developed for the Mengtuan Formation of the Lower Cretaceous Dasheng Group. Typical positive flower structures, duplex structures, and break‐through faults were found in these profiles. On the basis of analyses of the structural deformation and previous geochronological studies, it was concluded that the earlier transpressional faults of the profiles were triggered by the sinistral transpression of the Yishu fault belt in the Late Cretaceous–Early Paleogene, and that the later normal faults, formed during the Late Paleogene–Neogene extension, truncated the earlier transpressional faults. With consideration of the tectonic evolution of the Tan‐Lu fault belt and the different drift directions of the Pacific plate since the Cretaceous, we suggest that the major tectonic events of the Late Cretaceous–Neogene in eastern China were mainly controlled by the subduction of the Pacific plate.

Basement-cover relations in the southeastern Cape Breton Highlands, Nova Scotia, Canada

In the southeastern Cape Breton Highlands Neoproterozoic plutonic and metamorphic rocks outcrop in upland areas whereas Carboniferous sedimentary rocks are found in the river valleys and coastal lowlands. Detailed analysis of the contacts between these two groups of rocks including mapping, geometric constructions of the contact relations, structural geological investigations, petrographic analysis and geophysical map interpretations show that the basement rocks were emplaced by a thrust fault that extends at least from the Baddeck River valley to North River, and possibly includes klippen south and east of the highlands. The thrust fault transported a slab of rock with minimum thickness of 200 m a distance of at least 8 km over Horton and Windsor group rocks. East-directed translation of the thrust block likely occurred during the Alleghanian orogeny, and appears to mirror movement previously identified in the northern and western Cape Breton Highlands, implying that much of the upland geology is allochthonous, but likely rooted in the central highlands as positive flower structure.

New field and geophysical data about transpressional deformation: An improved model for the structural style of Sha Gou fault area in southern Ningxia, northeastern edge of Tibetan Plateau, China

Situated near the northeastern edge of the Tibetan Plateau, the Sha Gou fault area (SGFA) represents an important area to understand Cenozoic regional interactions between northeastern (NE) Tibetan Plateau and southwestern (SW) Liupan Shan Basin. Within this region, several km-scale arcuate fault systems such as the Lijun fault and the Madong Shan piedmont fault accommodate the transpressive deformation, but their structural style is still controversial. Predecessors regarded these bow-like faults as southwest-dipping thrust systems with large-scale nappes, however, this opinion is not compatible with the new field and geophysical data. In this study, we aim to ascertain the structural pattern of this area based on the analyses of field observation data, interpretation of seismic reflection profiles and two-dimensional gravity forward modeling. According to the present fieldwork, the structural cleavages, low-angle slickenlines, sub-vertical fault surfaces, “ribbon effect” as well as the linear geomorphic features in plane view indicate that these faults belong to a strike-slip system. Newly acquired seismic profiles, characterized by distinct positive flower structures, strongly suggest that this area is again a strike-slip fault system rather than a thrusting system. Furthermore, gravity forward modeling results show that the reverse strike-slip model without large-scale thrust nappes is closer to the present structural style of this area. The gravity forward modeling is an effective method to identify km-scale thrust nappes, which could be used for reference by the structural style analysis in other similar regions. Based on these evidences, a new transpressional shear model for the structural pattern is proposed. The overall structural style of the SGFA is not characterized by large-scale thrust nappes, but is dominated by a transpressional shear system with significant strike-slip faulting. Such a new model can be an additional evidence for the tectonic escape that is going on in the area north of the Himalaya and is dominated by reverse strike-slip deformation. The stepwise morphology (i.e., the Pre-Cretaceous strata in the west of strike-slip faults are higher than those in the east successively) in this model is also caused by the uplift of the Tibetan Plateau. Furthermore, the strike-slip deformation indicates that the SW Liupan Shan Basin is a continental sub-basin segmented by several km-scale strike-slip faults rather than the imbricated style of purely contractional system in typical foreland basin.

Field Study of the Positive Flower Structures of the Gombe Inlier, Upper Benue Trough, Northeastern Nigeria

Abstract The Gombe inlier can be considered as a geological microcosm of the Gongola basin as it vividly displays general stratigraphic and structural styles within a relatively small, easily accessible area. The Cretaceous lithostratigraphic sequence of the Gombe inlier has been affected by sinistral strike-slip faults; the Gombe and Wuro Ladde-Wurin Dole faults with a Benue and Gongola trend respectively. Detailed study of these two faults shows that the Gombe fault is older and synsedimentary fault movement started in at least the mid-Santonian. Precambrian basement upthrust along the Gombe Fault is likely to have initiated during the first of the two compressive events that affected the upper Benue trough; the mid-Santonian N - S to N 174° E compression. The Wuro Ladde - Wurin Dole fault is relatively younger because (1) it sinistrally truncates the Liji hill anticlines that occur at the northern end of Gombe hill, resulting in a NEE - SWW trend, and (2) the orientation of transpressional structures along this fault suggest they developed during the end-Cretaceous N 140° E to N 150° E compression. Well-preserved transpressional structures along these faults provide the structural geologist a rare field examples to study their 3-dimensional (3D) geometry and kinematic evolution; and also as an analog for interpreting seismic reflection data that images complex strike-slip structures in the sub-surface.

Determining the main strand of the Eskişehir strike-slip fault zone using subsidiary structures and seismicity: a hypothesis tested by seismic reflection studies

The Eskisehir Fault Zone is one of the major neotectonic structures of Turkey, extending from Inegol (Bursa) to Cihanbeyli (Konya). The fault zone presents a considerable seismic risk for the city of Eskisehir but the exact locations of active segments and the source of the major seismic event, the 1956 earthquake (M = 6.5) that occurred in the instrumental period (from 1900 to 2013), have been debated in recent literature. The structural data obtained from field studies indicate an approximately N60W-trending main strand of the right lateral strike-slip Eskisehir Fault Zone. This trend corresponds to the en echelon bends on the course of the Sarisu River. Using this concurrence, the positions of Bahcehisar and the Cukurhisar-Sultandere segments are proposed and checked by seismic reflection studies. The seismic sections disclosing positive flower structures confirm the hypothesized position of the Cukurhisar-Sultandere segment. The relocation of epicenters and focal mechanism solutions of seismic events in 1956, 1990, 2010, and 2013 indicate that the Cukurhisar-Sultandere segment might be the rupture source of the 1956 event and is a possible potential seismic source for an earthquake that could seriously affect the Eskisehir settlement.

Analysis of the North Anatolian Shear Zone in Central Pontides (northern Turkey): Insight for geometries and kinematics of deformation structures in a transpressional zone

The western part of the North Anatolian Shear Zone at the southern boundary of the Central Pontides in Turkey, was investigated in the Kurşunlu-Araç area by means of a geological-structural field study. In this area the North Anatolian Shear Zone results in a transpressional deformation zone that extends between two master faults striking parallel to the main shear direction. The main systems of structures identified in the deformation zone appear to be oriented parallel to the directions predicted by Riedel theoretical model. Nevertheless, the strain partitioning is more complicated than predicted by theory. The structural analysis suggests a polyphase deformation characterized by a steady component of transcurrence associated with alternance of compression and extension. Along each of theoretical directions the combination of double verging structures can be observed, with folds and thrust surfaces root into high-angle shear zones, according to flower-type geometries. The discrepancies of directions, kinematics and geometries from theoretical models are due to transpressive and/or transtensive nature of the deformation. According to the observed outcropping structures, we propose a conceptual model for the North Anatolian Shear Zone, interpreting it as a crustal-scale positive flower structure.

Neoproterozoic to Early Paleozoic polyorogenic deformation in the southeastern margin of the Yangtze Block: Constraints from structural analysis and 40Ar/39Ar geochronology

The southeastern margin of the Yangtze Block is a suitable region to decipher Neoproterozoic to Early Paleozoic polyorogenic deformation of the South China Block. Based on 1:50,000-scale geological mapping, four deformational phases were identified through structural analysis and 40Ar/39Ar dating. The earliest event (D1) corresponds to nearly E–W-striking folding and top-to-the south thrusting, developed during Neoproterozoic orogeny caused by the collision between the Yangtze Block and the Cathaysia Block. The D2 event is characterized by the nearly E–W-striking top-to-the north thrusting. The D3 deformation is marked by the NNE-striking folding, thrusting and dextral shearing. The D3 structures constitute a positive flower pattern, with opposing kinematics, rooted in the Jiangwan dextral shear zone. The D4 event is the nearly E–W-striking ductile dextral shearing. 40Ar/39Ar geochronology shows that the NNE-trending dextral shearing and the nearly E–W-striking dextral shearing occurred at 449±4Ma and 429±3Ma, respectively. Combining with previous geochronology, all the D2, D3, D4 events are related to the Early Paleozoic orogeny. Both the D2 top-to-the north thrusts and D3 NNE-striking positive flower structures are syn-orogenic products. These incompatible syn-orogenic structures indicate that the orientation of the principal stress changed from the N–S-striking to E–W-striking at ∼450Ma. The nearly E–W-striking ductile dextral shearing (D4) is the outcome of post-orogeny.

Structural evolution of the southern transfer zone of the Gulf of Suez rift, Egypt

We present a detailed study about the initiation and reactivations of Zeit-El Tor transfer zone, south Gulf of Suez rift, and its structural setting and tectonic evolution with respect to the Cretaceous-Cenozoic tectonic movements in North Egyptian margin. NE trending zone of opposed-dipping faults (22km wide) has transferred the NE and SW rotations of the sub-basins in central and south Gulf of Suez rift, respectively. The evolution of this zone started by reactivation of the NE oriented late Neoproterozoic fractures that controlled the occurrence of Dokhan Volcanics in the rift shoulders. Later, the Syrian Arc contraction reactivated these fractures by a sinistral transpression during the Late Cretaceous–Eocene time. N64°E extension of the Oligo-Miocene rift reactivated the NE fractures by a sinistral transtension. During this rifting, the NE trending faults forming the transfer zone were more active than the rift-bounding faults; the Upper Cretaceous reverse faults in the blocks lying between these NE trending faults were rotated; and drape-related reverse faults and the positive flower structures were formed. Tectonic inversion from contraction to extension controlled the distribution and thickness of the Upper Cretaceous–Miocene rocks.

Exploring for unconventional hydrocarbon plays in the Glyde Basin, Northern Territory, using FALCON® airborne gravity gradiometry (AGG) data

A FALCON® AGG and magnetic survey in the Glyde Sub-basin aims to define the structural pattern to identify unconventional hydrocarbon plays. The survey area consists of variable thick fluvial and lacustrine to shallow marginal marine carbonate-siliciclastic sequences and lesser volcanic rocks. The dominant tectonic feature identified on the AGG data is the Emu Fault Zone: a major structure of the central-southern part of the McArthur Basin. Seismic and surface geology suggest its overall sub-vertical strike-slip nature with positive flower structure geometry. In the north, a regional size pop-up structure, reverse, transpressional and strike-slip faults, and abundant synclines and anticlines identified in the AGG data indicate sinistral transpression. In the south, a transtensional segment of the Emu Fault Zone formed several regularly oriented, fault controlled depocentres. A geological cross-section across the Glyde Sub-basin supported by gravity modelling indicates a system of inverted transtensional faults. Offsets and bifurcations are common, forming local-scale transtensional or transpressional areas. The relationship between dolomitic carbonaceous siltstone, fault-related hydrothermal dolomite (HTD), and the tectonic pattern strongly suggests that the Emu Fault Zone controlled fluid migration and fault-related HTD deposition. Brecciated HTD reservoirs are best developed where a combination of strike-slip movement and extension allowed dolomitising and porosity-generating fluids to migrate along fracture networks, especially in transtensional pull-apart structures, and along the principal faults bounding elevated parts of the basement. This is consistent with the results of the Glyde–1 ST1 exploration well, which drilled 122 m of gas charged dolomitic breccia.

Microstructures and K-Ar illite fine-fraction ages of the cataclastic rocks associated to the Camburu Shear Zone, Ribeira Belt, Southeastern Brazil

The Camburu Shear Zone (CSZ) is recognized as a NE-SW trending dextral transcurrent fault and is related to the evolution of the Ribeira Belt, southeastern Brazil. The CSZ ductile regime dates from the Precambrian to the Cambro-Ordovician and it is characterized by a meter to hundreds of meters wide belt of quarzto-feldspathic mylonitic rocks organized in a positive-flower structure. Previous studies postulated that the fault underwent normal reactivation, probably during the Cenozoic, developing metric to centimetric thick intercalations of cemented cataclastic rocks. We concluded that these cataclastic rocks maintained their primary cohesion and were syntectonically silicified by feldspar-to-mica reactions. Cataclasis was shown by the fractal distribution of grains and fragments, dilatancy, rigid body rotation, cataclastic flow, microcracking and microfaulting. Two cataclastic events are described: (i) during the Lower Devonian (402 ± 6 Ma) in a ductile-to-brittle regime with temperatures up to 400°C and development of foliated protocataclasites, and (ii) during the Upper Carboniferous (310.9 ± 8 Ma) in a brittle regime with temperatures up to ~300°C and development of protocataclasites and crushed breccias. It is then suggested that the CSZ cataclasites were formed during two Paleozoic reactivation events associated to a far-field orogenic effect induced by the Precordillera and Chanica orogenic cycles in the western margin of the Gondwana Paleocontinent.

Polyphase deformation history and strain analyses of the post-amalgamation depositional basins in the Arabian–Nubian Shield: Evidence from Fatima, Ablah and Hammamat Basins

Post-amalgamation depositional basins <650Ma (PADBs), dominated by volcano–sedimentary assemblages, unconformably overlying Neoproterozoic juvenile (mantle-derived) arcs, represent one of the main collage in the Arabian–Nubian Shield (ANS). In this work, three distinguished PADBs; namely Fatima, Ablah and Hammamat PADBs, are the subject matter of detailed field investigations and quantitative strain analysis in an attempt to highlight the polyphase deformation history of these PADBs and to discern whether the ANS’s PADBs were deformed at the same time or not. The Fatima PADB is studied in its type locality along the northwestern flank of Wadi Fatima; between Jabal Abu Ghurrah and Jabal Daf, in Jeddah tectonic terrane. The Ablah PADB is examined around Wadi Yiba, further south of its type locality near Jabal Ablah in Al-Aqiq Quadrangle, in Asir tectonic terrane. The Hammamat PADB is investigated in Wadi Umm Gheig, Wadi Allaqi and Wadi Hodein in the Egyptian Eastern Desert tectonic terrane. It is supposed that the Fatima is a basin controlled by dextral transcurrent shearing occurred along the NE-oriented Wadi Fatima Shear Zone and the Ablah is a strike-slip pull-apart basin, and both basins were believed to be deposited during and soon after the Nabitah Orogeny (680–640Ma) that marked suturing of the Afif terrane with the oceanic ANS terranes to the west. They were affected by at least three Neoproterozoic deformation phases and show geometric and kinematic relationships between folding and thrusting. The Hammamat PADB is a fault-bounded basin affected by a NW–SE- to NNW–SSE-oriented shortening phase just after the deposition of the molasse sediments, proved by NW- to NNW-verging folds and SE- to SSE-dipping thrusts that were refolded and thrusted in the same direction. The shortening phase in the Hammamat was followed by a transpressional wrenching phase related to the Najd Shear System, which resulted in the formation of NW–SE sinistral-slip faults associated with positive flower structures that comprise NE-verging folds and SW-dipping thrusts. Strain results in the three studied PADBs are nearly consistent, indicating that they are correlated and underwent the same history of deformation. The ANOVA test indicates that there is no significant difference for the Vector mean and ISYM for the three PADBs. There is only a significant difference for the Harmonic mean (P-value<0.05). A Post Hoc test (Shefee) shows that the difference exists between the Allaqi and the Umm Gheig’s deformed polymictic conglomeratic pebbles of the Hammamat PADB.

Structural deformation and evolution of right-lateral strike-slip tectonics of the Liaohe western depression during the early Cenozoic

The Tan-Lu fault zone (TLFZ) traverses the Liaohe western depression (LHWD), affords an exceptional opportunity to reveal the structural deformation and evolution of a major strike-slip fault of the LHWD using three dimensional seismic data and well data. In this paper, based on structural interpretations of the 3-D seismic data of the LHWD, combined with depth slice and seismic coherency, a variety of structural features in relation to right-lateral strike-slip fault (the western branch of the Tan-Lu fault) have been revealed presence in the depression, such as thrust faults (Xinlongtai, Taian-Dawa, and Chenjia faults), structural wedges, positive flower structures, and en echelon normal faults. Fault cutoffs, growth strata and the Neogene unconformity developed in the LHWD verify that the activity of right-lateral strike-slip from the late Eocene to Neogene (ca. 43–23Ma). The study indicates that the right-lateral strike-slip played an important role in controlling the structural deformation and evolution of the LHWD in the early Cenozoic. Moreover, the front structural wedge generated the gross morphology of the Xinlongtai anticline and developed the Lengdong faulted anticline during the late Eocene, and the back structural wedge refolded the Lengdong faulted anticline zone in the late Eocene to the early Oligocene. Wrench-related structures (the Chenjia thrust fault and the en echelon normal faults) were developed during the late Oligocene. Uniform subsidence in the Neogene to Quaternary. Furthermore, the driving force of the right-lateral strike-slip deformation was originated from N–S extension stress related to the opening of the Japan Sea and NE–SW compression, as the far-field effect of India–Eurasia convergence.

STRUCTURAL STYLES AND THEIR DISTRIBUTION PATTERN IN THE SOUTHERN EAST CHINA SEA SHELF BASIN

Based on regional seismic data,we studied in this paper the structural characteristics of the southern East China Sea Shelf Basin.Our results show:(1) There are three structural styles,namely extensional,compressional,and complex structures,in the study area according to their dynamic mechanism.(2)The extensional structural style can be further subdivided into the half graben,composite graben,domino faulted graben,tilting block and magmatic structures.The compressional structural style can be subdivided into compressional anticline,faulted anticline and imbricated faults.The complex structural styles can be subdivide into positive inversion tectonics and negative flower structures.

Petrochemical and Sr-Nd isotope investigations of A-type granites in the east of Misho, NW Iran

The Misho plutonic complex consists of a series of granitic bodies which range from syenogranite, alkali granite to monzogranites. They include metaluminous to peraluminous compositions. The garnitoid bodies are intruded into the unmetamorphosed late Paleozoic rocks and are located between two dextral, oblique-slip fault systems along which they have been uplifted as a major positive flower structure. The Misho granitoid belongs to the alkaline granitoid series that have been attributed to a Late Permian post-collisional setting. The studied granitoid displays high SiO2 contents between 67.71 and 76.4 wt%. On both FeO/(FeO + MgO) and [(Na2O + K2O) − CaO] vs. SiO2 diagrams, the samples, plot in the ferroan and alkaline fields, therefore, show an A-type granitoid signature. Trace and rare earth elements distribution patterns for the Misho rocks indicate a distinctive depletion in Nb, Sr, Ba, P, and Ti relative to other trace elements and a greater enrichment in large-ion lithophile elements compared to high field strength elements that are also typical features of A-type granites. The granitoid samples are geochemically similar to typical A2-type granites, e.g., high K2O + Na2O, FeO/MgO, Ga/Al, and Y/Nb values and low CaO, Ba, Sr, and Eu contents. They have initial Sr isotopic ratios in the range >0.712 and negative e Ndt values of −1 to −3.2 for a time of generation of 232 Ma. We suggest that shear zones play an important role in providing suitable conduits for ascending asthenospheric material and heat influx in the lower crust continental. It is proposed that the Misho parental granitoid magmas were produced by the partial melting of the lower crust continental at extensional setting in active continental margin setting that was formed after the collision of the Eurasia plate and Iranian plate following closure of paleo-Tethyan oceanic crust during Middle Jurassic times.