Folding Phase Research Articles

СТРУКТУРА КЕРЧЕНСКО-ТАМАНСКОЙ СКЛАДЧАТОЙ ЗОНЫ АЗОВО-КУБАНСКОГО ПРОГИБА

The nrotectonic structure of the Kerch-Taman folded zone, the southern deformed part of the Azov-Kuban piedmont trough, has a number of structural features and a history of deformation development. The authors divide the zone into five transverse segments, differing in the age of the main phase of folding. In the central Taman segment, folding is still going on, while in the framing segments, the main phases of folding took place in the Pliocene. In the peripheral segments, the main phase of folding is older - Early-Middle Miocene. The boundaries of the Kerch-Taman zone, as well as its youngest, the Taman segment, coincide with the transverse fault (fault-flexure) zones. It is shown that the southern frame of the Kerch-Taman folded zone is the continuation of the structures of the Crimean Mountains and the Northwestern Caucasus. The correlation of mud volcanism manifestations with tectonic elements of the Taman segment is noted to be ambiguous.

Response of the Pliocene-Pleistocene carbonates to relative sea-level changes in Kish Island, Persian Gulf

Plio-Pleistocene period in the Persian Gulf, Iran was marked by the development of carbonate rocks of the Khark Formation. The shallow-water carbonates of the Khark Formation record fluctuations in sea-level. Khark limestones unconformably cover the calcareous marlstones of the Late Miocene Mishan Formation. This study used petrographic analysis and SEM-EDX analysis to determine microfacies, diagenetic products, sedimentary environments, sedimentary cycles, and relative sea-level changes during the Plio-Pleistocene. Based on the textural features and fossil content, six microfacies were recognized in the lagoon, shoal, back reef, and reef facies belts. The dominance of reef and grainstone facies shows a high-energy shallow-marine environment and the existence of a paleo-high. This paleo-high was formed due to the Late Pliocene deformation and folding in the Persian Gulf. The Khark carbonates were deposited as a reef complex on an anticline parallel to the Zagros Orogeny trend due to dominance of reef and grainstone facies, variable thickness, and irregular pre-existing topography during the Zagros folding phase. Morphology of cement crystals, the spatial distribution of cement, and their compositional variations display that the Low-Mg dogtooth calcite, gypsum cement, and moldic porosity were formed in the sandy bioclastic peloidal grainstone facies with meteoric diagenesis during the relative sea-level fall, whereas aragonite isopachous fringe of cement and High-Mg calcite (beachrocks) were developed in the reefal facies with marine phreatic diagenesis during relative sea-level rise. Khark Formation consists of two shallowing upward sequences that were marked by coral boundstone and oyster-coral floatstone facies during sea-level highstand at the top. These facies changes are in close agreement with the local sea-level changes curve during Plio-Pleistocene in the Persian Gulf. This kind of study can improve our understanding of reservoir characterization of the reefal carbonates in the subsurface sections.

Automated Quantification of Inflection Events in The Electroglottographic Signal

Certain aspects of the contacting and decontacting phases of the vocal folds can be analyzed indirectly through the electroglottographic (EGG1) signal. Since 19571 EGG has been widely used in the clinic and in voice research given that it provides information regarding the contact area of the vocal folds during phonation2. Its main quantitative parameters: contact quotient [3–9], open quotient [3,4,10–12] and fundamental frequency estimation [13–17] have been widely used in research studies and in the voice clinic.

Multidisciplinary Modeling of Mantle Lithosphere Structure Within the Superior Craton, North America

AbstractNew 3D multi‐azimuthal receiver function analysis identified four regional seismic discontinuities dipping at 7–13° within the mantle of the Superior craton of North America; most are discordant to known major upper crustal structures. Widely observed crustal‐scale structures with near‐vertical axial planes striking east‐west indicate that the most recent and dominant phase of folding and horizontal shortening strain occurred during the Kenoran (D2) crustal deformation concurrent with Au‐mineralization and peak metamorphism at 2.72–2.66 Ga. Two mantle discontinuities strike 065° and 249°, dipping to the southeast and northwest, respectively. These strikes roughly parallel the northern margin of the Superior craton and some intra‐cratonic features such as the axis of the Quetico Basin. Two discontinuities strike 355° and 187°, dipping to the east and west, respectively, and parallel to the western margin of the craton. Our new observations reveal neither moderately dipping, east‐west striking discontinuities nor coherent eclogitic layers characteristic of modern plate tectonic subduction zones. Prominent east‐ and west‐dipping mantle structures relate best to a Paleoproterozoic (Trans‐Hudson) deformation, which is rarely observed in the crust. A new analysis of mantle xenoliths and xenocrysts indicates that carbonatitic metasomatism predominates above some discontinuities where strongly localized conductivity occurs whereas kimberlitic metasomatism predominates below the discontinuities in the broadly conductive mantle.

Protein folding and surface interaction phase diagrams in vitro and in cells.

Protein stability is subject to environmental perturbations such as pressure and crowding, as well as sticking to other macromolecules and quinary structure. Thus, the environment inside and outside the cell plays a key role in how proteins fold, interact, and function on the scale from a few molecules to macroscopic ensembles. This review discusses three aspects of protein phase diagrams: first, the relevance of phase diagrams to protein folding and function in vitro and in cells; next, how the evolution of protein surfaces impacts on interaction phase diagrams; and finally, how phase separation plays a role on much larger length-scales than individual proteins or oligomers, when liquid phase-separated regions form to assist protein function and cell homeostasis.

Strain-partitioned dextral transpression in the Great Boundary Fault Zone around Chittaurgarh, NW Indian Shield

AbstractDelimiting the Aravalli mountain range in the east, the Great Boundary Fault (GBF) occurs as a crustal-scale tectonic lineament in the NW Indian Shield. The structural and tectonic characteristics of the GBF are, as yet, not well-understood. We attempt to fill this gap by using a combination of satellite image processing, high-resolution outcrop mapping and structural analysis around Chittaurgarh. The study area exposes the core and damage zone of the GBF. Three successive phases of folding, F1, F2 and F3, are associated with deformation in the GBF. The large-scale structural characteristics of the GBF core are: (i) a non-coaxial refolding of F1 folds by F2 folds; and (ii) the parallelism between the GBF and F2 axial traces. In addition, numerous metre-scale ductile shear zones cut through the rocks in the GBF core. The damage zone is characterized by the large-scale F1 folds and the mesoscopic-scale strike-slip faults, thrusts and brittle-ductile shear zones. Several lines of evidence, such as the inconsistent overprinting relationship between the strike-slip faults and thrusts, the occurrence of en échelon folds and the palaeostress directions suggest that the GBF is a dextral transpression fault zone. Structural geometry and kinematic indicators imply a wrench- and contraction-dominated deformation in the core and damage zone, respectively. We infer that the GBF is a strain-partitioned dextral transpression zone.

Two key switches in regional stress field during multi-stage deformation in the Carboniferous–Triassic southernmost Altaids (Beishan, NW China): Response to orocline-related roll-back processes

AbstractThe orogenic architecture of the Altaids of Central Asia was created by multiple large-scale slab roll-back and oroclinal bending. However, no regional structural deformation related to roll-back processes has been described. In this paper, we report a structural study of the Beishan orogenic collage in the southernmost Altaids, which is located in the southern wing of the Tuva-Mongol Orocline. Our new field mapping and structural analysis integrated with an electron backscatter diffraction study, paleontology, U-Pb dating, 39Ar-40Ar dating, together with published isotopic ages enables us to construct a detailed deformation-time sequence: During D1 times many thrusts were propagated northwards. In D2 there was ductile sinistral shearing at 336–326 Ma. In D3 times there was top-to-W/WNW ductile thrusting at 303–289 Ma. Two phases of folding were defined as D4 and D5. Three stages of extensional events (E1–E3) separately occurred during D1–D5. Two switches of the regional stress field were identified in the Carboniferous to Early Permian (D1-E1-D2-D3-E2) and Late Permian to Early Triassic (D4-E3-D5). These two switches in the stress field were associated with formation of bimodal volcanic rocks, and an extensional interarc basin with deposition of Permian-Triassic sediments, which can be related to two stages of roll-back of the subduction zone on the Paleo-Asian oceanic margin. We demonstrate for the first time that two key stress field switches were responses to the formation of the Tuva-Mongol Orocline.

Плиоценовый адакитоподобный акцент андезитов и дацитов на Орловском вулканическом поле (о. Сахалин)

Adakite-like geochemical signature (high Sr/Y ratio at a low Y concentration) is recognized in andesites and dacites, associated with intraplate basalts in the Orlov volcanic field of Sakhalin Island. These rocks denote the final (Pliocene) accent of intraplate volcanism in the Lesogorsk zone, which began in the Middle Miocene in an area of its junction with the Chekhov zone of the preceded (Oligocene-Early Miocene) suprasubduction one. The adakite-like accent was related to the Sakhalin folding phase that accompanied the general structural reorganization in the back-side region in the Japan arc system. Such a geological environment differed from the one of classical adakites generation resulted from melting of a young slab in the Aleutian island arc. It is supposed, that the Sakhalin adakite-like magmas were produced in deep-seated sources of the crust-mantle transition displayed in the Sakhalin-Hokkaido-Japan Sea zone of hot transtension due to drastic change of tectonic deformations from the thin crust of the South Tatar Basin to the thicker one of its northeastern extremity.

Западная часть Терско-Каспийского прогиба как зона разгрузки глубинных флюидных систем

The article describes the mechanisms of formation of the Terek and Sunzha anticlinoria as the main zones of oil and gas accumulation. An assumption is made about the formation of high-amplitude anticlinal folds in the Upper Cretaceous deposits as a result of vertical migration of high-pressure fluids along deep faults with a breakthrough of their upper horizons of the sedimentary cover into the late orogenic phases of folding. The main prerequisites for the deep genesis of oil and gas are listed – a pronounced unevenness in the distribution of hydrocarbon accumulations, abnormal pressure, hydrochemical anomalies.

Unmanned aerial vehicle oblique photography‐based superposed fold analysis of outcrops in the Xuhuai region, North China

Unmanned aerial vehicle (UAV) oblique photography technology is widely utilized in various fields owing to such advantages as true three‐dimensional (3D), high precision, and low expenses. We explored the application of UAV oblique photography in the superposed fold analysis conducted in the Xuhuai region. Three feasible and time‐efficient steps were established to fulfil the task. The tile images from UAV oblique photography are first synthesized on the Altizure website into a 3D outcrop model, which is then imported into ArcScene to extract bedding and lineation attitudes by GeoAnalysis Tools. The fold geometry and superposed style were characterized and analysed based on the 3D model, followed by extending the 3D structure morphology across the entire outcrop scale and illustrating the superposition style and sequence in the GOCAD platform. The geological conclusions were drawn by applying the method for analysing two outcrops in the Xuhuai region. Two phases of folds were identified, with the first generation nearly E‐W‐trending oblique‐recumbent folds overprinted by the second‐generation NNE‐NE‐trending wide and upright folds. The nearly E‐W‐striking fold is inferred to be related to the compressive orogeny in the Dabie Orogenic Belt in the Triassic. The NNE‐NE‐striking fold is related to the northwest subduction of the Pacific Plate or the northward thrust of the Sulu Orogenic Belt in the Jurassic. This example demonstrates that UAV oblique photography is a powerful and reliable method for structural analysis at the outcrop scale, especially for the inaccessible outcrops with weak vegetation cover.

Syn-Collision Folding and Multi-Layers Detachment in the Molassic Basin, Northeastern Tunisia

Tunisia had been the place of various tectonic episodes which have drawn the actual structural map of the country. The Neogene period was the most active period in which the collision contributed to the mountain ranges formation such as the Atlassic chain. The contrast of mechanical behavior between the different sedimentary units of the cover and the substratum is a determining factor that has controlled the deformation style of many folding structures. Detachment folding has been studied on the basis of field and seismic data examples from the Northeastern Tunisia. We discuss different aspects of detachment to constrain the chronology of structural events and understand the cover‒substratum relationship during the major folding phases. In the present paper, we found that the deformation style admitted previously do not reflect adequately the tectonic structure of Kechabta Neogene basin (North of Tunisia). The cover-substratum relationship study at this area revealed two major shortening phases; the first had been happened during the Upper Tortonian and the second in the Lower Quaternary. The resulting folding style is characterized by disharmonic and multi-layers detachment phenomena produced by incompetent evaporitic sequences. The two described folding phases are superimposed and testify at a large scale the continental collision which controls the North African margin during the Late Miocene to the Quaternary.

Thrust Shear Sense and Shear Zone Fabrics in the Higher Himalaya, Siyom Valley, Eastern Arunachal Himalaya, India

Abstract The Higher Himalayan Crystallines (HHC) in the Siyom river section of eastern Arunachal Himalaya, display top-to- ESE compressional ductile shear from Pene to Menchuka. In this part of the Himalayan Metamorphic Belt (HMB), the base of the Main Central Thrust (MCT) is the southern boundary of the ductile shear fabrics in HHC. Across the MCT, a significant break in the grade of metamorphism is observed between the HHC and the Lesser Himalayan Sequences (LHS). The ductile shear fabrics documented in the HHC are primary S-C and S-C′ fabrics, asymmetric folds, porphyroclasts and porphyrobalsts, brittle- ductile structures and asymmetric boudins. Three phases of folding representing three deformation episodes (D1-D3) in HHC are recorded in the area. The rocks of the HHC in Siyom valley are completely transposed by the D2 deformation into NNW dipping C- plane. Ductile shear represented by grain scale structures include sigmoidal foliation, rotation of the inclusion trails in garnet porphyroblasts, asymmetric folds with consistent top-to-ESE sense of shear. The ductile to brittle-ductile shear fabrics in the area indicate that the thrust sense of shear in the HHC is consistent without any shear sense reversal from Pene to Menchuka. These compressional shear fabrics provide invaluable field evidences for constraining the evolution of this part of the Higher Himalaya.

The Dynamism of Intrinsically Disordered Proteins: Binding-Induced Folding, Amyloid Formation, and Phase Separation.

Intrinsically disordered proteins (IDPs) or natively unfolded proteins do not undergo autonomous folding into a well-defined 3-D structure and challenge the conventional structure-function paradigm. They are involved in a multitude of critical physiological functions by adopting various structural states via order-to-disorder transitions or by maintaining their disordered characteristics in functional complexes. In recent times, there has been a burgeoning interest in the investigation of intriguing behavior of IDPs using highly multidisciplinary and complementary approaches due to the pivotal role of this unique class of protein chameleons in physiology and disease. Over the past decade or so, our laboratory has been actively investigating the unique physicochemical properties of this class of highly dynamic, flexible, rapidly interconverting proteins. We have utilized a diverse array of existing and emerging tools involving steady-state and time-resolved fluorescence, Raman spectroscopy, circular dichroism, light scattering, fluorescence microscopy, and atomic force microscopy coupled with site-directed mutagenesis and other biochemical and biophysical tools to study a variety of interesting and important aspects of IDPs. In this Feature Article, I describe our work on the conformational characteristics, solvation dynamics, binding-induced folding, amyloid formation, and liquid-liquid phase separation of a number of amyloidogenic IDPs. A series of these studies described here captures the role of conformational plasticity and dynamics in directing binding, folding, assembly, aggregation, and phase transitions implicated in physiology and pathology.

Illite 40 Ar– 39 Ar dating of Eocene deformation in the Chiapas Fold and Thrust Belt, southern Mexico

Abstract The Chiapas Fold and Thrust Belt (CFTB) of southern Mexico underwent widespread contraction during the well-documented middle Miocene ‘Chiapanecan’ Orogeny. However, earlier phases of folding have been documented in the region and might have affected the belt before the Miocene. We carried out a stratigraphic review and a structural analysis of the belt, complemented by 40 Ar– 39 Ar dating of synorogenic illite to identify the successive pulses of deformation. Reliable radiometric ages were obtained in three folds from the southern portion of the belt, and in one thrust gouge near the front of the belt. Authigenic illite-rich samples were located in Upper Cretaceous limestone successions that experienced bed-parallel shear during folding and thrusting. They yielded ages ranging from 35 to 40 Ma in the folds and 54.5 ± 7 Ma in the thrust, documenting thin-skinned folding and thrusting in the belt mostly in Eocene time. Some of the basement faults of the belt may have been active during this phase. However, most of the pervasive lateral faults that cross-cut the regional folds in the belt were mostly active from the Miocene onwards, causing transpression and fold amplification.

Geology and Structural Description of Shakrok Anticline; Northern Iraq

The studied area is a part of the Arabian plate located within the High Folded Zone of the Zagros Fold-Thrust Belt in northeastern Iraq (Kurdistan Region). The Study area deals with the Shakrok Anticlines is located between Safin Mountain and Sork Mountain. These structures are formed during the Alpine Orogeny in Cretaceous-Tertiary period. Generally, the folded structures are trending NW-SE direction which is parallel to the main Zagros Orogenic trends.
 The exposed stratigraphic succession of the studied area that represented by 4 formations deposited from the Early Cretaceous which are Shiranish, Aqrah, Bekhme and Qamchuqa formations. Shakrok Anticline are asymmetrical, double plunging and verging toward northeast. This establishes that Merawa is a Tertiary continuation part of Cretaceous Shakrok Anticline, but there is a deflection in the direction of the fold axis that affected the Merawa Anticline due to the effect of strike slip fault addition to Lineament. Shakrok Anticline with Cretaceous successions formed due to the effect of Cretaceous and Tertiary folding phases. But Merawa Anticline with Tertiary succession that formed due to the effect of Tertiary folding phases.
 The high stress and intensity of the major fault on the southwestern limb rotated and overturned Tertiary successions and changed its dip toward NE.
 The differences in fold geometry, fold axis, axial surface, and curvilinear hinge imply that the structure formed as a result of two folding phases & lateral growth of folds that developed by changing the direction of the compressional tectonic processes due to Alpine Orogene of Zagros. The fold axis of Shakrok Anticline rotated 16o in anticlockwise trend from Merawa to Sork anticlines. Because of anticlockwise rotation of the Arabian plate due to its collision with Iranian and Anatolian plates.

Deciphering the relationship between basement faulting and two-phase folding in the Hendijan anticline, northwest Persian Gulf, Iran

The Hendijan anticline in the northwestern part of the Persian Gulf, Iran, was analyzed using 2D/3D seismic and well data. Two folding phases of Late Cretaceous and Pliocene ages, associated with the 700 km long, NNE-SSW Hendijan-Bahregansar-Nowrooz strike-slip fault (HBNF), play an important role in the evolution of the anticline. The HBNF initiated as an oblique-normal basement fault during Late Proterozoic plate accretion on the Arabian margin of Gondwana, and in the Late Cretaceous due to regional compression and ophiolite obduction, it was reactivated as an oblique-reverse fault that formed a NNE-SSW forced fold in the cover. Based on seismic interpretation of key stratigraphic horizons, the analysis of sedimentary thicknesses, and restoration of a cross section across the anticline, the structural evolution of the Hendijan anticline comprises four stages: (1) Early to Middle Cretaceous which shows no evidence of folding, although the oblique normal slip of the HBNF controlled the deposition of sedimentary units in the NNE-SSW direction; (2) Late Albian to Middle Turonian which shows evidence of forced folding, growth strata, erosion, and the development of the Turonian unconformity; (3) Late Cretaceous to Middle Miocene which does not show significant thickness variations; and (4) Pliocene which shows growth strata and buckle folding related to the Zagros orogeny in response to compression associated with the collision of the Arabian and Eurasian plates. In this last stage, the Zagros orogeny overprinted the previously created NNE-SSW Arabian structures and reoriented them to their present NW-SE direction. The HBNF is still active as a blind fault and it has controlled the Miocene to present thickness variations although it tips out under the Lower Miocene Gachsaran evaporites.

Quantitative Analysis of Vocal Fold Vibration using High-Speed Videoendoscopy in Children with and without Bilateral Lesions

To provide data on the measurable vocal fold vibratory differences in children with and without vocal fold lesions using high-speed videoendoscopy. Prospective study, 24 participants (8 healthy; 16 with lesions) between the ages of 5 and 10. Rigid high-speed videoendoscopy at the rate of 8,000 frames per second was used to examine participants. Four objective vocal fold phase linearity measures were obtained to establish anterior-posterior contact and separation vibratory patterns. All objective measures showed a difference between nonlesion and bilateral vocal fold lesion groups. Contact-separation patterns in all nonlesion girls and young pre-pubertal boys exhibited an anterior-to-posterior contact and posterior-to-anterior separation; while older boys differed. The objective measures of open quotient, left-right relative phase asymmetry and speed index, showed linear anterior-posterior patterns within the nonlesion group; while the bilateral vocal fold lesion group displayed nonlinear patterns. Patterns in the posterior region of the vocal fold were similar in both groups; while patterns in the anterior region differed. This study suggests lesions have an effect on the anterior aspect of vocal fold vibratory patterns specifically anterior to the lesions. Age-related differences for males are also evidenced, prompting further investigation of laryngeal development in males and females from childhood to adulthood. This study could serve as a basis for the development of objective clinical measurements of vocal fold vibration in presence of lesions. Further findings could help redefine the theoretical framework of pediatric voice.

Late orogenic gold mineralization in the western domain of the Karagwe-Ankole Belt (Central Africa): Auriferous quartz veins from the Byumba deposit (Rwanda)

Gold mineralization in the KAB (Karagwe-Ankole Belt) of Central Africa dominantly occurs as quartz lode and ferruginous breccia systems. Primary gold mineralization in the KAB is possibly linked to a deformational event in the early-Neoproterozoic which is accompanied by shear movements and post compressional magmatism. The Byumba deposit is chosen due to its position in the KAB Mesoproterozoic metasedimentary stratigraphy (Akanyaru Supergroup), interesting structural trend (NW trending shear zone) and its closeness to magmatic intrusions. Explorative drillings from the Byumba deposit in Rwanda were logged and sampled for further petrographic investigation, in situ Rb-Sr geochronology (Laser Ablation Inductively-Coupled-Plasma Triple Quadrupole Mass Spectrometry) and Micro X-ray fluorescence (µXRF) major and trace element mapping. Distinct phases of folding and shear deformation are present at Byumba and three main phases of quartz veining are identified (pre-, syn-, post-folding). The first quartz vein generation is layer-parallel and folded along the bedding, indicative of a pre-folding origin (V1 generation). A second generation of quartz veins (V2a) is concentrated in fold hinges and related to the primary folding of the layers. Cleavage parallel and often boudinaged V2b quartz veins are emplaced during late-stage folding. Post-folding (V3) massive or sigmoidal quartz veins, crosscut the folds and cleavage. Element mapping of the gold by using µXRF shows that Chlorite-rich quartz veins (V3) host the primary gold mineralization in the form of sub-micron gold and of small disseminated blebs. Cores additionally recorded a supergene enrichment phase of gold at reduction zone boundaries. In situ Rb-Sr geochronology on white mica of the crosscutting post-folding quartz veins (V3) point towards an Early-Neoproterozoic age of ∼900 Ma. The gold mineralization at Byumba is interpreted to be related to the regional early-Neoproterozoic compressional deformation event based on 1) the post-folding timing of the auriferous veins, 2) the observation of shear-related textures both in the host-rock and the veins, and 3) the location of the Byumba deposit within a regional shear structure. This association with compressional shearing points towards an orogenic origin for gold mineralization. However, a magmatic-hydrothermal influence from contemporaneous granitic magmatism cannot be excluded.

Nepheline syenite intrusions from the Rengali Province, eastern India: Integrating geological setting, microstructures, and geochronological observations on their syntectonic emplacement

Ten nepheline syenite intrusions have been concordantly emplaced within or close to a polydeformed, regionally metamorphosed sedimentary sequence in the Rengali Province, eastern India during the Mesoproterozoic. The intrusions and the country rocks share a common deformation history and record three phases of folding. The nepheline syenites preserve deformation structures and textures indicative of continuous deformation that started in the presence of a melt and ended under sub-solidus conditions. This deformation in nepheline syenites is divided on the basis of mechanical behavior into three stages: an early one with the development of varied types of magmatic layering and flattened magmatic enclaves, a middle one with the development of asymmetrical magmatic folds and intramagmatic shear zones, and a late stage with melt-enhanced embrittlement. Igneous zircons from two of the intrusions, namely Chhatabar and Gunjighara are dated at 1356 ± 5 Ma and 1358 ± 4 Ma (U–Pb concordant age, LA–ICP–MS), respectively. Electron microprobe U–Th–total Pb geochronology of monazites from two samples of sillimanite grade mica schists in the host metasedimentary sequence of the Chhatabar nepheline syenite yields metamorphic ages of 1362 ± 12 Ma and 1376 ± 23 Ma, which indicate broad synchronism of regional metamorphism of the country rocks and the nepheline syenite magmatism. Contrary to the common proposition that nepheline syenite intrusions in eastern India and in some other regions of Precambrian crust were emplaced anorogenically in intracontinental rifts and subsequently deformed by continental collision, we develop a structural interpretation in which the nepheline syenites were emplaced syntectonically in the sense that magma transport and cooling occurred during regional metamorphism and deformation. The study shows that an integration of structural, textural and geochronological data from both nepheline syenite and country rock is crucial for an understanding of the spatial and temporal relationships between contractional deformation and alkaline magmatism. Our results imply that deformed nepheline syenites may not always be useful in constraining the initiation of a Wilson Cycle heralded by intracontinental rifting.

STRUCTURAL ANALYSIS OF FOLDS SYSTEM AND RELATED MESOSTRUCTURES IN THE AREA WEST OF IRBED, JORDAN

  The study area is located in the northwestern highlands of Jordan. It is located few kilometers to the west of Irbid city and about 10 kilometers east of Jordan Valley. The aim of the study is to analyze the folds system and the related mesostructural elements. The outcropping rocks in the study area are of Late-Cretaceous age, the measured structural elements were taken from outcrop hills, road cuts and quarries. The main structural elements in the study area are folds and fractures (faults and joints). Folds are mainly anticlines, which characterized by gently dipping strata (5º–20º), and gently plunging hinge lines (3º–18º).  Hinge lines of minor folds are mainly plunging toward SW and WSW, some folds are plunging either toward NNW, SSE, NNE, NE and SSW. The interlimb angles of the folds range between 136º–165º, so they are classified as gentle folds. About 2800 fracture measurements were taken from nine stations of the study area. The major trend of the fractures is NW-SE, in addition to minor trends in NNW-SSE, WNW-ESE and NE-SW. It is observed that the main trend of the fractures is normal to the hinge lines of the folds in stations 3,5 and 8, in which they parallel to the NW-SE compression direction of the Dead Sea stress system. In station -6 the main trend of the fractures is subparallel to the fold axis. Station-6 shows an over thrust fault (NNE-SSW) sub-parallel to the fold axis (NNW- SSE) in which both are resulted from ESE–WNW compression of the SAS. In stations 1 and 4, the main trend of the fractures is neither parallel nor perpendicular to the fold axes, this indicates that the fractures are post-formational structures i.e. formed in later stages of the formation of the folds. Some folds were truncated by major faults which indicate that the folding phase was followed by faulting phase. The study area has been affected by both stress fields in the region, these are the SAS since the Turonian to Oligocene, and the Dead Sea stress since Middle Miocene to Recent.