Positive Flower Structure Research Articles

Pulsating orogenesis and Neoproterozoic crustal architecture in the western part of Aravalli-Delhi Mobile belt, India: new evidence from structural, metamorphic, and U-Pb zircon geochronological data

ABSTRACT Structural, metamorphic, and geochronological study of the Delhi Supergroup rocks near the western margin of the Aravalli-Delhi Mobile Belt (ADMB) elucidate the Neoproterozoic tectonics of the South Delhi Fold Belt (SDFB) and its implication for the evolution of the Greater Indian Landmass (GIL). In this study, we establish three deformational events in the SDFB. While the D1 event produced isoclinal, reclined F1 folds synchronous with prograde amphibolite facies metamorphism (~5 kbar, 650°C), D2 formed outcrop to map-scale upright F2 folds. D3 comprised ‘partitioned transpression’ along two subvertical shear zones. Oblique dextral-reverse movement (D3a) along one shear zone formed an outcrop-scale positive flower structure, while sinistral-reverse movement along the other rotated and steepened the hinges of the F2 folds (D3b). U-Pb zircon dating of post-tectonic (post-D2, but pre-D3) and syntectonic (syn-D3) granite intrusives suggests >844 Ma age for D2 and ca. 820 Ma for D3. An older magmatic event (ca. 990 Ma) is recorded from sheared pink granites (pre- to syn-D1 intrusion). We suggest that the amalgamation of the ADMB and the Marwar Craton was initiated by the Grenville-age (ca. 1000 Ma) subduction-collision, while the younger events (ca. 844 Ma and 820 Ma) mark the final stitching of the ADMB – Marwar Craton along the Phulad-Ranakpur palaeo-suture zone to form the GIL. The distribution of early (ca. 1000–900 Ma) and late (ca. 800–700 Ma) Tonian magmatic and metamorphic ages in the SDFB suggest that the final growth of the GIL took place through multiple stages of oblique collision in a pulsating orogenesis through the Early Neoproterozoic.

Structural architecture and metamorphism of the Mayombe Chain and Niari Basin (West Congo Belt) in Congo Brazzaville

Geological mapping of the Mayombe Chain and Niari Basin of Congo Brazzaville allows for the first time defining the structural architecture and metamorphism of the West Congo Belt. Four different tectono-metamorphic domains, separated by crustal-scale shear zones, are now distinguished (Niari Basin (NB), Eastern (EMC), Central (CMC) and Western (WMC) Mayombe Chain).The NB is marked by only weak regional deformation under middle to upper diagenetic conditions. It is delimited in the west from the EMC by the Mount Belo Shear Zone forming the terminal thrust system of the West Congo orogen.The tectonic style in the EMC is characterized by discrete, widely-spaced low-angle thrusts, reverse faults and strike-slip faults resulting in the formation of duplex and/or positive flower structures. Off these high-strain zones, the rocks are folded into gentle syn- and anticlines. Penetrative schistosity starts in shales in the western part. The metamorphism increases from eastern anchizonal conditions to lower greenschist facies in the west. The EMC is juxtaposed along the Moukondo thrust/back-thrust system with the CMC.The CMC is typified by open to closed upright to NE-verging folds, S1 schistosity with moderate to steep SW dips, onset of regional crenulation cleavage (S2), frequent reverse thrusts and numerous faults. Metamorphic conditions remain in the greenschist facies. The Loukenéné-Mandji Thrust marks the CMC-WMC contact and coincides with a jump in metamorphic grade marked by biotite-in.The WMC consists of Palaeoproterozoic basement stacked with Neoproterozoic rocks. Autochthonous Palaeoproterozoic gneiss and schist record Late Eburnean sedimentation, magmatism and metamorphism between 2110 and 1970 Ma, which are compared with the Eburnean history in Gabon and the Transamazonian orogeny in Brazil. The allochthonous Bikossi Group was thrust during the Pan-African event from the west over Tonian metavolcaniclastic and plutonic rocks before further folding and stacking of both units. The intensity of Pan-African deformation increases from open to closed folds with spaced cleavage in the southeast of the WMC to thrust-dominated tectonics in the northwest, where the Palaeo- and Neoproterozoic rocks are transposed into parallelism with the pronounced schistosity.Geochronology of illite and muscovite documents two Pan-African events at 590-570 Ma (M1) and at 520-500 Ma (M2) that are related to the main collisional and late thermal events in the Araçuai-Ribeira Belt in Brazil. Metamorphic isogrades shifted from M1 to M2 for more than 30 km to the west. Detrital mica and metamorphic illite of the Mpioka Group record M1 and M2, respectively constraining sedimentary deposition between 570 and 520 Ma, which implies the interpretation of the group as molasse of the West Congo Belt.

Identification and Verification of the Movement of the Hidden Active Fault Using Electrical Resistivity Tomography and Excavation

Identifying the movement of the branches of the hidden Thakhek fault in Thailand is challenging due to the absence of evident landforms indicating an active fault. In this study, we analyzed a digital elevation model (DEM) to identify potential landforms. A 2D Electrical Resistivity Tomography (ERT) survey was conducted to locate the hidden Thakhek fault. The results reveal vivid images of resistivity contrast, interpreted as two reverse faults, with mudstone exhibiting low resistivity in the middle, flanked by thick sediment layers with higher resistivity. Three trenches were excavated perpendicular to the two interpreted reverse faults. The displacement of reverse faulting appears to have shifted mudstone over Quaternary sediments, with vertical offsets revealed in trenches NWY-1, NWY-2, and NWY-3. This movement could be identified as a positive flower structure. Additionally, lakes are identified as a negative flower structure along the traces. These features result from strike-slip strains under a locally appropriate compressional and extensional environment in a shearing strike-slip fault.

STRUCTURAL POSITION AND DISTRIBUTION OF THE LOWER CRETACEOUS BLACK SHALE DEPOSITS WITHIN THE SILESIAN NAPPE OF THE UKRAINIAN CARPATHIANS

The article presents the results of studying the structural position and distribution of potentially oil-generating, organic-enriched Lower Cretaceous black shale deposits of the Shypot Formation, developed within the Silesian Nappe, using the methods of geological mapping and structural analysis. We concluded, that these deposits, which are exposed in the Vicha River basin near the town of Volovets among a continuous field of Oligocene flysch, are the part of the stratigraphic succession of the Silesian Nappe, and they are not a large olistolith or an allochthonous tectonic remnant of another, more internal nappe. Shypot Formation fills a large (1 × 3 km) subvertical tectonic lens. The rocks of the Shypot Formation are represented here by medium-rhythmic flysch: sandstone beds alternating with dark gray and black foliated mudstone (black shale) layers. They are lithified products of both medium-density turbidite flows and hemipelagic deposition of clayey material with a significant amount of organic matter. In the contact zone of the tectonic lens with the surrounding rocks, the deposits are intensively deformed, almost isoclinal folds with subvetrical hinges are observed, which suggest the strike-slip movements. A tectonic mélange is recorded here, which is represented by small blocks (clastolites) of brittle sandstones, sometimes similar to Shypot sandstones, placed in a silt-pelitic ductile matrix. Foliation of the mélange matrix is also subvertical and close to the meridional and/or subcarpathian direction. The structural studies carried out show that in the zone of this contact there were compressive stresses perpendicular to the Carpathian orogen, and stress fields that caused strike-slip movements, most likely right-lateral along the Carpathian thrusts. The tectonic lens is located within the broad Latorytsa-Stryi shear zone, and probably extruded out from deep horizons by transpressive movements (compression and strike-slip) and forms a “positive flower structure”. The vertical foliation in the mélange suggests that small blocks of Shypot sandstones were extruded up together with the ductile mélange matrix during diapirism. Similar processes probably led to the rise of a large lens of Shypot sandstones as the positive flower structure. The studies suggests that the black shale deposits of the Shypot Formation, enriched with organic matter, are widespread at some depth within the Silesian Nappe, and in some places are pushed up to the level of the Oligocene flysch. As a result, the Shypot Formation and Oligocene flysch are now in direct contact along faults/mélange zones. The presence of Lower Cretaceous potentially oil- and gas-generating black shale deposits within the Silesian Nappe significantly increases the prospects for oil and gas exploration in this area.

Diverse Structural Styles of the Northeastern Tethyan Himalaya in Southern Tibet Reveal the Early Collisional Tectonics of India and Asia

AbstractThe poor understanding of the structural history of the Late Triassic flysch in the northeastern Tethyan Himalaya has caused many disputes regarding India‐Asia collisional tectonics. Here, we conducted an integrated study including tectonostratigraphic analysis, structural analysis, and zircon U‒Pb and muscovite 40Ar/39Ar dating to unravel the structural evolution of the Late Triassic flysch. Field geological mapping revealed that the flysch can be subdivided into three structural units, including the Gyaca mélange, Qiongjie‐Dengmu shear zone and Langjiexue fold‐thrust belt. The three units all contain voluminous siliciclastic rocks deposited in an abyssal submarine fan environment at the Indian passive continental margin. The Gyaca mélange shows a two‐stage deformation process that generated a collisional mélange resulting from the subduction of the Indian passive continental margin. 40Ar/39Ar dating of top‐to‐the‐south shear bands and block‐in‐matrix structure indicate that the India‐Asia collision happened no later than the Selandian (ca. 60 Ma). The divergent imbricated thrusting and folding of the Gyaca mélange and Langjiexue fold‐thrust belt formed a positive flower structure. The zircon U‒Pb and 40Ar/39Ar dating of syntectonic dikes and sericite flakes within the Gyaca mélange yield ages of ca. 56–55 Ma for the genesis of the divergent structures. Moreover, the Qiongjie‐Dengmu dextral shear zone yields a sericite 40Ar/39Ar age of ca. 35 Ma and thus indicates a transient strike‐slip stress regime. Generally, the early India‐Asia collision tectonics in the northeastern Tethyan Himalaya showed episodic evolution with changing structural styles from mélange formation to imbricate fold‐thrust belt development and finally strike‐slip shear generation.

Tectonic evolution of the Crotone Basin (central Mediterranean): The important role of two strike-slip fault zones

The middle Miocene to Quaternary evolution of the Crotone Basin (CB), on the Ionian side of the Calabrian Arc (southern Italy), was strongly controlled by the activity of the NNW- to NW-striking Rossano-San Nicola (RSFZ) and Petilia-Sosti (PSFZ) fault zones. The integration of low frequency 2D seismic reflection profiles, boreholes and geological maps has allowed the discovery of a positive flower structure, which is part of the RSFZ. Such a positive flower structure was responsible for the emplacement of an allochthonous unit in the Late Tortonian and contributed to the onset of gravitational collapse in the Pliocene. Dextral transpressional tectonics related to the RSFZ led to the expulsion of a S-verging thrust controlling the emergence of the northern sector (Cirò area), and the development of an elongated E-W-oriented depocenter in the southern sector of the Crotone Basin (Crotone area), from the Late Tortonian to Late Messinian. In the Late Messinian, the offshore area of the basin turned into a structural high marked by overall exposure conditions, as a consequence of the RSFZ activity. Contractional/transpressional activity also took place at the transition between the Early and Late Pliocene, when the PSFZ governed the superimposition of the Messinian Unit in the Crotone area. Conversely, phases of extensional/transtensional tectonics are inferred to have been occurred along the PSFZ during the Messinian, by the development of a tectonic trough in the south Crotone area. This tectonic regime is also supposed to have persisted during the Early Pliocene and the Pleistocene in the offshore area, where the development of local depocenters took place.

Physical Simulation Experimental Device for Basement Shear Structure: Simulation and Feasibility Study of Strike-Slip Fault Zones

Structural physical simulation research is an important means of studying the geometric evolution process of structures intuitively. We have designed a new basement shear structure physical simulation experimental device and applied it to the physical simulation of strike-slip fault zones. We recorded different stages of horizontal displacement along the underlying basal fault, the typical surface evolution of deformed quartz sand bodies, and evaluated the feasibility of the device for simulating strike-slip fault zones. The experimental results indicate that the evolution process of the strike-slip fault zone can be recorded on the top surface of the experimental model, and distinct positive flower structures can be observed on the final profile of the experimental model. Therefore, we believe that this experiment is feasible to a certain extent.

Cenozoic dextral transpressional tectonics in the northwestern Qaidam Basin, northern Tibet: Evidence from paleomagnetic and kinematic analysis of the arcuate belts

The mechanisms by which complex intracontinental deformation in the northern Tibetan Plateau was accommodated since the India-Asia collision remain debated. Characterization of the formation of arcuate structures in northern Tibet provides important constraints on this debate. We conducted a new paleomagnetic study on the mid- to late Miocene strata along the curved Lenghu-Nanbaxian and Eboliang-Hulushan belts of the Qaidam Basin, northern Tibet. Our results revealed that there is nonsignificant relative rotation within localities along these arcuate belts, which yielded a common mean direction of declination (D) = 3.6°, inclination (I) = 35.7° (α95 = 2.4°) after tilt correction, suggesting negligible Neogene vertical-axis rotation along the arcuate belts in the Qaidam Basin. Outcropped fault striations and the positive flower structures indicate dextral strike-slip−dominated motion along the faults since the mid- to late Miocene. By integrating the paleomagnetic results with the kinematics of these associated faults, we ruled out the possibility that these curved belts formed due to the frictional drag of the Altyn Tagh fault or due to differential shortening across the Qaidam Basin. Instead, we attribute the formation of these nonrotational arcuate belts to dextral transpressional deformation occurring within the basin since the mid- to late Miocene. Different from the orogenic belts in the northern Tibetan Plateau that absorbed postcollisional convergence through block rotation, crustal shortening, and lateral extrusion, the Qaidam Basin has also accommodated significant intracontinental deformation in the northern Tibetan Plateau through transpressional deformation within the basin. This inference underscores the importance of recognizing crustal extrusion within rigid blocks as a record of intracontinental deformation in the northern Tibetan Plateau.

Slip partitioning and seismogenic stress buildup adjacent to the junction of the Lenglongling fault and the Tuolaishan fault: Insights from kinematically constrained numerical simulations

Understanding fault kinematics plays a crucial role in estimating seismic hazards and linking the relationship between seismogenic stress buildup and tectonic deformation. The northwestern segment of the Qilian-Haiyuan fault zone (QHFZ) serves as a natural laboratory for investigating how the oblique block motion decomposes into a complex fault system. In this study, we constructed a 3D FEM model incorporating the active faults as contact discontinuities to obtain a continuous numerical image of fault slip rates. Our findings revealed that deformation partitioning within the context of oblique block convergence generates a spatially heterogeneous distribution of fault slip rates. The inferred strike-slip rates of the Tuolaishan fault and the Lenglongling fault (LLLF) range from approximately 2 to 4 mm/yr and 4 to 7 mm/yr, respectively. The Lenglongling fault's slip behavior exhibits a spatial transition, with a dominant strike-slip component dominating in the western part and gradually changing to a combination of reverse faulting and strike-slip in the eastern segment. The Northern Lenglongling fault (NLLLF), characterized by a listric shape, merges with the LLLF in the deep crust, resulting in the formation of a positive flower structure that enhances the accumulation of compressional seismogenic stress. The region with high shear strain rates within this area has experienced significant earthquakes, including the 2022 Menyuan MS 6.9 earthquake, the 2016 Menyuan MS 6.4 earthquake, and the 1986 Menyuan MS 6.4 earthquake. Our numerical study gained valuable insights into the relationship between slip partitioning, fault structures, and regional stress.

Coseismic and early postseismic deformation associated with the January 2022 Mw 6.6 Menyuan earthquake, NE Tibet, revealed by InSAR Observations

The 7 January 2022 Mw 6.6 Menyuan earthquake struck the Qilian-Haiyuan fault zone, NE Tibet, offering a chance for understanding the regional seismogenic structure and rupture behavior. We use Interferometric synthetic aperture radar data to study the coseismic and early postseismic deformation of the event. Coseismic modelling highlights that the earthquake activated two strike-variable high-angle strike-slip faults (one SE-trending main fault and one ENE-striking secondary fault) corresponding to only part of the Lenglongling and Tuolaishan faults. Further postseismic analysis not only reveals a localized postseismic signal of up to ∼3 cm related to the mainshock but identifies an obvious coseismic signal of up to ∼2.3 cm associated with an MW 5.1 aftershock characterized by sinistral strike-slip-faulting. The 2022 Menyuan earthquake, large aftershock and 2016 Mw 5.9 thrust-faulting Menyuan earthquake illuminate a positive flower structure of the Lenglongling fault. By a joint analysis of the inversions, fault kinematics and historical earthquake, we suggest that fault branches and low pre-stress jointly restrain the maximum rupture size in the 2022 Menyuan event.

Mesozoic strike-slip fault system at the margin of the Junggar Basin, NW China

The Junggar Basin in Northwest China is covered by thick sediments, causing challenges in recognizing buried structures. Seismic reflection and drilling data from petroleum exploration provide essential data for the study of subsurface structures. In this study, we focus on the Mesozoic structural characteristics and tectonic evolution along the margins of the Junggar Basin by using 2D and 3D seismic reflection, drilling data, and surface geology. Our results demonstrate that a unified dextral strike-slip fault system developed along the marginal area around the Junggar Basin. The structural style is characterized by both transpressional structures, such as positive flower structures, en echelon folds, restraining bends, and fan-shaped and horsetail fractures at the fault tip, and transtensional structures, including releasing bends, pull-apart basins (fault basins), and positive inverted structures. We further interpret that except for the southern margin of the Junggar Basin, the current structural pattern of the basin margin was mainly formed in the pre-Cretaceous, which was covered by Cretaceous and Cenozoic strata. Based on the timing and style of deformation, we propose that the vertical-axis counterclockwise rotation of the Junggar Basin during the Mesozoic caused right-lateral strike-slip faulting along the basin margin. Cenozoic reactivation of these structures has been localized in the southern margin of the Junggar Basin under the far-field influence of the India-Asia collision.

Differential deformation of a strike-slip fault in the Paleozoic carbonate reservoirs of the Tarim Basin, China

Ultra-deep carbonate reservoirs buried over 7000 m are distributed around strike-slip faults, which control hydrocarbon accumulation and enrichment in the Tarim Basin, China. This study proposes a fracture development index (FDI) method for analyzing the width of the strike-slip fault zone based on 3D seismic data. Based on the FDI method and geological and geophysical data, we analyze the structural characteristics of the SB5 strike-slip fault and the scaling of fault zone width and throw.In map view, at depth the strike-slip fault is characterized by single fault segments, extensional overlaps, and contractional overlaps, at intermediate depths by left-stepping en echelon normal faults, and in shallow layers by right-stepping en echelon normal faults. In cross section, we find composite flower structures and positive flower structures and medium-shallow layer negative flower structures or deep layer negative flower structures and medium-shallow layer negative flower structures. The formation time of deep, middle, and shallow layer faults is the middle Caledonian, Late Caledonian, and Late Hercynian. The heterogeneity of the strike-slip fault zone varies from strong to weak from contractional overlaps, to extensional overlaps, and single fault segments. Strike-slip fault-related fractures are dominated by three sets intersecting with strike-slip faults at small angles. Where throw is less than 100 m, the fault zone width and throw have a good power law relationship. Where the throw is over 100 m, the width tends to diminish with throw.

Early-middle Miocene Inversion of the Abu Jir Fault in the Western Iraq: a Possible Consequence of the Arabian Plate Northward Movement

The Abu Jir fault zone in western Iraq that marks the western limit of the Zagros foreland basin merges with the Anah graben in the north. The northern segment of the Abu Jir fault zone and the western Anah graben are inverted structures. In this study, we investigated the timing and mechanism of the northern Abu Jir fault zone inversion in comparison with other inverted structures like Tel Hajar and Sinjar, which are located in the north and closer to Arabia–Eurasia collision zone. In the study area the Abu Jir fault zone is characterized by a local-scale northwestern-trending asymmetric fold, associated with inverted normal faults, positive flower structures, right–lateral strike-slip faults, and seismically induced early middle Miocene slump structures. Based on the structural synthesis of the surface geology and age constraints from syntectonic deposits at the northern Abu Jir fault area, the Abu Jir fault inversion and its western block northward movement were inferred to be resulted from forces that originated from the south to the north, unlike the northern younger inverted structures. This early middle Miocene age of the Abu Jir fault inversion is comparable to the arrival time of the Afar plume hot mantle material flow from the south to the north in western Arabia. Therefore, we argue that the Abu-Jir fault inversion is more likely to be due to dragging of the Arabian plate by mantle flow from the south to the north rather than shortening propagation from the north to the south.

Fault‐Driven Differential Exhumation in a Transpressional Tectonic Setting: A Combined Microstructural and Thermochronologic Approach From the Liquiñe‐Ofqui Fault System, Southern Andes (39°S)

AbstractCrustal deformation in transpressive tectonic settings is partitioned across fault‐bounded tectonic blocks whose borders may represent ideal loci for enhanced rock exhumation. Field and petrographic analysis, geothermobarometry, zircon U‐Pb geochronology, and zircon and apatite (U‐Th)/He thermochronology were applied to intrusive and metamorphic rocks to investigate exhumation patterns of fault blocks delimited by the Liquiñe‐Ofqui Fault System (LOFS), Southern Andes (39°S). Our integrated analyses document the relative influences of magmatism, fault‐driven differential exhumation, and fault‐controlled geothermal flow along the LOFS. Magmatism was concentrated in the Early to Late Jurassic (∼182–151 Ma), Early Cretaceous (∼116–104 Ma), and Miocene (∼17–6 Ma). Dextral mylonitic deformation was most likely coeval with the Miocene pulse of magmatism. Tectonic exhumation occurred across a positive flower structure during the Late Miocene to Early Pleistocene (∼6–2 Ma), and affected kilometric‐scale tectonic blocks bound by N‐striking, steeply dipping faults of the LOFS. Fault‐controlled geothermal flow occurred from the Early Pleistocene to the present‐day (∼1.5 Ma‐present). Our results suggest that individual faults not only facilitate exhumation of tectonic blocks but also act as pathways for long‐term hydrothermal fluid flow.

Continent‐Continent Collision Between the South and North China Plates Revealed by Seismic Refraction and Reflection at the Southern Segment of the Tanlu Fault Zone

AbstractThe Tanlu Fault Zone (TFZ) is considered as a suture of the intra‐continental collision between the South and North China plates, and it has attracted considerable geological, geochemistry, and geophysical investigations. However, its deep structures still lack clear delineation and the related tectonic processes are still debated without a clear consensus. To better characterize the TFZ as a plate boundary in east China, a 2‐D land seismic survey extending 87 km was conducted across its southern segment to investigate the underlying complex structures. Acoustic full‐waveform inversion (FWI) is applied to the early arrivals of the land seismic data to reconstruct the high‐resolution P‐wave velocity model of the upper crust (above ∼3.5 km). Structures of the crust and the uppermost mantle are further constrained through deep seismic profiling (DSP). The integrated geological interpretation from the FWI and DSP results suggests massive magma upwelling activities, characterized by the reflection‐free zone revealed by DSP and the high‐velocity anomaly recovered by FWI. The TFZ in the study area is found to be a deeply seated fault system with a positive flower structure at its shallow part, which suggests it has undergone a transpression regime. Also, the DSP result provides evidence for the subduction of the South China plate under the North China plate. Finally, a three‐stage model including the compression, transpression, and extension stages is proposed based on the new seismic results to better constrain the tectonic evolution of the southern segment of the TFZ.

The Sukari Gold Deposit, Egypt: Geochemical and Geochronological Constraints on the Ore Genesis and Implications for Regional Exploration

AbstractThe Sukari gold deposit (>15 Moz Au) in the Eastern Desert of Egypt is hosted by a deformed granitoid stock (Sukari tonalite-trondhjemite intrusion) and mainly occurs as a network of crosscutting sulfide-bearing quartz (± carbonate) veins and intensely sulfidized-silicified-sericitized wall rock. Emplacement of the Sukari intrusion into a tectonized Neoproterozoic accretionary complex was controlled by a system of NE- to NNE-trending oblique faults that are related to a deep-seated positive flower structure. A robust genetic model has been hampered by the poorly understood relationships between gold mineralization and host rocks. In this study, zircon U-Pb ages of three samples from the Sukari intrusion define a crystallization age of ~695 ± 2 Ma. In contrast, hydrothermal sericite from the ore zone yields an 40Ar/39Ar age of ~625 ± 3 Ma, which coincides with the onset of major sinistral transpression in the region.Features including sigmoidal morphology of gold quartz veins and abundant subhorizontal tension gashes alongside widespread brecciation and recrystallization suggest that quartz veining occurred during renewed shortening and exhumation through the brittle-ductile transition. Petrographic and micro-X-ray fluorescence (µXRF) studies indicate that disseminated gold and sulfides, commonly associated with sericite and carbonate alteration, are mostly confined to stylolitic bands in the quartz veins. Oscillatory and sector zoning patterns, irregular As-rich bands, and truncations between early- and late-genetic pyrites reflect variations in temperature and mechanism of ore deposition, demonstrated by variable As/S and Co/Ni ratios in the different pyrite generations. Laser ablation-inductively coupled plasma-mass spectrometry analysis pinpoints the covariance of gold and arsenic contents in pyrite, but free milling gold inclusions in microfractures consistently have a mercury-bearing electrum composition, depicting different ore formation stages.Ore fluids with δ34SH2s values of –1.9 to –3.0‰, modeled from gold-associated pyrite and arsenopyrite assemblages with nearly identical δ34S values, suggest a likely single source of sulfur. Alternatively, multisourced sulfur could have extensively mixed and equilibrated by fluid reaction with carbonaceous wall rock. Gold deposition was triggered by abrupt changes in fluid pH and fO2. As an implication for future exploration, sites of maximized strain gradients adjacent to granitoid bodies along extensive transpression zones in the district could be highly prospective targets, particularly where imprinted by sericite-carbonate ± graphite alteration.

Evidence of structural transformation in the eastern part of the Altyn Tagh Fault, northern margin of the Tibetan Plateau, China, based on the kinematics and shortening rate of the Hongliuxia region

(a) Blocks distributed surround the Tibetan Plateau. (b) Active tectonics in the northeastern Tibetan Plateau. The black rectangle within the inset shows the study area. The thick grey line shows the block boundary. Blue arrows show the global positioning system (GPS) velocity with respect to the Eurasian Plate, and the green arrows represent the GPS velocity with respect to GAB. (c) Deformation rates of these faults and folds in the compressional stepover of the eastern ATF. JTF: Jinta Fault, HLF: Helishan Fault, LSF: Longshoushan Fault, NQLF: North Qilian Shan Fault, SS: sinistral strike-slip rate, Sh: shortening rate, V: vertical rate, HLX Fo.: Hongliuxia thrust-fold belt, HSG Anti.: Huoshaogou Anticline, NKTF: North Kuantanshan Fault, LJM Anti.: Laojunmiao Anticline, and BYF: Baiyang Fault. • Shortening rate of the Hongliuxia region was 0.7 ± 0.2 mm/yr in Late Pleistocene. • Hongliuxia region showed more N–S shortening than the W–E strike-slip. • Stepover was formed between the eastern Altyn Tagh fault and Jinta-Nanshan fault. The Altyn Tagh Fault (ATF) and the North Qilian Shan Fault, as the northern margin of the Tibetan Plateau, have always been the focus of attention while developing a propagation model of the plateau. However, rocks in the North Qilian Shan Fault are intensely deformed and understanding the deformation history is difficult. The ATF and North Qilian Shan Fault have propagated into the Hexi Corridor and led to a series of new faults and folds. Based on simple kinematics and insignificant deformations of these new faults and folds, the geological process can be easily understood. The Hongliuxia region, which represents a positive flower structure in the easternmost part of the ATF, is the binding transformation site between the ATF and North Qilian Shan Fault. In this study, the kinematics of the Hongliuxia region was determined based on structural profiling and fault surveys. The shortening rate (0.7 ± 0.2 mm/yr) was estimated from the deformation and 10 Be exposure age of fluvial terraces. We found that the ATF might be connected to the Jinta-Nanshan Fault by a compressional stepover on the northern part of the Yumen Basin, which transforms into a series of compressional ridges, including the Hongliuxia thrust-fold belt, Huoshaogou Anticline, and North Heishan Fault. We infer that the ATF and the Longshoushan Fault, which serve as boundary faults, might be linked by multiple compressional stepovers. The gradual changes of the striking angles by compressional stepovers indicated the transformation from strike-slip to compressional structures and these changes caused the two boundary faults (ATF and Longshoushan Fault) to jointly undergo crustal deformation associated with the northward propagation of the Tibetan Plateau. This study can advance our understanding of the relationship between ATF and the Qilian Shan thrust fault system.

Airborne Magnetic Survey and Remote Sensing Applied to Structural Study in Vohilava Area Madagascar

Mananjary district is known for its gold production. To better understand the gold mineralization distribution, a regional structural study was undertaken using airborne geophysics and remote sensing (RS). Magnetometry data, Landsat Operational Land Imager (OLI) 8 satellite-image and DEM (Digital Elevation Model) have been processed and interpreted. Signals associated with deep structures are weak and dominated by strong signals from surficial magnetic sources. To overcome this problem, local-phase based filters were used. A deep knowledge of each filter allows to use it separately or in combination with other filters. RS is a powerful tool for a regional study. Color composite technique and DEM analysis were helpful to bring out faults and structures. The combination of magnetometry and RS allows geologists to efficiently delineate prospective zones. The study has unveiled a dextral strike-slip fault (SSF) over 240km and associated faults, folds, flower structure and pull-apart basins within the Mananjary gold district. Moreover, the SSF structurally controlled the spatial distribution of Vohilava-Nosivolo and Maha groups. R Riedel shear faults appear as North North East – South South West faults. R’ Riedel shear faults occur in the north of the study area with East North East -West South West orientation. Tectonic block rotation occurred between Ampasinambo and Soavina. P’ shear faults striking West North West – East South East occur in Vohilava. Some folds are associated with the SSF as well. Vohilava positive flower structure which used to be a syncline and its antiform equivalent are SSF footprints. The latter was active since Mesoarchean.

Utilization of seismic attributes for structural pattern detection In Bualawn, Dor Mansour fields, Western Sirt Basin, Libya

An integrated approach to the study of fault patterns carried out in the complex geological structures of Bualawn, Dor Mansour fields by using multiple seismic attributes of 3-D seismic data. Each type of geological structure event usually generates a unique seismic signature that can be recognized and identified. This paper highlights the practical importance of analyze integrated attributes and interpret them within the context of an appropriate structural deformation. Many of discontinuity attributes such as variance, 3DEE (3D edge enhancement), ant tracking, chaos and structure smoothing have been selected to delineate fault styles and their displacement effectively, which cannot be fully delineated using seismic amplitude data. Conjugate growth faults in NW-SE and NE-SW direction, dipping toward SW with antithetic faults dipping in opposite direction to the growth faults and other minor faults. The faults were identified manually and then tested by discontinuity attributes. Fault system is represented by a fracture system comprising long en echelon seismic faults and several discontinuities. This system of en echelon faults was initiated by left-lateral wrenching movements. This wrenching system has been identified by negative and positive flower structure along the releasing and restraining bends. The current understanding that these faults are strike-slip faults despite the absence of extensive horizontal displacements along them as shown on different time slices. A periodic strike-slip movement along deep-seated basement faults have developed many structural features, such as horst-graben styles, which is the orientation of the transtensional movements linked to the Upper Cretaceous Succession.

Miocene Stratigraphy of Abu-Jir Fault Zone, Al-Baghdadi Sub-Basin, Western Iraq.

Stratigraphy of Late Oligocene to Middle Miocene age, suggested the carbonates evaporate succession in the area between Heet and Haditha cities within Abu-Jir fault zone has distinguished as “Al-Baghdadi sub-basin” after Al-Baghdadi city. It has NW–SE trending align the western bank of the Euphrates. Al-Baghdadi sub-basin is a local basin, which forms a part of the western marginal of the large foreland Tertiary basin (Zagros Basin) that was created on the Arabian shelf as a result of the collide of Arabian and Eurasian plates. The impact of the Abu-Jir fault on the formations on both regions of the Euphrates has been determined by observing the changes in thickness and lithofacies of the Euphrates, Jeribe and Fat’ha formations. On the western side, the Euphrates and Fat’ha formations were deposited with a relatively a little thickness, with absence of the Jeribe Formation between them and the top of the Euphrates Formation is above sea level. On the eastern side of the Euphrates River, the three formations were deposited with large thickness as compared to the western side, and the top of the Euphrates Formation is below sea level. This is enough to indicate that the western side was uplifting locally due to the activity of the Abu-Jir Fault as a positive flower structure during Miocene, while the eastern side was subsiding. Abu-Jir fault zone behaves as the basin bounding fault that acted like a growth fault. There are also variations in lithofacies between outcrops within Al-Baghdadi sub-basin as revealed from lateral missing or thinning of some layers.