Imbricate Zone Research Articles

Geochemical characteristics of dolomite: a case study from lower jurassic formations, imbricated zone, Iraqi Kurdistan region

Geochemical characteristics of dolomite: a case study from lower jurassic formations, imbricated zone, Iraqi Kurdistan region

High-P metamorphism in the Mesoproterozoic: Petrochronological insights from the Grenville Province

In the Grenville Province, high-P rocks that are discontinuously exposed along the margin of the allochthonous belt preserve the record of deep crustal processes and are an essential puzzle piece to understanding Mesoproterozoic geodynamics. The Manicouagan Imbricate zone (MIZ) is one of the three high-P domains from the Grenville Province. It is located in the Central Grenville between the Parautochthonous Belt to the North and the orogenic hinterland to the South, that were metamorphosed during the 1005–980 Ma Rigolet and 1080–1020 Ma Ottawan orogenic phases, respectively. In the western MIZ, the Lelukuau Terrane (LT) mostly consists of Labradorian-age (∼1650 Ma) mafic suites with a fringe of aluminous rocks at its southern edge. Metamafic samples from the Western and Eastern parts of the MIZ display a peak assemblage of garnet, clinopyroxene, plagioclase, rare pargasite or edenite, and quartz ± kyanite. Pseudosection modelling suggests high-P granulite peak conditions at ca. 14 to 16 kbar and 800–900 °C, with the scarcity of hydrous phases and quartz explaining the lack of evidence for partial melting. Zircon cores from the Western LT sample show a maximum magmatic age of ca 1.6 Ga. Lu–Hf and Sm–Nd dating on garnet from this sample yield ages of 1020 ± 7 Ma and 1005 ± 13 Ma, respectively, overlapping within error and inferred to represent peak metamorphic conditions followed by fast cooling. In the Eastern LT sample, garnet Lu–Hf dating yields two ages that are consistent with a petrographically preserved two stage growth, at 1033 ± 6 Ma and 1013 ± 6 Ma, while the Sm–Nd age indicates cooling at 1003 ± 8 Ma. The recorded high-P granulite facies conditions highlight a late Ottawan to Rigolet-age localized crustal thickening at the margin of the hinterland during the propagation of the orogen to the NW, with a possible younging of the high-P granulite-facies metamorphism from the Eastern to Western LT. These new results indicate that the high-P belt in the Central Grenville does not represent the exhumed base of an Ottawan age orogenic plateau, as previously proposed, and that no tectonic hiatus exists between the two orogenic phases, as generally thought. Finally, this publication highlights the diversity and diachronicity of the high-P domains in the Grenville Province.

Metamorphic Evolution of the Garnet Amphibolite Schist from Mawat Ophiolite, Kurdistan Region, Northeast Iraq: Geochemistry, Mineral Chemistry and Thermodynamic Approach

The garnet amphibolite schist is associated with the gabbroic unit of the Mawat ophiolite, Kurdistan region, Northeast Iraq, in the imbricated zone of the Zagros orogenic belt. Field observation, petrographic study, mineral chemistry, geochemical data, and thermodynamic modeling were used to demonstrate mineral identification, predict the observed stable mineral assemblages, and validate the protolith. The mineral assemblages of prograde are garnet (pyrope-almandine), chlorite (clinochlore), amphibole (grunerite), plagioclase (anorthite), iron oxides while the garnet (almandine-pyrope), chlorite (chamosite), amphibole (cummingtonite), and iron oxide represent retrograde assemblage. The relict pod of metagabbro in the center of the garnet amphibolite schist body consists mainly of plagioclase, amphibole, pyroxene, and iron oxide. Geochemical data reveals that the rock is depleted in SiO2 and CaO and enriched in refractory elements compared to the metagabbro. This may be attributed to the generation of silicic melts by partial melting and producing nearby plagiogranite. The rare earth elements (REE) patterns show that the garnet amphibolite schist is depleted in light rare earth elements (LREE) and gradually enriched in heavy rare earth elements (HREE). Thermodynamic modeling, field observation, combined with petrographic study constrains two metamorphic stages and one possible anticlockwise P-T-t path for garnet amphibolite schist, with increasing pressure and temperature of gabbroic rocks units of Mawat ophiolite. The rocks reached peak metamorphic conditions at more than 800 °C and 8–10 kbar, which partially melted the rock produced prograde resitite and melt. Later, the resitite rock retrograded to the lower stage at temperatures ranging from 620 to 650 °C and pressures ranging from 6.5 to 6.8 kbar. Anticlockwise P-T-t paths suggested based on geochemical and thermodynamic data for garnet amphibolite schist of the Mawat ophiolite. Moreover, the gabbro is considered to be the protolith of garnet amphibolite schist, which have been undergone eclogite facies metamorphism later overprinted by amphibolite facies.

Petrography and Geochemical Relationships of the Ultramafic Rocks in Galalah area within Erbil Governorate, NE Iraq

The current research to study the petrography, mineralogy and geochemical relationships of the ultramafic rocks in the Galalah area within Erbil Governorate, at the Unstable Shelf in the Imbricate Zone, to determine the origin of the ultramafic rocks. Dunite and Harzburgite are the most abundant rock bodies in the study area, and they represent most of the outer surface exposure of the ultramafic rock aggregates. The dunite rocks are characterized by pale brown color on the altered surface that is broken into olive green and dark green lithic. Dunite represents a homogenous lithologic feature that mainly consists predominately of olivine with accessory spinel and traces of orthopyroxene. While the harzburgite appears as a massive rock body consisting of olivine, orthopyroxene, and clinopyroxene. These rocks are mainly characterized by alteration to serpentinite, with accessory chromian spinel, secondary magnetite, chlorite, and talc. The studied ultramafic rocks are predominately rich in ferromagnesian minerals of less silica content, and other major elements affected by serpentinization are causing the deviation of elements. They have a strong decrease in sodium and calcium oxides relative to MgO and verified the silica and alumina with MgO and a slight increase in iron oxide. The low values of TiO2 in dunite and harzburgite are characteristic property of the Alpine type ophiolites during the primary process of the mantle in its upper part, before the tectonic emplacement of the ultramafic rocks, and also due to partial melting degree for the asthenospheric mantle. The MREE depletion relative to HREE and LREE may be attributed to the hornblende absence and the presence of olivine and pyroxenes minerals and/or to the source rock features. The U-shaped patterns of REE and their ratios are typical properties of ophiolitic ultramafic rocks, which are compatible with the supra-subduction zone. During the partial melting, the negative anomalies of Nb in ultramafic rocks with sequestration of the Nb concentration by sphene and ilmenite in various types of the source rocks have also been attributed to the crust contamination. These are also characterized by island arc conditions, and its depletion in the studied rocks may indicate the fore-arc tectonic environments

Geology of recently recognized lithologies inside the Red Bed Series in the Chwarta-Mawat area, Kurdistan Region, NE-Iraq

The sequence of the coastal siliciclastic facies of the Paleocene-Eocene Zagros Foreland Basin is well exposed in the Chwarta-Mawat area, north of Sulaimani Governorate, northeastern Iraq. According to previous studies, this sequence is designated as Red Beds Series (RBS), consisting of more than 2000 m of fine and coarse red and grey clastics. The present study found recently recognized lithologies (RRLs) about 100 thick inside the series and encompassed green marlstone with subsidiary detrital limestone which has significant tectonic and paleogeographic results. The petrography, biostratigraphy, and boundary conditions studies are applied to uncover their origin. The new lithologies are deposited in the subsiding basin in the Imbricate Zone during the Middle Eocene. During this age, the Tertiary Foreland Basin was separated by a paleohigh into two basins, (northern and southern basins). In the northern basin, the RRLs have deposited as deep facies of the Naopurdan Formation while in the southern basin the Pila Spi Formation was deposited as lagoonal facies. The former formation was deposited as reefal facies in the shelf area of the northern basin to the northeast Chawrta and Mawat Towns. The RRLs, units one and two of the series (in the Thrust Zone) are correlated respectively with Pila Spi, Sinjar and Gercus formations in the High Folded Zone. These correlations are shown on the stratigraphic columns and paleogeographic models with the aid of nannofossil and benthonic foraminiferal studies. This study is the most important step for solving the tectonic and paleogeographic setting of northeastern Iraq and for a better understanding of the Zagros Collisional belt.

Neo-Tectonism and Quantitative Morphotectonic Analysis of Roste Valley at Imbricated-Suture Zones, Kurdistan Region, Iraq

The morphotectonic analysis was done of the Roste valley, within the Imbricated and Suture zone of the Zagros Fold,Thrust Belt. The formations of the Imbricate Zone are of Jurassic and Cretaceous ages and the Suture Zone is covered by Zagros nappes of the Tertiary period. The Zagros Fold-Thrust Belt passes through several stages and tectonic phases. During the last stage of the Zagros Fold-Thrust Belt development from the Savian to Valahian and Pasadenian tectonic phases, the study area is influenced by active tectonic activity which is reflected by geomorphic properties in each subbasin. The migration of the Roste stream across oblique fault leaves 7 levels of the river terraces which are also signs of Neotectonics. The study area is divided into 18 subbasins for the morphotectonic analysis through applying geomorphic indices (HI, SL, Vf, Af, Smf, and Bs) and accordingly the index of relative active tectonics was indicted. The morphotectonic study reveals that the index of relative active tectonics is higher in the Suture Zone than in the Imbricated Zone. The index of relative active tectonics of the Suture Zone’s subbasins ranges from high to very high neotectonics activity (1.67-1.17), whereas of the Imbricate Zone’s subbasins ranges from medium to high active tectonic activity (2.33-1.67). The results are related to morphotectonic indices that show the balance between the tectonic and erosion process.

Stratigraphy and Mineralogy of Balambo Formation (Aptian - Cenomanian) near Chomabrok village, Imbrication Zone, Iraqi Kurdistan Region

The stratigraphy and mineralogy of Balambo Formation (Aptian - Cenomanian) in exposed surface section near Chomabrok village in the Imbrication zone, northeastern Iraq is studied. The Formation is 450 meters thick and consists of thin to medium to thick bedded yellowish-brown, and black to dark gray limestones, marly limestones, with thin- medium bedded, grayish - black marl and shale, with thin bands of black cherts and abundant nodules and lenses. From the field observations and petrographic studies, the formation mainly made from two main lithofacies types; marly limestone-marl lithofacies and cherty limestone lithofacies. The petrographic study of carbonate rocks deepened on 79 thin sections and demonstrated that the carbonates of Balambo Formation composed of micrite ground mass with abundant skeletal grains; planktonic and some benthic foraminifera, radiolaria, calcisphere, ostracods, pelecypods, larva-ammonoids, small-brachiopods, sponge spicules, echinoid spines, and bioclasts. Non-skeletal grains include peloids only. Using extraction method and according to an assessment of foraminiferal assemblages and based on the defined planktonic foraminifera the assigned age of Balambo Formation in the studied section is Aptian to Cenomanian as upper Balambo age. The results of X-ray diffraction (XRD) analysis for bulk mineralogy of selected shale and marl samples suggested the presence of phyllosilicate with abundant calcite, common quartz, and moderate Fluorapatite with minor dolomite content. Illite is the dominant clay mineral in the Balambo Formation and indicates a hot, arid climate during most of the Cretaceous period in the Imbrication zone, Northeastern Iraq.

Paleoecology and Depositional Environment of the Govanda Formation in the Kurdistan region, northeast of Iraq

The Govanda Formation was deposited during the Early-Middle Miocene Epoch in the intermountain areas between Zagros Suture and Imbricate zones. The Paleoecology and depositional environment of the Govanda Formation has been studied in detail in Mergasor and Penjwen districts for the first time. The formation in these two sections from bottom to top is comprised of thick bedded, oyster and chert bearing conglomerate, pebbly sandstone, red-brown shale and siltstone, fossiliferous limestone and detrital limestone. The formation in Mergasor, Beshkariya Village is 85 m thick and in Penjwen, Gole Village is 60 m thick. The study is based on the detailed microscopic analysis on the benthic and planktonic foraminifera with miscellaneous fossils that exists in the carbonate rocks of the Govanda Formation. Larger and smaller benthic foraminifera include the following genera: Operculina sp., Borelis melo sp., Austrotrilina sp., Peneroplis sp., Meanderopsina sp., Miogypsinoids and Miogypsina sp., Archaias sp., Amphistegina sp., Textularia sp., Lepidocyclina sp., Miliolids, Quenquiloculina sp., Pyrgo sp., Spiroloculina sp., Triloculina sp., Ammonia sp., Elphidium sp., Dendritina sp. and Rotalia venoti dominated the limestones of the Govanda Formation. Planktonic foraminifers are mostly includes the following genera: Globigerinoids sp., Globigerina sp., Globorotalia sp. and Orbulina sp. Moreover, miscellaneous fossils include corals, coralline red algae, echinoderms, bivalves, ostracods, bryozoans, brachiopods and serpulid worms (Ditrupa sp.). The paleoecological condition of the formation was interpreted as follow; the temperature of the Govanda basin ranges between 15-30 °C, nutrient level is between eutrophic to mesotrophic, salinity ranged between normal saline to hypersaline water, light intensity ranging from euphotic to mesophotic and less oligophotic zones, the water depths ranged between 0-120 m, the clastic influx was high in the basin, differences in size and shape within foraminifers of the Govanda Formation indicate various depositional environments and ecological conditions, the water energy was moderate. The environment of deposition is interpreted as being ramp environment. Depending on the different microfauna that exist in the formation, four main zones are distinguished in the ramp model of the Govanda Formation as follows; proximal inner ramp setting which includes open lagoon, distal inner ramp setting which includes back-reef environment, proximal middle ramp setting which includes reef and fore-reef environments, distal middle ramp/ proximal outer ramp setting, which includes open marine environment.

The distinct morphologic signature of underplating and seamounts in accretionary prisms, insights from thermomechanical modeling applied to Coastal Iranian Makran

The active structures of the Iranian Makran, especially the presence of normal faults, vary laterally in the upper plate of the subduction zone, and their relationship with the deep duplexes and seamounts at depth remains unknown due to poor coverage of data onshore. In this paper, we investigate the relationship between deep structures and the topographic slope using thermo-mechanical simulations. The initial and boundary conditions of the models, including basal heat flux and convergence rate, are calibrated using the depth of the seafloor, bottom seafloor reflectors and the few available well temperature. We specifically test the influence of seamount subduction and thermally controlled changes in rock strength and décollement on the relationship between topography and deep tectonic structures. The inclusion of the brittle-ductile transition and dehydration reactions like the smectite-illite transition produce the three slope segments observed in the Makran accretionary prism. The three segments correspond to a regular accretionary prism, a flat segment that marks the smectite-illite transition, and a rise in topography located above the zone where the tegument reaches its temperature-controlled brittle-ductile transition causing underplating. Nevertheless, the models show that neither the decrease in friction associated with dehydration nor the onset of underplating is sufficient for the observed normal faults to arise in a self-consistent manner from the simulations. Crustal-scale normal faults only emerge in simulations that include subduction of a large seamount. These simulations also produce a large-thrust-slice that is the scar of former subducting seamount and serves as a buttress for the formation of a new imbricated zone. Using offshore seismic reflection data, the published onshore tomographic profiles, and our thermo-mechanical simulations, we propose two onshore-offshore cross-sections of the Iranian Makran accretionary prism.

Deformation induced decoupling between U-Pb and trace elements in titanite revealed through petrochronology and study of localized deformation

In this contribution, we analyzed a pair of mafic samples collected from a recently identified shear zone and its proximal footwall from the Manicouagan Imbricate Zone (MIZ) of the central Grenville Province, Québec, Canada. Titanite petrochronology, metamorphic phase equilibria modelling, trace element thermometry, and electron backscattered diffraction data were used to define a Pressure-Temperature-time-Deformation path for the two samples. An interconnected dislocation network within titanite grains, as outlined with Kerneled Average Misorientation maps, are spatially correlated with variation in the U-Pb system but not with that observed for trace element These results suggest that the U-Pb system was decoupled from trace and rare earth elements and that deformation, rather than interface-coupled dissolution-precipitation reactions or re-crystallisation, was the main driver for this decoupling. In addition to highlighting a potential pitfall of titanite petrochronology, our P-T-t-D path reveals that ductile shear zones were active later than previously suggested within the MIZ.

Revised planktic foraminiferal biostratigraphy of the early late Albian of northern Tunisia (southern Tethys)

The upper Albian exposed near the Imbrication Zone of northern Tunisia is composed of a pelagic sequence that includes organic-rich beds. High-resolution biostratigraphy based on planktic foraminiferal bioevents across marker beds (i.e., organic-rich beds), allows revision of the lithostratigraphic subdivision and zonal scheme in comparison with late Albian time equivalents recorded in the northern Tethyan margins. In the present study, we proposed a new subdivision of the upper Albian lithostratigraphic section that now includes the Mellegue horizon as an equivalent of theAmadeus Segment rhythmic marl/limestone interval (central Italy). Three studied sections are subdivided into five biozones with the abundance and morphological trends of planktic foraminifera and inferred paleoenvironments: 1) The Biticinella breggiensis Total Range Zone is characterized by the appearance of ticinellids with pinched chambers (i,e., Ticinella praeticinensis) and is recorded a few meters above the first occurrence of Biticinella breggiensis. Agradual increase of trochospiral thick-walled (B. breggiensis, T. roberti, T. raynaudi) and Globigerinelloides taxa, reflecting mesotrophic conditions. 2) The Pseudothalmanninella subticinensis Interval Zone includes the first appearance of keeled forms (Ps.subticinensis), associated with abundant ticinellids with flattened chambers (B.breggiensis, T. roberti) below the base of the organic-rich Mellegue horizon, indicating an oligotrophic environment. 3) The Pseudothalmanninella ticinensis Interval Zone. The continuous occurrence of T. primula and the scarcity of Globigerinelloides throughout the lower part of this zone indicates an oligotrophic to weakly mesotrophic environment. The occurrences of radiolarian-rich horizons and abundant forms with elongated chambers (T. raynaudi) in the lower part of this zone indicate an abrupt shift to enhanced eutrophic and dysaerobic conditions. 4) The Thalmanninella appenninica Zone, which shows a decrease in abundance preceding the extinction of ticinellids, and a gradually increasing number of specialized keeled forms (i.e., Th. appenninica), indicates oligotrophic conditions. 5) The Planomalina buxtorfi Total Range Zone is characterized in its lower part by an increasing abundance of clavate forms with radially elongated chambers (i.e., Clavihedbergella) above the organic-rich bed of the Mouelha Member, indicating low-oxygen, oligotrophic to mesotrophic conditions.

The Role of Heavy Minerals in Understanding the Provenance of Sandstone: An Example from the Upper Cretaceous Tanjero Formation, Surdash Region, Northeastern Iraq

The Tanjero Formation is the Upper Cretaceous (Campanian-Maastrichtian) crops out in northeastern Iraq at the High-Folded and Imbricate Zones. To study heavy minerals, twenty sandstone samples were obtained from selected sites of the Tanjero Formation exposed at the southwestern limb of the Surdash anticline in the northeast part of Sulaimanyia city. The analyzed data indicates that the most abundant heavy minerals are opaque, followed by pyroxene, epidote, amphibole, chlorite, rutile, and garnet. The significant abundance of unstable and metastable minerals in the heavy mineral suites shows their direct derivation from the adjacent main basic igneous and metamorphic source rocks, which are situated in the High-Folded and Imbricate Zones in the northern and northeastern parts of Iraq. The estimated zircon-tourmaline-rutile index reveals that the majority of the sandstone samples have less than 75% zircon-tourmaline-rutile index, indicating that the sediments are generally immature. Furthermore, the relationship between an ultra-stable and a meta-stable heavy mineral indicated the immaturity of the Tanjero Formation sandstone and its moderate stability, proving that these minerals cannot be transported over extremely long distances close to the source rocks area. The heavy mineral assemblage demonstrated that the studied area is distinguished by high tectonic activity. In addition, according to the MF- MT-GM ternary diagram, the analyzed sandstone samples lie within the active continental margins field, which is distinguished by a higher percentage of MF minerals than GM minerals generated from mafic magmatic source rocks.

First record of the brachiopod Erymnaria in the Chruteren Member (Euthal Formation) from a new Palaeogene site in the Br\xfclisau Schuppenzone of northeastern Switzerland (Canton St. Gallen) with remarks on shell asymmetry

A small, smooth-shelled rhynchonellid brachiopod, Erymnaria Cooper, 1959 was discovered in a previously unknown locality in the so-called Brülisau Schuppenzone (imbricate zone) of the South Helvetic region of northeastern Switzerland. It is the first record of this genus in this region and in Switzerland in general. It is comparable to the type species of Erymnaria, E. polymorpha (Massalongo, 1850). Its specific identity is currently undetermined, and the species is referred to Erymnaria sp. 1. The main characteristic of Erymnaria sp.1 is its asymmetric shell. This prompted a comparison of E. sp. 1 with other known asymmetric brachiopods. Questions of asymmetry and variability within the same genus and with brachiopods in general are discussed. Another, larger brachiopod species found at the new site is tentatively named Erymnaria? sp. 2. The site can be assigned to the Chruteren Member (Euthal Formation) of Early Ypresian age, dated by large Foraminifera. Thus, the previous distribution area of the Chruteren Member can be extended.

Field Description and Lithostratigraphic Study of Sargelu Formation in Rania and Sargelu sections, Northern Iraq

The Sargule Formation was deposited during the Middle Jurassic, representing one of the most important source rocks in Iraq and surrounding areas.
 Jurassic successions are commonly exposed as an isolated patch at some eroded anticline’s cores and limbs in the High Folded Zone, Imbricate Zone, and Thrust Zones of northern Iraq. The Sargelu section is located in Sargelu village at Surdash anticline, while the Rania section is located in Rania city near Hanjira village at Shaweri anticline. Fieldwork in Rania and Sargelu Sections allow to divide Sargelu Formation lithostratigraphically into many subdivisions as follow:
 The Sargelu Formation in the Rania section is about 40 m and can be divided into two lithologic units; the upper thin to medium bituminous limestone beds alternated with thin chert beds, and the lower thin to medium bituminous limestone beds alternated with fissile gray shale beds.
 the The Sargelu section comprises 180m and is divided into three units; the upper unit consists of dark gray limestone beds and thin brownish-black of laminated shale. The middle unit includes dark chert alternated with dark gray bituminous limestone and brownish-black laminated shale. At the same time, the lower unit consists of dark gray bituminous limestone beds alternated with medium brownish-black laminated shale beds.

Petrography and geochemistry of sandstones from the Injana Formation, Hemrin South Mountain, Northern Iraq: Implications for provenance, weathering and tectonic setting

The sandstones of Upper Miocene Injana Formation were studied petrographically and geochemically in the Hemrin South Mountain area, northern Iraq. The sandstones vary between arkose and lithic arkose in composition (Q50F24L26) and are compositionally and texturally immature; meanwhile, the Log(Fe2O3/K2O)–Log(SiO2/Al2O3) diagram shows that they are divided between arkose, litharenite and wacke. These sandstones contain a wide spectrum of heavy minerals ranging from the most resistant ultrastable minerals (zircon, rutile and tourmaline), to the least resistant non‐stable minerals (amphiboles and pyroxenes). The provenance indicator diagrams QmFLt and QtFL indicate multi‐sources for these sandstones ranging from transitional craton, arc and recycled sediments. The major element provenance discriminant function plot shows that they are derived mostly from intermediate igneous provenance. All these suggest that the probable source of these sandstones is the igneous‐metamorphic rocks including the ophiolites of the Suture Zone, the imbricate zone, the Shalair‐Sanandaj‐Sirjan Terrane and the complimentary rock units in Turkey and Iran. The presence of glaucophane as the provenance indicator mineral for subduction zones is a further proof of the ophiolites having acted as the source rocks. Geochemically, the sandstones are enriched in Ca, V, Cr, Ni, Cu, Mo, Sn and Sb and depleted in all othe major, trace and rare earth elements (REE) relative to upper continental crust (UCC). The chondrite‐normalized REE pattern shows a distinct negative slope for the LREEs and a slight negative slope for the HREEs with an enrichment of LREE/HREE of 8.11–10.90 and a negative Eu anomaly of 0.70–0.83. The most probable source of REEs is the heavy minerals detected in the sandstones. Tectonically, the studied rocks were derived from collision rifting arc–related settings. The Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA) and Index of Composition Variation (ICV) values of the Injana sandstones suggest that they are compositionally immature and suffered from very weak weathering indicating the proximity of their source rocks and their deposition under dry continental conditions.

Brittle tectonics in the western Arunachal Himalayan frontal fold belt, northeast India: Change in stress regime from pre‐collisional extension to collisional compression

The study of brittle deformation of the collisional mountains can explain its shallow crustal tectonic evolution and the palaeostress regime. The Main Boundary Thrust (MBT) zone in the western Arunachal Himalaya displays imbrication in the Permian Gondwana sequence between the MBT‐1 (/Bome Thrust/MBT‐Upper) in the north and MBT‐2 (/MBT‐Lower) in the south with consistent northerly dip. The Lower Gondwana rocks occur in the footwall of the MBT‐1 with the Proterozoic Bomdila Group in the hangingwall. The upper Gondwana rocks constitute the hangingwall sequence for the MBT‐2 with Neogene Siwalik rocks in the footwall. This article analyses palaeostress using brittle fractures in the Gondwana rocks that crop out for ~120 km2 in the study area. The fault‐bounded imbricate zone depicts eight brittle shear indicators and four sets of joints (J1 and J2: inclined and J3 and J4: subvertical). The signatures of the inherited pre‐Himalayan extensional deformation are preserved in the Lower Gondwana Miri Formation. The Bichom and Bhareli rocks exhibit brittle deformation features of the Himalayan Orogeny under strong ~N‐S compression. The palaeostress analysis of all joint sets indicates three phases of brittle deformation in the Gondwana and Siwalik rocks of the area. The subvertical joint sets and normal faults in the Miri Formation indicate a north‐northwest (NNW)‐directed extensional phase of the pre‐Himalayan origin. The inclined joint sets of the Bichom and Bhareli formations of the Gondwana sequence depict Himalayan orogeny with ~N‐S compressional phases. The third phase of brittle deformation in the Siwalik sequence depicts an east‐west (~E‐W) extension. The arc‐parallel extension in the frontal fold belt of the Arunachal Himalaya may be due to oblique India‐Asia collisional tectonics.

Growth of the imbrication zone along the southeast Anatolian orogenic belt: evidencefrom fission track thermochronology from Gölbaşı region (SE Turkey)

One of the major components of continental collision zones is their imbricated zones. Such a zone along the Southeast Anatolian Orogenic Belt (SAOB) is solely controlled by a still-active convergence and accretion system between the Anatolian Plate and Arabian platform since at least Late Cretaceous. The zone is characterized by NEE/SWW-trending, northward-dipping thrust slices that are squeezed between the Tauride Block to the north and the Arabian platform to the south. The units cropping out within the zone comprise Neo-Tethysrelated magmatic, ophiolitic, sedimentary and metamorphic rocks with Late Cretaceous to Miocene formation/metamorphism ages. The Karanlıkdere granitoid intrudes into Late Cretaceous Meydan ophiolite, Helete volcanics, and Malatya metamorphics. These units thrust over Cenozoic volcanic and sedimentary rocks. Although various scenarios have been proposed for the late Cretaceous to Neogene evolution of the complex region, quantitative data aiming to understand the growth mechanism of the imbrication zone in the region are limited. The zircon U-Pb and the apatite fission track (AFT) thermochronology were applied to the Karanlıkdere granitoid within the imbrication zone of the Southeast Anatolian Orogenic Belt (SAOB). The LA-ICP-MS zircon U-Pb age yields 79.67 ± 0.24 Ma with 0.23?0.65 Th/U ratios. This age is slightly younger than the previously published ages, indicating that the main body of the Karanlıkdere granitoid formed 3-4 Ma later than the small dikes intruded into other units. The AFT ages are directly controlled by altitude and range between 40.38 ± 3.4 Ma and 22.81 ± 0.63 Ma. The oldest AFT age has the highest altitude, whereas the youngest has the lowest height. The age-temperature models show a slow uplift rate between 40 Ma and 22 Ma. The results indicate that the growth of the imbrication zone in front of the Nappes of the SAOB continued in a steady-state mode with a slow uplift rate of 0.02 ± 0.005 mm/a, during middle-late Eocene to early Miocene and increasing uplift rate during early-middle Miocene, which might be explained by continental collision during early-middle Miocene.

Determining the tempo of exhumation in the eastern Himalaya: Part 1. Geometry, kinematics and predicted cooling ages

AbstractQuantitative integration of cross‐section geometry, kinematics and cooling ages requires notably more complicated kinematic and exhumation pathways than are typically assumed with a simple in‐sequence model of cross‐section deformation. Incorporating measured basin thickness and depositional ages, determined from magnetostratigraphy or young detrital zircon fission track cooling ages, provide further constraints on the timing of fault motion, as changes in shortening rate that may not alter bedrock cooling ages can affect the depositional age of foreland basin strata. Thermokinematic models of balanced cross‐sections in Arunachal Pradesh, NE India demonstrate that the kinematic sequence and shortening rate exert the largest control over the pattern of predicted cooling ages for the region, by dictating the location and timing of rock uplift and exhumation (cooling) over ramps. The best fit to the measured bedrock cooling ages and basin constraints is achieved with a kinematic sequence involving early foreland propagation of four Lesser Himalayan faults combined with variable shortening rates. Fast rates (25–30 mm/yr) are required to accompany early foreland propagation at ca. 14–13 Ma followed by slower rates (18–20 mm/yr) until 10 Ma. Shortening rates increase to ca. 25–35 mm/yr at ca. 10 Ma until ca. 5–7 Ma. A decrease in shortening rate occurs between 7 and 5 Ma, with rates of 9–15 mm/yr until the present. Although non‐unique, the updated cross‐section geometry and kinematics highlight the components of geometry, deformation and exhumation that must be included in any valid cross‐section model for this portion of the eastern Himalaya such as the location of active ramps, and location and age of two key fault systems, the Bomdila imbricate zone and the thrust faults that form the Lumla duplex. Less unique are the specific geometries of faults, thickness of strata they carry, shortening rates, particularly between 14–8 Ma, and model parameters such as topography, heat production and flexure.

Stratigraphy, Geometry, and pattern of Imbricated zones, NW Zagros Fold and Thrust Belt in Iraqi Kurdistan Region

The High Folded and Imbricated zones are the formalized name represent the part of the Tectonic sub-division of Iraq and Kurdistan Region of Iraq (KRI). The study of compressional deformation and Stratigraphy are the keys to identify thrust faults structures and define the sequence of thrusting in High Folded and Imbrication zones as a part of Zagros Fold and Thrust Belts. Through this study, we try to describe the compressional thrust faults and stratigraphical unit description. Thrust faults make repetition of the sequences of Jurassic-Triassic Cretaceous sequence over thrust above Cretaceous sequences. In Iran-Iraq border close to Sirwan valley the large thrust faults (Sirwan-Sazan Thrust faults) identify. The fault system makes Triassic formations over-thrust the Valanginian-Albian Balambo Formations. In Balakayati area serious thrust fault exists, which creates twice repetition of Jurassic-Cretaceous formations forming imbrication thrusting system and fault propagation fold. In Bradost-Korek anticlines the Jurassic-Cretaceous formations over-thrust Cenozoic formations. In Kamosk anticline the thrust faults are in the Cretaceous formations. The dimension and the style of the thrust faults are different but generally, most of the decollement layers of the thrusting are the Early Triassic and Middle-Late Jurassic formations. The collection of all these results constrain geological cross-section in Imbricate Zone and restore to obtain the 7.5 km distance of Shortening due to folding and faulting.

Revised tectonostratigraphy and structural evolution of the Köli Nappe Complex, Central Caledonides in Nordland, Norway

The nappe stack in the Røssvatnet–Hattfjelldal region in the Central Norwegian Caledonides consists of seven nappes formed at the boundary between tectonostratigraphically upper and uppermost Caledonian levels. The rocks of all nappes share a polyphase tectonometamorphic evolution that is younger than the 491 ± 10 Ma depositional (volcanic) age of parts of the succession. Early stages of deformation characterized by centimetre- to kilometre-scale folding and intense shearing accompanied by greenschist to amphibolite facies peak metamorphism are correlated with the Early Ordovician Taconian accretionary orogeny along the Laurentian margin. The Taconian structures are cut by the Krutfjellet gabbro and diorite, which yield U–Pb zircon ages of 446 ± 5 and 444 ± 4 Ma, respectively. Large-scale nappe stacking and folding post-dating the emplacement of the gabbro is related to the collision of Laurentia with Baltica (Scandian orogeny) and was followed by late- to post-orogenic extension. The revised tectonostratigraphy assigns the structurally higher nappes to the Uppermost Allochthon, whereas the lower nappes are correlated with the Middle Köli Nappe Complex (Upper Allochthon). The boundary between these nappes is marked by an imbricate zone. Taconian deformation was probably much more penetrative and widespread than hitherto thought and therefore parts of the nappe stack were probably assembled before Scandian collision. Supplementary material: Electronic Supplement 1: U–Pb zircon data and Electronic Supplement 2: Methods (laser ablation inductively coupled plasma mass spectrometry U–Pb zircon geochronology) are available at https://doi.org/10.6084/m9.figshare.c.5357255