Adjacent Tectonic Units Research Articles

Fine Crust‐Mantle Structure of the Major Tectonic Boundaries Between the North China Craton and Central Asian Orogenic Belt Revealed From Rayleigh Wave Phase Velocities and Receiver Functions

AbstractThe Tanlu Fault Zone (TLFZ) and Chifeng‐Kaiyuan Fault (CKF) serve as tectonic boundaries between the North China Craton (NCC) and the Central Asian Orogenic Belt (CAOB). Clarifying the refined structure of these tectonic boundaries is crucial for understanding the relationships between the tectonic units and the heterogeneity in the destruction of the NCC. In this study, two linear seismic arrays were deployed across these tectonic boundaries. Based on the phase velocity dispersion and receiver functions extracted from the seismic arrays, the Hamiltonian Monte Carlo algorithm was employed for the joint inversion of the S‐wave velocity (Vs) in the crust and uppermost mantle. The Vs model was then used to correct the time differences in common conversion point (CCP) stacking. The CCP stacking results indicate that the boundary faults TLFZ and CKF are both whole‐crustal faults that separate the NCC and CAOB. The Vs structure showed a significant low‐velocity anomaly in the mantle beneath the NCC, with intense seismic activity within the crust. This suggests that the NCC was affected by the subduction of the Western Pacific, leading to crustal and mantle destruction. In contrast, the CAOB exhibited a clear high‐velocity anomaly with relatively stable crustal structures. We believe that the NCC and CAOB have undergone structural modification and destruction due to the closure of the Paleo‐Asian Ocean and the activities of the TLFZ since the Late Mesozoic. During the Cenozoic, the region east of the TLFZ experienced more significant destruction in the NCC than the other adjacent tectonic units.

Neotectonic Fault Pattern of the Salair Area (Southern West Siberia): Relation with the Pre-Cenozoic Tectonic Framework

Abstract —Neotectonic activity in the area of the Salair Ridge (southern West Siberia) rejuvenated a system of large arc-shaped faults separating the Salair tectonic arc from the adjacent tectonic units. These regional faults, which make up the general tectonic framework of the Altai–Sayan Folded Area, originated in the late Paleozoic and were repeatedly reactivated in the Mesozoic. The deformation within the major Salair thrust sheet is mainly brittle and follows small fault planes that crosscut the margins of Paleozoic thrusts. The neotectonic faulting has controlled the erosion pattern of the territory and produced a reticulate drainage system. The Salair tectonic unit is a single 80 × 250 km block consisting of multiple neotectonic blocks, with relative vertical offset no more than 100 m in the block interior and 100–200 m in its southern, northern, and eastern borders. The northwestern and southeastern border faults have reverse slip geometry, while the motions on the en-echelon northeastern fault boundary include reverse and right-lateral strike-slip components. The thickness of the Salair thrust sheet estimated from magnetotelluric (MT) data increases in the western direction from 5 to 15 km in the northern block part and from 10 to >20 km in the south. The allochthon base is delineated by a low-resistivity zone interpreted as a horizontal detachment. This boundary formed in the Mesozoic and was rejuvenated at the neotectonic stage. The lithology and deformation of Jurassic sediments filling piedmont basins around the Salair Ridge indicate that the Cenozoic fault pattern generally inherits the Mesozoic framework but differs in about ten times smaller vertical offset.

A multi-scale 3-D crust velocity model in the Hefei-Chao Lake area around the southern segment of Tanlu Fault Zone

Regional high-precision velocity models of the crust are an important foundation for examining seismic activity, seismogenic environments, and disaster distribution characteristics. The Hefei-Chao Lake area contains the main geological units of Hefei Basin, with thick sediments and the Chao Lake depression. Several major concealed faults of the southern NNE-trending Tanlu Fault Zone cross this area. To further explore the underground distribution characteristics of the faults and their tectonic evolutionary relationship with adjacent tectonic units, this study used ambient noise data recorded by a seismic array deployed in Hefei City and Chao Lake, constructing a 3-D velocity model at the depth of 1–8 km. Then a multi-scale high-resolution 3-D velocity model of this area was constructed by this new upper crustal velocity model with the previous middle and lower crustal model. The new model reveals that a high-velocity belt is highly consistent with the strike of the Tanlu Fault Zone, and a low-velocity sedimentary characteristic is consistent with the Hefei Basin and Chao Lake depression. The distribution morphology of high and low velocity bodies shows that the sedimentary pattern of Hefei-Chao Lake area is closely related to the tectonic evolution of the Tanlu Fault Zone since the Mesozoic. This study also identifies multiple low-velocity anomalies in the southeastern Hefei City. We speculate that strong ground motion during the 2009 Feidong earthquake (magnitude of 3.5) was related to amplification by the thick sediments in the Hefei Basin. We also discuss further applications of multi-scale high-resolution models of the shallow layer to strong ground motion simulations in cities and for earthquake disaster assessments.

Upper crustal Poisson’s ratio and coda-wave attenuation beneath Eastern Anatolia

The attenuation of seismic waves reflects the elastic nature of the media within which the waves propagate. In this study, we calculate the Coda-Q (Qc), frequency dependence (η), Vp/Vs and Poisson’s (υ) ratios by using 2621 vertical component seismograms generated by 987 earthquakes recorded by 13 seismic stations in Eastern Anatolia, and creat a 2-D seismic tomographic Qc model for the region. The obtained model provides significant information for exploring the boundaries of adjacent tectonic units within the upper crust and interpreting their dynamic characteristics. The 2-D Qc model and the other parameters are consistent with the seismotectonic features of Eastern Anatolia. Highly heterogeneous Qc values are observed in the study area dividing it into north-south directed bands of low and high attenuation. The highest η values were obtained beneath the northwestern and eastern parts of the study region. Clear, high and low υ values are obtained in the western and eastern parts of the study area, respectively. The spatial variations in the measured parameters are consistent with many geophysical observations including low Pn velocities, efficient Sn blockage, high heat flow, and widespread volcanism. Different upper crustal thicknesses and inhomogeneous stress distribution along the East and North Anatolian Fault Zones may also contribute to the observed heterogeneities.

Transpressional deformation during Ediacaran accretion of the Paranaguá Terrane, southernmost Ribeira Belt, Western Gondwana

The Paranaguá Terrane is mainly constituted by an Ediacaran arc-related granitic complex, spread in a NE-SW trending elongated stripe, located in the Southern Ribeira Belt, South-Southeastern Brazil. The basement of these granites occurs as a disrupted folded belt composed of metasedimentary and gneissic-migmatitic rocks. The integration of structural and geophysical (gamma spectrometry and magnetometry) data from the Paranaguá Terrane and the adjacent tectonic units, suggests that the deformation in the study area is partially controlled by the geometry of the Luis Alves Cratonic Block, as well as the northern part of Dom Feliciano Belt. The irregular shape of this cratonic unit associated with N-NW tectonic transport direction caused strain partitioning in the area and the development of two structural domains: southern and northern Paranaguá. The southern part is characterized by sinistral transpressional shear zones, while the northern sector is dominated by thrust shear zones that represent a large frontal collision with oblique components. The hierarchy of the structural and microstructural features in the Paranaguá Terrane associated with geochronologic data suggest two deformational phases (D1 and D2) during a transpressive collisional system. The D1 progressive deformational stage is correlated to the main period of granitic crystallization during the Ediacaran and was divided in two moments: i) early D1 (640–610) associated with the regional metamorphism and thrust and folding tectonics with N-NW tectonic transport and; ii) late D1 (610-580 Ma) linked to the strain partitioning and development of the southern (simple-shear dominated) and northern (pure-shear dominated) structural domains with sinistral kinematics, granite emplacement and high-temperature mylonites. The D2 deformation stage (540–500 Ma) is mainly represented by the low-temperature mylonites and deformation under retrograde conditions.

First data of structural-kinematic analysis of rock Rassoha zone and its border (Omuljovka uplift, Eastern Yakutia)

The Omuljovka uplift is located within the inner part of the Verkhoyansk-Kolyma folded system, the South-Eastern part of the Chersky collision belt and extends in the North-Western direction. In the South-West from Omuljovka uplift locates the Inyaly-Debin syncline, in the North, a structure is hidden under the sediments of the Moma-Zyrjanka deflection, in the East borders by Kolyma uplift. In the central part of the Omuljovka uplift allocated Rassokha tectonic zone formed Ordovician, Devonian - early Jurassic volcanogenic and sedimentaryformations. As a result of studying the history of geological development Rassokha zone, recorded in the structural features of its rocks in the northeastern part of Omuljovka uplift, was identified two main types of deformations: early plastic and late fragile. The conclusion about the presence of a few kinds of brittle deformation. Structural researches of rock ophiolite-clastic complex show that multistage deformation has occurred here. Dedicated five stages of deformation process, that match the basic stages of the tectonic evolution of the territory. Conducted structural-geological research and reconstructed of tectonic stress fields are corresponding with the stages of deformation identified by V. Oxman (2000) to the North of the region. Rassokha zone and adjacent tectonic units are unique geological-structural objects, allowing to study the evolution of the Omuljovka uplift because in a small area was identified tectonic structures all stages of deformations that are allocated for the Chersky collision belt. Separately noted the presence of shear-fault deformations in Arga-Tas zone, because with them, most likely associates gold ore deposits of the district. The earliest deformation stage requires further decoding and binding to the time interval.

From mountain summits to roots: Crustal structure of the Eastern Alps and Bohemian Massif along longitude 13.3°E

The crustal structure of the Eastern Alps and adjacent tectonic units investigated in this work sheds new light on the relationship of surface geology to geodynamic processes operating at depth. Of particular interest are the nature of a previously proposed Moho gap south and east of the Tauern Window, the plate tectonic affinity of the steeply dipping Eastern Alpine slab, and the relationship of the Alps to the Neogene sedimentary basins and the Bohemian Massif. To address these questions, we use various seismological approaches based on converted waves from the temporary passive experiment EASI (Eastern Alpine Seismic Investigation), a complementary experiment of the AlpArray project. The EASI is a densely spaced, 540 km long seismic network along 13.3°E we operated for more than a year. The uppermost-crustal structures in and near the Alps exhibit dipping layers and/or tilted anisotropy that correlate well with surface geology observations. The Moho, despite its variable appearance, is clearly identified along most of the swath. The Variscan lithospheric blocks beneath the Bohemian Massif are imaged with sub-vertical boundaries. Beneath the Eastern Alps, the shape of the Moho is consistent with bi-vergent orogenic thickening, with a steeper and deeper-reaching Adriatic plate plunging northwards beneath the European plate in the north. At the junction of these plates at depth, around the previously proposed Moho gap, the root of the Eastern Alps is a broad trough characterized by a zone of low velocity-gradient that is up to 20 km thick, transitioning between crust and mantle. Our receiver-function results corroborate earlier lithosphere-upper mantle seismic tomography images, and highlight the Adriatic affinity of the Eastern Alpine slab. The zigzag deployment pattern of stations in the EASI experiment also allows distinction of short-wavelength variations perpendicular to the profile, both within the shallow and the deep crust. This underlines the importance of applying 3D imaging in complex geodynamic systems.

The Longmenshan Tectonic Complex and adjacent tectonic units in the eastern margin of the Tibetan Plateau: A review

The Longmenshan Tectonic Complex (LSTC), along the eastern margin of the Tibetan Plateau, the site of devastating earthquakes such as the magnitude 8.0 (Wenchuan) earthquake on 12 May 2008, preserves an exceptionally complete history of the tectonic evolution of the Yangtze block and its relations to adjacent tectonic units. Due to sequential tectonic superposition and tectonic reactivation, the tectonic nature of the LSTC, and in particularly the older history, has been profoundly debated and many different tectonic models have been proposed. Herein we summarize the current understandings of the major tectonic events that have shaped this important tectonic complex, highlighting problems left to be solved by future work, including:(1) The nature and constraints for at least 6 regional tectonic events, i.e., building of the metamorphic basement (Art), the Columbia/Nuna supercontinent (Pt1t), the Rodinia supercontinent (Pt3t), the Paleozoic passive continental margin (Pzt), the Paleotethys orogeny (Mzt) and the Neotethys orogeny (Kzt); (2) Metamorphic basement exposures and their tectonic implications, including rock types and geochronological constraints for the Archean, Paleoproterozoic and Neoproterozoic basements; (3) Nature of the present LSTC and its affinity with adjacent tectonic units; (4) Consideration of the NE-striking Longmenshan thrust belt and arcuate-shape Yanyuan-Muli thrust belt as parts of a single tectonic feature; (5) Mountain-basin coupled systems recording past tectonic eposides. We draw the following conclusions and tectonic models based on published research combined with our own recent studies: (1) The well preserved Archean Yudongzi gneiss group in the LSTC has a genetic affinity with the Kongling group, and thus belongs to the Yangtze block; (2) The Paleoproterozoic Hejiayan group, juxtaposed adjacent to the Archean Yudongzi group, may represent a 2000–1800 Ma orogenic belt, which corresponds to the supercontinent Nuna/Columbia amalgamation event; (3) A Neoproterozoic trench-arc-basin system, which is reconstructed based on identification of a Neoproterozoic ophiolite complex, arc-type magmatic rock assemblages and volcaniclastic basinal deposits along the western margin of the Yangtze block and the LSTC, may represent the record of eastward subduction of the Neoproterozoic Mozambique oceanic lithosphere beneath the Yangtze block during the assembly of the Rodinia supercontinent; (4) A complete bidirectional Wilson cycle was reconstructed by the formation of the late Permian to the middle-late Triassic back-arc Ganze-Litang rift and ocean following the early Paleozoic Mianlue continental rift and ocean, and subsequent closure of the ocean basin by simultaneous bidirectional northward and southwestward subduction and later collision. This relatively uncommon bidirectional Wilson cycle might be attributed to the formation of the three-armed rift system in the eastern Paleotethys associated with the late Permian Eemeishan Large Igneous Province in the LSTC; (5) A three-stage tectonic sequence of, in-sequence imbricate thrust in the LSTC during India-Eurasian collisional orogeny at 55–15 Ma, extrusion from 15 to 5 Ma and the plateau uplift since ∼5 Ma resulting from lower crustal channel flow, is proposed for the formation of the present LSTC.

Crustal evolution in the South Tianshan Terrane: Constraints from detrital zircon geochronology and implications for continental growth in the Central Asian Orogenic Belt

The South Tianshan Terrane (STT) is located in the boundary between the south‐western Central Asian Orogenic Belt (CAOB) and the Tarim Craton and is a key area for understanding the geologic and tectonic history of the craton and the orogenic belt. In this paper, we report detrital zircon ages from the Late Palaeozoic and Mesozoic clastic sedimentary rocks from the southern part of STT. In combination with the U–Pb ages for felsic igneous and meta‐igneous rocks exposed in the STT and adjacent tectonic units, we identify several distinct age populations. Provenance analysis suggests that the detrital zircon grains were predominately derived from the felsic magmatic rocks in the Tarim Craton and South Tianshan Terrane. The pre‐Neoproterozoic age populations may be associated with the early history of the Tarim Craton. Several pulses of Neoproterozoic magmatism are revealed by our dataset, presumably related to the assembly and break‐up of the supercontinent Rodinia. The 995 to 901 Ma detrital zircon grains were likely sourced from magmatic rocks associated with the assembly of Neoproterozoic Tarim to Australia. Among the age population of 886 to 752 Ma, the older group might be related to the subduction‐related magmatism after the assembly of Rodinia, and the younger one records a protracted magmatic event in a continental rift‐related setting associated with the break‐up of Rodinia. Two younger Neoproterozoic age populations (736 to 694 Ma and 665 to 610 Ma), showing narrow spreads with weak peaks, represent the waning stages of igneous activities related to the break‐up of Rodinia. Regarding the Palaeozoic evolution, together with other evidence, our data indicate a two‐stage subduction model for the SW Palaeo‐Asian Ocean. The 490 to 384 Ma age population corroborates the existence of Early Palaeozoic continental arc magmatism at the northern margin of Palaeozoic Tarim generated by the bidirectional subduction of the South Tianshan Ocean. After a ~30 My period of tectonomagmatic quiescence, the second stage is marked by the northward subduction of the South Tianshan Terrane during Late Devonian to Early Carboniferous. The final collision of Tarim and the south‐western CAOB likely occurred during the Late Carboniferous, followed by syn‐ and post‐collisional magmatism, as represented by the 320 to 265 Ma age population. Based on the detrital zircon ages in conjunction with the Hf isotopic features of zircons from Palaeozoic igneous rocks, our study does not support the model of large‐scale Phanerozoic net continental growth in the South Tianshan Terrane.

Organic matter maturity and hydrocarbon potential of the Lower Oligocene Menilite facies in the Eastern Flysch Carpathians (Tarcău and Vrancea Nappes), Romania

Bulk organic geochemical and molecular composition data have been used to analyse the hydrocarbon potential and organic matter maturity of the Lower Oligocene Menilite facies from two adjacent tectonic units of the Eastern Flysch Carpathians (Tarcău and Vrancea Nappes), Romania due to the importance of these source rocks in hydrocarbon exploration in entire Paratethys realm. The data show strong variability in organic matter quantity and quality. Organic carbon content reaches peak values in the siliceous facies of the Lower Menilite Member (up to 8.6 wt% TOC), which contains type II kerogen. With increasing contribution of flysch sedimentation mixed type II/III kerogen gains importance. The biomarker distribution reveals strong variation in the supplied organic matter common for flysch-influenced sedimentary environments. Terrigenous input is marked by epicuticular wax imprint in n-alkane distribution and occurrence of conifer biomarkers, while marine organic matter origin is expressed by the occurrence of short-chain n-alkanes and hopanes especially in the siliceous facies. Thus, these source rocks can be classified as oil-prone and subordinately mixed oil/gas-prone. The maturity in the outer tectonic unit (Vrancea) is low (Tmax ∼425 °C, Ro ∼0.4%) but increases towards the inner Tarcău Nappe (Tmax ∼430 °C, Ro ∼0.5%) reaching onset of hydrocarbon generation. The studied rocks have good petroleum potential, but hydrocarbons were generated only in more mature Tarcău Nappe, where solid bitumen veins were observed. Bitumen impregnation of numerous vitrinite grains possibly suppressed vitrinite reflectance, thus leading to more accurate maturity assessment based on molecular proxies (biomarker maturity indices). The observed difference in maturity levels between the nappes results from the more inner position of the sampled Tarcău Nappe succession within the orogen relative to the Vrancea unit. This is related to different burial histories, as well as variation in subsequent erosion and exhumation levels. The actual hydrocarbon potential in the studied area varies due to local interplay of these critical factors.

The Dunhuang block is a Paleozoic orogenic belt and part of the Central Asian Orogenic Belt (CAOB), NW China

The Dunhuang region is located in the east of the Tarim Craton and has long been considered as part of a Precambrian terrane of the Tarim or North China Craton. Aiming to further understand the tectonic evolution of the Dunhuang region and its relations with the adjacent tectonic units, this study is to investigate the metamafic rocks in the Sanweishan area, Dunhuang region, and in turn to summarize the tectono-thermal events and re-examine the tectonic characteristics of the region.The metamafic rocks in the Sanweishan area include three types of amphibolites. They are garnet–clinopyroxene amphibolites, garnet-free amphibolites and garnet–mica amphibolites. The whole-rock major and trace element compositions suggest that their protoliths probably are E-MORB type tholeiitic basalts with some crustal addition. The LA-ICP-MS zircon U–Pb data of the garnet–clinopyroxene amphibolite and the garnet-free amphibolite yielded lower intercept ages of 410±11Ma and 403±8Ma, respectively, while the garnet–mica amphibolite gave three metamorphic ages of 441±3Ma, 408±12Ma and 370±2Ma. Three suites of metamorphic conditions have been estimated at 1.14–1.55Gpa and 458–548°C, 0.67–0.82Gpa and 590–600°C, and 0.47–0.66Gpa and 557–586°C for garnet–clinopyroxene amphibolite, using different mineral thermobarometers, which illustrate a collisional orogeny-related clockwise P–T path. Integrated with the study on the high-pressure granulite in the Mogutai area, it can be inferred that the metamafic rocks in the Sanweishan area obviously experienced amphibolite–facies metamorphism at ca. 410–400Ma, and they could also underwent high-grade metamorphism at ca. 440–430Ma. Therefore, we suggest that the E–W-trending collisional orogeny of ca. 440–400Ma could sweep cross the Dunhuang region.The Dunhuang region records multiple tectono-thermal events occurring at ca. 3.1–2.5Ga, ca. 2.3–1.6Ga, ca. 440–400Ma and ca. 370–310Ma. However, compared with the limited exposure of the Precambrian complex, the Early Silurian–Late Carboniferous (ca. 440–310Ma) orogeny-related metamorphic and magmatic rocks are widely distributed in the Dunhuang region, making up nearly 70% of the total exposure. Thus, it is proposed that the geological bodies in the Dunhuang region were mainly produced by a Paleozoic orogeny and represent a Paleozoic orogen, while the limited Precambrian complex probably is a microcontinental fragment or part of the margin of the Tarim or North China Cratons that was involved in this Paleozoic orogeny during the Early Silurian–Late Carboniferous. We infer that the Dunhuang orogenic belt is part of the Central Asian Orogenic Belt (CAOB), and thus the CAOB probably extends beyond the Beishan orogenic collage and southward into the Dunhuang region.

Compressive deformations and stress propagation in intracontinental lithosphere: Finite element modeling along the Dinarides–East European Craton profile

Neotectonic stage stress and strain evolution was analyzed along a vertical lithospheric profile crossing the Dinarides, Pannonian Basin, Carpathians and East European Craton. A structural and lithological model was constructed based on distribution of seismic wave velocity along the Cel05 deep seismic sounding line. Rheological properties of each lithospheric layer were calculated as an average value for component rocks. In the applied model a highly laterally heterogeneous section of the lithosphere underwent 2.5% of shortening during 7.5Myr, which corresponds to neotectonic inversion of the Pannonian–Carpathian–Dinaric region. The coupled viscoelastoplastic model predicts stress regime changes, within mechanically partitioned lithosphere, that together with complex rheological properties controls the deformation pattern. Long-wavelength lithospheric buckling was initiated during the first stage of inversion. It was followed by development of short wavelength minor folding in the detached upper crust. The topographic surface within the basin and over the transition to adjacent tectonic units was modified by buckling and swelling mechanisms producing folds of 800m amplitude. Buckling, more efficient in the initial stage of inversion, was over time substituted by crustal swelling that contribute to raising anticlines at the topographic surface due to isostatic compensation. Compound mechanism of folding causes migration of anticlines at the topographic surface and synclines at Moho, which finally produces gentle pinch-and-swell pattern in the crust. Efficient mechanism of continental lithosphere buckling was described under minor shortening and a low stress level.

A three-dimensional model of the Early Precambrian crust under the southeastern Fennoscandian Shield: Karelia craton and Belomorian tectonic province

The Early Precambrian structures of the Archaean Karelia craton and Belomorian tectonic province have been investigated by reflection seismology. Integration of the existing geological database for these two entities and adjacent tectonic units with the seismic data for the crust and upper mantle along the 1-EU geotraverse and cross-traverse 4B totaling c.1300 km allows development of a three-dimensional model of the deep structure of the southeastern Fennoscandian Shield. Interpretation of the seismic data provides evidence that the Early Precambrian crust is characterized by inclined layering. The crustal architecture is a combination of thrust–nappe and thrust–underthrust structural assemblages consisting of Neoarchaean and Palaeoproterozoic rocks that were subsequently further deformed during uplift and emplacement of granite-gneiss domes. The new model substantially modifies previous conceptions of this part of the shield as being constituted of blocks with sub-vertical margins and individual internal layering. It is apparent that the surface traces of gently dipping boundaries are defined by the erosion level and consequently these boundaries are not those of particular “tectonic blocks” in the traditional sense.

Late Cenozoic to recent transtensional deformation across the Southern part of the Gaoligong shear zone between the Indian plate and SE margin of the Tibetan plateau and its tectonic origin

Within the southeastern part of the Tibetan plateau the Gaoligong Shan shear zone forms the boundary between the Tengchong and Baoshan blocks and is one of the main Cenozoic strike–slip fault systems of the eastern Himalayan syntaxis. The mountain ranges rise to a maximum elevation of 3623 m, with a width of 20 km and a length of 400 km. The core of the shear zone consists of a narrow belt of mylonitic rocks with right-lateral strike–slip fabrics formed during the northward movement of India relative to Eurasia in Oligocene and Miocene time. To the south the mountains decreases in elevation and end against the Wanding fault. The latter is one of a series of NE–SW striking, active left-lateral strike–slip faults within the southeastern part of the Tibetan plateau. The cause and timing for the change in elevation of the Gaoligong Shan is unknown, but based on our recent structural and fission-track geochronological work, the decrease in elevation is the result of east-west extension across the southern part of the Gaoligong shear zone inferred from the late Cenozoic and active normal faults along its eastern and western boundaries. Southward the eastern boundary fault system merges with a series of splays of the Wanding strike–slip fault, while the western boundary fault system is bent into parallelism with the Wanding fault. This geometric relationship suggests that the normal faulting along the eastern and western boundary of the Gaoligong shear zone was caused by transfer of the NE–SW left-lateral movement along the Wanding fault into E–W extension on faults to the northeast. The resultant normal faulting caused the lowering of the topography in the southern part of the shear zone. Fission track data from 11 samples from the mylonitic rocks in the footwall of the Ruili oblique slip fault, (left-lateral thrust slip) yielded ages between 8.4 and 0.9 Ma, coeval with volcanism within the Jietou and Mangbang basins. The left-lateral strike–slip movement along the Wanding and Ruili faults is interpreted to have accommodated differential clockwise rotation of the Gaoligong shear zone and its adjacent tectonic units during late Cenozoic to Recent time, during the northward movement of the Indian plate with respect to the southeastern margin of the Tibetan plateau along the right-lateral Sagaing fault.

Fission track dates of Mandi granite and adjacent tectonic units in Kulu–Beas valley, NW Himalaya, India

We present zircon fission track (FT) ages from the lower parts of the Higher Himalayan crystalline (HHC) ranging from 3.9 to 4.3 Ma and apatite FT age as 1.9 ± 0.4 Ma . Combined with previous radiometric dates, these ages provide the low temperature data for the area and enable us to draw temperature–time plot which shows significant increase in cooling rates from 25 ∘ C / Ma in Oligocene and 4 ∘ C / Ma in Miocene to about 64 ∘ C / Ma during Pliocene. For the Mandi granite, the zircon FT ages range from 3.9 to 4.9 Ma while apatite FT obtained is 2.8 ± 0.5 Ma . The rapid Pliocene exhumation is characterized by a rapid increase in cooling rates from ∼ 3.4 ∘ C / Ma in Miocene to ∼ 77 ∘ C / Ma after 5.0 Ma. Our results confirm the rapid Pliocene to Pleistocene cooling of rocks of Kulu–Beas valley similar to that of the neighboring units from the frontal parts of HHC.

Tectonic control of facies architecture, sequence stratigraphy and drowning of a Liassic carbonate platform (Betic Cordillera, Southern Spain)

AbstractThis paper develops a tectono‐stratigraphic model for the evolution and drowning of Early Jurassic carbonate platforms. The model arises from outcrop analysis and Sr isotope dating of successions exposed in the Betic Cordillera in southeastern Spain. Here, an extensive Early Jurassic (Sinemurian) carbonate platform developed on the rifted Tethyan margin of the Iberian Plate. The platform was dissected by extensional faults in early jamesoni times (ca. 191 Ma) and again in late ibex times (ca.188 Ma) during the Pliensbachian stage. Extensional faults and fault block rotation are shown to control the formation of three sequence boundaries that divide the platform stratigraphy (the Gavilan Formation) into three depositional sequences. The last sequence boundary marks localised drowning of the platform and deposition of the deeper water Zegri Formation, whereas adjacent platforms remain exposed or continue as the site of shallow‐marine sediment accumulation. This study is based on mapping, facies analysis and dating of platform carbonates exposed in three tectonic units within the zone: Gabar, Ponce and Canteras. Facies analysis leads to the recognition of facies associations deposited in carbonate ramp environments and adjacent to synsedimentary, marine, fault scarps. Sr isotope dating enables us to correlate platform‐top carbonates from the different tectonic units at a precision equivalent to ammonite zones. A sequence stratigraphic analysis of sections from the three tectonic units is carried out using the facies models together with the Sr isotope dates. This analysis indicates a clear tectonic control on the development of the stratigraphy: depositional sequences vary in thickness, have wedge‐shaped geometries and vary in facies, internal geometries and systems tracts from one tectonic unit to another. Criteria characterising depositional sequences and sequence boundaries from the Gabar and Ponce units are used to establish a tectono‐stratigraphic model for carbonate platform depositional sequences and sequence boundaries in maritime rifts, which can be applied to other less well‐exposed or subsurface successions from other sedimentary basins. Onlapping transgressive and progradational highstand systems tracts are recognised on dip slope ramps. Falling stage and lowstand systems tracts are developed as thick breccia units in hangingwall areas adjacent to extensional faults. Sequence boundaries vary in character, amplitude and/or duration of sea‐level fall and persistence across the area. Some boundaries coalesce onto the Canteras unit, which remained as a relatively positive area throughout the early Pliensbachian (Carixian). The carbonate platform on the Ponce tectonic unit drowned in the latest Carixian (davoei biozone). However, the adjacent tectonic units remained emergent and developed a long‐lived sequence boundary, indicating tectonic subsidence as the major cause for platform drowning. The stratigraphic evolution of this area on the rifted southern Iberian margin indicates that a widespread restricted shallow‐water carbonate platform environment accumulating peritidal carbonates evolved with faulting to a more open‐marine setting. Sr dating indicates that this transition took place around the Sinemurian–Pliesbachian boundary and it was driven by local fault‐related subsidence together with likely post‐faulting regional subsidence.

Metallogeny in the Capricorn Orogen, Western Australia, the result of multiple ore-forming processes

The Capricorn Orogen includes metamorphosed tectonic units, intrusive igneous rocks, volcano-sedimentary and sedimentary basins situated between the Pilbara and Yilgarn cratons. These include the Gascoyne Complex, Ashburton, Blair, Bresnahan, Yerrida, Bryah, Padbury, and Earaheedy basins, and Edmund and Collier (former Bangemall) basins. Mineral deposits and occurrences in these units comprise stratabound base metals, including the giant Abra Pb–Cu–Ba (Edmund Basin) and Magellan Pb (Earaheedy Basin), and numerous hydrothermal veins and precious and/or base metal lodes. Some of the more important orogenic precious metal lodes are those of the Peak Hill group in the Bryah-Padbury basins and the Egerton field in the Gascoyne Complex. The metallogeny of the Capricorn Orogen reflects syn- to post-Capricorn orogenic events, linked to either protracted convergence tectonics between the Pilbara and Yilgarn cratons, or to a two-stage convergence history, one during the Capricorn Orogeny (ca. 1.83 Ga; Pilbara–Yilgarn convergence), the other during the Yapungku orogeny (ca. 1.79; North Australian–West Australian convergence). The metallogeny of the Capricorn Orogen was further sustained by continental mafic magmatism at about 1.45 and 1.07 Ga, during which heat advection may have caused widespread hydrothermal circulation, particularly in the Edmund, Collier, Earaheedy basins and adjacent tectonic units. An interesting, but as yet unexplained, aspect of the Capricorn metallogeny is the regional Pb–Ba enrichment. A conceptual model that attempts to explain the billion-year-long history of the metallogeny in the Capricorn Orogen is proposed. Mineral exploration in the Capricorn Orogen is somewhat limited and not as intensive as is in the brown-fields of the Archaean terranes of Western Australia.

Geophysical properties of the lower crustal granulites from the Qinling Orogenic Belt, China

The lower continental crust plays a crucial role in continental evolution and mountain building. It is widely accepted that the lower crust is dominated by granulites, mafic or felsic. In the present paper our studies are presented on the geophysical properties of granulites from two adjacent tectonic units, the Late Archean Taihau Complex along the southern margin of the North China craton in Lushan, and the Early Proterozoid Dahe Formation in the Qinling orogen in Tongbai, eastern Henan Province, China. The results indicate that the granulites from the two units were formed within the P– T regime of the lower crust, but in distinct environments.

Coalification in the northern Wildhorn nappe and adjacent units, western Switzerland. Implications for tectonic burial histories

Vitrinite reflectance of fourteen Eocene coal samples from the northern Wildhorn nappe in the Kander valley have been analyzed and compared to nine agewise similar coals from adjacent tectonic units. The degree of coalification decreases regularly from semi-anthracite in the Kander valley to lignite in the plateau molasse. The degree of coalification in the Tertiary coals appears to be solely dependent on their tectonic history and indicates and estimated 6 km of burial by higher (Pennine) nappes for the Kander valley. The rank at this locality (low-volatile bituminous to semi-anthracite) is significantly higher than in the Border chain at Beatenberg (high-volatile A bituminous). The latter locality therefore was never buried deeper than about 4 km. A further decrease in rank is found in the subalpine flysch and molasse (high-volatile B bituminous) which in turn is significantly more mature than lignites from the folded plateau molasse at Linden. Two samples of Dogger coal from the Pennine “Préalpes médianes” are medium- to low-volatile bituminous that is intermediate between the Kander valley and Beatenberg. Their rank, however, was achieved before their final emplacement north of the Wildhorn nappe. By comparing calculated TTI (Time-Temperature-Indices)-values for time-depth-burial curves with measured vitrinite reflectances, maximum burial temperatures were estimated for the various tectonic units. For the Wildhorn nappe, 160–180°C were obtained in the Kander valley and 100–130°C in the Border chain as a result of tectonic burial due to the thrusting by the Pennine Prealps. Sedimentary burial led to temperatures of 100–120°C in the subalpine molasse below the Border chain prior to its thrusting.

Late Permian paleomagnetic pole from dikes of the Tarim craton, China

Research Article| March 01, 1988 Late Permian paleomagnetic pole from dikes of the Tarim craton, China Yianping Li; Yianping Li 1Department of Geophysics, Stanford University, Stanford, California 94305 Search for other works by this author on: GSW Google Scholar Michael McWilliams; Michael McWilliams 1Department of Geophysics, Stanford University, Stanford, California 94305 Search for other works by this author on: GSW Google Scholar Allan Cox; Allan Cox 1Department of Geophysics, Stanford University, Stanford, California 94305 Search for other works by this author on: GSW Google Scholar Robert Sharps; Robert Sharps 1Department of Geophysics, Stanford University, Stanford, California 94305 Search for other works by this author on: GSW Google Scholar Yongan Li; Yongan Li 2Xinjiang Geology Research Institute, Urumqi, Xinjiang, People's Republic of China Search for other works by this author on: GSW Google Scholar Zhengjia Gao; Zhengjia Gao 2Xinjiang Geology Research Institute, Urumqi, Xinjiang, People's Republic of China Search for other works by this author on: GSW Google Scholar Zhengkun Zhang; Zhengkun Zhang 3Geology Institute, Chinese Academy of Geological Sciences, Beijing, People's Republic of China Search for other works by this author on: GSW Google Scholar Yongjian Zhai Yongjian Zhai 4Beijing Graduate School, Wuhan Geology College, Beijing, People's Republic of China Search for other works by this author on: GSW Google Scholar Author and Article Information Yianping Li 1Department of Geophysics, Stanford University, Stanford, California 94305 Michael McWilliams 1Department of Geophysics, Stanford University, Stanford, California 94305 Allan Cox 1Department of Geophysics, Stanford University, Stanford, California 94305 Robert Sharps 1Department of Geophysics, Stanford University, Stanford, California 94305 Yongan Li 2Xinjiang Geology Research Institute, Urumqi, Xinjiang, People's Republic of China Zhengjia Gao 2Xinjiang Geology Research Institute, Urumqi, Xinjiang, People's Republic of China Zhengkun Zhang 3Geology Institute, Chinese Academy of Geological Sciences, Beijing, People's Republic of China Yongjian Zhai 4Beijing Graduate School, Wuhan Geology College, Beijing, People's Republic of China Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1988) 16 (3): 275–278. https://doi.org/10.1130/0091-7613(1988)016<0275:LPPPFD>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Yianping Li, Michael McWilliams, Allan Cox, Robert Sharps, Yongan Li, Zhengjia Gao, Zhengkun Zhang, Yongjian Zhai; Late Permian paleomagnetic pole from dikes of the Tarim craton, China. Geology 1988;; 16 (3): 275–278. doi: https://doi.org/10.1130/0091-7613(1988)016<0275:LPPPFD>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract We have obtained a Late Permian paleomagnetic pole from dikes in the Tarim craton of China. Directions of magnetization from 21 mafic and ultramafic dikes at three localities pass a fold test at the 95% confidence level. The new paleomagnetic pole lies at lat 66°N, long 181° E; N = 21, K = 61, and α95 = 3.9°. On the basis of a comparison with paleomagnetic data from adjacent tectonic units, we conclude that (1) the Late Permian paleolatitude of the Tarim craton differs from that of the Sino-Korean craton, suggesting that the two cratons were distinct tectonic units in Late Permian time; (2) there was relative motion between the Tarim craton and the Siberian craton after Late Permian time; and (3) negligible relative motions have occured between different thrust sheets in the Keping-Bachu area of the north-western Tarim craton. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.