Tectonic Domains Research Articles

Transition in Thermal History and Recurring Burial-Exhumation Cycles along Colder Thermal Gradients at the Archaean-Proterozoic Boundary: New Insights from the Western Dharwar Craton, South India

Abstract The Hole Narsipur Greenstone Belt (HGB), in the Western Dharwar Craton, South India, preserves evidence for three cycles of metamorphism spanning the Archaean–Proterozoic transition. Changes in metamorphic style across the transition are investigated using integrated petrographic, mineral chemical, metamorphic evolutionary history, conventional geothermobarometry, and phase equilibria modeling studies of rocks of diverse bulk rock composition from the belt. These rocks record signatures of three overprinting metamorphic cycles (M2 → M3 → M4 in sequence), postdating a Mesoarchaean, M1 event in the craton. The M2 cycle represents characteristic LP–HT metamorphism along a counterclockwise (CCW) metamorphic P–T path, peak metamorphism at 4–5 kbar, 515–595°C, and high thermobaric ratios (T/P ~1050–1525°C/GPa) at the M2 peak. The intermediate M3 metamorphic cycle records a prograde burial of partially cooled M2 rocks to middle-lower crustal depths, peak metamorphism at P ~7.5–10.2 kbar, T ~630–655°C, and corresponding intermediate T/P ratios (T/P ~620–875°C/GPa) and a retrograde stage, marked by combined exhumation and cooling to P ~5.3–6.4 kbar, T ~530–575°C. The resultant P–T paths of evolution show variability of clockwise (CW) paths from classical hairpin type to two-stage prograde heating segments. During the M4 metamorphism (TMax ~630–640°C at ~8.9–10.3 kbar and with lower T/P ratios at ~610–720°C/GPa), the partially exhumed M3 crust is re-buried to lower crustal depths along an intermediate thermal gradient as during the M3 metamorphic cycle. We interpret the thermal transition, tectonic thickening along a cooler thermal gradient, repeated burial-exhumation cycles in the orogenic wedge, and tectonic mixing of the three metamorphic cycles in terms of a three-stage tectonic evolution of the HGB. These in a sequence are (a) the development of a hot and thinned crust (cf. M2 cycle), (b) the transition to a thickened crustal zone tectonic domain (cf. M3 cycle), with both the domains being part of the lithospheric peel-back driven convergence setting and (c) finally continental collision tectonics (cf. M4 cycle). The pulsating nature of orogenesis at the Archaean–Proterozoic boundary deduced here distinguishes the Western Dharwar Craton from other cratonic blocks globally at the same time frame.

Heat Flow in the Asian Continent and Surrounding Areas

Heat flow is a key parameter to describe the interior heat of the Earth and provides constraints on understanding the thermal structure of lithosphere and assessment of the geothermal resource potential. Based on the latest heat flow database, here we present the heat flow pattern of the Asian continent and its surrounding areas and discuss the correlation between heat flow and tectonics. The mean heat flow of Asian continent and its surrounding areas is 71 ± 34 mW/m2, slightly higher than the global continental mean value, and the overall heat flow pattern in Asia exhibits remarkable heterogeneity, characterized by higher values in the eastern marginal seas, the Red Sea, the Gulf of Aden and the Qinghai-Tibet Plateau, while lower in large areas of North Asia and Central Asia. Cratons show a lower mean heat flow and smaller standard deviation, indicating the tectonic stability. The Cenozoic rifts, marginal seas and the Neo-Tethyan Tectonic Domain all exhibit higher heat flow. The geothermal pattern in Asia is controlled by the geodynamic processes of the subduction of Pacific Plate, the Indo-Asia continental collision and the break-up between Arabia and Africa.

P‐wave Velocity Structure of Crustal and Upper Mantle beneath South China and its Tectonic Implications

AbstractThe 3D P‐wave velocity structure beneath the South China Block was determined by applying arrival times from 269 teleseismic events recorded by 240 seismic stations within the study region. Our tomographic results reveal the deep structural characteristics of major tectonic units and ore concentration areas. There are distinct high velocity anomalies beneath the ancient Yangtze and Cathaysia blocks, with the lithosphere of the Cathaysia Block being thinner than the Yangtze Block; the Jiangnan orogenic belt, located in the combined zone of two blocks, is a high and low velocity anomaly conversion zone; the famous metallogenic belts of Edongnan, the Youjiang Basin and the Cathaysia Block are obviously low velocity areas with different metallogenic mechanisms. The deep ore‐forming material source in the Edongnan metallogenic belt is different from that of the Cathaysia Block. The low velocity anomaly under the Cathaysia Block related to mineralization results from the upwelling of mantle material, caused by the joint action of the Paleo‐Tethys tectonic domain, the Paleo‐Pacific tectonic domain and the Hainan mantle plume migration and erosion, which has been occurring from northeast to southwest since 80 Ma. The low‐temperature mineralization mechanism of Youjiang Basin should be considered not only in terms of the influence of the Emeishan mantle plume in the west and the Paleo‐Tethys tectonic domain in the south, but also in the context of the influence of the upwelling of asthenospheric material from the Paleo‐Pacific tectonic domain in the east.

A synthesis of geochemistry of Mesozoic igneous rocks in NE China and tectonic superposition and transformation of the easternmost Central Asian Orogenic Belt

As the product of the amalgamation of multiple microcontinental massifs, Northeast China is located in the easternmost segment of the Central Asian Orogenic Belt (CAOB), which underwent multi-stage tectonic superposition in Mesozoic. Extensive and intensive igneous activities occurred throughout northeast China and the related igneous rocks can be considered as an effective probe for constraining tectonic evolution. In this study, numerous available ages and geochemical data are collected from published literature. The spatial-temporal distribution, rock assemblage, and geochemical characteristics of Mesozoic igneous rocks are systematically reassessed and summarized. A conclusion is drawn that NE China experienced the superposition and transformation of the Paleo-Asian Ocean (PAO) domain, the Mongol-Okhotsk Ocean (MOO) domain, and the Paleo-Pacific Ocean (PPO) domain in Mesozoic and detailed tectonic evolution is presented as follows. Firstly, NE China was under the joint effect of the MOO and the PAO during Early-Middle Triassic (ca. 252–237 Ma). Arc-type igneous rocks in the Erguna-Xing’an Block were induced by the southward subduction of the MOO Plate and adakites with high Sr/Y and (La/Yb)N ratios in the south segment of NE China were emplaced in the post-collision orogenic environment related to the closure of the PAO. Secondly, during Late Triassic, the influence of the PAO domain was gradually weakened, and igneous activities developed sporadically along the Solonker-Xar Moron-Changchun-Yanji suture zone. The MOO continued to subduct south until the Early Jurassic (ca. 220–190 Ma), and continental igneous rocks with arc-like features were widely distributed in the Erguna-Xing’an Block. During ca. 220–200 Ma, the Jiamusi-Khanka Massif was slipped away from the Songnen-Zhangguangcai Range Massif and this progress may be related to the PPO domain. Thirdly, in the Early Jurassic-Early Cretaceous (ca. 200–120 Ma), NE China came under the joint influence of the MOO and PPO tectonic domains. The subduction and closure of the MOO Plate and corresponding thickening of the lower crust resulted in widespread and intensive igneous activities in the Erguna and the Great Xing’an Range (GXAR). Two-stage subduction of the PPO and between which a period of change of subduction direction, induced the two-stage arc igneous activities of ca. 185–164 Ma and ca. 135–120 Ma, and the magmatic hiatus between ca. 163.5–135 Ma in the Zhangguangcai Range (ZGCR) and its east. Fourthly, the influence of the MOO domain was completed at ca. 120 Ma and numerous volcanic rocks corresponding chemically to A-type granite began to erupt violently, due to the rollback of the Paleo-Pacific oceanic slab. Since then, NE China has been completely under the control of the PPO domain.

Flexural subsidence modelling of post-rift paleobathymetry and sedimentary infill in the northern South China Sea margin

The South China Sea (SCS) is the largest marginal sea on the SE Asian continental margin, located at the junction of the Pacific, Indo-Australia and Eurasian plates, and has undergone the joint effect of the Tethys and Pacific tectonic domains. Currently, the SCS remains debatable for its evolution and origin. However, its northern margin preserves the Cenozoic tectonic and subsidence history, which allow us to restore the past continental margin (0–33.7 Ma), to estimate subsidence, thickness and sediment accumulation correlated with regional tectonics. This paper has employed a 2D flexural backstripping technique and spatio-temporal variations by enhancing the seismic profiles with flexurally interpolated modelled sections. According to our findings, the transition was mainly controlled by three structural stages. (1) Early-Late Oligocene: records the highest subsidence due to the initiation of seafloor spreading, isostatic response of continental breakup, associated uplifts therein, and retreat of the Pacific Plate. (2) Early-Middle Miocene: mature spreading attributed to a slow phase of subsidence during the Early Miocene and a rapid increase of subsidence associated with the closure of the SCS in the Middle Miocene. (3) Thermal subsidence: sediments shifted since the Late Miocene towards mechanically weak and stretched regions (central-southern and eastern) which were triggered by a gravitational pull force. A fault system and differential stretched crust relocated sediment to the regional stress directions of the Pacific Plate.

Geochemical characteristics and source apportionment of toxic elements in the Tethys–Himalaya tectonic domain, Tibet, China

Toxic elements (TEs) in soil threaten the eco-environmental system and human health. The identification and prediction of sources and high-risk areas of TEs in soil are fundamental for regional pollution prevention and control. In this study, geostatistical methods and GIS-based approaches were used to quantitatively analyze the spatial distribution, geochemical characteristics, key driving factors, and their interactive effects of TEs in soil from a typical area of the Tethys–Himalaya tectonic domain in Tibet based on an integrated approach combining positive matrix factorization and GeoDetector models. The mean contents of chromium, arsenic (As), cadmium, mercury and lead in the soil exceeded the Tibetan background values, with 66.20% of As being higher than the screening values. The spatial distribution of TEs content in the soil was primarily affected by geogenic source factors (primarily geology types, soil parent materials, soil types, and soil pH), and environmental source factors (primarily precipitation and vegetation types) and anthropogenic source factors (primarily income of residents and land-use types) also had the same contribution approximately. Compared with that for individual driving factors, the interaction between most pairs of driving factors enhanced their explanatory power. The high-risk areas for soil As pollution were primarily distributed in the valley areas of the upper reaches of the Longzi River Basin. Therefore, to guarantee the health of residents and the security and sustainability of agricultural production in the study area, regular monitoring and soil remediation should be used to reduce the migration and transformation of As in the local biogeochemical cycle. This study provides new ideas for the regional prediction of high-risk areas for soil pollution, which has guiding importance and reference value for the control and management of large-scale soil pollution.

A Short-Period Surface-Wave Dispersion Dataset for Model Assessment of Africa’s Crust: ADAMA

Abstract We present the first in a series of dataset and model assessment products for investigating Africa’s lithosphere (ADAMA). This is a comprehensive catalog of short-period interstation surface-wave dispersion measurements and uncertainties. It is derived from processing continuous recordings of all publicly available three-component seismograms, spanning four decades, from ∼1372 stations, across 62 seismic networks deployed in and around the African continent. It includes Love- and Rayleigh-wave dispersion derived from frequency-domain ambient noise cross-correlation functions (NCFs). Phase and group dispersion, as well as their uncertainties, are then obtained with an iterative nonlinear waveform fitting of the NCFs, using a spectral element representation of a path-average a priori Earth model. Our catalog represents the following advances: (1) a large distribution of short period dispersion measurements: ∼114,000 interstation pairs at periods between 5 s and 40 s, (2) inclusion of uncertainties useful for regularization in continent-wide model building, (3) preliminary model assessments for different tectonic domains on the continent, and (4) an exemplary Love-wave phase velocity map obtained by Bayesian inversion revealing detailed features not previously detected. ADAMA will be used to prepare short-period, high-resolution dispersion maps, and for assessment and updates of widely used seismic velocity models of the crust across a diversity of terranes on the continent.

Implications of the dominant LP–HT deformation in the Guanhães Block for the Araçuaí West-Congo Orogen evolution

The Araçuaí-West Congo Orogen is the result of convergence between the São Francisco and Congo cratons during the assembly of West Gondwana. Within this orogen, the Araçuaí Belt in SE Brazil reflects the western external domain. The Araçuaí Belt is characterized by major east-dipping structures and high- to medium pressure metamorphic rocks developed during crustal thickening at ca. 585–560 Ma and are juxtaposed along crustal-scale structures to the crystalline core of the orogen.The Guanhães Block in the southern Araçuaí Belt is characterized by higher metamorphic grade and dominantly shallowly west-dipping structures compared to the neighboring tectonic domains. While several studies have focused on the evolution of the axial crystalline core of the Araçuaí orogen and on the early collisional stages in the Araçuaí Belt, little attention has been given to the structural and metamorphic history of the poorly studied Guanhães Block.The supracrustal rocks in the central Guanhães Block record two tectono-metamorphic stages: D2/M2 and D3 /M3, with potential D1/M1 relicts rarely preserved within D2/M2 low-strain domains. The D2/M2 overprinting stage is associated with the development of a dominant, shallow axial planar foliation (S2) of isoclinal F2 folds under low-pressure and high-temperature (LP–HT) conditions (ca. 6 kbar and 750 °C). During this D2/M2 stage continuous segregation of syn-kinematic partial melting and generation of granitoid rocks occurred. The 530 Ma, syn- D2/M2 granitoid has negative εHf(i) at ca. −32 which indicates the source of magma from melting of older, isotopically evolved, Archaean or Paleoproterozoic crust.U–Pb geochronology on monazite, titanite and hydrothermal zircon constrain the retrograde D3/M3 event at ca. 510 Ma. The Guanhães Block uniquely records dominant deformation under LP–HT metamorphic conditions during the late-orogenic stages and its evolution could have important tectonic implications for the concurrent models suggested for the late Neoproterozoic Araçuaí-West Congo Orogen.

Petrogenesis and Tectonic Setting of the Madeng Dacite, SW Sanjiang Indosinian Orogen: Evidence from Zircon U-Pb-Hf Isotopes, and Whole-Rock Geochemistry and Sr-Nd Isotopes

The Sanjiang Indosinian orogen, located in the eastern part of the Paleo-Tethys tectonic domain, is a critical region to study the Paleo-Tethyan Ocean evolution. Middle Permian–Late Triassic magmatic rocks are widespread in the Deqin–Weixi–Madeng area of southwestern (SW) Sanjiang Indosinian orogen, yet their petrogenesis and tectonic setting remain disputed. In this study, LA-ICP-MS zircon U-Pb age and Hf isotopes, and whole-rock elemental and Sr-Nd isotope geochemistry of Madeng dacite were studied. The Madeng dacite was dated at ca. 241.7 and 243.4 Ma. The samples had high Al2O3 (12.91 to 14.39 wt.%) but low MgO (0.62 to 1.76 wt.%) contents, and were alkali-rich (Na2O + K2O = 6.97 to 8.66 wt.%) with A/CNK > 1.1, strongly resembling peraluminous S-type granites. The rocks were enriched in Rb, K, Th, U and LREE, but depleted in Ba, Sr, Nb, Ta, P and Ti, and showed obvious negative Eu anomalies, suggesting fractionation of Ti-bearing minerals (e.g., rutile and ilmenite) and plagioclase. The dacite had an initial 87Sr/86Sr value of 0.705698 to 0.710277, and negative εNd(t) (−11.28 to −10.64) and εHf(t) (−13.99 to −8.60), indicating a continental meta-sedimentary source. Their average Nb/Ta (12.24) and Th/U (4.65) were also consistent with continental crust. According to the lithological assemblage and geochemical features, we propose that the Deqin–Weixi–Madeng area intermediate-felsic magmatism was generated in a subduction-related tectonic setting.

Editorial of Special Issue “Tectonics and Morphology of Back-Arc Basins”

Back-arc basins are tectonic domains within subduction systems shaped mainly by extensional and transtensional tectonics or in some cases by compression, volcanism and intense hydrothermalism [...]

Subduction and carbonate platform interactions

AbstractPlate tectonics, as the unifying theory in Earth sciences, controls the functioning of important planetary processes on geological timescales. Here, we present an open‐source workflow that interrogates community digital plate tectonic reconstructions, primarily in the context of the planetary deep carbon cycle. We present an updated plate tectonic reconstruction covering the last 400 million years of Earth evolution and explore components of the plate–mantle system that is involved in the exchange and storage of carbon. First, the workflow enables us to estimate subduction zone lengths through time, which represent the “tap” of carbon that is released at convergent tectonic margins. Second, we explore the role of Andean‐style versus intra‐oceanic subduction regimes during Pangea assembly and breakup. Third, we provide an improved model for carbonate platform evolution since the Devonian and evaluate the interaction of subduction zones and buried carbonate platforms. Last, we present a new model for estimating oceanic age, carbon content in the upper oceanic crust, and estimated (carbon‐containing) sediment thicknesses through time and present methods to track the subduction of this material through time. These components of the deep carbon cycle are key mechanisms controlling, or at least modulating, atmospheric CO2 on geological timescales and hence strongly influencing long‐term climate. We find that the mid to Late Cretaceous greenhouse climates were likely driven by increased subduction fluxes of volatiles and increased subduction zone interactions with carbonate platforms in the Tethyan tectonic domain. Our work highlights the importance of community digital plate tectonic reconstructions as a framework for studying key systems, such as the deep carbon cycle, that influence the life‐support mechanisms on our planet.

Crustal modelling from Pan-African granites of the Colomine Gold District, SE Cameroon: Insights from zircon U-Pb dating and Lu-Hf isotope systematics

The Neoproterozoic Pan-African Orogeny in the Adamawa-Yadé domain (AYD) of Cameroon is characterized by intense magmatism of metaluminous to weakly peraluminous I-type granites spatially associated with transcurrent shear zones. This domain provides a critical geological record that is important for unravelling the regional tectonic evolution and geodynamic setting. We present new zircon U-Pb ages and Lu-Hf isotope data from pre-collisional biotite granite and porphyritic K-feldspar granite of the gold-producing Colomine district. Zircon U-Pb ages of biotite granite samples suggest emplacement at 727 ± 8 Ma and at 671 ± 6 for the porphyritic K-feldspar granite. Metamorphic-hydrothermal events between 600 and 550 Ma resulted in Pb-loss of most dated zircons. Lu-Hf isotope data of zircon grains form the porphyritic K-feldspar granite with ϵHf(t) values of −28.7 to −22.6 and TDMc ages of 2.4–2.1 Ga overlap with those of the biotite granite (ϵHf(t) values of −29.4 to −19.6; TDMc ages of 2.5–1.9 Ga). Depleted mantle model ages and ϵHf(t) values suggest that the granites were derived from crustal reworking of older Archean to Paleoproterozoic crust with minor mixing from a juvenile component during the Pan-African. The formation of these pre-collisional granites is interpreted as related to accretion tectonics that started around 750 Ma and incorporating tectonic domains of the Central African Fold belt, namely, the NW Cameroon domain, Mayo-Kebbi domain and the Adamawa-Yade domain.

Petrogenesis and tectonic implications of late Permian and Triassic granitoids on Hainan Island, South China

Hainan Island is a key part of the eastern Tethyan region and contains detailed geological information that can enhance our understanding of the tectonic evolution of this region since the late Palaeozoic. In this paper, we report geochronological, geochemical, and Sr–Nd isotopic data for granitoids from Baomei and Chahe in the northern part of Hainan Island. Three new zircon U–Pb ages of 243.3 ± 1.7 Ma, 237.1 ± 5.1 Ma, and 257.0 ± 4.0 Ma were obtained for these granitoids. The late Permian Chahe granite (257 Ma) is weakly peraluminous to peraluminous, and has rare earth element patterns and Ga/Al and FeOT/MgO ratios typical of A‐type granites formed in an extensional tectonic setting. The Middle Triassic Baomei granitoids (243–237 Ma) are weakly peraluminous, and exhibit a negative correlation between P2O5 and SiO2, which is typical of I‐type granites. All the granitoids have EM II‐type‐enriched mantle Sr–Nd isotopic compositions, which indicate that they were derived from a mantle source that had experienced enrichment and metasomatism. Hainan Island was in an extensional tectonic setting from the late Permian to Middle Triassic when widespread A‐ and I‐type granites were generated. We speculate that Hainan Island was mainly affected by the Tethyan tectonic domain during the Permian–Triassic, which involved closure of the Palaeo‐Tethys Ocean, collision of the Indochina and South China blocks, and subsequent post‐collisional extension.

Evidence for Post‐Assembly Modification of Western Laurentia by Back‐Arc Extension

The crystalline crust that underlies the Western Canada Sedimentary Basin in northern Alberta is composed of tectonic domains that accreted to the margin of the Archean Rae province of western Laurentia, ca. 2.1-1.8 Ga. Previous tectonic models in this region invoke complex plate dynamics, including oppositely verging subduction zones, to explain the assembly of various geologic domains. In this paper, we introduce a new tectonic model that invokes back-arc extension within the Chinchaga Domain (CD). The basement crust in the CD hosts a vast, mid-crustal reflection sequence (Winagami Reflection Sequence), previously interpreted as a mafic sill complex that intruded into an atypically wide domain of Paleoproterozoic arc magmatism. The latter has been interpreted to have formed during Paleoproterozoic tectonic assembly through near-synchronous closure of multiple small oceanic basins and/or magmatism in a plate interior setting. Based on reinterpretation of regional geophysical data and post-compressional fabrics observed by re-examination of drill cores, we propose that observed temporal relationships and present-day configuration of Paleoproterozoic arcs is better explained by post-assembly extension of the Chinchaga Domain. The proposed post-assembly modification is analogous to recent tectonic evolution of the Basin and Range and can be explained through back-arc extension linked to slab rollback and/or a proximal coeval transform plate boundary. Our model implies a back-arc setting for the Winagami sill complex; it also provides a tectonic framework for explaining the origin of an enigmatic low δ18O anomaly (Kimiwan anomaly) and reactivated basement faults associated with recent induced seismicity.

Mapping the Thermal Structure of the Amazon Craton to Constrain the Tectonic Domains

AbstractRheology of solids is primarily a function of temperature. Mapping depth to the bottom of the magnetic layer (DBML), which is assumed as a proxy for the depth to Curie temperature, can be used to constrain the thermal structure of the lithosphere. Heat flow data are commonly used to address the thermal structure of the lithosphere. However, these data are scarce for the Amazon Craton. Therefore, as an alternative, DBML was calculated using fractal magnetic source distribution. The Amazon craton is usually described in terms of geochronological provinces models. Nevertheless, geophysical data are poorly discussed in these models. We provide a DBML model that was integrated with the potential field, seismic tomography, and crustal thickness data to address this issue. Our model varies from 10 to 80 km, and almost 90% of the estimates are in the 20‐50 km range. The recurrence of long‐wavelength features on independent datasets supports the assessment that the model is robust and recovered real geophysical signals. Our model suggests that the limits between Carajás and Bacajás domains should be revisited as well as the limits between Tapajós and Iriri Xingú domains. Moreover, we also correlate the model with main mineral deposits. Further, the identified DBML anomaly suggests the mantle is serpentinized in the eastern Carajás domain. This feature is highly correlated with high p‐wave velocity indicating fertile mantle conditions, thus making this region favorable for world‐class mineral deposits.

Crustal Structure Beneath the Northern Appalachians and the Eastern Grenville Province

AbstractSoutheastern Canada and the northeastern USA include terranes that were tectonized since the Archean, making this region an excellent place to investigate the evolution of continental crust. Our study area covers the Archean southeastern Superior Province, the Proterozoic eastern Grenville, and the Phanerozoic northern Appalachians comprising terranes with either Peri‐Laurentian or Peri‐Gondwanan heritage. Adopting a Rayleigh wave ambient noise tomography method, we used noise data recorded between 2013 and 2015, and obtained high resolution anisotropic tomographic images of the crust enabling us to discuss tectonic implications. The azimuthal anisotropy orientations follow a dominant NE‐SW trend across the study area, but some localized changes of anisotropy direction in the Bay of Fundy and across the Appalachian front are observed. The crust beneath the older Superior and Grenville provinces is generally fast, whereas the Appalachians include strong slow anomalies, especially at upper crustal depths, where they represent thick sedimentary basins beneath the St. Lawrence valley, the Gulf of St. Lawrence, and the Bay of Fundy. We suggest that the boundary between the Peri‐Laurentian and the Peri‐Gondwanan terranes at depth is marked by a Moho‐offset feature observable in our models. A generally similar crustal seismic signature for the two youngest easternmost tectonic domains suggest that they were never separated by a wide ocean basin. Our results provide important evidence for evolution of the continental crust during and after accretionary/collisional episodes in the study area.

Review of the main Black Sea rifting phase in the Cretaceous and implications for the evolution of the Black Sea lithosphere

The Black Sea is a deep marine basin formed by lithosphere extension and active rifting in a back-arc tectonic setting, by general consensus, in the Cretaceous. Its present structural architecture, however, is mainly defined by compressional tectonics during the Cenozoic when large scale “basin inversion” reactivated extensional fault systems formed in the Cretaceous. Rifting during the Cretaceous is usually taken to represent the main process forming the present-day basin (that is, producing crustal thinning and concomitant subsidence prior to its modification during Cenozoic inversion). Rifting at this time took place within continental lithosphere that had been accreted to and, by the Cretaceous, formed part of the Eurasian lithospheric plate. The precise history of how and when pre-Cretaceous aged tectonic domains were accreted to Eurasia forming the continental lithosphere underlying the Black Sea is poorly known. A critical issue to the tectono-thermal evolution of the Black Sea basin with important implications for paleogeography and sedimentary depositional environments is the degree of crust (and lithosphere) thinning during Cretaceous rifting and whether oceanic or “sub-oceanic” crust was formed at that time. The main focus of this paper, in order to illuminate this issue, is on kinematic observations related to the Cretaceous (Albian-Cenomanian) rifting phase, including subsidence analysis, as well as the immediate post-rift sedimentation and stratigraphy. The results suggest that rifting during the Cretaceous was insufficient in its own right to reveal exhumed mantle or to promote ocean crust formation beneath the deep basins of the Black Sea. It is concluded that an important contribution to observed present-day crustal and lithosphere architecture of the Black Sea area are legacy extensional tectonic events affecting the area in pre-Cretaceous times, with implications for the Late Palaeozoic-Mesozoic paleogeography and paleotectonic evolution of this area.

Deformation of the Crust and Upper Mantle beneath the North China Craton and Its Adjacent Areas Constrained by Rayleigh Wave Phase Velocity and Azimuthal Anisotropy

The North China Craton (NCC) has experienced strong tectonic deformation and lithospheric thinning since the Cenozoic. To better constrain the geodynamic processes and mechanisms of the lithospheric deformation, we used a linear damped least squares method to invert simultaneously Rayleigh wave phase velocity and azimuthal anisotropy at periods of 10–80 s with teleseismic data recorded by 388 permanent stations in the NCC and its adjacent areas. The results reveal that the anomalies of Rayleigh wave phase velocity and azimuthal anisotropy are in good agreement with the tectonic domains in the study area. Low-phase velocities appear in the rift grabens and sedimentary basins at short periods. A rotation pattern of the fast axis direction of the Rayleigh wave together with a distinct low-velocity anomaly occurs around the Datong volcano. A NW–SE trending azimuthal anisotropy and a low-velocity anomaly at periods of 60–80 s are observed subparallel to the Zhangbo fault zone. The whole lithosphere domain of the Ordos block shows a high-phase velocity and counterclockwise rotated fast axis. The northeastern margin of the Tibetan plateau is dominated by a low-velocity and coherent NW–SE fast axis direction. We infer that the subduction of the Paleo-Pacific plate and eastward material escape of the Tibetan plateau mainly contribute to the deformation of the crust and upper mantle in the NCC.

Response of provenance transition of Middle Jurassic–Early Cretaceous sediments to tectonic domain transformation in the North Yellow Sea Basin, Eastern North China Craton

In the Late Mesozoic, the Eastern North China Craton changed from being controlled by the Palaeo‐Asian tectonic domain to the marginal Pacific tectonic domain. The Eastern North China Craton transformed the E–W compression to NNE–SSW extensional tectonics under the influence of two tectonic domain transformations. However, the timing of the transformation of the tectonic domains remains controversial. The North Yellow Sea Basin is located in an important position in the Eastern North China Craton at the junction of the Pacific and Eurasian plates and is controlled by two tectonic domains. Therefore, the sediments in the basin are faithful records of the transformation of the two tectonic domains. Based on the latest and high‐precision detrital zircon U–Pb dating data, sandstone modal analysis, and elemental geochemical analysis in the North Yellow Sea Basin combined with regional tectonic, palaeontological, and palaeoclimatic evidence, this paper discusses the provenance from the Middle Jurassic to Early Cretaceous, which responds to the Late Mesozoic tectonic domain transformation in the Eastern North China Craton, and provides important evidence of provenance in the North Yellow Sea Basin to determine the time of tectonic domain transformation. These results suggest that the source rocks of sediments in the North Yellow Sea Basin have changed from ancient sediments (ancient craton/recycle orogenic belt) in the Middle Jurassic to Late Jurassic, to felsic igneous rocks in the Early Cretaceous. The peak of zircon U–Pb ages changed from 234, 1,842, and 2,429 Ma in the Late Jurassic to 217 and 1,871 Ma in the Early Cretaceous. The provenance changed from the Sulu Orogenic Belt and Precambrian basement of the Jiaodong Peninsula in the Late Jurassic, to the igneous rocks and Precambrian basement of the Liaodong Peninsula and Korean Peninsula in the Early Cretaceous. The provenance direction of the sediments changed from south‐west in the Late Jurassic to the north and south‐east in the Early Cretaceous. The tectonic setting of the basin changed from compression to extension. The changes in the peaks of zircon U–Pb age, characteristics of the source rocks, provenance direction, and basin tectonic setting in the Middle Jurassic to Early Cretaceous in the North Yellow Sea Basin are a response to the change from E–W compression to NNE–SSW extensional tectonics caused by the transformation of two tectonic domains. In the Early Cretaceous, the Eastern North China Craton completed the transformation of two tectonic domains that were influenced and controlled by the marginal Pacific tectonic domain.

Neogene restoration of geometry of the Neotethyan suture zone in Central Anatolia (Turkey)

ABSTRACT We have restored the geometries of suture zones that involved various continental blocks in central Anatolia during the Neogene, using palaeomagnetic data. Previously, the Kırşehir Block was proposed to be an NNE-SSW striking tectonic block broken into three fragments that they underwent clockwise rotations in the north and counter-clockwise rotations in the south during the Palaeogene, due to collision and N-S shortening of the Kırşehir Block between Tauride-Menderes Block in the south and the Pontides in the north. Our new results point out five distinct Neogene tectonic domains with distinct rotation patterns that indicate the rotational deformation of Central Anatolia is far more complex than generally presumed. Among these, 1) Kırıkkale-Bala Domain is rotated ~18° clockwise, 2) the Tuz Gölü Domain underwent ~14° counter-clockwise rotation, 3) the Alcı-Orhaniye Domain rotated ~35° counter-clockwise sense, 4) the Northern Haymana Domain underwent ~12° counter-clockwise rotation while 5) the Southern Haymana Domain underwent very small (~5° clockwise) net rotation since the early Miocene. The results also indicated that pre-Neogene configuration of the Izmir-Ankara Suture Zone was striking almost E-W while Inner-Tauride and Ankara-Erzincan suture zones were almost N-S in the study area. In addition, the fault zones that define the these domains extend from the Kırşehir Block into the over-riding blocks (Pontides) continuously without any deflection indicating that they were active during the Neogene and fragmented and dislocated the suture zones in the region.