Thermal Structure Of Lithosphere Research Articles

Continental lithospheric structure from the East European Craton to the Pannonian Basin based on integrated geophysical modelling

Due to uncertainty of single-method interpretation we applied 2-D integrated lithospheric modelling along three CELEBRATION 2000 profiles CEL01, CEL04 and CEL05. Modelling of the lithospheric thermal structure is based on the joint interpretation of gravity, geoid, topography and surface heat flow data with temperature-dependent density. The models for each profile were constrained by seismic modelling results of the large-scale international project CELEBRATION 2000. The results indicate large variations of the lithosphere thickness from the old and cold East European Craton (~200 km) and the Trans European suture zone via the Western Carpathian orogeny to the young and hot Pannonian Basin (~90 km). Important differences in the lithospheric thickness were also found along-strike of the Western Carpathian orogeny and the Trans-European Suture Zone. The western part of the Western Carpathians is characterized by weak thickening of the lithosphere (only about 145 km), while their eastern segment presents strong lithospheric thickening (~190 km). The Małopolska unit in southern Poland has a lithospheric thickness of about 130 km. Thickest lithosphere (220 km) is observed around the junction of the Carpathian Foredeep and the East-European Craton. The crustal thickness follows generally the course of the lithosphere-asthenosphere boundary. The results suggest different geodynamic evolution of the collision of the ALCAPA microplate with the European platform on the one hand and the East-European Craton on the other hand. It is suggested that the tectonic evolution of this very complex area consisting of different tectonic units has changed in time and space.

Lithospheric structure of the Southwest South China Sea: implications for rifting and extension

ABSTRACT The South China Sea (SCS) is an excellent site for studying the process of conjugate margin rifting, and the origin and evolution of oceanic basins. Compared with the well-defined northern margin of the SCS, the western and southern segments of the SCS margin have not been researched in significant detail. To investigate the regional structure of the southwestern SCS, a gravity model is constructed, along with the lithospheric thermal structure along a wide-angle seismic profile. The profile extends across the conjugate margins of the Southwest Sub-Basin (SWSB) of the SCS and is based on the latest multiple geophysical measurements (including heat flow and thermo-physical parameters). The results show that the average thicknesses of the crust and thermal lithosphere along the profile are about 15 km and 57 km, respectively. The overall amount of extension of continental crust and lithosphere is more than 200 km. Thermal structure of the lithosphere shows that the continental margins are in a warm thermal state. The southwest SCS is characterized by ultra-wide, thinned continental crust and lithosphere, high Moho heat flow, early syn-rift faulted basins, undeformed late syn-rifting, and high seismic velocities in the lower crust. These various pieces of evidence suggest that the break-up of the mantle lithosphere occurred before that of the continental crust favouring a depth-dependent extension of the southwestern SCS margin.

Thermal conductivity of sedimentary rocks in the Sichuan basin, Southwest China

The optical scanning method was adopted to measure the thermal conductivities of 418 drill-core samples from 30 boreholes in Sichuan basin. All the measured thermal conductivities mainly range from 2.00 to 4.00 W/m K with a mean of 2.85 W/m K. For clastic rocks, the mean thermal conductivities of sandstone, mudstone, and shale are 3.06 ± 0.73, 2.57 ± 0.42, and 2.48 ± 0.33 W/m K, respectively; for carbonate rocks, the mean thermal conductivities of limestone and dolomite are 2.53 ± 0.44 and 3.55 ± 0.71 W/m K, respectively; for gypsum rocks, the mean thermal conductivity is 3.60 ± 0.64 W/m K. The thermal conductivities of sandstone and mudstone increase with burial depth and stratigraphic age, but this trend is not obvious for limestone and dolomite. Compared with other basins, the thermal conductivities of sandstone and mudstone in Sichuan basin are distinctly higher, while the thermal conductivities of limestone are close to Tarim basin. The content of mineral composition such as quartz is the principal factor that results in thermal conductivity of rocks differing from normal value. In situ thermal conductivity of sandstones was corrected with the consideration of water saturation. Finally, a thermal conductivity column of sedimentary formation of the Sichuan basin was given out, which can provide thermal conductivity references for the research of deep geothermal field and lithospheric thermal structure in the basin.

Reassessing the Thermal Structure of Oceanic Lithosphere With Revised Global Inventories of Basement Depths and Heat Flow Measurements

AbstractHalf‐space cooling and plate models of varying complexity have been proposed to account for changes in basement depth and heat flow as a function of lithospheric age in the oceanic realm. Here, we revisit this well‐known problem by exploiting a revised and augmented database of 2,028 measurements of depth to oceanic basement, corrected for sedimentary loading and variable crustal thickness, and 3,597 corrected heat flow measurements. Joint inverse modeling of both databases shows that the half‐space cooling model yields a mid‐oceanic axial temperature that is >100°C hotter than permitted by petrologic constraints. It also fails to produce the observed flattening at old ages. Then, we investigate a suite of increasingly complex plate models and conclude that the optimal model requires incorporation of experimentally determined temperature‐ and pressure‐dependent conductivity, expansivity, and specific heat capacity, as well as a low‐conductivity crustal layer. This revised model has a mantle potential temperature of 1300 ± 50°C, which honors independent geochemical constraints and has an initial ridge depth of 2.6 ± 0.3 km with a plate thickness of 135 ± 30 km. It predicts that the maximum depth of intraplate earthquakes is bounded by the 700°C isothermal contour, consistent with laboratory creep experiments on olivine aggregates. Estimates of the lithosphere‐asthenosphere boundary derived from studies of azimuthal anisotropy coincide with the 1175 ± 50°C isotherm. The model can be used to isolate residual depth and gravity anomalies generated by flexural and sub‐plate convective processes.

Present-day geothermal regime of the Uliastai Depression, Erlian Basin, North China

In this study, we calculated the present-day terrestrial heat flow of the Uliastai Depression in Erlian Basin by using systematical steady-state temperature data obtained from four deep boreholes and 89 thermal conductivity measurements from 22 boreholes. Then, we calculated the lithospheric thermal structure, thermal lithospheric thickness, and lithospheric thermo-rheological structure by combining crustal structure, thermal conductivity, heat production, and rheological parameter data. Research from the Depression shows that the present-day terrestrial heat flow ( qs) is 86.3 ± 2.3 mW/m2, higher than the average of 60.4 ± 12.3 mW/m2 of the continental area of China. Mantle heat flow ( qm) in the Depression ranges from 33.7 to 39.3 mW/m2, qm/ qs ranges from 40 to 44%, show that the crust plays the dominant position in the terrestrial heat flow. The thermal thickness of the lithosphere is about 74–88 km and characterized by a “strong crust–weak mantle” rheological characteristic. The total lithospheric strength is 1.5 × 1012 N/m under wet mantle conditions. Present-day geothermal regime indicates that the Uliastai Depression has a high thermal background, the activity of the deep-seated lithosphere is relatively intense. This result differs significantly from the earlier understanding that the area belongs to a cold basin. However, a hot basin should be better consistent with the evidences from lithochemistry and geophysical observations. The results also show the melts/fluids in the study area may be related to the subduction of the Paleo-Asian Ocean. The study of the geothermal regime in the Uliastai Depression provides new geothermal evidence for the volcanic activity in the eastern part of the Central Asian Orogenic Belt and has significant implications for the geodynamic characteristics.

Evaluate best-mixing model for estimating thermal conductivity for granitoids from mineralogy: A case study for the granitoids of the Bundelkhand craton, central India

Granitoid is an important part of the upper continental crust, and therefore its thermal conductivity (TC) plays an important role in understanding the lithospheric thermal structure in a region and for geotechnical or geoengineering purposes. In above context, due to the lack of TC data or absence of proper sample for its measurements, TC values are assumed which can lead to erroneous results. In such scenario, when direct measurements are not possible, TC can be estimated by indirect methods with proper precautions. An attempt is made here to arrive at the best mixing model for granitic rocks by using TC of the individual minerals and compare the deviation between the measured and calculated values. The considered mean models are: arithmetic, geometric, harmonic, effective, Voigt-Reuss-Hill and Hashin-Shtrikman along with its lower and upper bound. Studied rocks are potassic granitoid (PG), biotite granitoid (BG), sodic granitoid (GG) and gneisses (BnG) from the Bundelkhand craton, central India. Measurements of TC are done in the laboratory on 21 samples using steady-state method. Data show wide variations in TC values for granitoids (PG: 2.7 − 3.2, BG: 2.6 − 2.9, GG: 2.9 − 3.0 Wm−1 K−1) and gneisses (2.9 − 3.7 Wm−1 K−1). Modal mineralogy of the rocks are determined using petrological and geochemical data through modal analysis and normative (CIPW-NORM) methods. The calculated TC arrived by both the methods provide a satisfactory agreement for the harmonic mean model, showing deviation from −10.9 to 17.6% for modal analysis and −16.1 to 11.5% for NORM method. Deviations from the above methods decrease further (−23.3 to 2.8% and −27.7 to −3.1%, respectively) using minimum mineral TC. Therefore, we suggest that, in the case of non-availability of the proper sample for direct measurement, the TC of very low porous granitoids could be satisfactorily determined by assessing their modal mineralogy and considering the harmonic mean model.

Temperature and pressure effects on basalt thermal diffusivity – a review

Studying basalt thermal diffusivity under high temperature or high pressure is helpful to understand the lithospheric thermal structure and dynamics of subduction zone and to evaluate the heat-transmission mechanisms in basalt stratum. To explore the temperature and pressure effects on basalt thermal diffusivity, the authors collected data from literature reviews. A decrease in the basalt thermal diffusivity by an elevated temperature was obtained by an exponential function. An increase in basalt thermal diffusivity by pressure was found. The internal reasons of these two findings were explained by a classical physics theory. Moreover, the physical property changes by temperature and pressure are also the reasons of thermal-diffusivity change, which include crack generation, increase in porosity and decrease in density at elevated temperature and crack close, porosity decrease and grain contact under pressure.

Deep thermal structure of Southeast Asia constrained by S-velocity data

Southeast Asia, located in the southeastern part of the Eurasian Plate, is surrounded by tectonically active margins, exhibiting intense seismicity and volcanism, contains complex geological units with a perplexing evolution history. Because tectonic evolution is closely related to the deep thermal structure, an accurate estimation of the lithosphere thermal structure and thickness is important in extracting information on tectonics and geodynamics. However, there are significant uncertainties in the calculated deep thermal state constrained only by the observed surface heat flow. In this study, in order to obtain a better-constrained deep thermal state, we first calculate the deep thermal structure of Southeast Asia by employing an empirical relation between S-velocity and temperature, and then we estimate the base of the thermal lithosphere from the calculated temperature-depth profiles. The results show that, in general, the temperature is higher than the dry mantle solidus below the top of the seismic low-velocity zone, possibly indicating the presence of partial melt in the asthenosphere, particularly beneath oceanic basins such as the South China Sea. The temperature at a depth of 80 km in rifted and oceanic basins such as the Thailand Rift Basin, Thailand Bay, Andaman Sea, and South China Sea is about 200 °C higher than in plateaus and subduction zones such as the Khorat Plateau, Sumatra Island, and Philippine Trench regions. We suggest that the relatively cold and thick lithosphere block of the Khorat Plateau has not experienced significant internal deformation and might be extruded and rotated as a rigid block in response to the Indo-Eurasia collision. Our results show that the surface heat flow in the South China Sea is mainly dominated by the deep thermal state. There is a thermal anomaly in the Leiqiong area and in the areas adjacent to the northern margin of the South China Sea, indicating the presence of a high-temperature and thin lithosphere in the area of the well-known and controversial Hainan plume. The thermal lithosphere-asthenosphere boundary uplift area along the Xisha and southeastern Vietnam margin, in the western margin of South China Sea, which corresponds to the volcanic belt around this area, might indicate upwelling of hot mantle materials. The temperature values at 100 and 120 km depths through most regions of Southeast Asia are about 1400–1500 and 1550–1600 °C, respectively, which are nearly uniform with a small temperature difference. Our results also show that the lithosphere becomes thinner from the continent blocks toward the oceanic basins, with the smaller thickness values of 65–70 km in the South China Sea. The estimated base of the lithosphere corresponds approximately to the 1400 °C isotherm and shows good correlation with the tectonic setting.

Thermophysical parameters and lithospheric thermal structure in Guide Basin, Northeast Qinghai–Tibet Plateau

Comprehensive knowledge in lithospheric thermal structure and subsurface temperature distribution is indispensable for the research and utilization of geothermal resources. This paper studies the characteristics of heat generation rate and heat conductivity of shallow rocks and deep rocks encompassing Guide Basin by sampling, measuring, data collection and analysis, establishes the conceptual model of its lithospheric thermal structure. The research shows that the mantle heat flow of Guide Basin is about 35 mW/m2, and the ratio of crust heat flow to mantle heat flow is 1.2. With the one-dimensional steady-state thermal conduction formula, the temperature at different depth is calculated in the research area. Ground temperature at the depth of 1.5 and 3 km is about 72 and 115 °C, respectively. The depth of Curie surface is about 21–22.5 km with the temperature of 570–600 °C, and the temperature of Moho is about 1100 °C. Most of the analysis results above are consistent with previous research findings in the research area and its vicinities, proving the reasonability of the lithospheric thermal structure model established by this paper. As the geothermal research of Guide Basin still stays at a low level, the conceptual model of lithospheric thermal structure in Guide Basin established in this paper still needs to be improved and corrected with new methods and data in further study.

Dynamics of unstable continental subduction: Insights from numerical modeling

Numerical experiments are used in this study to systematically investigate the effects of convergence rate, crustal rheological strength, and lithospheric thermal structure on the dynamics of continental collision. The study focuses on the types, conditions and processes of unstable continental subduction. Modelling results suggest that the development of unstable continental subduction can be promoted by conditions that tend to decrease rheological strength of the lithosphere, such as low crustal rheological strength, “hot” thermal structure of the lithosphere, or low convergence rate. Unstable subduction mode can be further categorized into three types: (1) multi-stage slab breakoff, (2) continuously “flowing” of fluid-like slab into the upper mantle, and (3) large-scale detachment of the thickened orogenic root. These three types of unstable continental subduction are respectively associated with (1) a low convergence rate, (2) “hot” thermal structure of the lithosphere with a high convergence rate, and (3) moderate-high crustal rheological strength with a low convergence rate. It is also revealed that the evolution of crustal melting is dominated by the deformation pattern of continental collision, which is mainly controlled by crustal rheological strength. The modelling results have important implications for understanding of continental subduction mode selection under specific geodynamic conditions.

Lithospheric thermal structure of the North China Craton and its geodynamic implications

We conduct 2-D numerical modeling of the lithospheric thermal structure of the North China Craton (NCC) on basis of twenty-four crustal velocity structure profiles. About five hundred heat flow data constitute the principal constraints for our modeling. The modeling results demonstrate marked lateral variations in thermal regime of the crust-lithosphere system in the NCC. The average mantle heat flow decreases from 38±5mWm−2 under the Bohai Bay Basin in the eastern NCC to 27±4mWm−2 under the Ordos Basin in the western NCC, characterized by a ‘cold crust but hot mantle’ structure and a ‘hot crust but cold mantle’ structure, respectively. Thermal lithospheric thickness varies from ∼65km beneath the Tan-Lu Fault zone to ∼160km beneath the western and northern Ordos Basin, with similar trend to the seismic lithosphere. However, the disparities in thickness between the thermal and seismic lithosphere are within 20km beneath the Bohai Bay Basin, but 30–90km beneath the Shanxi-Weihe Graben and 50–120km beneath the Ordos Basin. This may imply a westward thickening trend of the rheological boundary layer, which might be attributed to the reducing of asthenosphere viscosity due to hydrous fluid released by dehydration of the subducting Pacific Plate under the eastern NCC. Combined with other pieces of evidence, we suggest that vigorous mantle processes may occur beneath the eastern NCC, whereas the western NCC is relatively stable.

Meso–Cenozoic lithospheric thermal structure in the Bohai Bay Basin, eastern North China Craton

The Bohai Bay Basin is a region where part of the North China Craton has been thinned and destroyed. It has experienced two periods of crustal thinning that occurred during the Cretaceous and Paleogene, but investigations of its Mesozoic and Cenozoic lithospheric thermal structure are limited. Therefore, in this study, the distributions of mantle heat flow, crustal heat flow, and Moho temperatures during the Meso–Cenozoic are calculated based on analyses of the thermal history of the Bohai Bay Basin. The results indicate that the ratio of mantle heat flow to surface heat flow peaked during the late stages of the early Cretaceous and during the middle to late Paleogene. The corresponding mantle heat flow was more than 65% of the surface heat flow. Moho temperatures reached three peaks: 900–1100 °C in the late stages of the early Cretaceous; 820–900 °C in the middle to late Paleogene; and (in the Linqing Depression, Cangxian Uplift, and Jizhong Depression) 770–810 °C during the early Neogene. These results reveal that the Bohai Bay Basin experienced significant geological change during the Cretaceous, including the transformation of lithospheric thermal structure from “cold mantle and hot crust” before the Cretaceous to “hot mantle and cold crust” after the Cretaceous. The results also indicate that the basin experienced two large-scale rifting events. Therefore, this work may provide the thermal parameters for further investigations of the geodynamic evolution of eastern China.

Magmatic expressions of continental lithosphere removal

AbstractGravitational lithosphere removal in continental interior has been inferred from various observations, including anomalous surface deflections and magmatism. We use numerical models and a simplified theoretical analysis to investigate how lithosphere removal can be recognized in the magmatic record. One style of removal is a Rayleigh‐Taylor‐type instability, where removal occurs through dripping. The associated magmatism depends on the lithosphere thermal structure. Four types of magmatism are predicted: (1) For relatively hot lithosphere (e.g., back arcs), the lithosphere can be conductively heated and melted during removal, while the asthenosphere upwells and undergoes decompression melting. If removal causes significant lithospheric thinning, the deep crust may be heated and melted. (2) For moderately warm lithosphere (e.g., average Phanerozoic lithosphere) in which the lithosphere root has a low density, only the lithosphere may melt. (3) If the lithosphere root has a high density in moderately warm lithosphere, only asthenosphere melt is predicted. (4) For cold lithosphere (e.g., cratons), no magmatism is induced. An alternate style of removal is delamination, where dense lithosphere peels along Moho. In most cases, the lithosphere sinks too rapidly to melt. However, asthenosphere can upwell to the base of the crust, resulting in asthenospheric and crustal melts. In delamination, magmatism migrates laterally with the detachment point; in contrast, magmatism in Rayleigh‐Taylor‐type instability has a symmetric shape and converges toward the drip center. The models may explain the diversity of magmatism observed in areas with inferred lithosphere removal, including the Puna Plateau and the southern Sierra Nevada.

Surface heat flow and lithosphere thermal structure of the Rhenohercynian Zone in the greater Luxembourg region

Comprehensive knowledge of surface heat flow and subsurface temperature distribution is indispensable for the interpretation and quantification of crustal/mantle processes as well as for the evaluation of the geothermal potential of an area. In cases where subsurface temperature data are sparse, thermal modeling may be used as a tool for inferring the geothermal resource at depth but requires profound structural, geological, and petrophysical input data. The study area encompasses the Trier–Luxembourg Basin and the western realm of the Rhenish Massif, itself subdivided into the Ardennes region in the west as well as the Eifel and Hunsrück regions in the east. For the study area, 2-D steady-state and conductive thermal models were established based on geological models of lithosphere-scale which were parameterized using thermal rock properties including thermal conductivity, radiogenic heat production, and density. The thermal models are constrained by surface heat flow (qs) and the geophysically-estimated depth of the lithosphere–asthenosphere boundary (LAB). A qs of 75±7 (2σ)mWm−2 was determined in the area. A LAB depth of 100km, as seismically derived for the Ardennes, provides the best fit with the measured qs. Modeled temperatures are in the range of 120–125°C at 5km depth and of 600–650°C at the Moho, respectively. The mantle heat flow amounts to ∼40mWm−2. Possible thermal consequences of the 10–20Ma old Eifel plume, which caused elevation of the LAB to 50–60km depth, were modeled in a steady-state thermal scenario resulting in a qs of 91mWm−2 in the Eifel region. Available qs values (65–80mWm−2) are significantly lower and do indicate that the plume-related heating has not yet reached the surface in its entirety.

Along‐axis hydrothermal flow at the axis of slow spreading Mid‐Ocean Ridges: Insights from numerical models of the Lucky Strike vent field (MAR)

AbstractThe processes and efficiency of hydrothermal heat extraction along the axis of mid‐ocean ridges are controlled by lithospheric thermal and permeability structures. Hydrothermal circulation models based on the structure of fast and intermediate spreading ridges predict that hydrothermal cell organization and vent site distribution are primarily controlled by the thermodynamics of high‐temperature mid‐ocean ridge hydrothermal fluids. Using recent constraints on shallow structure at the slow spreading Lucky Strike segment along the Mid‐Atlantic Ridge, we present a physical model of hydrothermal cooling that incorporates the specificities of a magma‐rich slow spreading environment. Using three‐dimensional numerical models, we show that, in contrast to the aforementioned models, the subsurface flow at Lucky Strike is primarily controlled by across‐axis permeability variations. Models with across‐axis permeability gradients produce along‐axis oriented hydrothermal cells and an alternating pattern of heat extraction highs and lows that match the distribution of microseismic clusters recorded at the Lucky Strike axial volcano. The flow is also influenced by temperature gradients at the base of the permeable hydrothermal domain. Although our models are based on the structure and seismicity of the Lucky Strike segment, across‐axis permeability gradients are also likely to occur at faster spreading ridges and these results may also have important implications for the cooling of young crust at fast and intermediate spreading centers.

Characteristics of Heat Flow and Lithospheric Thermal Structure in the Junggar Basin, Northwestern China

AbstractCharacteristics of present‐day heat flow and thermal structure of lithosphere in basins are essential constraints to reveal the tectonic‐thermal evolution process and to reconstruct thermal history of the basins, which are of great significance for research of basin dynamics and evaluation of petroleum resources. This work is based on 11 newly measured high‐quality heat flow values from well‐log temperature data in 102 boreholes, oil‐test temperature data in over 400 new boreholes, and thermal conductivity data of 187 samples from 15 wells measured by optical scanning in the Junggar basin. Our purpose is to analyze features of heat flow and reveal thermal structure of lithosphere in this basin. The results show current geotemperature gradients between 11.6∼27.6 °C/km, 21.3+3.7 °C/km on average; and surface heat flow between 23.4∼56.1 mW/m2; 42.5+7.41 mW/m2 on average; which imply a cold basin with low geotemperature gradients and low heat flow. These values in the Junggar basin are distributed in largely consistent patterns, primarily controlled by the structural shape of the basement. They are the highest at the uplift in the east, next at the Luliang uplift, relatively low in the Wulungu depression, central depression, and the uplift in the west, and lowest in the range‐front depression of the North TianShan. Beneath the Junggar basin, the crustal heat flow is 18.8∼26.0 mW/m2, mantle heat flow 16.5∼23.7 mW/m2, the ratio of the former to the latter is 0.79∼1.58, indicative of a thermal structure of cold crust and cold mantle. The distribution of mantle heat flow values accords with topography of the Moho interface, which are high below uplifts and low beneath depressions in the basin.

A preliminary study on the lithospheric thermal structure and rheology of the Tibetan plateau

The lithosphere temperature beneath the Tibetan plateau was estimated by local isostasy equilibrium constrained geothermal calculation. Maps of the lateral temperature variation at depths of 40 km, 70 km, and Moho are presented for the Tibetan plateau, and the thermal thickness of the lithosphere is also presented. The Tibetan plateau has a warm and thick lithospheres, but the thinner lithospheres are identified in the northern Tibet and the eastern margin of the plateau. The warm and soft lithospheres in the Tibetan plateau may represent a snapshot of the early stage of convective thinning of the convergent lithosphere. The “crème brûlée” layering demonstrates the rheological behavior of the Tibetan plateau.

Thermal and rheological structures along the seismic POLAR profile in the northern Fennoscandian Shield

Terra Nova, 25, 2–12, 2013AbstractExtensive study is carried out to resolve the detailed lithospheric thermal and rheological structures of the seismic profile POLAR in the northern Fennoscandian Shield. The constructed 2‐D models are based on the latest seismic velocity models, material parameters and measured heat flow (HF) values. Thermal results indicate the mantle HF to be low (13–15 mWm−2) and the thermal lithosphere‐asthenosphere boundary to be at a depth of 190–225 km. Rheologically southwest (SW) and northeast (NE) parts of the profile differ significantly, e.g. the depth of the brittle‐ductile transition varies from 24–38 km in the SW to 12–18 km in the NE. The estimated values of the effective elastic thickness of the lithosphere show large variation between the depths of 63 and 132 km.

Lithospheric thermal structure and rheology of the eastern China

Temperature distributions of the lithosphere beneath the eastern China were estimated by local isostasy equilibrium constrained geothermal calculation in this study. Maps of the lateral temperature variation at depths of 50 and 100km as well as Moho boundary are presented for the eastern China continent, and the 600°C and 1100°C isotherm depth maps are also given. Meanwhile, the thermal thickness of lithosphere is calculated as the depth of 1350°C isotherm. The rheological strength of lithosphere is calculated based on a four-layer model, which consists of the upper, lower, lowermost crust layers and a wet lithospheric mantle layer. The results show that, the lithosphere of 160–180km thick exists under Sichuan basin in the western part of Yangtze Craton, but keel is absent beneath the entire North China Craton. It is notable that the lithospheric thickness is only 130–140km beneath Ordos basin in the western part of North China Craton; accordingly, there is no lithospheric keel beneath Ordos basin. These geothermal modeling results are in good agreement with those of seismic tomography and other geothermal studies. The temperatures in the lower crust of the North China Craton estimated are in range of 500–600°C. Consequently, the composition of lower crust of the North China Craton should be more mafic than that of previous estimation based on much cooler geotherms. The spatial variation of lithospheric rheology in the eastern China is influenced by local geotherms and crustal compositions. The “crème brûlée” model, which is represent by a strong crust portion but a weak lithospheric mantle portion in vertical strength profile, approximates the lithospheric rheological layering for the regions of the western half of North China Craton and the northern part of NE China, which has thicker crust or moderate-to-high geotherm. On the other hand, the “jelly sandwich” model demonstrates the rheological layering of the western part of the Yangtze Craton and the eastern half of the North China Craton, which has low-to-moderate geotherm and/or thinner crust. In general, thermal age of the tectonic province controls the present-day thermal structure and rheology of the lithosphere of the eastern China.

Eastern South China Sea Basin Expansion Numerical Simulation

AbstractThe formation and evolution of South China Sea has been one of the hot spot of attention at home and abroad. The expansion of the South China Sea happened in early Oligocene‐early Miocene, and the expansion of South China Sea includes ridge transition once at least. This paper uses a model of rising divergent mantle flow and convection coupling to simulate the expansion of eastern sea basin of the South China Sea, the ridge jump, and the process of lithosphere thermal structure evolution and melting of magma after expansion. Numerical simulation results indicate that a ridge jump is an important process of the South China Sea expansion. Ridge jump forms a magma chamber between the two ridges, and the existence of the magma chamber makes the submarine volcanoes relatively more and the terrain relatively high between the ridges. At the same time, it also leads to the terrain of both sides of south side ridge and the distribution of submarine volcano asymmetric, which in turn can demonstrate the reasonability of ridge jump model.