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

This article discusses the Meso–Cenozoic thermal history, thermal lithospheric thinning, and thermal structure of the lithosphere of the Bohai Bay Basin, North China. The present-day thermal regime of the basin features an average heat flow of 64.5 ± 8.1 mW m^–2, a lithospheric thickness of 76–102 km, and a ‘hot mantle but cold crust’-type lithospheric thermal structure. The Meso–Cenozoic thermal history experienced two heat flow peaks in the late Early Cretaceous and in the middle to late Palaeogene, with heat flow values of 82–86 mW m^?2 and 81–88 mW m^?2, respectively. Corresponding to these peaks, the thermal lithosphere experienced two thinning stages during the Cretaceous and Palaeogene, reaching a minimum thickness of 43–61 km. The lithospheric thermal structure transformed from the ‘hot crust but cold mantle’ type in the Triassic–Jurassic to the ‘cold crust but hot mantle’ type in the Cretaceous–Cenozoic, according to the ratio of mantle to surface heat flow (q_m/q_s). The research on the thermal history and lithospheric thermal structure of sedimentary basins can effectively reveal the thermal regime at depth in the sedimentary basins and provide significance for the study of the basin dynamics during the Meso–Cenozoic.     

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℃ in the late stages of the early Cretaceous;820-900℃ in the middle to late Paleogene; and(in the Linqing Depression, Cangxian Uplift, and Jizhong Depression) 770-810℃ 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.     

Wide rift model in Bohai Bay Basin: insight into the destruction of the North China Craton

The Bohai Bay Basin is a Cenozoic extensional basin along the eastern aspect of Asia. Whether the Bohai Bay Basin is a pull-apart or rift basin is controversial. The Bohai Bay Basin exhibits a high density of extensional faults and records destruction of the North China Craton. Many structural analyses have been performed on the Bohai Bay Basin, especially the Tan-L and Taihang Mountain fault systems which control its boundary. The initial deposition of Kongdian Formation was mainly distributed along the boundary of Bohai Bay Basin during the Palaeocene–early Eocene. Subsequently, tectonic activity migrated toward the interior of the basin during deposition of Shahejie Formation in the middle Eocene–early Oligocene. Bohai Bay Basin crust was thickened in early Mesozoic time and has thinned since late Mesozoic time. The crustal strength profile of Bohai Bay Basin is characterized by very weak lower crust, which differs from that of adjacent crust. In regard to the crustal structure, lithospheric thickness, and extensional style, an alternative rift model is proposed. Initial Bohai Bay Basin rifts were characterized by metamorphic core complexes affecting the North China Craton, which reflects collapse of parts of the early Mesozoic intra-plate orogen. Furthermore, westward subduction of the Palaeo-Pacific Plate led to upwelling of asthenosphere mantle. Persistent upwelling of mantle decreased the strength of lower crust and led to the warm heat-flow regime and generation of a lower crustal fluid layer and wide rifting. Outward flow of ductile lower crust following late Cretaceous extension thinned the lower crust and generated the overall sag appearance of the basin in early Cenozoic time. The model supports a model whereby a wide rift narrows with time. For the Bohai Bay Basin, extension and strike-slip faulting were two independent deformation systems superimposed on each other.     

Tectono-metamorphic evolution of the Karakorum Metamorphic complex (Dassu–Askole area, NE Pakistan): exhumation of mid-crustal HT–MP gneisses in a convergent context

The South Karakorum margin, east of the Himalayan syntaxis, consist of an E–W elongated zone of young (10–3 Ma) high‐grade metamorphic rocks (M2) and related migmatitic domes. This late tectono‐metamorphic event post‐dates the Palaeogene (55–37 Ma) phase of thickening of the belt featured by NW–SE structures and associated M1 amphibolite facies metamorphism (0.7 GPa, 700 °C). This M2 metamorphism is characterised by low‐pressure, high‐temperature conditions coeval with migmatite formation in response to a thermal increase of c. 150 °C compared to M1, culminating at a temperature of c. 770 °C and a pressure of 0.5–0.6 GPa. Rapid exhumation of migmatitic domes, at a rate of 5 mm yr^?1, was accommodated by vertical extrusion, in the core of E–W crustal‐scale folds. These crustal‐scale folds formed in response to N–S syn‐collisional shortening and were enhanced by thermal weakening of the migmatised continental crust. M2 metamorphism is spatially and temporarily associated with granitoids showing a mantle affinity, firmly suggesting that this could be the advective heat source for the granite and syenite generation and the subsequent migmatisation of the mid‐crustal level. Such relationships between a mantle‐related magmatism and a high‐temperature metamorphism in a convergent shortening context are suggestive of the breakoff of the subducted Indian slab since 20 Ma.     

High-T, low-P metamorphism in the Palaeoproterozoic Halls Creek Orogen, northern Australia: the middle crustal response to a mantle-related transient thermal pulse

High‐T, low‐P metamorphic rocks of the Palaeoproterozoic central Halls Creek Orogen in northern Australia are characterised by low radiogenic heat production, high upper crustal thermal gradients (locally exceeding 40 °C km^?1) sustained for over 30 Myr, and a large number of layered mafic‐ultramafic intrusions with mantle‐related geochemical signatures. In order to account for this combination of geological and thermal characteristics, we model the middle crustal response to a transient mantle‐related heat pulse resulting from a temporary reduction in the thickness of the mantle lithosphere. This mechanism has the potential to raise mid‐crustal temperatures by 150–400 °C within 10–20 Myr following initiation of the mantle temperature anomaly, via conductive dissipation through the crust. The magnitude and timing of maximum temperatures attained depend strongly on the proximity, duration and lateral extent of the thermal anomaly in the mantle lithosphere, and decrease sharply in response to anomalies that are seated deeper than 50–60 km, maintained for <5 Myr in duration and/or have half‐widths <100 km. Maximum temperatures are also intimately linked to the thermal properties of the model crust, primarily due to their influence on the steady‐state (background) thermal gradient. The amplitudes of temperature increases in the crust are principally a function of depth, and are broadly independent of crustal thermal parameters. Mid‐crustal felsic and mafic plutonism is a predictable consequence of perturbed thermal regimes in the mantle and the lowermost crust, and the advection of voluminous magmas has the potential to raise temperatures in the middle crust very quickly. Although pluton‐related thermal signatures significantly dissipate within <10 Myr (even for very large, high‐temperature intrusive bodies), the interaction of pluton‐ and mantle‐related thermal effects has the potential to maintain host rock temperatures in excess of 400–450 °C for up to 30 Myr in some parts of the mid‐crust. The numerical models presented here support the notion that transient mantle‐related heat sources have the capacity to contribute significantly to the thermal budget of metamorphism in high‐T, low‐P metamorphic belts, especially in those characterised by low surface heat flow, very high peak metamorphic geothermal gradients and abundant mafic intrusions.     

Formation Laws of Inorganic Gas Pools in the Northern Jiangsu Basin

In the Northern Jiangsu basin there are high pure CO2 gas pools, low condensed oil-containing CO2 gas pools, high condensed oil-containing CO2 gas pools and He-containing natural gas pools, with the δ13Cco2 (PDB) values ranging from -2.87‰ to -6.50‰, 3He/4He 3.71×10-6 to 6.42×10-6, R/Ra 2.64 to 4.5, 40Ar/36Ar 705 to 734, belonging to typical mantle source inorganic gas pools which are related to young magmatic activity. The gas layers occur in two major reservoir-caprock systems, the terrestrial Meso-Cenozoic clastic rock system and the marine Meso-Palaeozoic carbonate rock-clastic rock system. Controlled by the difference in the scale of traps in the two reservoir-caprock systems, large and medium-scale inorganic gas pools are formed in the marine Meso-Palaeozoic Group and only small ones are formed in the terrestrial Meso-Cenozoic strata. Inorganic gas pools in this basin are distributed along the two deep lithospheric faults on the west and south boundaries of the basin. Gas pools are developed     

Velocity structure and geothermics of the Earth's crust along the European Geotraverse

Crustal isovelocity lines are constructed along the European Geotraverse for the seismic velocities 6.0, 6.4, 7.1 and 7.8 km/s. Using this velocity structure and a correlation between heat generation and seismic velocity for crustal rocks, the contribution of the crust to the surface heat flow density value is calculated. The heat flow density at the Moho varies from 5 to 40 mW/m² from Paleo-Europe in the north to Neo-Europe in the south, while the mantle heat flow density is close to zero beneath the Alps; the temperatures calculated for the Moho are 260°–390°C for Paleo- to Meso-Europe, 420°–520°C for Neo-Europe and 700°C for the mountain-root beneath the Alps.     

A tentative 2D thermal model of central India across the Narmada-Son Lineament (NSL)

This work deals with 2D thermal modeling in order to delineate the crustal thermal structure of central India along two Deep Seismic Sounding (DSS) profiles, namely Khajuriakalan–Pulgaon and Ujjan–Mahan, traversing the Narmada-Son-Lineament (NSL) in an almost north–south direction. Knowledge of the crustal structure and P-wave velocity distribution up to the Moho, obtained from DSS studies, has been used for the development of the thermal model. Numerical results reveal that the Moho temperature in this region of central India varies between 500 and 580 °C. The estimated heat flow density value is found to vary between 46 and 49 mW/m². The Curie depth varies between 40 and 42 km and is in close agreement with the Curie depth (40±4 km) estimated from the analysis of MAGSAT data. Based on the present work and previous work, it is suggested that the major part of peninsular India consisting of the Wardha–Pranhita Godavari graben/basin, Bastar craton and the adjoining region of the Narmada Son Lineament between profiles I and III towards the north and northwest of the Bastar craton are characterized with a similar mantle heat flow density value equal to ∼23 mW/m². Variation in surface heat flow density values in these regions are caused by variation in the radioactive heat production and fluid circulation in the upper crustal layer.     

The thermal structure of continental crust in active orogens: insight from Miocene eclogite and granulite xenoliths of the Pamir Mountains

Rare ultrahigh‐temperature–(near)ultrahigh‐pressure (UHT–near‐UHP) crustal xenoliths erupted at 11 Ma in the Pamir Mountains, southeastern Tajikistan, preserve a compositional and thermal record at mantle depths of crustal material subducted beneath the largest collisional orogen on Earth. A combination of oxygen‐isotope thermometry, major‐element thermobarometry and pseudosection analysis reveals that, prior to eruption, the xenoliths partially equilibrated at conditions ranging from 815 °C at 19 kbar to 1100 °C at 27 kbar for eclogites and granulites, and 884 °C at 20 kbar to 1012 °C at 33 kbar for garnet–phlogopite websterites. To reach these conditions, the eclogites and granulites must have undergone mica‐dehydration melting. The extraction depths exceed the present‐day Pamir Moho at ～65 km depth and suggest an average thermal gradient of ～12–13 °C km^?1. The relatively cold geotherm implies the introduction of these rocks to mantle depths by subduction or gravitational foundering (transient crustal drip). The xenoliths provide a window into a part of the orogenic history in which crustal material reached UHT–(U)HP conditions, partially melted, and then decompressed, without being overprinted by the later post‐thermal relaxation history.     

渤海湾盆地形成与华北克拉通破坏

渤海湾盆地是一个中、新生代盆地,位于华北克拉通的东部地块上,是华北克拉通破坏的中心区域。渤海湾盆地的结构、构造记录了华北克拉通破坏的构造过程。文章综合10a来据三维地震资料揭示的渤海湾盆地构造,和20a来渤海湾盆地周边华北克拉通区域中、新生代构造和地球化学研究成果,系统提出华北克拉通破坏期间,渤海湾盆地深、浅部的构造机制分别为:中生代浅部构造机制是挤出构造成因,深部构造机制为局部有限的拆沉+底侵模式;新生代构造机制是北西向壳内伸展机制,与印度和欧亚板块碰撞激发的软流圈的东扩远程效应和太平洋俯冲带的跃迁式东撤的联合效应——区域性"西进东退"的深部机制有关。     

Thermal structure of lithosphere in Central Asian and Pacific belts and their adjacent cratons,from data of geoscience transects

We investigate the 2D thermal structure of lithosphere in the Central Asian and Pacific tectonic belts and adjacent cratonic areas of Siberia and North China using a synthesis of geothermal data from six geoscience transects covered by seismic, resistivity, and gravity surveys. The patterns of rock density, radiogenic heat production derived from U and Th abundances, thermal conductivity, temperatures, and respective heat flows reveal a layered structure. The model with layers distinguished according to density and thermal parameters includes well pronounced dome-shaped features in the crust which correlate with upwarps of the asthenospheric top. The domes are marked by high heat flows of 60–90 mW/m² with a mantle component higher than the crustal one (30–60 mW/m² against 20–30 mW/m²) and temperatures as high as 800–1100 °C at the Moho. Many of these features correspond to known and potential petroleum basins.     

Present Terrestrial Heat Flow Measurements of the Geothermal Fields in the Chagan Sag of the YingenEjinaqi Basin,Inner Mongolia,China

Owing to the lack o f terrestrial heat flow data, studying lithospheric thermal structure and geodynamics of the Yingen-Ejinaqi Basin in Inner Mongolia is limited. In this paper, the terrestrial heat flow o f the Chagan sag in the YingenEjinaqi Basin were calculated by 193 system steady-state temperature measurements of 4 wells, and newly measuring 62 rock thermal conductivity and 20 heat production rate data on basis o f the original 107 rock thermal conductivity and 70 heat production data. The results show that the average thermal conductivity and heat production rate are 2.11 ±0.28 W/(m.K) and2.42±0.25 nW/m~3 in the Lower Cretaceous o f the Chagan sag. The average geothermal gradient from the Lower Suhongtu 2 Formation to the Suhongtu 1 Fonnation is 37.6 °C/km, and that o f the Bayingebi 2 Formation is 27.4 °C/km. Meanwhile, the average terrestrial heat flow in the Chagan sag is 70.6 mW/m~2. On the above results, it is clear that there is an obvious negative correlation between the thermal conductivity o f the stratum and its geothermal gradient. Moreover, it reveals that there is a geothermal state between tectonically stable and active areas. This work may provide geothermal parameters for further research o f lithospheric thermal structure and geodynamics in the Chagan sag.     

Peak‐temperature patterns of polyphase metamorphism resulting from accretion,subduction and collision (eastern Tauern Window,European Alps) – a study with Raman microspectroscopy on carbonaceous material (RSCM)

Raman microspectroscopy on carbonaceous material (RSCM) from the eastern Tauern Window indicates contrasting peak‐temperature patterns in three different fabric domains, each of which underwent a poly‐metamorphic orogenic evolution: Domain 1 in the northeastern Tauern Window preserves oceanic units (Glockner Nappe System, Matrei Zone) that attained peak temperatures (T_p) of 350–480 °C following Late Cretaceous to Palaeogene nappe stacking in an accretionary wedge. Domain 2 in the central Tauern Window experienced T_p of 500–535 °C that was attained either within an exhumed Palaeogene subduction channel or during Oligocene Barrovian‐type thermal overprinting within the Alpine collisional orogen. Domain 3 in the Eastern Tauern Subdome has a peak‐temperature pattern that resulted from Eo‐Oligocene nappe stacking of continental units derived from the distal European margin. This pattern acquired its presently concentric pattern in Miocene time due to post‐nappe doming and extensional shearing along the Katschberg Shear Zone System (KSZS). T_p values in the largest (Hochalm) dome range from 612 °C in its core to 440 °C at its rim. The maximum peak‐temperature gradient (≤70 °C km^?1) occurs along the eastern margin of this dome where mylonitic shearing of the Katschberg Normal Fault (KNF) significantly thinned the Subpenninic‐ and Penninic nappe pile, including the pre‐existing peak‐temperature gradient.     

Heat flow and lithospheric thermal regime in the Northeast German Basin

New values of surface heat flow are reported for 13 deep borehole locations in the Northeast German Basin (NEGB) ranging from 68 to 91 mW m^− 2 with a mean of 77 ± 3 mW m^− 2. The values are derived from continuous temperature logs, measured thermal conductivity, and log-derived radiogenic heat production. The heat-flow values are supposed free of effects from surface palaeoclimatic temperature variations, from regional as well as local fluid flow and from thermal refraction in the vicinity of salt structures and thus represent unperturbed crustal heat flow. Two-D numerical lithospheric thermal models are developed for a 500 km section along the DEKORP-BASIN 9601 deep seismic line across the basin with a north-eastward extension across the Tornquist Zone. A detailed conceptual model of crustal structure and composition, thermal conductivity, and heat production distribution is developed. Different boundary conditions for the thickness of thermal lithosphere were used to fit surface heat flow. The best fit is achieved with a thickness of thermal lithosphere of about 75 km beneath the NEGB. This estimate is corroborated by seismological studies and somewhat less than typical for stabilized Phanerozoic lithosphere. Modelled Moho temperatures in the basin are about 800 °C; heat flow from the mantle is about 35 to 40 mW m^− 2. In the southernmost part of the section, beneath the Harz Mountains, higher Moho temperatures up to 900 to 1000 °C are shown. While the relatively high level of surface heat flow in the NEGB obviously is of longer wave length and related to lithosphere thickness, changes in crustal structure and composition are responsible for short-wave-length anomalies.     

Interaction of metamorphism, deformation and exhumation in large convergent orogens

Coupled thermal‐mechanical models are used to investigate interactions between metamorphism, deformation and exhumation in large convergent orogens, and the implications of coupling and feedback between these processes for observed structural and metamorphic styles. The models involve subduction of suborogenic mantle lithosphere, large amounts of convergence (≥ 450 km) at 1 cm yr^?1, and a slope‐dependent erosion rate. The model crust is layered with respect to thermal and rheological properties — the upper crust (0–20 km) follows a wet quartzite flow law, with heat production of 2.0 μW m^?3, and the lower crust (20–35 km) follows a modified dry diabase flow law, with heat production of 0.75 μW m^?3. After 45 Myr, the model orogens develop crustal thicknesses of the order of 60 km, with lower crustal temperatures in excess of 700 °C. In some models, an additional increment of weakening is introduced so that the effective viscosity decreases to 10¹⁹ Pa.s at 700 °C in the upper crust and 900 °C in the lower crust. In these models, a narrow zone of outward channel flow develops at the base of the weak upper crustal layer where T≥600 °C. The channel flow zone is characterised by a reversal in velocity direction on the pro‐side of the system, and is driven by a depth‐dependent pressure gradient that is facilitated by the development of a temperature‐dependent low viscosity horizon in the mid‐crust. Different exhumation styles produce contrasting effects on models with channel flow zones. Post‐convergent crustal extension leads to thinning in the orogenic core and a corresponding zone of shortening and thrust‐related exhumation on the flanks. Velocities in the pro‐side channel flow zone are enhanced but the channel itself is not exhumed. In contrast, exhumation resulting from erosion that is focused on the pro‐side flank of the plateau leads to ‘ductile extrusion’ of the channel flow zone. The exhumed channel displays apparent normal‐sense offset at its upper boundary, reverse‐sense offset at its lower boundary, and an ‘inverted’ metamorphic sequence across the zone. The different styles of exhumation produce contrasting peak grade profiles across the model surfaces. However, P–T–t paths in both cases are loops where P_max precedes T_max, typical of regional metamorphism; individual paths are not diagnostic of either the thickening or the exhumation mechanism. Possible natural examples of the channel flow zones produced in these models include the Main Central Thrust zone of the Himalayas and the Muskoka domain of the western Grenville orogen.     

Geochemical and isotopic characteristics of fluids in the Niutuozhen geothermal field,North China

Niutuozhen geothermal field is located in the Jizhong graben, belonging to the northern part of Bohai Bay Basin in North China. Chemical and isotopic analyses were carried out on 14 samples of the geothermal fluids discharged from Neogene Minghuazhen (Nm), Guantao (Ng), and Jixianian Wumishan (Jxw) formations. The δ²H and δ¹⁸O in water, δ¹³C in CH₄, δ¹³C in CO₂, and ³He/⁴He ratio in the gases were analyzed in combination with chemical analyses on the fluids in the Niutuozhen geothermal field. The chemical and isotopic compositions indicate a meteoric origin of the thermal waters. The reservoir temperatures estimated by chemical geothermometry are in the range between 60 and 108 °C. The results show that the gases are made up mainly by N₂ (18.20–97.42 vol%), CH₄ (0.02–60.95 vol%), and CO₂ (0.17–25.14 vol%), with relatively high He composition (up to 0.52 vol%). The chemical and isotopic compositions of the gas samples suggest the meteoric origin of N₂, predominant crustal origins of CH₄, CO₂, and He. The mantle-derived He contributions are calculated to be from 5 to 8% based on a crust–mantle binary mixing model. The deep temperatures in the Jxw reservoir were evaluated based on gas isotope geothermometry to be in the range from 141 to 165 °C. The mantle-derived heat fraction in the surface heat flow is estimated to be in the range of 48–51% based on ³He/⁴He ratios.     

Geothermal structure of the eastern Pontides orogenic belt： Implications oceanic lithosphere Black Sea basin and the eastern for subduction polarity of Tethys

The numerical results of thermal modeling studies indicate that the lithosphere is cold and strong beneath the Black Sea basin.The thermal lithospheric thickness increases southward from the eastern Pontides orogenic belt（49.4 km） to Black Sea basin（152.2 km）.The Moho temperature increases from 367℃in the trench to 978℃in the arc region.The heat flow values for the Moho surface change between 16.4 mW m^-2 in the Black Sea basin and 56.9 mW m^-2 in the eastern Pontides orogenic belt. Along the southern Black Sea coast,the trench region has a relatively low geothermal potential with respect to the arc and back-arc region.The numerical studies support the existence of southward subduction beneath the Pontides during the late Mesozoic-Cenozoic.     

Anomalous crustal and lithospheric mantle structure of southern part of the Vindhyan Basin and its geodynamic implications

Tectonically active Vindhyan intracratonic basin situated in central India, forms one of the largest Proterozoic sedimentary basins of the world. Possibility of hydrocarbon occurrences in thick sediments of the southern part of this basin, has led to surge in geological and geophysical investigations by various agencies. An attempt to synthesize such multiparametric data in an integrated manner, has provided a new understanding to the prevailing crustal configuration, thermal regime and nature of its geodynamic evolution. Apparently, this region has been subjected to sustained uplift, erosion and magmatism followed by crustal extension, rifting and subsidence due to episodic thermal interaction of the crust with the hot underlying mantle. Almost 5–6 km thick sedimentation took place in the deep faulted Jabera Basin, either directly over the Bijawar/Mahakoshal group of mafic rocks or high velocity-high density exhumed middle part of the crust. Detailed gravity observations indicate further extension of the basin probably beyond NSL rift in the south. A high heat flow of about 78 mW/m² has also been estimated for this basin, which is characterized by extremely high Moho temperatures (exceeding 1000 °C) and mantle heat flow (56 mW/m²) besides a very thin lithospheric lid of only about 50 km. Many areas of this terrain are thickly underplated by infused magmas and from some segments, granitic–gneissic upper crust has either been completely eroded or now only a thin veneer of such rocks exists due to sustained exhumation of deep seated rocks. A 5–8 km thick retrogressed metasomatized zone, with significantly reduced velocities, has also been identified around mid to lower crustal transition.     

The role of viscous heating in Barrovian metamorphism of collisional orogens: thermomechanical models and application to the Lepontine Dome in the Central Alps

Thermal models for Barrovian metamorphism driven by doubling the thickness of the radiogenic crust typically meet difficulty in accounting for the observed peak metamorphic temperature conditions. This difficulty suggests that there is an additional component in the thermal budget of many collisional orogens. Theoretical and geological considerations suggest that viscous heating is a cumulative process that may explain the heat deficit in collision orogens. The results of 2D numerical modelling of continental collision involving subduction of the lithospheric mantle demonstrate that geologically plausible stresses and strain rates may result in orogen‐scale viscous heat production of 0.1 to >1 μW m^?3, which is comparable to or even exceeds bulk radiogenic heat production within the crust. Thermally induced buoyancy is responsible for crustal upwelling in large domes with metamorphic temperatures up to 200 °C higher than regional background temperatures. Heat is mostly generated within the uppermost mantle, because of large stresses in the highly viscous rocks deforming there. This thermal energy may be transferred to the overlying crust either in the form of enhanced heat flow, or through magmatism that brings heat into the crust advectively. The amplitude of orogenic heating varies with time, with both the amplitude and time‐span depending strongly on the coupling between heat production, viscosity and collision strain rate. It is argued that geologically relevant figures are applicable to metamorphic domes such as the Lepontine Dome in the Central Alps. We conclude that deformation‐generated viscous dissipation is an important heat source during collisional orogeny and that high metamorphic temperatures as in Barrovian type metamorphism are inherent to deforming crustal regions.     

Early Cretaceous Magma Mingling in Xiaocuo, Southeastern China Continental Margin: Implications for Subduction of Paleo-Pacific Plate

Magma mingling has been identified within the continental margin of southeastern China.This study focuses on the relationship between mafic and felsic igneous rocks in composite dikes and plutons in this area,and uses this relationship to examine the tectonic and geodynamic implications of the mingling of mafic and felsic magmas.Mafic magmatic enclaves(MMEs) show complex relationships with the hosting Xiaocuo granite in Fujian area,including lenticular to rounded porphyritic microgranular enclaves containing abundant felsic/mafic phenocrysts,elongate mafic enclaves,and back-veining of the felsic host granite into mafic enclaves.LA-ICP-MS zircon U-Pb analyses show crystallization of the granite and dioritic mafic magmatic enclave during ca.132 and 116 Ma.The host granite and MMEs both show zircon growth during repeated thermal events at-210 Ma and 160-180 Ma.Samples from the magma mingling zone generally contain felsic-derived zircons with well-developed growth zoning and aspect ratios of 2-3,and maficderived zircons with no obvious oscillatory zoning and with higher aspect ratios of 5-10.However,these two groups of zircons show no obvious trace element or age differences.The Hf-isotope compositions show that the host granite and MMEs have similar ε_(Hf)(t) values from negative to positive which suggest a mixed source from partial melting of the Meso-Neoproterozoic with involvement of enriched mantlederived magmas or juvenile components.The lithologies,mineral associations,and geochemical characteristics of the mafic and felsic rocks in this study area indicate that both were intruded together,suggesting Early Cretaceous mantle—crustal interactions along the southeastern China continental margin.The Early Cretaceous magma mingling is correlated to subduction of Paleo-Pacific plate.