Global geophysical observations show the presence of the enigmatic mid‐lithospheric discontinuity... more Global geophysical observations show the presence of the enigmatic mid‐lithospheric discontinuity (MLD) at depths of ca. 80–150 km which may question the stability and internal structure of the continental lithosphere. While various mechanisms may explain the MLD, the dynamic processes leading to the seismic observations are unclear. Here we present a physical mechanism for the origin of MLD by channel flow in the cratonic mantle lithosphere, triggered by convective instabilities at cratonic margins in the Archean when the mantle was hot. Our numerical modeling shows that the top of the frozen‐in channel flow creates a shear zone at a depth comparable to the globally observed seismic MLD. Grain size reduction in the shear zone and accumulation of percolated melts or fluids along the channel top may reduce seismic wave speeds as observed below the MLD, while the channel flow itself may explain radial anisotropy of seismic wave speeds and change in direction of the seismic anisotropic...
We interpret the crustal and upper mantle structure along ~2500 km long seismic profiles in the n... more We interpret the crustal and upper mantle structure along ~2500 km long seismic profiles in the northeasternpart of the Sino-Korean Craton (SKC). The seismic data with high signal-to-noise ratio were acquired with a nuclearexplosion in North Korea as source. Seismic sections show several phases including Moho reflections (PmP)and their surface multiple (PmPPmP), upper mantle refractions (P), primary reflections (PxP, PL, P410), exceptionallystrong multiple reflections from the Moho (PmPPxP), and upper mantle scattering phases, which wemodel by ray-tracing and synthetic seismograms for a 1-D fine-scale velocity model. The observations require athin crust (30 km) with a very low average crustal velocity (ca. 6.15 km/s) and exceptionally strong velocity contrastat the Moho discontinuity, which can be explained by a thin Moho transition zone (< 5 km thick) withstrong horizontal anisotropy. We speculate that this anisotropy was induced by lower crustal flow during delaminationdripping...
We present a model of thermal lithospheric thickness (the depth where the geotherm reaches a temp... more We present a model of thermal lithospheric thickness (the depth where the geotherm reaches a temperature of 1300°C) and surface heat flow in Tibet and adjacent regions based on the new thermal-isostasy method. The method accounts for crustal density heterogeneity, is free from any assumption of a steady-state lithosphere thermal regime, and assumes that deviations from crustal Airy-type isostasy are caused by lithosphere thermal heterogeneity. We observe a highly variable lithospheric thermal structure which we interpret as representing longitudinal variations in the northern extent of the subducting Indian plate, southward subduction of the Asian plate beneath central Tibet, and possible preservation of fragmented Tethyan paleo-slabs. Cratonic-type cold and thick lithosphere (200-240 km) with a predicted surface heat flow of 40-50 mW/m2 typifies the Tarim Craton, the northwest Yangtze Craton, and most of the Lhasa Block that is likely refrigerated by underthrusting Indian lithosphe...
(by Huang S.H., Thybo H., Dong S.W., Artemieva I.M., et al.) The Ordos Block in the western part ... more (by Huang S.H., Thybo H., Dong S.W., Artemieva I.M., et al.) The Ordos Block in the western part of the North China Craton is enigmatic in having contrasting topographic structure in the northern and southern parts, while previous geophysical studies show little difference in crustal and upper mantle structure across the region. Here we present a new model of upper mantle structure in the Ordos Block region in order to test the importance of mantle heterogeneity for topographic differences. Our model is based on P-and S-wave seismic receiver functions calculated for data from 171 stations. It documents the presence of an uppermost mantle low-velocity zone between the Mid Lithospheric Discontinuity (MLD) and the Lehmann discontinuity. Clear converters at the 410 and 660 km discontinuities show constant Mantle Transition Zone (MTZ) thickness within the Ordos Block region, which indicates that no deep mantle thermal anomaly affects its present dynamics. However, the amplitude of the MTZ-converters is higher in the southern than the northern Ordos Block. In contrast, the conversions from MLD and the Lehmann discontinuity are strongest in Northern Ordos, which we interpret as a block with essentially preserved cratonic lithospheric mantle. We speculate that smaller amplitudes of the MLD and Lehmann converters in Southern than Northern Ordos may be related to either rheological weakening of cratonic lithosphere during the Mesozoic convergence between the North and South (Yangtze) China Cratons, or northeast extrusion of Tibetan lower crust and upper mantle in the Cenozoic caused by the India-Asia collision.
&amp;amp;lt;p&amp;amp;gt;The Sino-Korean Craton (SKC), which consists of the North China ... more &amp;amp;lt;p&amp;amp;gt;The Sino-Korean Craton (SKC), which consists of the North China Craton (NCC) in China and North Korea, is one of the oldest cratons on earth. Since the Paleozoic, the SKC has experienced multiple subductions of the peripheral plates and the northeastern SKC is located in a junction area. Its characteristics are being investigated by geophysical and geochemical methods, which provides insights into the formation and subsequent evolution of the continental lithosphere.&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;We interpret&amp;amp;amp;#160;the crustal&amp;amp;amp;#160;structure of the northeastern SKC with the refraction/wide-angle reflection perspective using North Korean Nuclear Explosion sources recorded by 40 permanent and 7 temporary broadband stations, which were operated by the China Earthquake Administration and the Institute of Geology and Geophysics, Chinese Academy of Science, respectively.&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;Primary reflection phases from a discontinuity at 30km depth have an apparent velocity of about 6.2 km/s. This phase is observed to 1200km ultra-long offset, which shows that the average crustal velocity is extremely low. Another spectacular observation is of extremely strong phases which we interpret as Moho to surface multiples of all main phases in the seismic sections. Clear upper mantle refractions (Pn) are observed with an apparent velocity around 8.05 km/s as first arrivals over the offset range 300-1000 km. All observations show that the crust of northeastern SKC is very thin (about 30km), it has a low average crust velocity (6.2km/s), and the velocity contrast at the Moho discontinuity is extraordinarily strong.&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;We detect the &amp;amp;amp;#8220;Seismic Moho&amp;amp;amp;#8221; discontinuity, which is marked by a very strong and sharp increase in velocity. We interpret this &amp;amp;amp;#8220;Seismic Moho&amp;amp;amp;#8221; as the top of a layer consisting of the lower crust in eclogite facies. This &amp;amp;amp;#8220;Seismic Moho&amp;amp;amp;#8221; does not coincide with the true Crust-Mantle Boundary, which is defined by a change from felsic/intermediate/mafic crustal rocks to the dominantly ultramafic rocks of the upper mantle in petrological terms.&amp;amp;lt;/p&amp;amp;gt;
&amp;amp;lt;p&amp;amp;gt;The whole North Atlantic region has highly anomalous topography ... more &amp;amp;lt;p&amp;amp;gt;The whole North Atlantic region has highly anomalous topography and bathymetry. Observations show evidence for anomalously shallow bathymetry in the ocean as well as recent rapid topographic change with onshore uplift close to the Atlantic coast and simultaneous subsidence of basins on the continental shelves, most likely throughout the Mesozoic. We present a geophysical interpretation of the whole region with emphasis on data relevant for assessing hypsometric change&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;Most of the North Atlantic Ocean has anomalously shallow bathymetry by up-to 4 km compared to other oceans. Bathymetry is elevated by up-to 2 km and follows the square-root-of-age model, except for the region between Greenland Iceland Faroe Ridge (GIF) and the Jan Mayen Fracture Zone as well as in the Labrador Sea to Baffin Bay. Heat flow follows with large scatter the square-root-of-age model in parts of the ocean and is anomalously low on the Reykjanes and Mohns spreading ridges. Near-zero free-air gravity anomalies indicate that the oceanic areas are generally in isostatic equilibrium except along the mid-oceanic ridges, whereas anomalously low Bouguer anomalies in the oceanic areas indicate low density in the uppermost mantle. Anomalously thick crust is observed along GIF and extends into the Davies Strait. There is no correlation between bathymetry and heat flow, which indicates that the anomalous bathymetry mainly is caused by compositional variation and isostatic compensation of low density continental lithosphere within the oceanic regions. The location of major oceanic fracture zones and continental fragments appears to be controlled by onshore structures.&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;The onshore circum-Atlantic areas show rapid uplift close to the coast with rates of up-to 3 cm/yr. This is surprisingly mainly associated with strong positive free-air gravity anomalies, which would predict isostatic subsidence. Some parts of the high topography, however, appear supported by low-density anomalies below the seismic Moho. It is enigmatic that the presumed Archaean-Proterozoic continental Barents Sea region is submerged and includes deep sedimentary basins.&amp;amp;lt;/p&amp;amp;gt;
inside the coastline of ice and bedrock. In our recent study (Artemieva and Thybo, 2020) we recon... more inside the coastline of ice and bedrock. In our recent study (Artemieva and Thybo, 2020) we reconsider the conventional extent of this continent and demonstrate that 1/3 of Antarctica is not a continent. Here we present a brief summary of our results. Most of the Antarctica continent is covered by a 0.5–3.0 km thick ice sheet, and the only direct information on its geology and geodynamic evolution comes from tiny outcrops of bedrock exposed mostly along the edge of the ice sheet and in the Trans-Antarctic Mountains that separate tectonically stable cratonic East Antarctica from a much younger West Antarctica. Based on existing geophysical data, East Antarctica shows all characteristics of a normal cratonic lithosphere, with a 38–55 km thick crust, fast seismic velocities in the upper mantle, and thicker than 150–250 km lithosphere (Baranov and Morelli, 2013; Hansen et al., 2014; An et al., 2015). Sparse geochemical data indicate Archean-Proterozoic ages for basement outcrops along t...
Global geophysical observations show the presence of the enigmatic mid‐lithospheric discontinuity... more Global geophysical observations show the presence of the enigmatic mid‐lithospheric discontinuity (MLD) at depths of ca. 80–150 km which may question the stability and internal structure of the continental lithosphere. While various mechanisms may explain the MLD, the dynamic processes leading to the seismic observations are unclear. Here we present a physical mechanism for the origin of MLD by channel flow in the cratonic mantle lithosphere, triggered by convective instabilities at cratonic margins in the Archean when the mantle was hot. Our numerical modeling shows that the top of the frozen‐in channel flow creates a shear zone at a depth comparable to the globally observed seismic MLD. Grain size reduction in the shear zone and accumulation of percolated melts or fluids along the channel top may reduce seismic wave speeds as observed below the MLD, while the channel flow itself may explain radial anisotropy of seismic wave speeds and change in direction of the seismic anisotropic...
We interpret the crustal and upper mantle structure along ~2500 km long seismic profiles in the n... more We interpret the crustal and upper mantle structure along ~2500 km long seismic profiles in the northeasternpart of the Sino-Korean Craton (SKC). The seismic data with high signal-to-noise ratio were acquired with a nuclearexplosion in North Korea as source. Seismic sections show several phases including Moho reflections (PmP)and their surface multiple (PmPPmP), upper mantle refractions (P), primary reflections (PxP, PL, P410), exceptionallystrong multiple reflections from the Moho (PmPPxP), and upper mantle scattering phases, which wemodel by ray-tracing and synthetic seismograms for a 1-D fine-scale velocity model. The observations require athin crust (30 km) with a very low average crustal velocity (ca. 6.15 km/s) and exceptionally strong velocity contrastat the Moho discontinuity, which can be explained by a thin Moho transition zone (< 5 km thick) withstrong horizontal anisotropy. We speculate that this anisotropy was induced by lower crustal flow during delaminationdripping...
We present a model of thermal lithospheric thickness (the depth where the geotherm reaches a temp... more We present a model of thermal lithospheric thickness (the depth where the geotherm reaches a temperature of 1300°C) and surface heat flow in Tibet and adjacent regions based on the new thermal-isostasy method. The method accounts for crustal density heterogeneity, is free from any assumption of a steady-state lithosphere thermal regime, and assumes that deviations from crustal Airy-type isostasy are caused by lithosphere thermal heterogeneity. We observe a highly variable lithospheric thermal structure which we interpret as representing longitudinal variations in the northern extent of the subducting Indian plate, southward subduction of the Asian plate beneath central Tibet, and possible preservation of fragmented Tethyan paleo-slabs. Cratonic-type cold and thick lithosphere (200-240 km) with a predicted surface heat flow of 40-50 mW/m2 typifies the Tarim Craton, the northwest Yangtze Craton, and most of the Lhasa Block that is likely refrigerated by underthrusting Indian lithosphe...
(by Huang S.H., Thybo H., Dong S.W., Artemieva I.M., et al.) The Ordos Block in the western part ... more (by Huang S.H., Thybo H., Dong S.W., Artemieva I.M., et al.) The Ordos Block in the western part of the North China Craton is enigmatic in having contrasting topographic structure in the northern and southern parts, while previous geophysical studies show little difference in crustal and upper mantle structure across the region. Here we present a new model of upper mantle structure in the Ordos Block region in order to test the importance of mantle heterogeneity for topographic differences. Our model is based on P-and S-wave seismic receiver functions calculated for data from 171 stations. It documents the presence of an uppermost mantle low-velocity zone between the Mid Lithospheric Discontinuity (MLD) and the Lehmann discontinuity. Clear converters at the 410 and 660 km discontinuities show constant Mantle Transition Zone (MTZ) thickness within the Ordos Block region, which indicates that no deep mantle thermal anomaly affects its present dynamics. However, the amplitude of the MTZ-converters is higher in the southern than the northern Ordos Block. In contrast, the conversions from MLD and the Lehmann discontinuity are strongest in Northern Ordos, which we interpret as a block with essentially preserved cratonic lithospheric mantle. We speculate that smaller amplitudes of the MLD and Lehmann converters in Southern than Northern Ordos may be related to either rheological weakening of cratonic lithosphere during the Mesozoic convergence between the North and South (Yangtze) China Cratons, or northeast extrusion of Tibetan lower crust and upper mantle in the Cenozoic caused by the India-Asia collision.
&amp;amp;lt;p&amp;amp;gt;The Sino-Korean Craton (SKC), which consists of the North China ... more &amp;amp;lt;p&amp;amp;gt;The Sino-Korean Craton (SKC), which consists of the North China Craton (NCC) in China and North Korea, is one of the oldest cratons on earth. Since the Paleozoic, the SKC has experienced multiple subductions of the peripheral plates and the northeastern SKC is located in a junction area. Its characteristics are being investigated by geophysical and geochemical methods, which provides insights into the formation and subsequent evolution of the continental lithosphere.&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;We interpret&amp;amp;amp;#160;the crustal&amp;amp;amp;#160;structure of the northeastern SKC with the refraction/wide-angle reflection perspective using North Korean Nuclear Explosion sources recorded by 40 permanent and 7 temporary broadband stations, which were operated by the China Earthquake Administration and the Institute of Geology and Geophysics, Chinese Academy of Science, respectively.&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;Primary reflection phases from a discontinuity at 30km depth have an apparent velocity of about 6.2 km/s. This phase is observed to 1200km ultra-long offset, which shows that the average crustal velocity is extremely low. Another spectacular observation is of extremely strong phases which we interpret as Moho to surface multiples of all main phases in the seismic sections. Clear upper mantle refractions (Pn) are observed with an apparent velocity around 8.05 km/s as first arrivals over the offset range 300-1000 km. All observations show that the crust of northeastern SKC is very thin (about 30km), it has a low average crust velocity (6.2km/s), and the velocity contrast at the Moho discontinuity is extraordinarily strong.&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;We detect the &amp;amp;amp;#8220;Seismic Moho&amp;amp;amp;#8221; discontinuity, which is marked by a very strong and sharp increase in velocity. We interpret this &amp;amp;amp;#8220;Seismic Moho&amp;amp;amp;#8221; as the top of a layer consisting of the lower crust in eclogite facies. This &amp;amp;amp;#8220;Seismic Moho&amp;amp;amp;#8221; does not coincide with the true Crust-Mantle Boundary, which is defined by a change from felsic/intermediate/mafic crustal rocks to the dominantly ultramafic rocks of the upper mantle in petrological terms.&amp;amp;lt;/p&amp;amp;gt;
&amp;amp;lt;p&amp;amp;gt;The whole North Atlantic region has highly anomalous topography ... more &amp;amp;lt;p&amp;amp;gt;The whole North Atlantic region has highly anomalous topography and bathymetry. Observations show evidence for anomalously shallow bathymetry in the ocean as well as recent rapid topographic change with onshore uplift close to the Atlantic coast and simultaneous subsidence of basins on the continental shelves, most likely throughout the Mesozoic. We present a geophysical interpretation of the whole region with emphasis on data relevant for assessing hypsometric change&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;Most of the North Atlantic Ocean has anomalously shallow bathymetry by up-to 4 km compared to other oceans. Bathymetry is elevated by up-to 2 km and follows the square-root-of-age model, except for the region between Greenland Iceland Faroe Ridge (GIF) and the Jan Mayen Fracture Zone as well as in the Labrador Sea to Baffin Bay. Heat flow follows with large scatter the square-root-of-age model in parts of the ocean and is anomalously low on the Reykjanes and Mohns spreading ridges. Near-zero free-air gravity anomalies indicate that the oceanic areas are generally in isostatic equilibrium except along the mid-oceanic ridges, whereas anomalously low Bouguer anomalies in the oceanic areas indicate low density in the uppermost mantle. Anomalously thick crust is observed along GIF and extends into the Davies Strait. There is no correlation between bathymetry and heat flow, which indicates that the anomalous bathymetry mainly is caused by compositional variation and isostatic compensation of low density continental lithosphere within the oceanic regions. The location of major oceanic fracture zones and continental fragments appears to be controlled by onshore structures.&amp;amp;lt;/p&amp;amp;gt;&amp;amp;lt;p&amp;amp;gt;The onshore circum-Atlantic areas show rapid uplift close to the coast with rates of up-to 3 cm/yr. This is surprisingly mainly associated with strong positive free-air gravity anomalies, which would predict isostatic subsidence. Some parts of the high topography, however, appear supported by low-density anomalies below the seismic Moho. It is enigmatic that the presumed Archaean-Proterozoic continental Barents Sea region is submerged and includes deep sedimentary basins.&amp;amp;lt;/p&amp;amp;gt;
inside the coastline of ice and bedrock. In our recent study (Artemieva and Thybo, 2020) we recon... more inside the coastline of ice and bedrock. In our recent study (Artemieva and Thybo, 2020) we reconsider the conventional extent of this continent and demonstrate that 1/3 of Antarctica is not a continent. Here we present a brief summary of our results. Most of the Antarctica continent is covered by a 0.5–3.0 km thick ice sheet, and the only direct information on its geology and geodynamic evolution comes from tiny outcrops of bedrock exposed mostly along the edge of the ice sheet and in the Trans-Antarctic Mountains that separate tectonically stable cratonic East Antarctica from a much younger West Antarctica. Based on existing geophysical data, East Antarctica shows all characteristics of a normal cratonic lithosphere, with a 38–55 km thick crust, fast seismic velocities in the upper mantle, and thicker than 150–250 km lithosphere (Baranov and Morelli, 2013; Hansen et al., 2014; An et al., 2015). Sparse geochemical data indicate Archean-Proterozoic ages for basement outcrops along t...
by Starostenko, V.I., Janik T., Stephenson R., Gryn D., Rusakov O., Czuba W., Sroda P., Grad M., ... more by Starostenko, V.I., Janik T., Stephenson R., Gryn D., Rusakov O., Czuba W., Sroda P., Grad M., Guterch A., Flueh E., Thybo H., Artemieva I.M., and 8 authors more
The DOBRE-2 wide-angle reflection and refraction profile was acquired in June 2007 as a direct, southwestwards prolongation of the 1999 DOBREfraction’99 that crossed the Donbas Foldbelt in eastern Ukraine. It crosses the Azov Massif of the East European Craton, the Azov Sea, the Kerch Peninsula (the easternmost part of Crimea) and the northern East Black Sea Basin, thus traversing the entire Crimea–Caucasus compressional zone centred on the Kerch Peninsula. The DOBRE-2 profile recorded a mix of onshore explosive sources as well as airguns at sea. A variety of single-component recorders were used on land and ocean bottom instruments were deployed offshore and recovered by ship. The DOBRE-2 datasets were degraded by a lack of shot-point reversal at the southwestern terminus and by some poor signal registration elsewhere, in particular in the Black Sea. Nevertheless, they allowed a robust velocity model of the upper crust to be constructed along the entire profile as well as through the entire crust beneath the Azov Massif. A less well constrained model was constructed for much of the crust beneath the Azov Sea and the Kerch Peninsula. The results showed that there is a significant change in the upper crustal lithology in the northern Azov Sea, expressed in the near surface as the Main Azov Fault; this boundary can be taken as the boundary between the East European Craton and the Scythian Platform. The upper crustal rocks of the Scythian Platform in this area probably consist of metasedimentary rocks. A narrow unit as shallow as about 5 km and characterized by velocities typical of the crystalline basement bounds the metasedimentary succession on its southern margin and also marks the northern margin of the northern foredeep and the underlying successions of the Crimea–Caucasus compressional zone in the southern part of the Azov Sea. A broader and somewhat deeper basement unit (about 11 km) with an antiformal shape lies beneath the northern East Black Sea Basin and forms the southern margin of the Crimea–Caucasus compressional zone. The depth of the underlying Moho discontinuity increases from 40 km beneath the Azov Massif to 47 km beneath the Crimea–Caucasus compressional zone.
Granitic rocks play special role in the dynamics and evolution of the Earth and its thermal regim... more Granitic rocks play special role in the dynamics and evolution of the Earth and its thermal regime. First, their compositional variability, reflected in the distribution of concentrations of radiogenic elements, provides constraints on global differentiation processes and large scale planetary evolution, where emplacement of granites is considered a particularly important process for the formation of continental crust. Second, heat production by radioactive decay is among the main heat sources in the Earth. Therefore knowledge of heat production in granitic rocks is pivotal for thermal modelling of the continental lithosphere, given that most radiogenic elements are concentrated in granitic rocks of the upper continental crust whereas heat production in rocks of the lower crust and lithospheric mantle is negligible. We present and analyze a new global database GRANITE2017 (with about 500 entries) on the abundances of heat producing elements (Th, U, K) and heat production in granitic rocks based on all available published data. Statistical analysis of the data shows a huge scatter in all parameters, but the following conclusions can be made. (i) Bulk heat production in granitic rocks of all ages is ca. 2.0 μW/m 3. It is very low in Archean-Early Proterozoic granitic rocks (1.67 ± 1.49 and 1.25 ± 0.83 μW/m 3 , respectively) and there is a remarkable peak in heat production in Middle Proterozoic granites (presently 4.36 ± 2.17 μW/m 3) followed by a gradual decrease towards Cenozoic granites (3.09 ± 1.62 μW/m 3). Low heat production in the ancient continental crust may be important for preservation of cratonic lithosphere. (ii) There is no systematic correlation between the tectonically controlled granite-type and bulk heat production, although A-type (anorogenic) granites are the most radioactive, and many of them were emplaced in Middle Proterozoic. (iii) There is no systematic correlation between heat flow and concentrations of radiogenic elements. (iv) The present-day global average Th/U value is 4.75 ± 4.27 with a maximum in Archean-Early Proterozoic granites (5.75 ± 5.96) and a minimum in Middle-Late Proterozoic granites (3.78 ± 2.69). The Th/U ratio at the time of granite emplacement has a minimum in Archean (2.78). (v) The present-day K/U ratio is close to a global estimate for the continental crust only for the entire dataset (1.46 ± 1.63) × 10 4 , but differs from the global ratio for each geological time, and all anomalously high values are observed only in Archean-Early Proterozoic granites. (vi) We do not observe a systematic difference in radiogenic heat production between Archean and post-Archean granites, but rather recognize a sharp change in radiogenic concentrations and ratios from the Early Proterozoic to Middle Proterozoic granites. The Protero-zoic anomaly may be caused by major plate reorganizations possibly related to the supercontinent cycle when changes in the granite forming processes may be expected, or it may even indicate a change in global thermal regime, mantle dynamics and plate tectonics styles.(vii) Our results provide strong evidence that secular change in the Urey ratio was not monotonous, and that plate motions may have been the fastest in Middle Proterozoic and have been decreasing since then. (viii) We estimate the total present-day heat production in the granitic crust as 5.8–6.8 TW and in the continental crust as 7.8–8.8 TW.
Supplementary data to:
Artemieva I.M., Thybo H., Jakobsen K., Sørensen N.K., and Nielsen L.S.K., ... more Supplementary data to: Artemieva I.M., Thybo H., Jakobsen K., Sørensen N.K., and Nielsen L.S.K., 2017. Heat production in granitic rocks: Global analysis based on a new data compilation GRANITE2017. Earth Science Reviews, ref. no. EARTH_2017_162
Supplementary data to:
Artemieva I.M., Thybo H., Jakobsen K., Sørensen N.K., and Nielsen L.S.K.,... more Supplementary data to:
Artemieva I.M., Thybo H., Jakobsen K., Sørensen N.K., and Nielsen L.S.K., 2017.
Heat production in granitic rocks: Global analysis based on a new data compilation GRANITE2017.
Earth Science Reviews, 2017
We present a summary of geophysical models of the subcrustal lithosphere of Europe. This includes... more We present a summary of geophysical models of the subcrustal lithosphere of Europe. This includes the results from seismic (reflection and refraction profiles, P-and S-wave tomography, mantle anisotropy), gravity, thermal, electromagnetic, elastic and petro-logical studies of the lithospheric mantle. We discuss major tectonic processes as reflected in the lithospheric structure of Europe, from Precambrian terrane accretion and subduction to Phanerozoic rifting, volcanism, subduction and continent –continent collision. The differences in the lithospheric structure of Precambrian and Phanerozoic Europe, as illustrated by a comparative analysis of different geophysical data, are shown to have both a compositional and a thermal origin. We propose an integrated model of physical properties of the European subcrustal lithosphere, with emphasis on the depth intervals around 150 and 250 km. At these depths, seismic velocity models, constrained by body-and surface-wave continent-scale tomography, are compared with mantle temperatures and mantle gravity anomalies. This comparison provides a framework for discussion of the physical or chemical origin of the major lithospheric anomalies and their relation to large-scale tectonic processes, which have formed the present lithosphere of Europe.
(by Artemieva I.M., Thybo H., and Shulgin A.)
Convergent margins, being the boundaries betwee... more (by Artemieva I.M., Thybo H., and Shulgin A.)
Convergent margins, being the boundaries between colliding lithospheric plates, form the most disastrous areas in the world due to intensive, strong seismicity and volcanism. We review global geophysical data in order to illustrate the effects of the plate tectonic processes at convergent margins on the crustal and upper mantle structure , seismicity, and geometry of subducting slab. We present global maps of free-air and Bouguer gravity anomalies, heat flow, seismicity, seismic Vs anomalies in the upper mantle, and plate convergence rate, as well as 20 profiles across different convergent margins. A global analysis of these data for three types of convergent margins, formed by ocean–ocean, ocean–continent, and continent–continent collisions, allows us to recognize the following patterns. (1) Plate convergence rate depends on the type of convergent margins and it is significantly larger when, at least, one of the plates is oceanic. However, the oldest oceanic plate in the Pacific ocean has the smallest convergence rate. (2) The presence of an oceanic plate is, in general, required for generation of high-magnitude (M N 8.0) earthquakes and for generating intermediate and deep seismicity along the conver-gent margins. When oceanic slabs subduct beneath a continent, a gap in the seismogenic zone exists at depths between ca. 250 km and 500 km. Given that the seismogenic zone terminates at ca. 200 km depth in case of continent–continent collision, we propose oceanic origin of subducting slabs beneath the Zagros, the Pamir, and the Vrancea zone. (3) Dip angle of the subducting slab in continent–ocean collision does not correlate neither with the age of subducting oceanic slab, nor with the convergence rate. For ocean–ocean subduction, clear trends are recognized: steeply dipping slabs are characteristic of young subducting plates and of oceanic plates with high convergence rate, with slab rotation towards a near-vertical dip angle at depths below ca. 500 km at very high convergence rate. (4) Local isostasy is not satisfied at the convergent margins as evidenced by strong free air gravity anomalies of positive and negative signs. However, near-isostatic equilibrium may exist in broad zones of distributed deformation such as Tibet. (5) No systematic patterns are recognized in heat flow data due to strong heterogeneity of measured values which are strongly affected by hydrothermal circulation, mag-matic activity, crustal faulting, horizontal heat transfer, and also due to low number of heat flow measurements across many margins. (6) Low upper mantle Vs seismic velocities beneath the convergent margins are restricted to the upper 150 km and may be related to mantle wedge melting which is confined to shallow mantle levels.
We present a new digital model (NCcrust) of the seismic crustal structure of the Neoarchean North... more We present a new digital model (NCcrust) of the seismic crustal structure of the Neoarchean North China Craton (NCC) and its surrounding Paleozoic-Mesozoic orogenic belts (30 ∘ –45 ∘ N, 100 ∘ –130 ∘ E). All available seismic profiles, complemented by receiver function interpretations of crustal thickness, are used to constrain a new comprehensive crustal model NCcrust. The model, presented on a 0.25 ∘ × 0.25 ∘ grid, includes the Moho depth and the internal structure (thickness and velocity) of the crust specified for four layers (the sedimentary cover, upper, middle, and lower crust) and the Pn velocity in the uppermost mantle. The crust is thin (30–32 km) in the east, while the Moho depth in the western part of the NCC is 38–44 km. The Moho depth of the Sulu-Dabie-Qinling-Qilian orogenic belt ranges from 31 km to 51 km, with a general westward increase in crustal thickness. The sedimentary cover is 2–5 km thick in most of the region, and typical thicknesses of the upper crust, middle crust, and lower crust are 16–24 km, 6–24 km, and 0–6 km, respectively. We document a general trend of westward increase in the thickness of all crustal layers of the crystalline basement and as a consequence, the depth of the Moho. There is no systematic regional pattern in the average crustal V p velocity and the Pn velocity. We examine correlation between the Moho depth and topography for seven tectonic provinces in the North China Craton and speculate on mechanisms of isostatic compensation.
(By Thybo H., Youssof M. and Artemieva I.M.)
The long-term stability of Precambrian continent... more (By Thybo H., Youssof M. and Artemieva I.M.)
The long-term stability of Precambrian continental lithosphere depends on the rheology of the lithospheric mantle as well as the coupling between crust and mantle lithosphere, which may be inferred by seismic anisotropy. Anisotropy has never been detected in cratonic crust. Anisotropy in southern Africa, detected by the seismological SKS-splitting method, usually is attributed to the mantle due to asthenospheric flow or frozen-in features of the lithosphere. However, SKS-splitting cannot distinguish between anisotropy in the crust and the mantle. We observe strong seismic anisotropy in the crust of southern African cratons by Receiver Function analysis. Fast axes are uniform within tectonic units and parallel to SKS axes, orogenic strike in the Limpopo and Cape fold belts, and the strike of major dyke swarms. Parallel fast axes in the crust and mantle indicate coupled crust-mantle evolution for more than 2 billion years with implications for strong rheology of the lithosphere.
(by Vahid Teknik, Abdolreza Ghods, Hans Thybo, and Irina M. Artemieva)
We present a new 2D cru... more (by Vahid Teknik, Abdolreza Ghods, Hans Thybo, and Irina M. Artemieva)
We present a new 2D crustal-scale model of the northwestern Iranian plateau based on gravity-magnetic modeling along the 500 km long China-Iran Geological and Geophysical Survey in the Iranian plateau (CIGSIP) seismic profile across major tectonic provinces of Iran from the Arabian plate into the South Caspian Basin (SCB). The seismic P-wave receiver function (RF) model along the profile is used to constrain major crustal boundaries in the density model. Our 2D crustal model shows significant variation in the sedimentary thickness, Moho depth, and the depth and extent of intra-crustal interfaces. The Main Recent Fault (MRF) between the Arabian crust and the overriding central Iran crust dips at approximately 13° towards the northeast to a depth of about 40 km. The geometry of the MRF suggests about 150 km of underthrusting of the Arabian plate beneath central Iran. Our results indicate the presence of a high-density lower crustal layer beneath Zagros. We identify a new crustal-scale suture beneath the Tarom valley between the South Caspian Basin crust and Central Iran and the Alborz. This suture is associated with sharp variation in Moho depth, topography, and magnetic anomalies, and is underlain by a 20 km thick high-density crustal root at 35-55 km depth. The high-density lower crust in Alborz and Zagros may be related to partial eclogitization of crustal roots below about 40 km depth. The gravity and magnetic models indicate a highly extended continental crust for the SCB crust along the profile. Low observed magnetic susceptibility of the Kermanshah ophiolites likely indicates that the ophiolite rocks only form a thin layer that has been thrust over the sedimentary cover. Résumé : Nous présentons un nouveau modèle d'échelle crustale en 2D du nord-ouest du plateau iranien reposant sur la modélisation gravimétrique-magnétique le long du profil sismique CIGSIP de 500 km qui traverse de grandes provinces tectoniques d'Iran, de la plaque arabe jusque dans le bassin sud-caspien (BSC). Le modèle des ondes sismiques P reposant sur la méthode des fonctions récepteur le long du profil est utilisé pour déterminer l'emplacement de grandes limites crustales dans le modèle de densité. Notre modèle crustal en 2D montre d'importantes variations de l'épaisseur des sédiments, de la profondeur du Moho et de la profondeur et de l'étendue d'interfaces intracrustales. La faille récente principale (FRP) entre la croûte arabe et la croûte d'Iran central sus-jacente a un pendage d'environ 13° vers le NE jusqu'à une profondeur de 40 km. La géométrie de la FRP indiquerait un sous-charriage sur 150 km de la plaque arabe sous l'Iran central. Nos résultats indiquent la présence d'une couche de croûte inférieure de haute densité sous le Zagros. Nous avons cerné une nouvelle suture d'ampleur crustale sous la vallée de Tarom entre la croûte du bassin sud-caspien et l'Iran central et l'Elbourz. Cette suture est associée à une variation marquée de la profondeur du Moho, du relief et des anomalies magnétiques, et est sous-tendue par une racine crustale de haute densité de 20 km d'épaisseur à des profondeurs de 35 km à 55 km. La croûte inférieure de haute densité dans l'Elbourz et le Zagros pourrait être associée à l'éclogitisation partielle de racines crustales à des profondeurs de plus de 40 km. Les modèles gravimétriques et magnétiques indiquent la présence d'une croûte continentale fortement distendue pour le BSC le long du profil. La faible susceptibilité magnétique observée dans les ophiolites de Kermanshah reflète probablement le fait que les roches ophiolitiques ne forment qu'une mince couche qui a été charriée sur la couverture sédimentaire. [Traduit par la Rédaction] Mots-clés : modélisation crustale prospective en 2D, anomalies gravimétriques et magnétiques, fonction récepteur, plateau iranien, Moho, épaisseur de sédiments.
Formation of new oceans by continental break-up is understood as a continuous evolution from rift... more Formation of new oceans by continental break-up is understood as a continuous evolution from rifting to ocean spreading. The Red Sea is one of few locations on Earth where a new plate boundary presently forms. Its evolution provides key information on how the plate tectonics operates and how the plate boundaries form and evolve in time. While the new plate boundary has already been formed in the southern Red Sea where ocean spreading is active, the north-central segment still experiences continental rifting. The region also has west-east asymmetry: in the north-central Red Sea the rift-related magmatism is not located beneath the rift axis, as conventional models predict, but instead is offset by ca 300 km into Arabia.
We propose a new geodynamic model which explains the enigmatic asymmetry of the Red Sea region and is fully consistent with various types of geological and geophysical observations. We demonstrate that the north-central rift is a transient feature that will not develop into coincident ocean spreading. Instead, the new plate boundary forms across Arabia. Our numerical experiments, supported by geological, seismic and gravity observations, predict that in 1-5 Myr the north-central extensional axis will jump ~300 km eastward into Arabia. The Ad Damm strike-slip fault, normal to the central Red Sea rift axis, will evolve into a transform fault between the ongoing ocean spreading in the southern Red Sea and the future spreading in north-central Arabia.
We demonstrate that crustal-scale weakness zones control lithosphere extension and lead to long-distance jumps of extensional axes in continental lithosphere not affected by hotspots. Therefore, our model also provides theoretical basis for understanding dynamics and mechanisms of the transition from rifting to continental break-up at passive continental margins not affected by hotspots.
(by V. Teknik, H. Thybo, I.M. Artemieva, A. Ghods)
The Iranian plateau is one of the most com... more (by V. Teknik, H. Thybo, I.M. Artemieva, A. Ghods)
The Iranian plateau is one of the most complex geodynamic settings within the Alpine-Himalayan belt. The Paleo-Tethys and Neo-Tethys ocean subduction is responsible for the formation of several magmatic arcs and sedimentary basins within the plateau. These zones mostly are separated by thrust faults related to paleo-suture zones, which are highlighted by ophiolites. Sediment cover and overprint of a different magmatic phase from late Triassic to the Quaternary impede identification of some magmatic arcs and ophiolite belts. We track the known magmatic arcs, such as the Urmia-Dokhtar Magmatic Arc (UDMA), and unknown, sediment covered magmatic arcs by aeromagnetic data. We present a new map of average susceptibility calculated by the radially averaged power spectrum method. High average susceptibility values indicate the presence of a number of lineaments that correlate with known occurrences of Magmatic-Ophiolite Arcs (MOA), and low average susceptibility coincides with known sedimentary basins like Zagros, Makran, Kopeh-Dagh, and Tabas. In analogy to Zagros, low average susceptibility values indicate sedimentary basins to the south of the Darouneh fault and in the northern part of the Lut, Tabas and Yazd blocks. We interpret the Tabas basin as a pull-apart or back-arc basin. We identify hitherto unknown parallel MOAs in eastern Iran and the SE part of UDMA which both indicate steeply dipping (> 60°dip) paleo-subduction zones. In contrast, we interpret shallow subduction (< 20°dip) of Neo-Tethys in the NW part of UDMA as well as in the Sabzevar-Kavir MOA.
Journal of Geophysical Research: Solid Earth, 2020
(by B. Xia, H. Thybo, I.M. Artemieva) We constrain the lithospheric mantle density of the North C... more (by B. Xia, H. Thybo, I.M. Artemieva) We constrain the lithospheric mantle density of the North China Craton (NCC) at both in situ and standard temperature-pressure (STP) conditions from gravity data. The lithosphere-asthenosphere boundary (LAB) depth is constrained by our new thermal model, which is based on a new regional heat flow data set and a recent regional crustal model NCcrust. The new thermal model shows that the thermal lithosphere thickness is <120 km in most of the NCC, except for the northern and southern parts with the maximum depth of 170 km. The gravity calculations reveal a highly heterogeneous density structure of the lithospheric mantle with in situ and STP values of 3.22-3.29 and 3.32-3.40 g/cm 3 , respectively. Thick and reduced-density cratonic-type lithosphere is preserved mostly in the southern NCC. Most of the Eastern Block has a thin (90-140 km) and high-density lithospheric mantle. Most of the Western Block has a high-density lithospheric mantle and a thin (80-110 km) lithosphere typical of Phanerozoic regions, which suggests that the Archean lithosphere is no longer present there. We conclude that in almost the entire NCC the lithosphere has lost its cratonic characteristics by geodynamic processes that include, but are not limited to, the Paleozoic closure of the Paleo-Asian Ocean in the north, the Mesozoic Yangtze Craton flat subduction in the south, the Mesozoic Pacific subduction in the east, the Cenozoic remote response to the Indian-Eurasian collision in the west, and the Cenozoic extensional tectonics (possibly associated with the slab roll-back) in the center.
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Papers by Hans Thybo
The DOBRE-2 wide-angle reflection and refraction profile was acquired in June 2007 as a direct, southwestwards prolongation of the 1999 DOBREfraction’99 that crossed the Donbas Foldbelt in eastern Ukraine. It crosses the Azov Massif of the East European Craton, the Azov Sea, the Kerch Peninsula (the easternmost part of Crimea) and the northern East Black Sea Basin, thus traversing the entire Crimea–Caucasus compressional zone centred on the Kerch Peninsula. The DOBRE-2 profile recorded a mix of onshore explosive sources as well as airguns at sea. A variety of single-component recorders were used on land and ocean bottom instruments were deployed offshore and recovered by ship. The DOBRE-2 datasets were degraded by a lack of shot-point reversal at the southwestern terminus and by some poor signal registration elsewhere, in particular in the Black Sea. Nevertheless, they allowed a robust velocity model of the upper crust to be constructed along the entire profile as well as through the entire crust beneath the Azov Massif. A less well constrained model was constructed for much of the crust beneath the Azov Sea and the Kerch Peninsula. The results showed that there is a significant change in the upper crustal lithology in the northern Azov Sea, expressed in the near surface as the Main Azov Fault; this boundary can be taken as the boundary between the East European Craton and the Scythian Platform. The upper crustal rocks of the Scythian Platform in this area probably consist of metasedimentary rocks. A narrow unit as shallow as about 5 km and characterized by velocities typical of the crystalline basement bounds the metasedimentary succession on its southern margin and also marks the northern margin of the northern foredeep and the underlying successions of the Crimea–Caucasus compressional zone in the southern part of the Azov Sea. A broader and somewhat deeper basement unit (about 11 km) with an antiformal shape lies beneath the northern East Black Sea Basin and forms the southern margin of the Crimea–Caucasus compressional zone. The depth of the underlying Moho discontinuity increases from 40 km beneath the Azov Massif to 47 km beneath the Crimea–Caucasus compressional zone.
Artemieva I.M., Thybo H., Jakobsen K., Sørensen N.K., and Nielsen L.S.K., 2017.
Heat production in granitic rocks: Global analysis based on a new data compilation GRANITE2017.
Earth Science Reviews, ref. no. EARTH_2017_162
Artemieva I.M., Thybo H., Jakobsen K., Sørensen N.K., and Nielsen L.S.K., 2017.
Heat production in granitic rocks: Global analysis based on a new data compilation GRANITE2017.
Earth Science Reviews, 2017
Convergent margins, being the boundaries between colliding lithospheric plates, form the most disastrous areas in the world due to intensive, strong seismicity and volcanism. We review global geophysical data in order to illustrate the effects of the plate tectonic processes at convergent margins on the crustal and upper mantle structure , seismicity, and geometry of subducting slab. We present global maps of free-air and Bouguer gravity anomalies, heat flow, seismicity, seismic Vs anomalies in the upper mantle, and plate convergence rate, as well as 20 profiles across different convergent margins. A global analysis of these data for three types of convergent margins, formed by ocean–ocean, ocean–continent, and continent–continent collisions, allows us to recognize the following patterns. (1) Plate convergence rate depends on the type of convergent margins and it is significantly larger when, at least, one of the plates is oceanic. However, the oldest oceanic plate in the Pacific ocean has the smallest convergence rate. (2) The presence of an oceanic plate is, in general, required for generation of high-magnitude (M N 8.0) earthquakes and for generating intermediate and deep seismicity along the conver-gent margins. When oceanic slabs subduct beneath a continent, a gap in the seismogenic zone exists at depths between ca. 250 km and 500 km. Given that the seismogenic zone terminates at ca. 200 km depth in case of continent–continent collision, we propose oceanic origin of subducting slabs beneath the Zagros, the Pamir, and the Vrancea zone. (3) Dip angle of the subducting slab in continent–ocean collision does not correlate neither with the age of subducting oceanic slab, nor with the convergence rate. For ocean–ocean subduction, clear trends are recognized: steeply dipping slabs are characteristic of young subducting plates and of oceanic plates with high convergence rate, with slab rotation towards a near-vertical dip angle at depths below ca. 500 km at very high convergence rate. (4) Local isostasy is not satisfied at the convergent margins as evidenced by strong free air gravity anomalies of positive and negative signs. However, near-isostatic equilibrium may exist in broad zones of distributed deformation such as Tibet. (5) No systematic patterns are recognized in heat flow data due to strong heterogeneity of measured values which are strongly affected by hydrothermal circulation, mag-matic activity, crustal faulting, horizontal heat transfer, and also due to low number of heat flow measurements across many margins. (6) Low upper mantle Vs seismic velocities beneath the convergent margins are restricted to the upper 150 km and may be related to mantle wedge melting which is confined to shallow mantle levels.
The long-term stability of Precambrian continental lithosphere depends on the rheology of the lithospheric mantle as well as the coupling between crust and mantle lithosphere, which may be inferred by seismic anisotropy. Anisotropy has never been detected in cratonic crust. Anisotropy in southern Africa, detected by the seismological SKS-splitting method, usually is attributed to the mantle due to asthenospheric flow or frozen-in features of the lithosphere. However, SKS-splitting cannot distinguish between anisotropy in the crust and the mantle. We observe strong seismic anisotropy in the crust of southern African cratons by Receiver Function analysis. Fast axes are uniform within tectonic units and parallel to SKS axes, orogenic strike in the Limpopo and Cape fold belts, and the strike of major dyke swarms. Parallel fast axes in the crust and mantle indicate coupled crust-mantle evolution for more than 2 billion years with implications for strong rheology of the lithosphere.
We present a new 2D crustal-scale model of the northwestern Iranian plateau based on gravity-magnetic modeling along the 500 km long China-Iran Geological and Geophysical Survey in the Iranian plateau (CIGSIP) seismic profile across major tectonic provinces of Iran from the Arabian plate into the South Caspian Basin (SCB). The seismic P-wave receiver function (RF) model along the profile is used to constrain major crustal boundaries in the density model. Our 2D crustal model shows significant variation in the sedimentary thickness, Moho depth, and the depth and extent of intra-crustal interfaces. The Main Recent Fault (MRF) between the Arabian crust and the overriding central Iran crust dips at approximately 13° towards the northeast to a depth of about 40 km. The geometry of the MRF suggests about 150 km of underthrusting of the Arabian plate beneath central Iran. Our results indicate the presence of a high-density lower crustal layer beneath Zagros. We identify a new crustal-scale suture beneath the Tarom valley between the South Caspian Basin crust and Central Iran and the Alborz. This suture is associated with sharp variation in Moho depth, topography, and magnetic anomalies, and is underlain by a 20 km thick high-density crustal root at 35-55 km depth. The high-density lower crust in Alborz and Zagros may be related to partial eclogitization of crustal roots below about 40 km depth. The gravity and magnetic models indicate a highly extended continental crust for the SCB crust along the profile. Low observed magnetic susceptibility of the Kermanshah ophiolites likely indicates that the ophiolite rocks only form a thin layer that has been thrust over the sedimentary cover. Résumé : Nous présentons un nouveau modèle d'échelle crustale en 2D du nord-ouest du plateau iranien reposant sur la modélisation gravimétrique-magnétique le long du profil sismique CIGSIP de 500 km qui traverse de grandes provinces tectoniques d'Iran, de la plaque arabe jusque dans le bassin sud-caspien (BSC). Le modèle des ondes sismiques P reposant sur la méthode des fonctions récepteur le long du profil est utilisé pour déterminer l'emplacement de grandes limites crustales dans le modèle de densité. Notre modèle crustal en 2D montre d'importantes variations de l'épaisseur des sédiments, de la profondeur du Moho et de la profondeur et de l'étendue d'interfaces intracrustales. La faille récente principale (FRP) entre la croûte arabe et la croûte d'Iran central sus-jacente a un pendage d'environ 13° vers le NE jusqu'à une profondeur de 40 km. La géométrie de la FRP indiquerait un sous-charriage sur 150 km de la plaque arabe sous l'Iran central. Nos résultats indiquent la présence d'une couche de croûte inférieure de haute densité sous le Zagros. Nous avons cerné une nouvelle suture d'ampleur crustale sous la vallée de Tarom entre la croûte du bassin sud-caspien et l'Iran central et l'Elbourz. Cette suture est associée à une variation marquée de la profondeur du Moho, du relief et des anomalies magnétiques, et est sous-tendue par une racine crustale de haute densité de 20 km d'épaisseur à des profondeurs de 35 km à 55 km. La croûte inférieure de haute densité dans l'Elbourz et le Zagros pourrait être associée à l'éclogitisation partielle de racines crustales à des profondeurs de plus de 40 km. Les modèles gravimétriques et magnétiques indiquent la présence d'une croûte continentale fortement distendue pour le BSC le long du profil. La faible susceptibilité magnétique observée dans les ophiolites de Kermanshah reflète probablement le fait que les roches ophiolitiques ne forment qu'une mince couche qui a été charriée sur la couverture sédimentaire. [Traduit par la Rédaction] Mots-clés : modélisation crustale prospective en 2D, anomalies gravimétriques et magnétiques, fonction récepteur, plateau iranien, Moho, épaisseur de sédiments.
We propose a new geodynamic model which explains the enigmatic asymmetry of the Red Sea region and is fully consistent with various types of geological and geophysical observations. We demonstrate that the north-central rift is a transient feature that will not develop into coincident ocean spreading. Instead, the new plate boundary forms across Arabia. Our numerical experiments, supported by geological, seismic and gravity observations, predict that in 1-5 Myr the north-central extensional axis will jump ~300 km eastward into Arabia. The Ad Damm strike-slip fault, normal to the central Red Sea rift axis, will evolve into a transform fault between the ongoing ocean spreading in the southern Red Sea and the future spreading in north-central Arabia.
We demonstrate that crustal-scale weakness zones control lithosphere extension and lead to long-distance jumps of extensional axes in continental lithosphere not affected by hotspots. Therefore, our model also provides theoretical basis for understanding dynamics and mechanisms of the transition from rifting to continental break-up at passive continental margins not affected by hotspots.
The Iranian plateau is one of the most complex geodynamic settings within the Alpine-Himalayan belt. The Paleo-Tethys and Neo-Tethys ocean subduction is responsible for the formation of several magmatic arcs and sedimentary basins within the plateau. These zones mostly are separated by thrust faults related to paleo-suture zones, which are highlighted by ophiolites. Sediment cover and overprint of a different magmatic phase from late Triassic to the Quaternary impede identification of some magmatic arcs and ophiolite belts. We track the known magmatic arcs, such as the Urmia-Dokhtar Magmatic Arc (UDMA), and unknown, sediment covered magmatic arcs by aeromagnetic data. We present a new map of average susceptibility calculated by the radially averaged power spectrum method. High average susceptibility values indicate the presence of a number of lineaments that correlate with known occurrences of Magmatic-Ophiolite Arcs (MOA), and low average susceptibility coincides with known sedimentary basins like Zagros, Makran, Kopeh-Dagh, and Tabas. In analogy to Zagros, low average susceptibility values indicate sedimentary basins to the south of the Darouneh fault and in the northern part of the Lut, Tabas and Yazd blocks. We interpret the Tabas basin as a pull-apart or back-arc basin. We identify hitherto unknown parallel MOAs in eastern Iran and the SE part of UDMA which both indicate steeply dipping (> 60°dip) paleo-subduction zones. In contrast, we interpret shallow subduction (< 20°dip) of Neo-Tethys in the NW part of UDMA as well as in the Sabzevar-Kavir MOA.