GM9.14

The compilation of global heat-flow data is currently under major revision by the International Heat Flow Commission (IHFC) of the International Association of Seismology and Physics of the Earth's Interior (IASPEI). Heat flow represents a fundamental parameter in thermal studies, e.g., the evolution of hydrocarbons or mineral and geothermal resources. Comparable, comprehensible and reliable heat-flow data are of utmost interest also for geophysical and geological studies on the global scale. Here, we present the first results of a stepwise revision of the IHFC Global Heat Flow Database based on a researcher driven, collaborative approach. The first step comprises the review and revision of the most recent database structure established in 1976. The revised structure of the Global Heat Flow Database considers the demands and opportunities presented by the evolution of scientific work, digitization and the breakthroughs in database technologies over the past decades.  Based on the new structure, the existing dataset will be re-assessed and new data incorporated. By supporting the ideas of FAIR and open data principles, the new database facilitates interoperability with external data services, like DOI and IGSN numbers, and other data resources (e.g., world geological map, world stratigraphic system, and International Ocean Drilling Program data). We give an overview of the new database and introduce the community workflow of global heat-flow data revision.

How to cite: Fuchs, S., Beardsmore, G., Chiozzi, P., Espinoza-Ojeda, O. M., Gola, G., Gosnold, W., Harris, R., Jennings, S., Liu, '., Negrete-Aranda, R., Neumann, F., Norden, B., Poort, J., Rajver, D., Ray, L., Richards, M., Smith, J., Tanaka, A., and Verdoya, M.: The Global Heat Flow Database: a collaborative and fundamental revision process to ensure comprehensible and reliable heat-flow records, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10257, https://doi.org/10.5194/egusphere-egu21-10257, 2021.

The Southern Andes Volcanic zone (SVZ) is located between latitudes 33-46°S in the western margin of the South American continental plate, above the subducting Nazca oceanic plate. Although the slab dip angle is constant (~25°) along strike, the distance between the volcanic arc and the subduction trench decreases southward. In the northern segment (33-41°S) the volcanoes are co-located with the main orogenic water divide, whereas in the southern segment (41-46°S) the water divide is shifted eastward and the volcanic arc is shifted westward. The eastward water divide migration in the southern segment is explained by an orographic effect due to the westerlies winds, which causes high precipitation (>2 m/yr) and erosion rates (>1.5 mm/yr) on the upwind side of the orogen. Thermomechanical visco-elasto-plastic numerical models exploring the effects of the topographic shift on the magma upwelling path explain the westward migration of the volcanic arc. Results show that when the topographic barrier is shifted to the east with respect to a central magmatic source, asymmetric strain due to the magma emplacement into the crust drives preferential westward magma upwelling. The southern segment of the SVZ is proximal to an important strike slip fault system, the Liquiñe-Ofqui fault zone. We propose that the (re-)activation of these fracture zone on the western side of the Southern Andes is related to the orographic migration of the water divide during magma upwelling. This conclusion is further supported by the lack of structures accommodating magma emplacement/eruption and volcanoes east of the water divide. If correct, this is the first-recognized example of a climatic control on the location of a volcanic arc in convergent settings.

How to cite: Paiva Muller, V. A., Sternai, P., and Sue, C.: Climatic control on the Southern Andean volcanic arc location, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-591, https://doi.org/10.5194/egusphere-egu21-591, 2021.

We explore the coastal morphology along an uplifting 500 km-long coastal segment of   the Central Andes, between the cities of Chala (Peru) and Arica (Chile). We use accurate DEM and field surveys to extract sequences of uplifted shorelines along the study area. In addition, we consider continental pediment surfaces that limit both the geographical and vertical extent of the marine landforms. We establish a chronology based on published dates for marine landforms and pediment surfaces. We expand this corpus with new ¹⁰Be data on uplifted shore platforms. The last 12 Ma are marked by three periods of coastal stability or subsidence dated ~12-11 Ma, ~8-7 Ma and ~5-2.5 Ma ago. The uplift that accumulated between these stability periods has been ~1000 m since 11 Ma; its rate can reach 0.25 mm/a (m/ka). For the last period of uplift only, during the last 800 ka, the forearc uplift has been accurately recorded by the carving of numerous coastal sequences. Within these sequences, we correlated the marine terraces with the sea level highstands (interglacial stages and sub-stages) up to MIS 19 (790 ka), i.e., with a resolution of ~100 ka. The uplift rate for this last period of uplift increases westward from 0.18 mm/a at the Peru-Chile border to ~0.25 mm/a in the center of the study area. It further increases northwestward, up to 0.45 mm/a, due to the influence of the Nazca Ridge. In this study, we document an unusual forearc cyclic uplift with ~4 Ma-long cycles. This periodicity corresponds to the predictions made by Menant et al. (2020) based on numerical models, and could be related to episodic tectonic underplating (subducting slab stripping) beneath the coastal forearc area.

How to cite: Regard, V., Martinod, J., Saillard, M., Carretier, S., Leanni, L., Hérail, G., Audin, L., and Pedoja, K.: 4 Ma-long uplift cycles of the southern Peru forearc since Late Miocene, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7172, https://doi.org/10.5194/egusphere-egu21-7172, 2021.

How to cite: Hollyday, A., Austermann, J., Lloyd, A., Hoggard, M., Richards, F., and Rovere, A.: Differential uplift of three Pliocene sea level indicator sites in southern Argentina driven by upwelling asthenosphere through the Patagonian slab window, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13740, https://doi.org/10.5194/egusphere-egu21-13740, 2021.

Convective circulation in the mantle supports some fraction of Earth’s topography. It is challenging to observe this topographic expression of mantle convection because it is contaminated by crustal and lithospheric isostatic processes. In the oceanic realm, residual bathymetry has been calculated by removing the effects of sedimentary and crustal thickness variations and comparing to the well-known plate cooling trend, revealing sub-plate topographic support that is up to 1–2 km in amplitude and varies on wavelengths of ~1000 km. On the continents, crustal thickness and density variations support a much larger fraction of topography. Similarly, the density and thickness of the lithospheric mantle do not follow a simple predictive relationship. It is therefore significantly more challenging to calculate the component of sub-plate topographic support in the continental realm. Here, we assemble a database of > 20,000 continental crustal thickness estimates from published active and passive source seismic experiments with a goal of exploring the topographic expression of crustal, lithospheric, and sub-plate mantle structure. A subset of these studies provides constraints on crustal seismic velocity structure which can be used to estimate local density structure of the continental crust. We exploit a database of laboratory-determined density and velocity measurements of crustal rocks to develop a velocity to density conversion scheme. We use these constraints on crustal structure to remove the effects of crustal thickness and density variations and calculate an estimate of residual topography that arises from mantle processes. We compare these values of residual topography to an independent, tomographically derived map of lithospheric thickness. We find that residual topography is negatively correlated with lithospheric mantle thickness, which is expected and consistent with oceanic lithospheric observations. Next, we exploit a pressure and temperature-dependent density parametrisation to calculate and remove the expected topographic contribution of the lithospheric mantle. This approach demonstrates that up to 3 km of residual topography is positively correlated with lithospheric thickness even after removing the effects of cooling and thickening of the plate, indicating that compositional factors may lead to decreasing density with increasing lithospheric thickness. This relationship is in broad agreement with constraints on lithospheric mantle composition from xenoliths. Our analysis demonstrates the importance of accounting for lithospheric structure in the continental realm in constraining the sub-plate, dynamic contribution to Earth’s topography. An important corollary is that changes to the density and thickness of lithospheric mantle drive rapid vertical motions of the Earth’s surface which are increasingly recognised as causes of regional epeirogenic uplift.

How to cite: Stephenson, S., Hoggard, M., and White, N.: Global Continental Residual Topography, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15505, https://doi.org/10.5194/egusphere-egu21-15505, 2021.

The shape of the Earth's surface is the result of complex interactions between deep and surface processes operating on a range of spatial and temporal scales. However, generating sufficient geological observations at the spatial and temporal scales relevant to investigating deep-Earth processes (~100–1000 km, ~1–100 Ma) remains a challenge. To address this challenge, I exploit a paleobiological database to generate a new compilation of >24,000 spot measurements of net surface uplift across all continents. The present-day elevation of marine fossil assemblages that crop out at the Earth’s surface provides a direct constraint on the timing and amplitude of net surface uplift on geological timescales. I explore how these surface observations can be used to explore the evolution of sub-plate processes in three key regions: Western North America, Borborema Province in northeast Brazil, and Northern Africa. This new data compilation provides self-consistent, and in places high resolution measurements for Cretaceous to Recent net uplift. Geophysical observations (e.g., free-air gravity, shear-wave topography) and isostatic calculations are combined with net uplift measurements from these regions to explore how mantle thermal anomalies and lithospheric thinning might generate the observed uplift patterns. Uncertainties associated with paleo-bathymetry, post-deposition compaction and glacio-eustasy are assessed. The results emphasise the importance of large inventories of paleobiological data for understanding the history of tectonic and mantle convective processes as expressed at the Earth's surface.

How to cite: Milanez Fernandes, V. and Roberts, G.: Exploiting a paleobiological database to constrain sub-plate support: Examples from western North America, northeast Brazil and northern Africa, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8822, https://doi.org/10.5194/egusphere-egu21-8822, 2021.

The Finke River in central Australia is counted among the world’s oldest drainage systems, raising the prospect that it holds a geomorphic record relevant to testing ideas about the role of sub-lithospheric mantle flow in shaping the Australian landscape. The Finke’s upper reaches preserve an enigmatic set of intertwined active and relict gorges that suggest a complex history of incision, aggradation and re-incision. We measured cosmogenic ¹⁰Be and ²⁶Al in fluvial gravels stored in the gorges, and we applied a Markov chain Monte Carlo-based inversion model to test two limiting-case hypotheses about the timing of the gravel deposition and exhumation. Our results suggest that the nuclide memory contained within the gravels was essentially erased during protracted sediment storage. Previous studies attribute landscape evolution to the intensified post-Miocene aridity in tune with the perception that central Australia experienced limited deformation during the Cenozoic. However, the close correlation between drainage network patterns and the gravity field leads us to propose, instead, that incision/aggradation phases in the upper Finke are driven by a flexural response (at ~10² km length scales) to extreme uncompensated loads embedded in the crust. Further, we suggest that dynamic mantle processes have deformed the central Australian topography over longer (~10³ km) wavelengths via the in-situ stress field, with horizontal stress variations of order 1–10 MPa. Acting together, these crustal and sub-lithospheric structures have imposed to-and-fro tilting on the Finke, triggering the phases of incision/aggradation on a million-year timescale that created the unusual intertwined bedrock gorges. The amplitude of topographic responses in the upper Finke to inferred variations in end-loading on the plate helps resolve an ongoing debate about the effective elastic thickness of the central Australian lithosphere to no more than 35 km.

How to cite: Jansen, J., Sandiford, M., Fujioka, T., Cohen, T., Struck, M., Anderson, S., Anderson, R., and Egholm, D.: Geomorphic imprints of dynamic topography and intraplate tectonism in central Australia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9165, https://doi.org/10.5194/egusphere-egu21-9165, 2021.

Net rotation is the process whereby the entire lithosphere can rotate with respect to the Earth’s mantle. The plates and continents retain their location with respect to each other, but they change their position with respect to global reference frames such as the Earth’s magnetic dipole, and structures in the Earth’s mantle such as plumes and hotspots. Constraining lithospheric net rotation is therefore one factor in building an absolute plate motion model. However, the amount of net rotation occurring at present day is poorly contained, and the drivers of net rotation are very poorly understood. Many absolute plate motion models therefore attempt to minimise net rotation, because there is no way to constrain rotation in the geological past. 

In previous geodynamical studies, the presence of thick continents and large viscosity contrasts were found to be controlling factors in the development of net rotation. We investigate the effects of different convection parameters and tectonic states on the magnitude and evolution of net rotation in 2D simulations. The use of 2D simulations allows us to run enough simulations to study a wide range of model parameters. We intend to compare our 2D conclusions with 3D simulations, to investigate how much of a difference the third dimension makes.

We find that net rotation varies on much shorter timescales than any other geodynamic feature. Net rotation is not cleanly correlated with any tectonic behaviours or settings, and that the magnitude and duration is unpredictable. We do however find that the distribution of net rotation within the lifetime of a particular simulation is Gaussian, with standard deviation dependent on the viscosity structure and contrasts of the simulation, in agreement with previous studies. However, in contrast to previous studies, the presence and thickness of continents makes very little difference to the speed of lithospheric rotation, although this may be because we are working in 2D. If the 2D results are also relevant in 3D, net rotation is a continuously varying and unpredictable value, but with a predictable statistical range. This may provide a way to better constrain net rotation for plate motion models.

How to cite: Atkins, S. and Coltice, N.: A search for constraints on lithospheric net rotation in 2D convection simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1562, https://doi.org/10.5194/egusphere-egu21-1562, 2021.

Arc-continent collision is the process by which intra-oceanic arc crust is accreted to continental margins and the most important mechanism that enables the growth of the continental crust since Phanerozoic times. We use numerical visco-plastic mechanical models to explore: (i) the role of lithospheric-mantle dynamics in controlling the spatio-temporal evolution of stress in arc-continent collision settings, and (ii) the role of density contrasts in the evolution of the stress regime. We performed a series of simulations only varying the thickness of the arc based on natural examples as the arc thickness controls the buoyancy of intra-oceanic arcs. Therefore, we investigated a range of density contrasts between the arc and the continental plate. Modelling results show that arc-continent collision can evolve into two contrasting scenarios: (i) slab-anchoring and arc transference in dense arcs where the density contrast between the arc and the adjacent continental lithosphere is above -3% (15-31 km in thickness); and (ii) slab break-off in buoyant arcs where the density contrast between the arc and the adjacent continental lithosphere is below -3% (32-35 km in thickness). We conclude that the large-scale mantle return flow emerged from slab-anchoring facilitates the simultaneous occurrence of compression and extension in the margin by enhancing: (i) compression and lithospheric thickening of the buoyant intra-oceanic arc crust; and (ii) the density contrast between the accreted arc and the continental margin that triggers the release of a gravitational flow. In the particular case of buoyant arcs, the compressional body force applied by the deformed arc to the subducting plate drives its passive retreat. The results of our numerical modelling highlight the importance of the role of lithospheric-mantle dynamics on controlling the spatio-temporal evolution of stress.

How to cite: Rodriguez Corcho, A. F., Morón, S., Farrington, R., Beucher, R., Moresi, L., and Montes, C.: Dynamics of arc-continent collision: the role of crustal-mantle dynamics on controlling the spatio-temporal evolution of stress, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13842, https://doi.org/10.5194/egusphere-egu21-13842, 2021.

The South China Sea (SCS) is situated at the junction of Eurasian, Indo-Australian, and Philippine sea plates. Its stress state provides significant information about the regional tectonic structure associated with interaction among the three plates. The stress field of the SCS is composed of horizontal and vertical stress fields. We calculate the vertically averaged deviatoric stress field using horizontal gradients of gravitational potential energy obtained by high-resolution sea-surface height data (SSH) from satellite Haiyang-2A. The vertical tectonic stress field is computed based on the Bouguer gravity anomaly derived from SSH and topographic data.

The vertically averaged deviatoric stress field is consistent with the GPS velocity field, the focal mechanism, and the mantle flow stress field of the South China Sea. Moreover, it also indicates the Red River-Ailaoshan Fault zone on the west of the SCS and the Manila subduction on the east. The vertical tectonic stress field removing the influence of sediment indicates upward stress of the lithosphere in the SCS ocean basin. The stress field model therefore provides a powerful tool for understanding regional tectonic activities around the SCS.

How to cite: Shi, H., Gao, J., Xu, M., and Guan, Q.: The stress field model of the South China Sea calculated by sea level data from satellites, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14684, https://doi.org/10.5194/egusphere-egu21-14684, 2021.

We describe a major new Neoproterozoic orogenic system belonging to the larger Pan-African deformational realm, the Saharides, in North Africa, by using various tools such as magnetic maps and our own remote-sensing based structural interpretation to aid us in following the orogenic trend-lines in addition to a large compilation of geochronological data. The Saharides, a Turkic-type orogenic complex similar to the Altaids of central and northwestern Asia, involved major subduction accretion complexes occupying almost the entire Arabian Shield and much of Egypt and Sudan and the small inliers of such complexes farther west to and including the Ahaggar mountains. These complexes are formed at least by half from juvenile material representing at least 5 million km2 new continental crust formed during the Neoproterozoic from about 900 to 500 Ma ago. Contrary to conventional wisdom in the areas they occupy, the Saharides involved no continental collisions until the very end of their history, but evolved by subduction and strike-slip stacking of arc material mainly by pre-collisional coast-wise transport of arc fragments shaved off the Congo/Tanzania cratonic nucleus in a manner very similar to the development of the Nipponides in east Asia, parts of the North American Cordillera and the Altaids. The entire Sahara is shown to be underlain by a double orocline much like the Hercynian double orocline in western Europe and northwestern Africa and not by an hypothetical ‘Saharan Metacraton’. The method here followed may be a fruitful procedure to untangle the structure of some of the Precambrian orogenic belts before life evolved sufficiently to make biostratigraphy feasible.

How to cite: Şengör, A. M. C., Lom, N., Zabcı, C., Sunal, G., and Öner, T.: The Saharides: Turkic-Type Orogeny in Afro-Arabia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5494, https://doi.org/10.5194/egusphere-egu21-5494, 2021.