GD8.1

Variations in subduction configuration and mantle dynamics can be detected in retroarc foreland basins.  Modern and ancient examples from western South America show how discrete geodynamic mechanisms drive regional unconformity development in the Andean foreland basin.  Positive dynamic topography in the basin, fold-thrust belt, and broader convergent plate margin can be generated by (1) flat slab subduction, (2) slab window formation, (3) slab breakoff, (4) elevated intraplate (in-plane) stress, or (5) mantle flow variations.  A survey of long duration (>1–20 Myr) unconformities considers these and alternative mechanisms, including (6) local shortening-induced uplift in the frontal thrust belt and proximal foreland, (7) growth and advance of a broad flexural forebulge in the distal foreland, (8) uplift of intraforeland basement blocks along crustal-scale reverse faults, (9) tectonic quiescence with regional isostatic rebound, and (10) diminished accommodation or sediment supply due to changes in sea level, climate, erosion, or sediment transport.  These contrasting mechanisms can be readily observed in the modern foreland, particularly in the case of increased interplate coupling during active flat slab subduction and slab window generation associated with subduction of an active oceanic spreading ridge.  In the ancient record, the operative geodynamic mechanisms can be distinguished on the basis of the spatial distribution, stratigraphic position, paleoenvironmental context, and duration of foreland unconformities within the Cretaceous to Quaternary geodynamic framework of the Andean orogenic system.

How to cite: Horton, B. K.: Stratigraphic record of dynamic topography in the Andean foreland basin, South America, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6749, https://doi.org/10.5194/egusphere-egu22-6749, 2022.

One of the greatest challenges of modeling the plate tectonic history of Earth during the Mesozoic and Cenozoic eras lies in reconstructing the Pacific Ocean and its predecessor ocean, Panthalassa.  A major reason for the plate tectonic uncertainty in this region is extensive subduction, which has consumed most (>95%) of the Pacific-Panthalassan ocean lithosphere formed since 150 Ma (Törsvik et al., 2019) and recycled it into the mantle, destroying the information on past plate motions recorded by seafloor magnetic lineations.  Consequently, many circum-Pacific margin plate tectonic models, including the popular GPlates models (e.g. Matthews et al., 2016; Müller et al., 2019), necessarily extrapolate 1000’s of km of subducted seafloor (i.e. synthetic seafloor isochrons).  Given the limited constraints, it is understandable that such models also prefer more straightforward solutions with a smaller number of larger plates, avoiding the complexities of modeling intra-oceanic subduction despite geological evidence from accreted circum-Pacific oceanic terranes.

Here we build the first topologically-closed, global plate tectonic model of the circum-Pacific using structurally-restored slabs from mantle seismic tomography as our primary constraint.  We use the numerical code TERRA to assimilate three variants of our ‘tomographic’ global plate model into mantle circulation forward models and assimilate the default GPlates model as a reference.  We show our preliminary geodynamic modeling results and test our model predictions against observed mantle structure, Earth’s geoid, and oceanic realm dynamic topography. 

All cases favor plate models that incorporate intra-oceanic subduction within Pacific-Panthalassa, particularly within the northern Pacific.  We find robust support for significant slab lateral advections (i.e. non-vertical slab sinking) under NW Pacific basin.  We discuss similarities and differences between our new ‘tomographic’ plate models and the GPlates model, which has been used for almost all geodynamic studies of the circum-Pacific to date. 

How to cite: Wu, J., Lin, Y.-A., Colli, L., Chen, Y.-W., Fuston, S., and Wu, T.-J. J.: First views from assimilation of a new ‘tomographic’ circum-Pacific plate reconstruction into mantle circulation models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10560, https://doi.org/10.5194/egusphere-egu22-10560, 2022.

The back-arc marginal sea is a small ocean basin located between the volcanic arc and the continental crust. This area is not only an important gathering place for natural resources, but also an important place for plate interaction. Therefore, clarifying the origin and evolution of marginal seas can produce a huge boost for us to explore natural resources and improve the plate interaction mechanism. At present, the back-arc marginal sea with the largest opening rate of the Earth is the Lau Basin, and most marginal seas are generally in a state of medium-to-low-speed opening, such as the Mariana Trough, the Aegean Sea and the Caribbean Sea, and a small amount of marginal seas are even shortening, such as the Sea of Japan. What caused the marginal seas to open at different speeds?  In order to answer this question systematically and give a unified model for the origin and evolution of the marginal seas of the Earth, we must first figure out when the marginal sea will grow up. Therefore, we run 2-D and 3-D numerical experiments to test the possible effects of different factors on the evolution of the marginal sea. The results of our dynamic models can not only fit the evolution of the global marginal sea well, but also come to a robust conclusion: when the subducting plate stagnate in the transition zone, the opening rate of the marginal sea may decrease; but the marginal sea that stopped opening may still grow up again under special conditions. Furthermore, we explain the diversity of the current marginal sea evolution, which provides more theoretical foundations for the discipline of plate tectonics.

How to cite: Jian, H., Yang, T., and Guo, P.: When will the marginal sea grow up?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2715, https://doi.org/10.5194/egusphere-egu22-2715, 2022.

 The Mangatolu Triple Junction (MTJ) and the Fonualei Rift and Spreading Center (FRSC) are two prominent bathymetric features in the northern Lau Basin in the southwest Pacific Ocean. We present the results of six W-E running Multi-Channel Seismic (MCS), magnetic and sediment echo sounding profiles acquired during the ARCHIMEDES-I expedition. These profiles cover the MTJ, the FRSC and the region just south of the FRSC to investigate the tectonic history and current tectonic activity of the Lau Basin. 

On all MCS profiles, we observe a heavily faulted basement on both sides of the MTJ and FRSC with faults that are covered with sediments, confirmed by the sediment echo sounding data. We consider these buried faults inactive today. We also observe faults that reach the seafloor. These faults are generally located closer to the MTJ and the FRSC and they correlate well with seismic activity recorded in the region. We thus consider these faults currently active. Seismically transparent bodies are observed on most profiles as well. We have interpreted those as volcanic intrusions, i.e. sills, or as volcanoes that pierce through the stratigraphy, especially closer to the volcanic arc. 

The two sets of faults, the notion that extension rates are higher at the MTJ (32 mm/yr) than at the southern tip of the FRSC (8 mm/yr) and the results from our newly acquired and interpreted magnetic data, have led to the interpretation that an earlier rift phase accommodated extension in a wide rift tectonic setting between 2.15 Ma and 0.85 Ma at the MTJ and 2.15 and 1.61 Ma at the FRSC. Today, the extension is accommodated in a narrow rift tectonic setting close to the MTJ and FRSC with a higher extension rate at the MTJ than at the southern tip of the FRSC. These findings suggest that the MTJ and FRSC are one, single intra-plate extension zone that is in the process of breaking apart the overriding Niuafo’ou-Tonga microplate along the MTJ and FRSC.

How to cite: Beniest, A., Schnabel, M., Barckhausen, U., Dannowski, A., Schmid, F., Riedel, M., Jegen, A., and Kopp, H.: Tectonic activity at Mangatolu Triple Junction and the Fonualei Rift and Spreading Center: breaking apart the intra-oceanic Niuafo’ou-Tonga microplate, Lau Basin, South West Pacific Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5762, https://doi.org/10.5194/egusphere-egu22-5762, 2022.

The Cascadia Subduction Zone is characterized by young subducting lithosphere, its isolation from other subducting slabs, and its ability to produce megathrust earthquakes (M>9.0) and devastating tsunamis. Due to its high potential hazard and risk, it is also a well-studied subduction zone where modern, diverse and detailed observational datasets are available through the USGS and initiatives like GeoPrisms and EarthScope. These datasets include high quality GPS, onshore and offshore geophysical imaging, magmatic and seismic anisotropy data. These datasets present an opportunity to gain insight into slab structure, tectonic evolution, and present-day seismic hazards. Still, many questions remain about the physical processes that can self-consistently explain all the observations, and better estimate seismic hazards. For example, for the slab, geologic and geophysical data suggest that there may be one or two prominent slab gaps or tears, while tomographic data does not fully constrain the depth extent of the slab. Furthermore, the overriding plate is composed of several different terranes and contain numerous active and slowly moving faults, complicating efforts to accurately constrain variations in the overriding plate present-day stress and deformation rates.

In this study we test whether comparison of observations to model predictions can distinguish between different slab geometries for the Cascadia Subduction Zone. To this end, we have created regional 3D geodynamic models of Cascadia including the Cascadia slab based on the Slab 2.0 dataset. The model setup is built with the Geodynamic World Builder and, and the models are run using the mantle convection and lithospheric dynamics code ASPECT. During the evolution of these models we track the development of the CPO (Crystal Preferred Orientation), so we can compare it against seismic anisotropy data of the region. Our presentation will focus on the preliminary results of these models and demonstrate workflows for linking the model results to surface tectonics.

How to cite: Fraters, M., Billen, M., Naliboff, J., Staisch, L., and Watt, J.: Exploring the Cascadia slab structure coupling 3D thermomechinal and CPO modeling., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6764, https://doi.org/10.5194/egusphere-egu22-6764, 2022.

It is widely accepted that the subduction system along an active continental margin has significant impacts on continental motions and deformation. The longest strike-slip fault in East Asian, the Tan-Lu Fault extends through the lithosphere and parallels the East Asian margin trench could be recognized as weak zone and left more significant geological information of plate tectonics than surrounding areas ( Collettini et al., 2019 ). Previous studies have gained some common sense about the motion of the East Eurasia continent margin from the Tan-Lu fault in the Late Mesozoic. The Tan-Lu fault experienced two phases sinistral strike-slip motion under compression with a striking-length about 150~200 km ( Zhu et al.,2005, 2009; Zhao et al.,2016 ), one stage is the Late Jurassic of the obtained age of 162~150 Ma and the other stage is the Early Cretaceous of the gained age of 143Ma~132Ma ( Zhu et al.,2005, 2010, 2018; Zhang and Dong, 2008 ). However, the formation mechanism of the large strike motion is still in doubt. Zhu et al., (2018) suggest that the Mesozoic tectonism of the Tan-Lu fault zone is dominated by paleo-Pacific plate subduction and thus can reflect its subduction history, while some others think the geodynamics of the Tan-Lu fault is controlled by the combined influences of the collision between the Tibetan blocks and Eurasia and the paleo-Pacific plate subduction ( Zhang et al., 2010 ).

To understand whether the paleo-Pacific subduction could have a dominant impact on the tectonic activities along the Tan-Lu fault and how does it influence the overriding plate, we perform 3-D numerical simulations of oceanic-continental subduction with a weakened fault zone simulating the Tan-Lu Fault. The results indicate that the motion and deformation of the East Asian continental plate can be strongly influenced by the interaction between the paleo-Pacific plate and East Asia, especially by the coupling degree between the subduction plate and the overriding plate. The coupling degree could significantly improve when there is micro-continent from subduction plate collide with overriding plate and the overriding plate would undergo compression. The collision between micro-continents with East Eurasia continent in Late Jurassic and Early Cretaceous has been observed ( Li et al.,2020; Charvet,2013 ). From the plate reconstructions ( Müller et al.,2016 ), in the Late Mesozoic had a northward component with an average velocity 40~50 mm/yr. In our numerical model, the generation of large sinistral strike-length could explained by strong coupling caused by collision of micro-continents with Eurasia plate.

How to cite: Zhou, M., Yang, T., Deng, L., and Guo, P.: Strike-slip motion in the Late Mesozoic on the East Asian continental margin: Insight from 3-D numerical models with the Tan-Lu fault, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6782, https://doi.org/10.5194/egusphere-egu22-6782, 2022.

Decoding tectonic and climatic signatures from continental successions has become important in basin analysis. However, tectonic and climatic signatures can still be difficult to discriminate from each other. The late Mesozoic Xuanhua basin in the western Yanshan fold‑and‑thrust belt represents a representative intramontane basin and allows detailed stratigraphic, sedimentological, and provenance analyses. The work entailed an analysis of alluvial fan, fluvial, lake‑delta, and lacustrine systems in the Tuchengzi Fm. Lateral correlation of sedimentary columns reveals two large‑scale upward‑coarsening cyclothems each 80-240m thick, with prominent vertical changes from lacustrine through deltaic and fluvial to alluvial fan deposits. Two intervals of thrust‑related growth strata identified in the Tuchengzi Fm suggest that the cyclothems were controlled by tectonic uplift and accommodation change related to the Likouquan and the Mapu thrusting. In the lower upward‑coarsening cyclothem, stacking of small‑scale (3-16 m thick) upward‑fining cyclothems was revealed and argued to have been generated by alternating wet‑dry cycles. The wet half‑cycle started with discharge and deposition of flood‑generated mass‑flows into the lake and ended with accumulation of lacustrine mudstones as lake level rose. The lake deposits include the maximum flooding during the wet half‑cycle. The dry half‑cycle was characterized by continued lacustrine deposits, but with increased evidence of subaerial exposure indicated by rooting, paleosols and mudcracks resulting from falling of the lake level under dry conditions.

How to cite: Lin, C., Liu, S., and Steel, R.: Tectonic and climatic controls on the Late Jurassic-Early Cretaceous stratigraphic architecture of the Xuanhua basin, North China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13356, https://doi.org/10.5194/egusphere-egu22-13356, 2022.