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(a) Bathymetry and (b) side-scan sonar images of a relatively low relief, high acoustic reflectivity region in the northwest corner of the GLIMPSE study region (box H in Figure 2). The lava flows inferred from the side-scan sonar image appear to collect in topographic lows in the region. There is no clear indication of cracking parallel to spreading direction associated with renewed volcanism, and there is no clear relationship to any of the other bathymetric features in the region. There is a complex pattern of abyssal hill topography around 11°45 0 S reflecting the location near a dying pseudofault and near the possible origin of the Garrett transform. Relatively fresh, highly vesicular, ''popping rocks'' were recovered from one of the flows (orange dot). Artificial illumination of the bathymetry is from the east.
Source publication
Lithospheric cracking by remotely applied stresses or thermoelastic stresses has been suggested to be the mechanism responsible for the formation of intraplate volcanic ridges in the Pacific that clearly do not form above fixed hot spots. As part of the Gravity Lineations Intraplate Melting Petrology and Seismic Expedition (GLIMPSE) project designe...
Citations
... In the Pacific, previous studies have suggested a possible link between small-scale convection and gravity rolls (e.g., Harmon et al., 2006Harmon et al., , 2007Harmon et al., , 2011, which are visible in satellite data (Haxby & Weissel, 1986). Additionally, a broadband Rayleigh-wave dispersion array analysis in the oldest Pacific seafloor indicates average 1-D V S profile with significantly slow asthenosphere, providing evidence of reheating processes such as small-scale convection in the study region (Kawano, Isse, Takeo, et al., 2023). ...
The oldest oceanic basin (160–180 Ma) in the western Pacific is the birthplace of the Pacific Plate and is thus essential for understanding the formation and evolution of the oceanic plate. However, the upper mantle structure beneath the region has not been thoroughly investigated because of the remoteness and difficulties of long‐term in situ seismic measurements at the ocean bottom. From 2018 to 2019, the Oldest‐1 experiment on the oldest seafloor was conducted as part of the international Pacific Array initiative. We present the first three‐dimensional P‐wave velocity structure down to a depth of 350 km based on the relative travel time residuals of teleseismic earthquakes recorded by 11 broadband ocean‐bottom seismometers operated during the Oldest‐1 experiment. Our result shows a fast P‐wave velocity anomaly (VP perturbation of 2%–4% faster than average) at a depth of 95–185 km beneath the northeast of the study area. This structure is interpreted as evidence of dry, viscous, and rigid materials at depths below the lithosphere. Two slow anomalies (VP perturbation of 2%–4% slower than average) are seen beneath the southwestern and eastern (the oldest seafloor >170 Ma) parts of the array site. The low‐velocity zones are found at depths of 95–305 km. The observed velocity structures can be indicative of plume activities that affected the upper mantle as the Pacific Plate migrated over hotspots from the southeast. Alternatively, the observed velocity features may provide seismic evidence for small‐scale sublithospheric convection.
... Sparse island stations and ocean basin-traversing seismic rays offer only coarse imaging of the oceanic upper mantle. A previous study, the GLIMPSE ocean bottom seismometer (OBS) experiment (Forsyth et al., 2006), aimed to probe gravity lineations in ∼2-10 Ma Pacific plate just west of the East Pacific Rise. Body (Harmon et al., 2007) and Rayleigh wave (Weeraratne et al., 2007) imaging revealed elongate low-velocity lineaments beneath volcanic ridges with lateral wavelength of order ∼250 km. ...
Small‐scale convection beneath the oceanic plates has been invoked to explain off‐axis nonplume volcanism, departure from simple seafloor depth‐age relationships, and intraplate gravity lineations. We deployed 30 broadband ocean bottom seismometer stations on ∼40 Ma Pacific seafloor in a region notable for gravity anomalies, measured by satellite altimetry, elongated parallel to plate motion. P‐wave teleseismic tomography reveals alternating upper mantle velocity anomalies on the order of ±2%, aligned with the gravity lineations. These features, which correspond to ∼300°–500°K lateral temperature contrast, and possible hydrous or carbonatitic partial melt, are—surprisingly—strongest between 150 and 260 km depth, indicating rapid vertical motions through a low‐viscosity asthenospheric channel. Coherence and admittance analysis of gravity and topography using new multibeam bathymetry soundings substantiates the presence of mantle density variations, and forward modeling predicts gravity anomalies that qualitatively match observed lineations. This study provides observational support for small‐scale convective rolls beneath the oceanic plates.
... Sparse island stations and ocean basin-traversing seismic rays offer only coarse imaging of the oceanic upper mantle. A previous study, the GLIMPSE ocean bottom seismometer (OBS) experiment (Forsyth et al., 2006), aimed to probe gravity lineations in ∼2-10 Ma Pacific plate just west of the East Pacific Rise. Body (Harmon et al., 2007) and Rayleigh wave (Weeraratne et al., 2007) imaging revealed elongate low-velocity lineaments beneath volcanic ridges with lateral wavelength of order ∼250 km. ...
... Different types of magmatic activities were recorded in the passive margins, such as saucer-shaped sills developed in the NW Australia margin (Magee et al., 2016), U-reflection sills developed in the Newfoundland margin (Peron-Pinvidic et al., 2010;Peace et al., 2017), sill-related to force folds and bedding-parallel sills, as well as volcanoes developed in the southern Australia margin Meeuws et al., 2016), etc. Many theories have been proposed to account for the post-rift magmatism, such as the mantle plume (Pe-Piper et al., 1994;Karner and Shillington, 2005), delayed effect of regional extension induced by the seafloor spreading , lithospheric delamination (O'Reilly and Zhang, 1995;Ducea and Saleeby, 1998;Lustrino, 2005), cracking of the lithosphere (McKenzie and Bickle, 1988;Forsyth et al., 2006), shear-driven upwelling (Conrad et al., 2010(Conrad et al., , 2011, edge-controlled convection (King and Ritsema, 2000;Pe-Piper et al., 2007;Ballmer et al., 2009), and off-axis magmatism during early seafloor spreading (Canales et al., 2012), etc. Previous studies suggest that the northern margin of the South China Sea (SCS) is a magma-poor margin for lacking seaward dipping reflectors (SDRs) and intense magmatism during the breakup process of the lithosphere (Yan et al., 2001(Yan et al., , 2006Barckhausen and Roeser, 2004;Zhou and Yao, 2009;Li, 2011;Franke, 2013;Savva et al., 2014;Zhang et al., 2016). ...
The South China Sea, which is located to the southeast of Eurasian continent, developed as the result of intra-continental rifting and seafloor spreading on the South China margin. Passive margins are traditionally classified as one of two end-member types, the magma-rich and magma-poor margins, based on the relative abundance or scarcity of magmatism during rifting and breakup. Previous studies suggest that the northern margin of the South China Sea is a magma-poor margin for lacking abundant magmatic activities during the breakup. A growing body of work is beginning to recognize that significant, widespread magmatism may also be present on margins that are presently considered to be magma-poor margins. In this study, we use high resolution 2D/3D seismic profiles, industrial well data, basalt geochemistry (major oxides, trace elements and isotopes) and published results to outline post-rift magmatism developed within the northern margin of the South China Sea. Four magmatic stages occurred since lithospheric breakup. The first stage, from 32 to 23.6 Ma and mainly within the distal margin of the northern South China Sea, was dominated by magma intrusions and corresponded to the spreading of the East Sub-basin. The second stage, from 23.6–19.1 Ma, was mainly in the Baiyan Sag and surrounding uplifts and explosive eruptions dominated. The third Stage, from 19.1–10 Ma, was east of the Zhu III Depression and west of the Enping Sag and dominated by quiet eruptions. The fourth stage, since 10 Ma, and widely distributed in the southern Dongsha uplift, experienced scattered volcanic eruptions. Two basalt samples from 23.6–19.1 Ma (industrial well HJ1, Stage 2) and seven samples from 19.1–10 Ma (industrial well EP1, Stage 3) are analyzed for major oxides, trace elements and Sr-Nd-Pb-Hf isotope compositions. Geochemical features of trace elements show that these samples are characterized by OIB-like basalts, being highly enriched in LREEs (light rare earth elements) relative to HREEs (heavy rare earth elements). Geochemical features of Sr-Nd-Pb-Hf isotope compositions show that the samples all resemble ocean-island basalts with two mixing endmembers: depleted mid-ocean ridge basalt mantle (DMM) and enriched mantle II (EMII). Pb isotopic characteristics show the Dupal isotope anomaly in the northern margin of the South China Sea. And geochemistry data of all the samples signals the contribution of Hainan Plume. Previous studies have revealed the existing of southeastward mantle flow from Tibet to South China Sea and a branch of Hainan Plume existing beneath the northern South China Sea using geophysical methods by different researchers. Based on our latest research and published geological evidences by other researchers, we propose that Stage 1 magmatism was caused by southeastward mantle flow stemming from Indo-Eurasian collision, the stage 2 and stage 3 magmatism was caused by Hainan Plume and the activation of Yangjiang-Yitongansha Faut Zone, whereas the last stage magmatic activity was mainly related with the combination of Hainan Plume and activation of the faults caused by the subduction of the SCS beneath the Luzon Arc at the Manila trench.
... Lonsdale (2005), in the only publication to discuss their origin, concluded (based on "a few traverses of bathymetric data" and the fact that they did not offset magnetic anomalies) that they were not linked to fracture zones but instead "closely resemble the linear volcanic ridges built over eruptive fractures that extend down the young flanks of active eastern Pacific rises, such as Sojourn Ridge on the Pacific-Nazca EPR". The Sojourn Ridge extends between 50 and 550 km to the west of the EPR and is younger than the underlying crust by up to 5 Ma (Forsyth et al., 2006). Lonsdale (2005) notes that the Alvarado and Sarmiento Ridges extend westward from the trench to EPR crustal ages of ca. 25 Ma, meaning that if their origin is similar to Sojourn Ridge they will have been inactive for the last 20 Ma. ...
... Lonsdale (2005) notes that the Alvarado and Sarmiento Ridges extend westward from the trench to EPR crustal ages of ca. 25 Ma, meaning that if their origin is similar to Sojourn Ridge they will have been inactive for the last 20 Ma. Evidence that such off-axis linear ridges do at some distance from the ridge cease to be active comes from the Puka Puka ridge which, although extending up to 2000 km across the Pacific plate from the EPR, is known to be inactive in all but its most near-ridge part (Forsyth et al., 2006). We note additionally that the DISCOL region is not in line with either the Alvarado or the Sarmiento Ridges and that a characteristic feature of the off-axis ridges such as Sojourn or Puka Puka is their elongated form and constant direction over many hundreds of kilometers. ...
... Evidence for plate extension and cracking in response to far-field (plate tectonic) or within-plate thermal contraction stresses as a cause or focusser of intraplate volcanism has been sought in many places. Sandwell and Fialko (2004) suggested that cooling and contraction of the Pacific Plate was responsible for lineaments in the gravity field associated with the Sojourn, Puku Puka etc. Ridges, although Forsyth et al. (2006) failed to find any evidence for it in the field and found that even young, small volcanoes did not appear to be associated with lineation-parallel cracks or graben in the plate. Cormier et al. (2011), studying the Cocos Plate, found that the gravity lineations there were perpendicular to crustal isochrons and suggested that this was evidence for thermal contraction. ...
The abyssal plains are generally assumed to be geologically inactive parts of the ocean plate interiors where processes (such as pelagic sedimentation or manganese crust and nodule formation) occur at very slow rates. In terms of intraplate volcanic activity, almost all is assumed to occur at hotspots, leading to little exploration in other intraplate regions. The Peru Basin is an abyssal plain known to host Mn-nodule fields. We present remotely-operated underwater vehicle (ROV) investigations of a small seamount adjacent to such a Mn-nodule field on 20Ma Nazca Plate crust, showing that it appears to have been recently volcanically and hydrothermally active. The seamount lies 1600km east of the nearest spreading axis (East Pacific Rise) and 600km from both the Galapagos Plateau (to the north) and the subduction zone off Peru (to the east), making off-axis, hotspot or petit-spot processes unlikely as a cause of the volcanism. The shallow mantle below the Nazca (and conjugate Pacific) Plate shows globally anomalous low seismic shear-wave velocities, perhaps reflecting higher-than-normal amounts of melt in the mantle below this region which may provide a source for the magmas. Our own regional mapping work and literature sources highlight several similar sites of probable young volcanism elsewhere in the Peru Basin which may also be related to this anomaly. The Nazca abyssal plain may be much more geologically active than previously thought. If so, this could have wider implications for, among other things, chemosynthetic ecosystem connectivity.
... Previous works suggested that the source of low-volume intraplate volcanics could be asthenospheric mantle ( Aldanmaz et al., 2006;Hoernle et al., 2006;Pang et al., 2012), litho- spheric mantle (Weinstein et al., 2006;Valentine and Hirano, 2010), or lithosphere-asthenosphere interaction (Ma et al., 2011). Possible mechanisms of low-volume intraplate volcanism are various, such as small-scale mantle convection ( Ballmer et al., 2009;McGee et al., 2011), deformation-driven melt collection (Valentine and Hirano, 2010), lithospheric removal/delamination ( Hoernle et al., 2006;Pang et al., 2012), lithospheric cracking ( Forsyth et al., 2006), astheno- spheric shearing (Conrad et al., 2011), small plume (Sobel and Arnaud, 2000;Simonov et al., 2015) or slab detachment (Davies and von Blanckenburg 1995). ...
High-volume volcanic fields which are observed at continental intraplate setting are generally known as the large igneous provinces (LIPs), fed by hot and active plumes upwelling from the deep mantle. However, the source and mechanism of low-volume effusive volcanism within continental interiors remains poorly unknown. Here, we present a combined study of ⁴⁰Ar/³⁹Ar geochronology, mineral chemistry, whole-rock major and trace elements as well as Sr-Nd isotopes of Jurassic basalts from the Karamay area, Junggar terrane (NW China), aiming to determine their formation ages, constrain the petrogenesis and reveal their tectonic implications. New whole-rock ⁴⁰Ar/³⁹Ar dating yields consistent ages of 189.4–193.3 Ma for magma emplacement. The basalts exhibit a columnar joint structure and porphyritic texture with phenocryst minerals of olivine (Fo63–79), clinopyroxene (Wo39–46En38–47Fs12–22) and plagioclase (An25–54). They have SiO2 contents ranging from 45.0–51.8 wt% and belong to alkaline series (δ[dbnd]2.7–13.3, average of 5.0). The basalts are characterized by oceanic island basalt (OIB)-like trace element distribution patterns with enrichment in L-MREE, HFSE (e.g., Nb and Ta) and LILE (e.g., K, Sr and Ba), and slight depletion in HREE, relative to normal mid-ocean ridge basalt (N-MORB). Positive εNd(t) (+3.0), low to moderate ⁸⁷Sr/⁸⁶Sri (0.7048–0.7049) isotopic compositions, and trace element ratios (e.g., high Nb/U > 49.0 and Ce/Pb > 13.9) suggest that crust contamination was insignificant in the formation process. P–T estimates of major phenocryst minerals in these basalts reflect high crystallization temperatures (>1100 °C) but low pressures (<9.8 kbar). Geochemical features and REE modeling indicate that the basaltic magmas were likely derived by low degrees of partial melting (~5% – 10%) of an asthenospheric mantle source in the garnet stability field. Calculated lithospheric thickness and initial melting depths for the studied basalts are about 120 km and 180–200 km, respectively. Based on the available data and regional secular geological evolution, we suggest that decompression melting of upwelling asthenosphere triggered by small-scale removal of thickened lithospheric root could be a possible mechanism to explain Jurassic low-volume intraplate volcanism in the Junggar terrane.
... Sheet-like flow sequences (tens of kilometers long) in the range of~200 m thick are sufficient to reproduce the observed gravity anomalies. Other possible origins of apparently acausal anomalies include ridge-axis discontinuities and off-axis volcanism, the latter of which can be productive up to several hundred kilometers from the ridge axis in the modern Pacific Ocean (26). ...
... To make estimates of the excess volumes erupted at K-Pg time, we used global topographic and gravity anomalies at K-Pg time to constrain one-dimensional models for enhanced crustal production at MORs, accounting for the flexural response of anomalous loading from a combination of intrusions and excess surface lava extrusion. We implement the Fourier domain technique of Forsyth et al. (26) and Ali et al. (48), as described in section S4. This procedure constrains the ratio of intruded to extruded loads, assumed to be spatially in phase, that explain the range of the observed gravity and topography anomalies. ...
Eruptive phenomena at all scales, from hydrothermal geysers to flood basalts, can potentially be initiated or modulated by external mechanical perturbations. We present evidence for the triggering of magmatism on a global scale by the Chicxulub meteorite impact at the Cretaceous-Paleogene (K-Pg) boundary, recorded by transiently increased crustal production at mid-ocean ridges. Concentrated positive free-air gravity and coincident seafloor topographic anomalies, associated with seafloor created at fast-spreading rates, suggest volumes of excess magmatism in the range of ~10⁵ to 10⁶ km³. Widespread mobilization of existing mantle melt by post-impact seismic radiation can explain the volume and distribution of the anomalous crust. This massive but short-lived pulse of marine magmatism should be considered alongside the Chicxulub impact and Deccan Traps as a contributor to geochemical anomalies and environmental changes at K-Pg time.
... Open questions range from asking (i) when plate tectonics really started, (ii) whether in the Archean plate tectonics resembled as at present time, (iii) whether is the mantle causing plates to move or are the plates driving the plate tectonics process [157], (iv) whether the upper and lower mantle of the Earth are coupled [56,114,133], (v) whether the blobs observed below the Pacific and the below Africa are involved in the general plate tectonics processes, (vi) whether mantle plumes are substantially fixed and therefore hot spots can be used to determine the past position of the tectonic plates [148], (vii) what is the real strength of the tectonic plates, and if elasticity plays a role [139,145,154,160] (viii) why Earthquakes exist down to 670 km depth, and why not deeper, (ix) is the maximum magnitude of the thrust earthquakes related to the dynamics of the downgoing slab, and if so how, [136] (x) what is the energy budget of the plate tectonics phenomena, where is the energy thermally dissipated and whether it is generated internally in the mantle and flowing from the core into the mantle [143,151,158], (xi) whether the rheology of the mantle is strongly nonlinear, or if a linear behavior emerges at a certain scale [131,150,153], (xi) how are the global measured stress field and plate tectonics related [157], (xii) whether the evolution of plate tectonics on Earth is changing in a continuous manner or through sudden jumps of kinematic patterns [155,159], (xiii) the relationship between the global geodynamics and the observed Earth's geoid [152] and many more questions. It is in summary an extremely active research field, just only looking at global and regional geodynamics open questions. ...
Examples are introduced here in which Python can be used to visualize Scientific data in 2D and 3D. Data can originate from both observation and numerical models. Examples in this chapter focus more on observational data. The most used visualization library in Python, MatPlotLib, is introduced from the historical point of view. Datasets are downloaded from the web, among them simple data like the length of the day. A mathematical 3D object called Moebius stream is created and visualized with several techniques. Python is mostly used as a wrapper for general visualization software such as Paraview and VisIt. More in general there exists a Scientific Python Ecosystem, embedding tools such as iPython (now Jupyter), MatPlotLib, and many more. Although this system has been conceived to practice science, it is largely a set of tools that allows practicing, visualizing, and sharing technologies applied to Science. Finally, two projects directly applied to the Earth Sciences are quickly illustrated.
... Open questions range from asking (i) when plate tectonics really started, (ii) whether in the Archean plate tectonics resembled as at present time, (iii) whether is the mantle causing plates to move or are the plates driving the plate tectonics process [157], (iv) whether the upper and lower mantle of the Earth are coupled [56,114,133], (v) whether the blobs observed below the Pacific and the below Africa are involved in the general plate tectonics processes, (vi) whether mantle plumes are substantially fixed and therefore hot spots can be used to determine the past position of the tectonic plates [148], (vii) what is the real strength of the tectonic plates, and if elasticity plays a role [139,145,154,160] (viii) why Earthquakes exist down to 670 km depth, and why not deeper, (ix) is the maximum magnitude of the thrust earthquakes related to the dynamics of the downgoing slab, and if so how, [136] (x) what is the energy budget of the plate tectonics phenomena, where is the energy thermally dissipated and whether it is generated internally in the mantle and flowing from the core into the mantle [143,151,158], (xi) whether the rheology of the mantle is strongly nonlinear, or if a linear behavior emerges at a certain scale [131,150,153], (xi) how are the global measured stress field and plate tectonics related [157], (xii) whether the evolution of plate tectonics on Earth is changing in a continuous manner or through sudden jumps of kinematic patterns [155,159], (xiii) the relationship between the global geodynamics and the observed Earth's geoid [152] and many more questions. It is in summary an extremely active research field, just only looking at global and regional geodynamics open questions. ...
Several applications to Geodynamics are here synthetically addressed. Subduction, the driving mechanism of plate tectonics, can be simulated with all the techniques illustrated in this book. In particular by using the Particles in Cell (PIC) the details of the small scale thermo-mechanic processes can be modelled. Instead the Tree Code Boundary Element (BE) can have applications in modeling the far field interaction between tectonics plates. It is shown that the same technique can be applied to modeling the interaction between diapirs in magma and between crustal faults. Finally a traditional convection simulation is performed using the PIC method.
... Open questions range from asking (i) when plate tectonics really started, (ii) whether in the Archean plate tectonics resembled as at present time, (iii) whether is the mantle causing plates to move or are the plates driving the plate tectonics process [157], (iv) whether the upper and lower mantle of the Earth are coupled [56,114,133], (v) whether the blobs observed below the Pacific and the below Africa are involved in the general plate tectonics processes, (vi) whether mantle plumes are substantially fixed and therefore hot spots can be used to determine the past position of the tectonic plates [148], (vii) what is the real strength of the tectonic plates, and if elasticity plays a role [139,145,154,160] (viii) why Earthquakes exist down to 670 km depth, and why not deeper, (ix) is the maximum magnitude of the thrust earthquakes related to the dynamics of the downgoing slab, and if so how, [136] (x) what is the energy budget of the plate tectonics phenomena, where is the energy thermally dissipated and whether it is generated internally in the mantle and flowing from the core into the mantle [143,151,158], (xi) whether the rheology of the mantle is strongly nonlinear, or if a linear behavior emerges at a certain scale [131,150,153], (xi) how are the global measured stress field and plate tectonics related [157], (xii) whether the evolution of plate tectonics on Earth is changing in a continuous manner or through sudden jumps of kinematic patterns [155,159], (xiii) the relationship between the global geodynamics and the observed Earth's geoid [152] and many more questions. It is in summary an extremely active research field, just only looking at global and regional geodynamics open questions. ...
This book addresses students and young researchers who want to learn to use numerical modeling to solve problems in geodynamics. Intended as an easy-to-use and self-learning guide, readers only need a basic background in calculus to approach most of the material. The book difficulty increases very gradually, through four distinct parts. The first is an introduction to the Python techniques necessary to visualize and run vectorial calculations. The second is an overview with several examples on classical Mechanics with examples taken from standard introductory physics books. The third part is a detailed description of how to write Lagrangian, Eulerian and Particles in Cell codes for solving linear and non-linear continuum mechanics problems. Finally the last one address advanced techniques like tree-codes, Boundary Elements, and illustrates several applications to Geodynamics. The entire book is organized around numerous examples in Python, aiming at encouraging the reader to le
arn by experimenting and experiencing, not by theory.
