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Oceanic crustal accretion at mid-ocean ridges is a function of spreading rate, mantle temperature, and composition, which are intertwined in affecting melt production and oceanic crustal thickness. Sparse and irregular seismic and geochemical observations on a global scale showed no correlation between crustal thickness and spreading rate along slow to fast-spreading centers. Here, we compile a global oceanic crustal thickness model from gravity data to revisit this issue at a high resolution. Gravity-observed melt volume shows a positive correlation with spreading rate globally, implying that spreading rate is the dominant factor in melt production. However, oceanic crustal thickness is negatively correlated with spreading rate from slow to fast-spreading centers, and this trend is further consolidated by the increase in Curie point depth (a geothermal proxy) and ridge depth with increasing spreading rate. Thus, a decreasing near-ridge temperature probably contributes to crustal thinning from slow to fast-spreading centers. Inferred low melt volume anomalies beneath fast-spreading centers are consistent with a 20 °C temperature drop in the near-ridge mantle, likely caused by efficient hydrothermal cooling.

The Philippine archipelago comprises accreted terranes, including ophiolites, island arcs, and continental fragments. It absorbs the approximately 9 cm/year convergence between the Sundaland Plate to the west and the Philippine Sea Plate to the east. Understanding the crustal thickness variations across the Philippines is crucial for distinguishing collision boundaries and comprehending the complexities of tectonic evolution. In this study, we conducted ambient noise autocorrelation combined with receiver function analysis to estimate crustal thickness in the northern Philippines. To resolve ambiguities in the PmP phase in autocorrelation signals, Moho depth information from receiver function was utilized. We successfully identified coherent signals of PmP autocorrelation from 20 vertical seismograms, with two-way travel time ranging from 6.64 s to 13.79 s. These times correspond to crustal thicknesses of 19.8 to 46.0 km, respectively, as derived from the average CRUST1.0 P-wave velocity model. Our main findings and interpretations indicate that the crust beneath Luzon is slightly thicker in the western regions compared to the eastern parts. This suggests a limited influence of magmatic processes in the latter. Furthermore, our observations identified a tear in the slab at 17°N and 14°N latitude, characterized by thinner crust. We observed that the crust beneath Mindoro thickens in proximity to the collision of the microcontinental fragments with Mindoro-Panay island, whereas it thins toward the extension of the Pleistocene Macolod Corridor rifting.

The Bouguer gravity anomaly derived from observed gravity data and calculated from a 3-D P-wave velocity model were used to investigate the compatibility between the two to understand the crust structure of the Taiwan region. The seismic velocity model determined by Kuo-Chen et al. (2012) was used for our study. We converted the velocity model to a density model using the relationship between Pwave velocity and rock density proposed by Brocher (2005), and then calculated the corresponding gravity anomaly. The differences between observed gravity anomaly and calculated gravity anomaly in vicinity of the dense TAIGER seismic stations are in general small. To discuss the anomaly discrepancy between shallow and deep structure, we used the upward and downward continuation method to separate the gravitational signal into shallow and deep effects for the comparison of gravitational effect of the 3-D velocity model. A conspicuous gravity low which is lower than the observed Bouguer gravity anomaly occurred beneath the main edge of the Central Range, as shown in the calculated deep-structure gravitational map. This indicates that the Moho depth estimated by the seismic tomography is deeper than that estimated by the gravity data. The negative anomaly location differences resulted from deep-structure effects suggest that the locations of crustal thickening estimated by gravity and seismic tomography are different.

Crustal accretion at mid-ocean ridges governs the creation and evolution of the oceanic lithosphere. Generally accepted models 1 – 4 of passive mantle upwelling and melting predict notably decreased crustal thickness at a spreading rate of less than 20 mm year −1 . We conducted the first, to our knowledge, high-resolution ocean-bottom seismometer (OBS) experiment at the Gakkel Ridge in the Arctic Ocean and imaged the crustal structure of the slowest-spreading ridge on the Earth. Unexpectedly, we find that crustal thickness ranges between 3.3 km and 8.9 km along the ridge axis and it increased from about 4.5 km to about 7.5 km over the past 5 Myr in an across-axis profile. The highly variable crustal thickness and relatively large average value does not align with the prediction of passive mantle upwelling models. Instead, it can be explained by a model of buoyant active mantle flow driven by thermal and compositional density changes owing to melt extraction. The influence of active versus passive upwelling is predicted to increase with decreasing spreading rate. The process of active mantle upwelling is anticipated to be primarily influenced by mantle temperature and composition. This implies that the observed variability in crustal accretion, which includes notably varied crustal thickness, is probably an inherent characteristic of ultraslow-spreading ridges. Results from a high-resolution ocean-bottom seismometer experiment at the ultraslow-spreading Gakkel Ridge show unexpected highly variable crustal thickness and a relatively large average value, which can be explained by an active mantle upwelling model.

Rifting and magmatism are fundamental geological processes in the evolution of the lithosphere; however, quantitative investigations of their relationship are rare. The Okavango Rift Zone (ORZ) is in the early stages of rifting and magmatic activity and thus is an ideal locale to study this relationship. We examine the relationship using two primary crustal structure parameters: crustal thickness and average Vp/Vs ratio obtained from receiver functions. Our large Vp/Vs estimates indicate the existence of melts within the crust of the ORZ. Comparing our results with those of other continental rifts, we identify a quantitative relationship between rifting and crustal melt fraction. Additionally, the comparative analysis suggests that melts within a rift crust are introduced only when the stretching magnitude reaches that of the ORZ. We also propose a model suggesting that with the progression of rifting, melts would be introduced into the crust and increased gradually, potentially triggering rift‐related volcanism.

During the Late Triassic, tropical Pangea drifted northward into subtropical latitudes and became progressively drier. In contrast, South China, despite experiencing a similar latitudinal shift, transitioned from an arid to humid climate. Based on the sedimentary record of the Zigui Basin, this study constrains the arid to humid climatic shift to the period of ca. 228−207 Ma in northern South China. Detrital zircons of Triassic ages were derived from the Qinling Orogen. They show an increase in Eu/Eu* ratios and a marked decrease in εHf(t) values. These geochemical trends suggest an increase in crustal thickness from ca. 40−50 km to >60 km in the Late Triassic in the Qinling Orogen and reveal a strong mountain building event with surface elevations of up to 5,000 m. Using these geological records, climate modeling indicates a significant orographic effect on regional precipitation during the Late Triassic in the Eastern Tethys.

The East Kunlun Shan (EKLS) in northern Tibet occupies boundaries of the low‐relief topography and lower crustal low‐velocity zone in the interior plateau, making it ideal for exploring the relationship of surface deformation with underlying geodynamic processes. We used previous and new apatite (U‐Th)/He data to analyze the exhumation history and pattern throughout the EKLS and link surface deformation to deep structures. Integrated (U‐Th)/He ages reveal the rapid exhumation at 27–25 Ma, due to the coeval orogen‐scale tilting of the EKLS. Along with the crustal structures beneath the EKLS, it is inferred that orogen‐scale tilting is the isostatic response of the nonuniform crustal thickening related to northward injection of the Tibetan lower crust. This study highlights the role of ductile deformation within the lower crust in mountain building in northern Tibet, which shares a similarity with mountain building pattern in the eastern plateau margin. Plain Language Summary How deep geodynamic process affects shallow crustal deformation in Tibet is one of the key issues in understanding continental dynamics. The East Kunlun Shan (EKLS) defines northern boundaries of low‐relief topography and crustal low‐velocity zone in the interior plateau. In this study, we explore the relationship between surface deformation and underlying geodynamic processes in the EKLS by analyzing the shallow crustal exhumation pattern in conjunction with deep structures. Amounts of apatite (U‐Th)/He ages across the EKLS reveal the late Oligocene orogen‐scale tilting, indicating the involvement of indistinctive shallow crustal shortening in the mountain building process. Such a regional tilting may be the reflection of nonuniform crustal thickening related to the injection of the Tibetan lower crust when considering the crustal structures beneath the EKLS. By comparing the mountain building patterns in the northern and eastern margins of Tibet, we conclude that ductile deformation in the lower crust may be a common phenomenon to mountain building in plateau margins. Key Points Apatite (U‐Th)/He data reveal the accelerated exhumation at 27‐25 Ma and southward increasing exhumation across the East Kunlun Shan (EKLS) The EKLS has experienced the orogen‐scale tilting during the late Oligocene Orogen‐scale tilting of the EKLS may be the isostatic response of northward injection of the Tibetan weak lower crust

Constraining the spatial variability of the thickness of the ice shell of Enceladus (i.e., the crust) is central to our understanding of the internal dynamics and evolution of this small Saturnian moon. In this study, we develop a new methodology to infer regional variations in crustal thickness using measurements of tidally‐driven elastic strain that could be made in the future. As proof of concept, we recover thickness variations from synthetic finite‐element crustal models subjected to diurnal eccentricity tides. We demonstrate recovery of crustal thickness to within ∼2 km of true values across the crust with ∼10% error in derived spherical harmonic coefficients at degrees l ≤ 12. Our computed uncertainty is significantly smaller than the inherent ∼10 km ambiguity associated with crustal thickness derived solely from gravity and topography measurements. Therefore, future measurements of elastic strain can provide a robust approach to probe crustal structure at Enceladus. Plain Language Summary Inferences of the thickness of Enceladus's ice shell—or crust—can provide valuable insights for understanding the processes which control the long‐term evolution and heating of this moon of Saturn. We develop a new method to infer regional variations in crustal thickness at Enceladus using proposed measurements of deformation caused by tidal interactions with Saturn. Using models of Enceladus's ice shell, we demonstrate recovery of crustal thickness with a deviation of ∼2 km (i.e., ∼10%) relative to input values. Our approach to inferring crustal thickness complements traditional methods that rely solely on analyzing gravity and surface topography to constrain the crustal structure of the satellite. Key Points Determinations of variations in ice shell (i.e., crustal) thickness are crucial for understanding the dynamics and evolution of Enceladus We develop a new method to infer spatially‐varying crustal thickness using proposed measurements of tidally‐driven elastic strain Using our method, we demonstrate recovery of crustal thickness to within ∼2 km of true values with ∼10% accuracy over length scales >60 km

It is widely recognized that collisional mountain belt topography is generated by crustal thickening and lowered by river bedrock erosion, linking climate and tectonics 1 – 4 . However, whether surface processes or lithospheric strength control mountain belt height, shape and longevity remains uncertain. Additionally, how to reconcile high erosion rates in some active orogens with long-term survival of mountain belts for hundreds of millions of years remains enigmatic. Here we investigate mountain belt growth and decay using a new coupled surface process 5 , 6 and mantle-scale tectonic model 7 . End-member models and the new non-dimensional Beaumont number, Bm, quantify how surface processes and tectonics control the topographic evolution of mountain belts, and enable the definition of three end-member types of growing orogens: type 1, non-steady state, strength controlled (Bm > 0.5); type 2, flux steady state 8 , strength controlled (Bm ≈ 0.4−0.5); and type 3, flux steady state, erosion controlled (Bm < 0.4). Our results indicate that tectonics dominate in Himalaya–Tibet and the Central Andes (both type 1), efficient surface processes balance high convergence rates in Taiwan (probably type 2) and surface processes dominate in the Southern Alps of New Zealand (type 3). Orogenic decay is determined by erosional efficiency and can be subdivided into two phases with variable isostatic rebound characteristics and associated timescales. The results presented here provide a unified framework explaining how surface processes and lithospheric strength control the height, shape, and longevity of mountain belts. Using the new Beaumont number presented, it is concluded that the topographic evolution of collisional mountain belts is determined by the combination of plate velocity, crustal rheology and surface process efficiency.

Recent estimates of the crustal thickness of Mars show a bimodal result of either ∼20 or ∼40 km beneath the InSight lander. We propose an approach based on random matrix theory applied to receiver functions (RFs) to further constrain the subsurface structure. Assuming a spiked covariance model for our data, we first use the phase transition properties of the singular value spectrum of random matrices to detect coherent arrivals in the waveforms. Examples from terrestrial data show how the method works in different scenarios. We identify three previously undetected converted arrivals in the InSight data, including the first multiple from a deeper third interface. We then use this information to jointly invert RFs with the absolute S‐wave velocity information in the polarization of body waves. Results show a crustal thickness of 43 ± 5 km beneath the lander with two mid‐crustal interfaces at depths of 8 ± 1 and 21 ± 3 km. Plain Language Summary Recent analysis of seismic data from InSight shows that the crustal thickness beneath the InSight lander can be either 20  or 40 km. To resolve this ambiguity, we apply results from random matrix theory to receiver function (RF) analysis. The distribution of singular values of a random matrix shows well‐behaved deterministic properties that can be used to separate them from those of an underlying coherent signal if present. We use examples from terrestrial data to show how the method works. When applied to RFs computed from InSight seismic data, we identify three new energy arrivals, including one that supports the existence of a deeper third layer. Using this information, we simultaneously inverted the RF data along with the measured incidence angle of body waves. Results show a crustal thickness of 43 ± 5 km beneath the lander with two mid‐crustal interfaces at depths of 8 ± 1 and 21 ± 3 km. Key Points We apply recent results from random matrix theory to identify crustal phases in noisy receiver functions for Mars from InSight data Once identified, we jointly invert these phases with frequency‐dependent apparent S‐wave velocity curves Results show a crustal thickness of 43 km with two inter‐crustal discontinuities at 8 and 21 km beneath the lander