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Continental breakup represents the successful process of rifting and thinning of the continental lithosphere, leading to plate rupture and initiation of oceanic crust formation. Magmatism during breakup seems to follow a path of either excessive, transient magmatism (magma-rich margins) or of igneous starvation (magma-poor margins). The latter type is characterized by extreme continental lithospheric extension and mantle exhumation prior to igneous oceanic crust formation. Discovery of magma-poor margins has raised fundamental questions about the onset of ocean-floor type magmatism, and has guided interpretation of seismic data across many rifted margins, including the highly extended northern South China Sea margin. Here we report International Ocean Discovery Program drilling data from the northern South China Sea margin, testing the magma-poor margin model outside the North Atlantic. Contrary to expectations, results show initiation of Mid-Ocean Ridge basalt type magmatism during breakup, with a narrow and rapid transition into igneous oceanic crust. Coring and seismic data suggest that fast lithospheric extension without mantle exhumation generated a margin structure between the two endmembers. Asthenospheric upwelling yielding Mid-Ocean Ridge basalt-type magmatism from normal-temperature mantle during final breakup is interpreted to reflect rapid rifting within thin pre-rift lithosphere.

We present high-pressure experiments up to 8 GPa that constrain the solidus and liquidus of a composition, Fe0.69Ni0.23Cu0.01S1.00, typical of upper mantle sulfide. Solidus and liquidus brackets of this monosulfide are parameterized according to a relation similar to the Simon-Glatzel equation, yielding, respectively, T (°C)=1015.1 [P(GPa)/1.88+1]0.206 and T (°C)=1067.3 [P(GPa)/1.19+1]0.149 (1≤P≤8). The solidus fit is accurate within ±15°C over the pressure intervals 1-3.5 GPa and within ±30°C over the pressure intervals 3.5-8.0 GPa. The solidus of the material examined is cooler than the geotherm for convecting mantle, but hotter than typical continental geotherms, suggesting that sulfide is molten or partially molten through much of the convecting upper mantle, but potentially solid in the continental mantle. However, the material examined is one of the more refractory among the spectrum of natural mantle sulfide compositions. This, together with the solidus-lowering effects of O and C not constrained by the present experiments, indicates that the experimentally derived melting curves are upper bounds on sulfide melting in the Earth's upper mantle and that the regions where sulfide is molten are likely extensive in both the convecting upper mantle and, potentially, the deeper parts of the oceanic and continental lithosphere, including common source regions of many diamonds.

The Curie Point Depth (CPD) is a key thermal boundary in the deep lithosphere and is widely used to constrain its thermal structure. However, uncertainties in magnetization and the non‐uniqueness of inversion lead to considerable inter‐study differences. We present a prior‐constrained equivalent source inversion framework that derives a spatially heterogeneous, layered susceptibility model from vertically integrated susceptibility and, by jointly enforcing lithospheric magnetic field and thermal constraints, yields a new CPD model for the conterminous United States. The resulting CPD resolves features within tectonic provinces and belt‐like structures that were muted in existing products. Surface heat flow inferred from CPD agrees well with independent thermal model estimates (RMSE = 16.36 mW/m2). The results further demonstrate the importance of a priori constraints in inversion, and that inappropriate starting models can lead to systematic biases. The inversion framework is portable, enabling rapid construction of reliable deep‐thermal constraints on the lithosphere.

Crustal shortening and thickening to c. 70-85 km in the Tibetan Plateau occurred both before and mainly after the c. 50 Ma India-Asia collision. Potassic-ultrapotassic shoshonitic and adakitic lavas erupted across the Qiangtang (c. 50-29 Ma) and Lhasa blocks (c. 30-10 Ma) indicate a hot mantle, thick crust and eclogitic root during that period. The progressive northward underthrusting of cold, Indian mantle lithosphere since collision shut off the source in the Lhasa block at c. 10 Ma. Late Miocene-Pleistocene shoshonitic volcanic rocks in northern Tibet require hot mantle. We review the major tectonic processes proposed for Tibet including \"rigid-block', continuum and crustal flow as well as the geological history of the major strike-slip faults. We examine controversies concerning the cumulative geological offsets and the discrepancies between geological, Quaternary and geodetic slip rates. Low present-day slip rates measured from global positioning system and InSAR along the Karakoram and Altyn Tagh Faults in addition to slow long-term geological rates can only account for limited eastward extrusion of Tibet since Mid-Miocene time. We conclude that despite being prominent geomorphological features sometimes with wide mylonite zones, the faults cut earlier formed metamorphic and igneous rocks and show limited offsets. Concentrated strain at the surface is dissipated deeper into wide ductile shear zones.

This study reports halogen contents (F and Cl) of amphibole and phlogopite derived from mantle xenoliths and one peridotite massif, for amphibole and phlogopite megacrysts and ultramafic magmatic cumulates (hornblendites) found in alkaline volcanic rocks from 12 localities in Europe and Africa. Amphibole and phlogopite contain more F than Cl with F/Cl ratios reaching about 160 in phlogopites and 50 in amphiboles. Phlogopites are higher in F (median of 3400 μg/g) than amphibole (median of 1000 μg/g), while median Cl contents are higher in amphibole (290 μg/g) compared to phlogopite (180 μg/g). The Cl contents and the F/Cl ratios in amphibole and phlogopite from mantle xenoliths exhibit large differences between samples of the same region, recording very large variations of halogen contents in the continental lithosphere. We suggest that the halogen content in such samples largely depends on the initial composition of percolating melts and fluids in the continental lithosphere. During reaction of these agents with peridotitic wall-rocks, Cl is preferentially retained in the fluid as it is much more incompatible compared to water and F. This desiccation effect continuously increases salinity (Cl content) and decreases the F/Cl ratio in the agent with time, causing variable Cl contents and F/Cl ratios in amphibole and phlogopite at a specific locality. Subsequent partial melting processes may then sequester and re-distribute, especially Cl among amphibole, phlogopite and melts/fluids as a result of its strong incompatibility, whereas F is much less affected as it behaves slightly compatible. The impact of even small amounts of amphibole and mica on the total halogen budget in the continental lithosphere is significant and both minerals can effectively contribute to the high halogen contents typical of alkaline melts.

Following the release of global continental effective elastic thickness (Te) maps obtained using different approaches, we now have the opportunity to provide better constraints on Te. We improve previous estimates of Te derived from thermo‐rheological models of lithospheric strength (or Ter) using new equations that consider variations of the Young's Modulus in the lithosphere. These new values are quantitatively compared with those obtained from an inverse approach (or Tei) based on a comparison of the spectral coherence between topography and gravity anomalies with the flexural response of an equivalent elastic plate to loading. The two models show in general a good agreement, having equal means (at the 95% significance level) in about half of the continental areas. In other regions Tei exceeds Ter in about 65% of the data points, showing that Tei provides an upper bound on Te. The two data sets have a similar range, but demonstrate different distributions. Ter has a bimodal distribution, with the two peaks representative of the cratons and of the areas outside of them. In contrast, Tei has more uniform distribution without predominant peaks. Our models show higher similarities in the Meso‐Cenozoic orogens than in the Archaean and Proterozoic shields and platforms, due to the methods employed. For the regions with the most robust determinations of Ter and Tei, the relationship between them is close to linear. The results of this work can be used for further studies on the mechanical properties of the lithosphere. Key Points Comparison of the Te of the lithosphere based on two different methods The two models have equal means in about half of the continental areas The two models show higher similarities in the orogens than in the cratons

The sub-continental lithosphere mantle (SCLM) represents a mechanical barrier that separate the converting mantle from the exosphere, and possesses the ability to sequester and release volatiles, making it an integral part in deep volatile cycling. Here we explore the SCLM in modulating F and Cl cycling through a case study from the Early Cretaceous Dabeigou basalts in the North China Craton (NCC). These lavas are associated with decratonization of the NCC, a process involving significant removal and replacement of the ancient SCLM. The Dabeigou basalts, characterized by arc magma-like trace element signatures, evolved initial 87 Sr/ 86 Sr (0.70574–0.70578), ε Nd ( t ) (−11.2–−11.1), and ε Hf ( t ) (−13.7–−13.4) values, along with high Fe/Mn ratios, Ni contents, and δ 18 O values (5.8‰–6.8ε) of olivine phenocrysts, are compatible with their origination from a veined, pyroxene-rich source formed through the infiltration and interaction of hydrous silicate melts from the subducting Pacific slabs with ambient SCLM. Olivine-hosted melt inclusions of the Dabeigou basalts have compositions similar to the whole rocks, indicating that they record pre-eruptive melt compositions forming the whole rocks. The melt inclusions exhibit high F (1371–2316 ppm) and moderate Cl (688–900 ppm) contents, with high F/Cl ratios of 2.1±0.3 (1 σ ). The F and Cl signatures of the Dabeigou basalts are different from those of typical arc magmas, which are commonly characterized by high Cl contents (median of ∼1200 ppm) and low F/Cl ratios (<1). The observed differences can be attributed to chromatographic reaction that fractionates elements of different compatibility in the metasomatic agents, with amphibole as the main mineral phase for fractionating and preserving F and Cl. That is, amphibole crystallization prefers to retain F rather than Cl, making the metasomes in vein enriched in F and exhibiting elevated F/Cl ratios compared to original metasomatic agents. It is further suggested that the scenario inferred from the Dabeigou basalts might be common for crystallization of hydrous minerals during chromatographic metasomatism, which causes significant heterogeneity with respect to F and Cl in the SCLM, and might have played a crucial role in regulating F and Cl cycling within the SCLM environments.

Delineating mantle interfaces can provide important clues for understanding the formation of continents. We use S‐wave receiver functions to investigate lithospheric structure along a transect extending from Vancouver Island to Baffin Island. Observed Sp converted waves allow for interpretation of boundaries in the depth range expected for tectonic plates. Receiver functions show a distinct negative amplitude feature, interpreted as the lithosphere‐asthenosphere boundary, at shallow depths beneath British Columbia (∼85km), deepening abruptly at the eastern edge of the Cordillera to ∼260km beneath the Canadian Shield. Dipping mid‐lithospheric discontinuities extend beneath several giant ca. 1.8 Ga epicontinental magmatic arcs, consistent with formation of cratonic lithosphere by arc accretion. This model provides a plausible explanation for global mid‐lithospheric discontinuities within cratons and aids in understanding their formation.