Journal of Geophysical Research: Solid Earth最新文献

The Late Cretaceous Oman ophiolite includes a series of volcanic rocks generated during the transition from spreading ridge to protoarc associated with subduction initiation. We analyzed major and trace elements and Sr, Nd, and Pb isotope compositions of lavas and dikes of the protoarc stage, especially boninites. We also analyzed amphibolites and metacherts of the metamorphic sole, as subducted slab materials. Furthermore, we examined trace element patterns reconstructed based on analyses of whole rocks and relict clinopyroxene phenocrysts from volcanic rocks of both axial and protoarc stages. The compositions of protoarc tholeiites, which represent the first and most voluminous magmas generated in the protoarc stage, are consistent with flux melting of residual depleted mantle, metasomatized by aqueous fluids liberated from the amphibolite-facies slab. On the other hand, the successively produced calc-alkaline, low-Si boninites show distinctly radiogenic Sr, Nd, and Pb isotope ratios, spoon-shaped rare earth patterns, and low Nb/Ta ratios, which require addition of amphibolite slab fluids formed at higher temperatures as well as small amounts of mafic-sedimentary hybrid slab melt to the residual highly depleted mantle. Although axial lavas lack enrichment in fluid-mobile elements except for K, later off-ridge lavas exhibit clear K, Sr, and Pb enrichments, suggesting decompression melting of fluid-metasomatized mantle associated with subduction initiation near the dying spreading ridge. The resultant hot subduction zone is favorable for mantle wedge melting to generate tholeiitic and boninitic magmas in the protoarc stage.

We present a suite of 13 uniaxial deformation experiments on fine grained polycrystalline α-quartz conducted in a D-DIA apparatus monitored with in situ synchrotron x-rays. Experimental temperatures range from 25°C to 1199°C with pressures between 1.4 and 3.2 GPa, and strain rates between 3.4 × 10⁻⁶ s⁻¹ and 1.8 × 10⁻⁵ s⁻¹. Powder diffraction data from the ($��10�\bar{1}�1�$), ($��11�\bar{2}�0�$), ($��20�\bar{2}�1�$), ($��10�\bar{1}�2�$) and ($��11�\bar{2}�2�$) lattice planes were forward modeled using elastic plastic self-consistent (EPSC) simulations to derive differential stresses. We consistently observe temperature dependent inelastic behavior at low strain which we simulate using an isotropic deformation system in the EPSC model. Our mechanical data is broadly consistent with mechanical data from previous deformation studies conducted in the Griggs solid-medium deformation apparatus and can be described by a combination of a Guyot and Dorn rate equation for plasticity limited by lattice resistance below 800°C and with a dislocation creep flow low above 800°C.

Deep mantle downwellings are typically located away from the two Large Low-Velocity Provinces (LLVPs) in Earth's mantle. Geodynamic models based on global seismic tomography generally predict that convective flow at the core-mantle boundary spreads laterally away from downwelling regions and toward LLVPs. While this offers a framework for understanding large-scale deformation in the lowermost mantle, it has yet to be confirmed by seismic constraints. This study investigates seismic anisotropy and wave reflections in the deepest mantle beneath Alaska, linking a known reflector to the inferred deformation. To capture large-scale deformation, the analysis utilizes waves with long raypaths through the deepest mantle. Mantle shear direction is then determined using global wavefield simulations that incorporate mineral physics constraints. The inferred North-South shear direction agrees with findings for an adjacent region beneath the northeastern Pacific Ocean, together forming a continuous $��\sim �3000��\text{km}�\times �3000��\text{km}�$ region where the inferred southward shear aligns with geodynamic model predictions. These results support a first-order framework of lowermost mantle deformation driven by flow away from downwellings and toward LLVPs.

Eastern China has undergone significant intracontinental extension and intraplate magmatism since the Cenozoic, but related geodynamic mechanisms remain controversial. Here we use calculations of Residual Topography (RT) and Dynamic Topography (DT) as diagnostic indicators of active mantle flow in the region. The latest crustal structure is adopted to calculate new RT estimates, and 3D spherical mantle convection experiments based on a high-resolution seismic velocity model are constructed to estimate the DT across Eastern China. Comparative analyses reveal several insights: (a) RT and DT are correlated at medium wavelength, showing a low-west and high-east pattern. High positive values dominate Northeastern China, Cathaysia Block, and the South China Sea (SCS), whereas low negative values concentrate in the Ordos, Sichuan, and Songliao basins; (b) Positive DT in Northeastern China correlates with Quaternary intraplate volcanism, linked to mantle upwelling induced by the Pacific Plate subduction. Conversely, negative DT in Songliao Basin and Eastern North China Block (ENCB) reflects mantle downwelling associated with lithospheric delamination; (c) The stable Ordos and Sichuan basins display pronounced negative RT and DT, indicative of dense cratonic roots, while the elevated topography in the ENCB and Cathaysia Block is driven by mantle upwelling from the Pacific-Philippine plate subduction; (d) High positive RT and DT in the SCS correspond to widespread recent magmatism, primarily fueled by large-scale mantle upwelling beneath the SCS. The findings suggest that mantle convection caused by surrounding subduction systems plays a significant role in Cenozoic intraplate volcanism and lithospheric evolution in Eastern China.

The eastern margin of Eurasia records complex tectonic events from its interaction with the Paleo-Asian, Mongol-Okhotsk, and Paleo-Pacific Ocean plates during the late Paleozoic to early Mesozoic. However, the subduction histories remain controversial. We employed detrital zircon U-Pb geochronology and trace element analyses to investigate the provenance of strata of this age within the Jiamusi Massif of NE China. To mitigate age bias from variations in zircon fertility, we compiled zirconium concentrations from 338 granitoid samples across the massif, grouped into four categories: Neoproterozoic (996–722 Ma), early Paleozoic (538–446 Ma), late Paleozoic-early Mesozoic (338–209 Ma), and Cretaceous (112–92 Ma). Applying the zircon fertility factors (ZFFs) revealed no difference between the early Paleozoic and late Paleozoic-early Mesozoic suites, which we combined, resulting in values of 1.58, 1.45, and 1.0, respectively. After correcting detrital zircon age spectra using these ZFFs, a sediment provenance shift was evident from active magmatic arcs along the eastern margin of the Jiamusi Massif during the early Permian, to collisional orogenesis between the Jiamusi and Songliao massifs in the Late Triassic along the western margin. Integration with regional tectonic data defines a transition in geodynamics from subduction of the Mongol-Okhotsk Ocean in the early Permian to combined subduction and collision related to the Paleo-Pacific domain in the Late Triassic. This study improves the accuracy of interpreting provenance evolution through multi-dimensional provenance analysis using ZFF correction procedures and offers a reproducible methodology for refining tectonic reconstructions of accretionary orogens and other tectonically complex regions worldwide.