Myanmar is located on the eastern margin of the India-Eurasia collision zone, where the Indian sub-continent is subducting beneath the Burma microplate. Magmatic processes during subduction and collision in orogenic belts are significant and well-studied for oceanic subduction; however, the magmatism associated with continental subduction remains poorly understood. Seismic attenuation is highly sensitive to changes in lithospheric thermodynamics and fluid content. Understanding arc volcanism is vital for comprehending a key manifestation of subduction-related processes. However, there is still no high-resolution 3D attenuation model for this region. Here, we use the coda-normalized method to image the lithospheric-scale 3D attenuation structure in the Indo-Burma subduction zone. Our results reveal high attenuation in major sedimentary basins. The prominent high-attenuation anomalies in the mid-to-lower crust of the Indo-Burma Ranges (IBR) may represent thick, fluid-rich sediments scraped off from the subducting Indian Plate and accumulated beneath the IBR. Low-attenuation anomalies at depths of 30-50 km beneath the Monywa volcano are a clear signature of a cooled mantle wedge, which currently overlies strong attenuation anomalies deeper than 50 km, likely associated with the upwelling of hot asthenospheric material. Compared to oceanic subduction systems, the insufficient water content of the continental subduction plate, coupled with the compressional regime induced by oblique subduction, leads to weak attenuation within the mantle wedge.
Nesting behavior represents a pivotal adaptive strategy in insects, providing protective environments for offspring and optimizing resource allocation1. Among aculeate (stinging) Hymenoptera, the vespid subfamily Eumeninae (potter wasps) exemplifies sophisticated solitary nesting strategies, employing unique mud nest structures and specialized brood care behaviors2. However, the evolutionary origins of these complex behaviors have remained poorly understood due to the scarcity of relevant fossil evidence. Here, we report the discovery of fossilized potter wasp nests preserved in mid-Cretaceous Kachin amber (∼99 Ma), providing the first direct evidence of eumenine nesting behavior in the fossil record. These nests exhibit striking morphological similarities to those of the extant species of the tribe Eumenini, including bottle-shaped architecture, mud-based construction, and preserved eggs, demonstrating that nesting behaviors had already evolved by the Cenomanian.
Abstract The Cenozoic convergence between the Indian and Asian plates has driven large‐scale mantle convection that interacts with both plates. Understanding this convergence benefits from clear imaging of the lithosphere‐asthenosphere boundary (LAB). Beneath the northeastern Indian plate margin, our Sp receiver functions (RFs) computed from dense array data reveal a regionally shallow LAB at an average depth of ∼70 km, except beneath the Indo‐Burma Ranges, where the Indian LAB dips eastward at an average of ∼20° down to ∼140 km; this dipping geometry is resolved primarily through SKS‐derived RFs. Farther east, a positive velocity gradient emerges ∼50–80 km beneath the Burma LAB, indicating an upper‐asthenospheric low‐velocity layer. Waveform modeling further indicates a sharp LAB, characterized by a Vs drop of up to ∼6%–10% over <∼20 km. These observations support melt presence below the LAB, potentially linked to the asthenospheric flow induced by the Indian plate subduction and subsequent rollback and/or tearing.
Abstract Slab tearing has been increasingly recognized as a key geodynamic process influencing the evolution of the eastern Himalayan syntaxis. However, whether, where and how the subducted Indian slab beneath the Indo‐Myanmar subduction zone has been torn remains poorly constrained. Applying seismic tomography to new wide‐aperture data in and around Myanmar, we image the detailed architecture of the Indian slab. Our results especially show two high‐velocity anomalies with opposing dips in the upper mantle: an east‐dipping anomaly representing the subducting Indian slab and a west‐dipping body preferentially interpreted as a detached slab fragment. The intersection angle between the two anomalies decreases southward, and their along‐dip lengths vary inversely, indicating southward‐shallowing slab tearing likely induced by the oblique subduction setting. Tearing‐induced mantle upwelling may be impeded by the subducting Indian slab at shallow depths and the limited gap between slab segments, likely explaining the sporadic volcanism in Myanmar since the Mid‐Miocene.
Eastern Myanmar is the key position linking between SW Yunnan and northern Thailand for better understanding of Tethyan evolution. However, the actual location and evolution of the Tethyan suture zone are still unclear in eastern Myanmar. The present study focuses on the geochronological, geochemical and zircon Lu-Hf isotopic study on the plutonic rocks, including granite, diorite and gabbroic rocks, from the Tachileik area, eastern Myanmar. These plutonic rocks yielded zircon U-Pb weighted mean ages of ca. 353–355 Ma, suggesting the Early Carboniferous emplacement. The Tachileik granites are high-K calc-alkaline, weakly peraluminous and have low P2O5 contents, which are typical features of I-type granites. They have positive zircon εHf(t) values (+4.5 − +7.4) with TDM2 ages of 981–825 Ma, indicating a juvenile mafic lower crust source. The Tachileik gabbros and diorites show high Al2O3 contents and Mg#, but low TiO2 and K2O contents, belonging to tholeiitic and calc-alkaline basalt series. They are characterized by enrichments in large ion lithophile elements (LILEs, e.g., Rb, Ba and Sr), depletions in high field strength elements (HFSEs) and distinctly negative Nb and Ta anomalies, similar to the volcanic arc basalt. The zircon Hf isotopic (+4.7− +7.1) and whole-rock geochemical data imply that the Tachileik gabros and diorites probably resulted from partial melting of lithospheric mantle in the spinel stability field within an arc-related setting. The magmatic rocks can be grouped to the Late Devonian–Early Carboniferous magmatic rock and pyroclastic rock zone from SW Yunnan to northern Thailand based on their age and geochemical characters. The zone was formed in the post-collisional extension-related tectonic setting of the Proto-Tethys. This study provides important evidences for the evolution of the Proto-Tethys in Southwest Yunnan and Southeast Asia.
