Abstract Miyahisaite, ideally Sr2Ba3(PO4)3F, a member of the apatite supergroup, was identified in pegmatite-like veins hosted by melilite–nephelinite volcanic rocks at the Graulai quarry, Hillesheim, West Eifel, Germany. This represents the second occurrence of this rare mineral, previously known only from the hydrothermally altered chert at the Shimoharai mine, Japan. At Graulai, miyahisaite occurs as colorless anhedral crystals, up to 300–400 μm in size, within a complex late-stage mineral assemblage that includes leucite, nepheline, diopside, fluorapatite, götzenite, delhayelite, lamprophyllite-group minerals, magnetite, fresnoite, oxyphlogopite, and perovskite. Electron-microprobe analyzes yielded the empirical formula (Sr0.97Ca0.87Ba0.12Na0.04)Σ2.00(Ba3.00)(P2.87S0.06V0.04Al0.04)Σ3.01(F1.00Cl0.03)Σ1.03 confirming a Sr- and Ba-dominant fluorophosphate member of the hedyphane group. Previously unavailable, single-crystal X-ray diffraction data show that miyahisaite has an apatite-type structure and crystallizes in the hexagonal P63/m, with unit-cell parameters a = 9.8876(5) Å, c = 7.4142(3) Å, and V = 627.74(5) Å3. Structure refinement indicates Sr dominance at the M1 site and Ba at M2 site. The X anion site, occupied by F, shows positional disorder along the channel, reflecting structural adjustment to large divalent cations, a feature typical of apatite-supergroup members. Raman spectroscopic data, obtained for the first time, revealed that the spectrum is dominated by PO43− vibrations, with the most intense band at 948 cm−1 assigned to the ν1 symmetric stretching mode. The absence of OH-related bands confirms F dominance at X site. Genetically, the Graulai occurrence of miyahisaite differs fundamentally from the sediment-hosted hydrothermal origin reported from Japan. Unlike the previously described setting, miyahisaite in the Eifel volcanic system crystallized during a late-magmatic, pneumatolytic stage from volatile-rich fluids enriched in incompatible elements. This discovery expands the known genetic environments of miyahisaite and refines its characterization within the apatite supergroup.
Abstract New and published geochronologic, geochemical, and isotopic data indicate that the Sabine terrane of the northern US Gulf Coast originated as a Proterozoic peri-Gondwanan continental crustal fragment, exotic to Laurentia. A continental margin arc developed on Sabine during the Early Mississippian-Middle Pennsylvanian northwestward convergence between Gondwana and Laurentia. Reappraisal of U-Pb zircon geochronology from Carboniferous Stanley Group (Gp) tuffs, along with new trace element data, links the tuffs to the Pennsylvanian Sabine arc and not the Yucatán/Maya (Chicxulub) Mississippian arc. U-Pb zircon data indicate that crystallization ages of porphyritic granite intrusives, previously reported as Middle Pennsylvanian or older porphyritic rhyolite flows, post-date the Stanley tuffs. Bimodal zircon populations in these and nearby granites yielded Middle Carnian and Early Permian age peaks. Triassic ages reflect hydrothermal alteration of older zircons, plus the addition of new zircons during Mesozoic rifting; Permian ages reflect anatexis within Sabine terrane crust. Sabine Nd isotopic data are unlike data from proximal Laurentian and southern Appalachian sources. However, Nd isotopic data from the Wiggins arch are similar to data from the Uchee/Milledgeville/Savannah River terranes; these combined terranes are interpreted as a Neoproterozoic–Cambrian forearc/arc/back-arc complex, genetically related to the Suwannee–Charleston superterrane. Pennsylvanian siliciclastic sediments and Upper Pennsylvanian tuff from the Pottsville Formation, Black Warrior foreland basin, record northwestward translation of the Sabine arc terrane and Yucatán/Maya block along the southern Laurentian continental margin. The nearby Texarkana retro-arc basin was formed by regional slab rollback and subduction of Laurentian crust by the Sabine terrane and infilled by Pennsylvanian–Permian Morehouse Fm carbonates and siliciclastics derived from the Sabine arc terrane.
Understanding the evolution of diagenetic systems is crucial for elucidating the formation mechanisms of high-quality carbonate reservoirs. This study focuses on hydrothermal dolomite reservoirs developed in the platform margin zone of the Qixia Formation in the southwestern Sichuan Basin. Based on core observations, thin sections, porosity, and permeability data, carbon-oxygen isotopes, trace element geochemistry, fluid inclusions, and geophysical data, the genesis and evolution of these reservoirs were systematically analyzed. The diagenetic evolution of the reservoir can be described within the framework of penecontemporaneous (near-surface), shallow-burial, and intermediate- to deep-burial diagenetic settings. During the near-surface stage, the system was predominantly open, and the Qixia Formation experienced early dissolution, which significantly enhanced reservoir quality. During the shallow-burial stage, hydrothermal dolomitization driven by thermal convection associated with the Emeishan Large Igneous Province contributed to the preservation of primary porosity. By the Middle-Late Permian transition, intensified volcanic activity reactivated deep faults, facilitating the influx of hydrothermal fluids into the Qixia Formation. With increasing burial depth, the system evolved toward intermediate- to deep-burial conditions, becoming progressively more closed. This led to the precipitation of abundant saddle dolomite, which occluded pore space and reduced reservoir quality. These results indicate that open-system conditions in near-surface settings are more favorable for pore development, whereas reservoir formation and preservation depend on the dynamic coupling between geological processes and the evolution of diagenetic systems.
The Bangong-Nujiang Meso-Tethyan Suture in eastern Tibet is still difficult to trace, mainly because Cenozoic shortening has juxtaposed narrow terranes, basins, and suture-related m & eacute;langes. We present field observations, zircon U-Pb ages, Lu-Hf isotopes, and whole-rock geochemistry for three granitic samples from the Lhasa-Tengchong and South Qiangtang-Baoshan blocks east of the eastern syntaxis. The work addresses three related questions: whether the Bangong-Nujiang and Bitu/Longmu Co-Shuanghu sutures merge in this region, whether the Cretaceous granites record the eastern continuation of Bangong-Nujiang subduction, and whether a ca. 455 Ma granite block can be linked to the South Qiangtang-Baoshan basement. Samples WX-14 and WX-17 yield zircon U-Pb ages of 94 +/- 0.7 and 109 +/- 2.0 Ma, respectively, and are interpreted as high-K calc-alkaline I-type to mixed-source granitoids formed in an arc-related, post-collisional setting. Sample WX-15 yields a crystallization age of 455 +/- 5 Ma and negative zircon epsilon Hf(t) values, consistent with derivation from ancient crust comparable to Early Paleozoic basement magmatism along the northern Gondwanan margin. Because WX-15 occurs as a fault-bounded block within Carboniferous m & eacute;lange, for this reason, it is taken as evidence for South Qiangtang-Baoshan affinity only when considered together with regional stratigraphic continuity, neighboring Chongshan Group basement, and published mapping. Taken together, these data support, but do not by themselves prove, a tectonic framework in which the Bangong-Nujiang and Bitu/Longmu Co-Shuanghu sutures remain separate and subparallel across the narrowed Zuogong Basin in eastern Tibet.
Due to the particularity of the roof lithology, weakly cemented soft rock roadways in western China are prone to roof subsidence and even roof collapse. To solve this challenge, this manuscript combines theoretical research, numerical simulation, and field measurements. First, it proposes the characteristic of overall roof collapse in weak cementation soft rock roadways and introduces a collapse instability mechanism involving "delamination between the top coal and roof strata, fracture outside the support range, and overall roof subsidence." Second, it highlights the characteristics of weak cementation soft rock and the main influencing factors of roof collapse, which include the failure of anchoring due to the roadway exceeding the design width. Finally, based on the characteristics of surrounding rock, a control method for weak cementation soft rock roadways is proposed, combining the adjustment of anchor rod (cable) length with combined deep-shallow grouting. The field application has achieved significant results, effectively controlling the roof subsidence of the roadway.
