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Pressure ( P)-temperature ( T) pseudosection analyses were carried out on metapelites from Sambagawa belt by using Perple_X 07 so as to determine mineral equilibria and the stability of sodic phases, in the model system MnO-NaO-KO-CaO-FeO-MgO-AlO-SiO-HO-(CO) under high-pressure (HP) conditions (0.5-2.5 GPa/400-600 °C). A pressure- X [=Na/(Na+Al-2K-1.5Ca)] pseudosection at 500 °C is also calculated to examine the effect of Na/Al value of the bulk-rock composition on the stabilities of sodic minerals. The bulk-rock compositions of Sambagawa metapelite are variable in X values. The calculation results of stable assemblages in metapelites under the blueschist and eclogite facies conditions indicate that: (i) paragonite and glaucophane are stable throughout the wide X range of bulk-rock compositions of host rocks; (ii) stable P-T conditions of sodic pyroxene enlarge with increasing X value; and (iii) the stability field of paragonite enlarges with the presence of CO in the metamorphic fluid. The suggested wide stability of paragonite in metapelites and the relationships between the stability of sodic pyroxene and the bulk-rock compositions explain the reasons why (i) the occurrence of omphacite in metapelites from several subduction-related terranes is rare; and (ii) paragonite commonly occurs as inclusions in garnet of metapelites from the Besshi region of the Sambagawa belt. Paragonite is an important sodic phase of HP metapelites, and a combination of paragonite and quartz with high residual pressure included in garnet may be a useful indicator to verify the evidence for the eclogite facies metamorphism recorded in metapelites. [ABSTRACT FROM AUTHOR]

Silicate spherules have been identified from the ca. 3.4 Ga-old Strelley Pool Formation (SPF) in the Pilbara Craton, Western Australia. Their origins and geochemical characteristics, including the Re and platinum-group elements of their host clastic layer and the overlying and underlying microfossil-bearing finely laminated carbonaceous cherts, were examined. The spherules have various morphologies (completely spherical to angular), sizes (∼20 to >500 μm), textures (layered, non-layered, and fibrous), mineralogy (various proportions of microcrystalline quartz, sericite, anatase and Fe-oxides), and chemistry (enriched in Ni and/or Cr), commonly with thin anatase-rich walls. Their host clastic layer is characterized by rip-up clasts, suggesting a suddenly occurring high-energy depositional environment, such as tsunamis. Although various origins other than asteroid impact were considered, none could unequivocally explain the features of the spherules. In contrast, non-layered spherical spherules that occur as individual framework grains or collectively comprise angular-shaped rock fragments appear to be more consistent with the asteroid impact origin. The calculated Re-Os age of the cherts (3331 ± 220 Ma) was consistent with the established age of the SPF (3426-3350 Ma), suggesting that the Re-Os system was not significantly disturbed by later metamorphic and weathering events.

Purpose: To evaluate the predictors of long-term tumor control following stereotactic radiosurgery (SRS) for Koos grade 4 vestibular schwannomas (VSs)., Methods: Overall, 203 sporadic VS patients with compression of the brainstem were treated with SRS. The median tumor volume was 6.7 cm 3 (range, 2.0-28.9 cm 3 ) and the median marginal dose was 12 Gy (range, 9-13.5 Gy)., Results: The median follow-up period was 152 months (range, 12-277 months). Tumor control (TC) rates at 3, 5, and 10 years were 89%, 85%, and 82%, respectively. Operation-free survival (OFS) rates at 3, 5, and 10 years were 92%, 85%, and 83%, respectively. Middle cerebellar peduncle (MCP) compression on pre-SRS magnetic resonance imaging scans was significant for both TC (p < 0.001, hazard ratio 1.332) and OFS (p < 0.001, hazard ratio 1.306). The 3-, 5-, and 10-year OFS rates were 98%, 94%, and 92% in the low-risk group (MCP compression < 9.8 mm and > 48 years old), and 58%, 25%, and 17% in high-risk group (MCP compression ≥ 9.8 mm and ≤ 48 years old), respectively. Ten patients (4.9%) developed delayed cyst-related complications. Eleven patients (5.4%) developed newly developed or worsened trigeminal neuralgia. No patient developed persistent facial palsy as an adverse radiation effect. A ventricular peritoneal shunt was required in six patients (3%) who developed hydrocephalus after SRS., Conclusion: SRS is an acceptable treatment option in selected patients with Koos grade 4 VSs. Risk group classification based on patient age and MCP compression is useful in decision-making of Koos grade 4 VSs.