Official journal of Japan Association of Mineralogical Sciences (JAMS), focusing on mineralogical and petrological sciences and their related fields. Journal of Mineralogical and Petrological Sciences (JMPS) is the successor journal to both “Journal of Mineralogy, Petrology and Economic Geology” and “Mineralogical Journal”. Journal of Mineralogical and Petrological Sciences (JMPS) is indexed in the ISI database (Thomson Reuters), the Science Citation Index-Expanded, Current Contents/Physical, Chemical & Earth Sciences, and ISI Alerting Services.
The spatial variation in initial 87Sr/ 86Sr ratios (SrI) in the Toki granite, Central Japan, shows heterogeneity ranging from 0.708942 to 0.710069, which provides information on the intrusion and cooling processes of plutons. The Toki granite has three mineralogy-based rock facies: muscovite-biotite granite (MBG), hornblende-biotite granite (HBG) and biotite granite (BG). Large SrI values were found to be distributed at the western margin (west MBG) and the lithologically central region (central BG), while small SrI values were found at the northeast margin (northeast MBG). Regions with high and low Sr concentrations were also found in the Toki granite. In the Sr-rich samples, SrI (0.708942-0.709789) increases with 100/Sr (0.7-1.5). This geochemical trend extends towards the country sedimentary rocks of the Mino Terrane, which can be interpreted to result from assimilation and fractional crystallization (AFC) between the original granitic magma and the Mino sedimentary rocks. The SrI values in the Sr-rich regions show a correlation with the Alumina Saturation Index (ASI). In particular, the west MBG, with large SrI values, is classified as a peraluminous granitoid with large ASI, suggesting that the western margin of the pluton was strongly affected by assimilation during the intrusion process. The Sr-poor samples are present both in the central BG, with large SrI values, and in the northeast MBG, with small SrI values. The Sr-poor samples have small ASI and large differentiation indices, indicating that the central BG and the northeast MBG were generated either by different AFC process with different amounts of contaminants or by the intrusion and fractionation of different source magma with different SrI values. Overall, the geochemical spatial variations found in the Toki granite can be explained by various degrees of assimilation and fractional crystallization in the magma chamber and/or multi-stage intrusions with different degrees of crystallization of plural source magmas with different SrI values. Previous petrographical and thermochronological studies revealed that the Toki granite effectively cooled from the wall at the western margin in the cooling stage at temperatures below 500 °C. Larger SrI and ASI values found in this study corresponded to the western margins where the earlier and more rapid cooling took place, indicating that the Toki granite was preferentially cooled from the peraluminous marginal regions where the assimilation of country rock was the most extensive.
We studied basal lherzolites that are exposed along the metamorphic sole at the base of the central Oman ophiolite (Wadi Sarami). We recognized two types of lherzolites (Types I and II) based on field occurrences, textures, and mineral compositions. Type I lherzolites are massive and transition into harzburgites, whereas Type II lherzolites are strongly foliated with mylonitic to porphyroclastic textures. Type II lherzolites only crop out within a direct contact with the amphibolitic sole to few meters above this sole and are overlain and/or surrounded by Type I. The clinopyroxenes [Mg# = Mg/(Mg + Fe) = 0.89-0.94] of Type II lherzolites show higher contents of Al2O3 (4.5-7.3 wt%), Na2O (0.5-1.2 wt%), Cr2O3 (0.6-1.4 wt%), and TiO2 (0.2-0.4 wt%) than those of Type I lherzolites. Positive correlations among the Al2O3, Na2O, and TiO2 contents of clinopyroxenes show a pronounced residual trend from Type I lherzolites to depleted harzburgite, giving rise to chemical heterogeneities at the base of the mantle section. Clinopyroxenes in lherzolites and harzburgites show compositional trends that are similar to those in abyssal peridotites from normal ridge segments. Olivines (Fo89.4-Fo91.5) show a residual character of the Sarami peridotites. Primary spinels show a wide range of Cr# [= Cr/(Cr + Al) from 0.04 to 0.53] and low YFe [Fe3+/(Cr + Al + Fe3+), <0.046], similar to spinels in abyssal peridotites. The wide range of spinel Cr# is a result of a wide range of partial-melting degrees, which are up to 10% for lherzolites and ∼ 10-25% for harzburgites. The Type II lherzolites, which occur near the paleo-fracture zone located to the east of Wadi Sarami, represent a remnant of asthenospheric materials trapped at the base of oceanic lithosphere mantle (Type I) during detachment and obduction. The Type I lherzolites experienced high-degree partial melting, resulting in the formation of harzburgites at the refractory end. The modal and compositional variations of Sarami pyroxenes and spinels indicate intrinsic mantle heterogeneity of Oman ophiolite formed as residues at an oceanic spreading center.
Oxidation states of Fe and precipitates within olivine in orthopyroxene-olivine-clinopyroxene andesite (Opx-Ol-Cpx andesite) lava from Kasayama volcano, Hagi, Yamaguchi Prefecture, were investigated to reveal the oxidation process of the lava at high temperatures, using electron microprobe analysis, Raman spectroscopy and transmission electron microscopy. Although the Opx-Ol-Cpx andesite lava is generally black in color, in places it has a red-brown surface and reddish-black subsurface. Olivines from the black lava have normal zoning with Fo68.5-74.9 cores and Fo64.9-72.9 rims. Olivine in the black lavas with red-brown tint and red-brown lava contains precipitates of Ti-rich hematite, hematite, magnesioferrite and enstatite, and tends to be Mg-rich (cores: Fo74.1-78.6; rims: Fo76.4-83.8) in comparison with black lava. Stronger red coloration of the lavas is related to greater volume of cryptocrystalline precipitates within olivine. This results in increased Mg contents in olivine. Olivines in red-brown lava are extremely Mg-rich (Fo91.0-95.4). By applying the correlation between FeLβ- and FeLα-intensity ratio and Fe2+/Fe3+-ratio, small amounts of Fe3+ (0.05 atoms per formula unit at maximum) were invariably detected in olivine from the black lava with red-brown tint. Even in olivine in the black lava, Fe3+ was detected in the rims, although Fe is ferrous in the cores. These facts on the chemical compositions and oxidation state of Fe within olivine phenocrysts and the occurrence of vermicular rod-form titanohematite and magnesioferrite precipitates in olivine provide the evidence for high temperature oxidation, at temperatures above 800 °C.
Iseite, Mn2Mo3O8, a new mineral that is a Mn-dominant analogue of kamiokite, is found in the stratiform ferromanganese deposit, Shobu area, Ise City, Mie Prefecture, Japan. It is the first mineral species that includes both Mn and Mo as essential constituents. Iseite is iron-black in color and has a submetallic luster. It occurs as aggregates up to about 1 mm in size made of minute crystals (<20 μm). Iseite has a zoned structure closely associated with undetermined Mn-Fe-Mo oxide minerals with hexagonal forms, and it occasionally coexists with small amounts of powellite. Its Mohs hardness is 4-5, and its calculated density is 5.85 g/cm3. The empirical formula of iseite is (Mn1.787Fe0.193)Σ1.980Mo3.010O8. Its simplified ideal formula is written as Mn2Mo3O8. The mineral is isostructural with kamiokite (hexagonal, P63mc). The unit cell parameters are a = 5.8052 (3) Å, c = 10.2277 (8) Å, V = 298.50 (4) Å3, and Z = 2. The Rietveld refinement using synchrotron radiation (λ = 0.413 Å) powder XRD data converges to Rwp = 3.11%, and confirms two independent Mn sites—tetrahedral and octahedral—in the crystal structure of iseite, indicating the structure formula MnIVMnVIMo3O8.
The Central Asian Orogenic Belt consists of various terranes amalgamated in several periods from the Late Precambrian/Early Paleozoic to the Late Mesozoic. Mongolia is situated in the center of this belt. Foliated garnet granite (Grt metagranite) and andalusite-bearing massive leucogranite (Leucogranite) are exposed in the Hanhohiyn region of northwest Mongolia. The results of monazite Th-U-Pb dating of the Grt metagranite and Leucogranite give ages of 508 ± 10 Ma and 496 ± 4 Ma, respectively. Cambrian granite with an age of ∼ 500 Ma is also reported from the south-central part of Mongolia. Combined with previously published age data of metamorphic and intrusive rocks, these results show that the Cambrian orogenic belt spans over 800 km, from the northwest to the south-central part of Mongolia.
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