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.
We report here petrological characteristics of metamorphosed granite and metagabbro from the Kanja Malai hills, the southern margin of the Salem Block in southern India. Field observations suggest that both these rock types experienced high-grade metamorphism, and exhibit strong foliation. Many of cores of zircons extracted from the granite show an internal structure suggesting magmatic crystallization. In contrast, rims of the zircons commonly display metamorphic overgrowth. We also present geochronological data utilizing laser ablation ICP mass spectrometry technique on the zircons that show the weighted means of 207Pb/206Pb age of 2647 ± 11 Ma (error: 1σ) for the timing of magmatism, and 2442 ± 20 Ma (error: 1σ) for the subsequent high-grade metamorphism. Together with a previous geochronological study on charnockites from the Salem Block, our results also provide an important constraint on the Neoarchean magmatism (2.65-2.53 Ga) in southern India, correlating the magmatism with a major global crust formation event during the Neoarchean.
Geochemical and geochronological studies were conducted on granitoids in central-southern Laos. S-type ilmenite-series granitoids associated with Sn mineralization are distributed in the Truong Son fold belt of central Laos. Plateau ages determined by 40Ar/39Ar incremental heating method for biotite and muscovite of the granitoids range from 253 Ma to 247 Ma and from 244 Ma to 199 Ma in the southwest and northeast of the fold belt, respectively. During this period, the fractionated granites in the early stage are related to mineralization of medium-large Sn deposits. The granitoids of the Truong Son fold belt formed in the Indosinian orogeny are contemporaneous with the Late Permian-Early Jurassic Sn-bearing granites in the Southeast Asian Sn Belt. In contrast, I-type magnetite-series granitoids are distributed in the Kontum massif of southeasternmost Laos. Plateau ages for biotite and previously reported mineral ages of the magnetite-series granitoids range widely from 414 Ma to 252 Ma. The Carboniferous-Permian granitoids represents adakitic characteristics and the Permian adakitic granodiorites are associated with Cu ± Au mineralized quartz veins.
We present 210Pb/226Ra and 87Sr/86Sr data of barite separates from mineralized hydrothermal sulfate-sulfide chimneys collected from two young and active back-arc basins (i.e., Okinawa Trough and southern Mariana Trough), to examine the age of chimney formation and the relationship between the fluid chemistry and the field occurrence. Precipitation ages of purified barites in the mineralized chimneys are 24.8 (±1.3)-73.9 (±13.6) years BP2005 for chimney #220 from the Hakurei site in the Izena Cauldron (middle Okinawa Trough), 14.1 (±0.6)-53.4 (±2.8) years BP2005 for chimney #562-R13 from the Yaeyama graben (southern Okinawa Trough), and 29.8 (±1.4)-39.2 (±2.9) years BP2005 for chimney #903-R7 from the Archaean site in the southern Mariana Trough. Therefore, the time required for hydrothermal fluid venting to form these chimneys is of the order of decades. 87Sr/86Sr values for barites from chimney #220 are ∼ 0.7094; these values are higher than those of the JADE site (0.7091) at the slope of the Izena Cauldron and ambient seawater (0.70918). Given the relatively high Ag and Sb contents in chimney #220 bulk samples, we suggest that interactions have occurred between the hydrothermal fluid and the sediment cover. In contrast, barites from the southern Mariana Trough have relatively low 87Sr/86Sr values (∼ 0.7046), implying that magmatic fluids play a significant role in mineralization in this sediment-starved setting.
Olivine that has well-developed parting similar to cleavage, i.e., so-called “cleavable olivine”, occurs in peridotites at many localities of orogenic belts and the seafloor. Some conflicting hypotheses for the genesis of the parting have been proposed but not yet fully proved or disproved. We present new data of structural, petrological and mineralogical analyses of cleavable olivine and host ultramafic rocks in the Oeyama ophiolitic complexes, SW Japan. The following are our key findings to understand the genesis of cleavable olivine. 1) Cleavable olivine is distributed in the ultramafic complexes regardless of metamorphic grade of contact aureoles. 2) Cleavable olivine from contact aureoles has variable chemical compositions by the effect of thermal metamorphism. 3) Cleavable olivine commonly occurs in or near serpentinite mylonites. 4) Antigorite blades commonly occur along the parting planes of olivine, and the parting planes along with antigorite blades are locally bent to the direction of foliation. 5) Poles of the parting planes of olivine tend to be distributed around a plane vertical to the foliation of host serpentinite mylonite. From these facts we conclude that cleavable olivine was produced during a sequence of localized plastic deformation and alteration of peridotites at temperatures around 600 °C or lower. The parting is likely to have derived from dislocation arrangement by recovery processes after plastic deformation of hydrous peridotites and have been brought into prominence during syntectonic serpentinization. The preferred orientation of the parting planes suggests that cleavable olivine is a potential indicator of regional tectonics of the upper mantle at supra-subduction zones.
Tsumebite was discovered in a dump at the Kisamori mine, Daisen City, Akita Prefecture, northeast Japan. The mineral occurs as nodular aggregates (up to 0.5 mm in diameter) of platy crystals, up to 0.1 mm in length and 0.02 mm in thickness, in association with pyromorphite, quartz, limonite, and a clay mineral (potassic aluminum silicate). It is emerald green in color with a vitreous luster. The unit cell parameters obtained from the powder X-ray diffraction data are a = 7.850(2), b = 5.797(1), c = 8.712(2) Å, β = 111.92(2)°, V = 367.8(1) Å3, and Z = 2. Electron microprobe analyses indicate the empirical formula Pb2.02(Cu0.99Al0.01Zn0.01)Σ1.01(PO4)1.01(SO4)0.96(OH)1.12 on the basis of total cations = 5 atoms per formula unit in the anhydrous part and the amount of OH calculated from a charge balance. The calculated density is 6.23 g/cm3. It is likely that the present tsumebite was formed from a solution containing Pb, Cu, PO4, and SO4 ions after crystallization of pyromorphite.
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