The Triassic gabbroic intrusions and associated basaltic lavas from Chukotka are mainly tholeiitic with both ocean island basalt (OIB) and island arc basalt (IAB)–type geochemical signatures. Mg–number [Mg# = 100 × Mg/(Mg + Fe2+)] is around 40 for OIB–type gabbros, ranges from 48 to 66 for IAB–type hornblende–rich gabbros, and 43 to 65 for IAB–type basaltic rocks (ankaramites, lamprophyres, pyroxene–phyric basalts and hornblende–phyric basaltic andesite). TiO2 contents of the IAB–type gabbros and basaltic rocks are low (<2 wt%), but are high in OIB–type gabbros (4.3–5.3 wt%). OIB–type gabbros are typically enriched in FeO* (16–18 wt%) as compared to IAB–type gabbros (10–14 wt%) and IAB–type lavas (ankaramites, ~ 10 wt%; lamprophyres, ~ 14; pyroxene–phyric basalt, 11 wt% and basaltic andesite, 9–10 wt. %). In the primitive mantle normalized trace element patterns, IAB–type basalts and gabbros are characterized by depletion in HFSE (Nb, Ta, Zr and Hf) and enrichment in LILE. OIB–type gabbros can be distinguished from the rests by the absence of HFSE depletion, with strong negative Sr anomaly. The positive Ti anomaly in the OIB–type gabbros can be attributed to high content of ilmenite in these rocks. Trace element characteristics of IAB–type gabbroic rocks and basalts are compatible with their magmas derived from subduction influenced melts, whereas OIB–type gabbros show within–plate geochemical characteristics. IAB–type gabbros and basaltic rocks display similar geochemical features to the low–Ti Nadezhdinsky suit (Noril’sk region) and Bel’kov dolerite (New Siberian Islands) of the Siberian large igneous province (LIP) in view of HFSE depletion and high H2O content of the magma to crystallize abundant hornblende not only in gabbros but also as phenocrysts in basalts. The Triassic gabbroic and basaltic rocks of both OIB and IAB types may as a whole represents the eastern end of the Siberian LIP.
Raman spectra of carbonaceous materials were observed for 20 chondrite samples (one R, four CV, four CO, two CM, one CR, one CB, one C–ung, three LL, one L, and two H chondrites). The observed specimens were chips (fifteen samples) and thin sections (five samples). The obtained spectra were decomposed into four components: GL, D1, D3, and D4 bands at 1600, 1350, 1510, and 1245 cm−1, respectively. The full width at half maximum of the D1 band (ΓD1) decreased with increasing peak metamorphic temperature (PMT) of the parent body, as published previously. By increasing the number of band components to four, the applicable range of the Raman spectroscopic thermometer using ΓD1 extended its lower limit to 20–30 °C. The upper limit of the present Raman spectroscopic thermometer is 540 °C, which is derived from the bottoming out of ΓD1. This thermometer was applied to chondrites whose PMT are unknown. The obtained temperature values were consistent with the order of petrological type.
Color cathodoluminescence (CL) images of zircon from southern Malawi (MZ) show mottled yellow CL emissions on a dull luminescent background by the annealing below 600 °C, and relatively homogeneous blue emissions above 800 °C. CL spectroscopy of the samples reveals a change of the luminescent features with an annealing temperature, and explains a variation of their colors and luminance observed by a CL microscope. Emission bands at 310 and 380 nm in an ultraviolet (UV) to blue CL are assigned to intrinsic centers in host lattice, narrow peaks at 475 and 580 nm to Dy3+ impurity centers, and broad bands at 500 to 650 nm to Frenkel–type defects and SiOmn− groups. The former two show increases in emission intensities against annealing temperature, but the latter exhibits an increase in intensity up to 300 °C and a decrease above 300 to 700 °C. An increase in an annealing temperature leads to a reproduction of the intrinsic centers, which is responsible for an increase in UV–blue emission, in host lattice accompanied with a recrystallization from metamict state. An increase in the intensities of narrow peaks activated by Dy3+ impurities may result possibly from a recovery of ionization due to the self–radiation and an energy transfer of other REEs to Dy3+ activator. A gradual increase in yellow emission bands up to 300 °C might be caused by a migration of the hole around a thermally–instable lattice defect and/or activated impurities into a more stable site related to Frenkel–type defects and SiOmn− groups, whereas the yellow should be subsequently reduced due to an elimination of these defects.
We performed high–temperature friction experiments to investigate the effect of temperature on the frictional behavior of smectite and illite. Friction coefficients (μ) of these clay minerals increase with increasing temperature as a result of dehydration of absorbed and interstitial water. At a constant normal stress of 60 MPa, μ of Ca–smectite gouge increases from 0.27 at room temperature to 0.67 at 200 °C, and μ of illite gouge increase from 0.53 at room temperature to 0.68 at 200 °C. Velocity dependence of steady–state friction for smectite and illite gouges changes with temperature so that the transition from velocity–strengthening to velocity–weakening behavior occurs at 150 °C at a normal stress of 60 MPa. Temperature at which this change takes place corresponds to the temperature at the updip limit of the seismogenic zone along subducting plates. Thus, the effect of temperature on the frictional behavior of these clay minerals possibly play an important role in controlling the updip limit of subduction thrust earthquakes.
Bismuth minerals are described in 10 W–Mo–Sn deposits (Wakikawa, Shintoku, Takane, Shionomachi, Juseki, Nabekura, Nogeyama, Kanamaru, Kanzeon, and Daitoku) in the ilmenite–series Iwafune granitoids, located in the Uetsu region, Niigata Prefecture, Japan. The results are compared with those in the Cu–Pb–Zn–Bi deposits hosted in the magnetite–series Wasada granodiorite in the same region. Native bismuth and bismuthinite occur as major Bi minerals, accompanied by minor Pb–Bi–S sulfosalts (cannizzarite, cosalite, and lillianite) and Bi–tellurosulfides (joséite–A, joséite–B, ingodite, tetradymite, and ikunolite) in the Iwafune deposits. The Bi mineralogy of the Iwafune and Wasada deposits shows the following three characteristics: Native bismuth and bismuthinite are abundant in the Iwafune deposits; Pb–Bi–S sulfosalts and Bi–tellurosulfides are common in the Iwafune and Wasada deposits; and Cu–rich Bi–sulfosalts are restricted to the Wasada deposits. Since the major mineralization in the Iwafune deposits (W–Mo–Sn) and Wasada deposits (Cu–Pb–Zn–Bi) is largely controlled by the related granitoid–series, the difference in Bi minerals between the Iwafune and Wasada deposits might reflect the oxidized/reduced mineralization associated with the granitioid–series.
Vol.31 (1944) No. 5 and No.6 in the predecessor journal ″The Journal of the Japanese Association of
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April 03, 2015
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