Magnitude of σ1, σ2, and σ3 at mid-crustal levels in an orogenic belt: Microboudin method applied to an impure metachert from Turkey

We revised an equation for estimating palaeostress magnitude using the microboudin technique by incorporating the influence of time on the fracture strength of minerals. The equation was used to estimate triaxial palaeostresses from a rare sample of metachert from Turkey that contains microboudinaged, columnar tourmaline grains in a wide range of orientations within the foliation plane. The estimated principal palaeostresses are σ₁ = 605 MPa, σ₂ = 598 MPa, and σ₃ = 597 MPa. As the microboudinage is considered to have occurred immediately before the rock encountered the brittle-plastic transition during exhumation, these stress values correspond to conditions at approximately 18 km depth and 300 °C within a Cretaceous orogenic belt.     

Determination of the lithium and rubidium in sea water by double channel flame emission spectrophotometry

A precise and accurate technique for the determination of Li and Rb in sea water has been developed by using a double channel flame emission spectrophotometer. The advantage of this technique is that it is possible to correct the background emission by making use of the double channel system of the apparatus and to obtain constant intensity of emission even if there are large scale changes in the salinity of the sample. Sea water samples collected in the open sea and coastal areas of Japan were analyzed by this method. In one of the coastal areas, an extraordinarily high concentration of Li was found.     

Direct determination of barium in Sea water by inductively coupled plasma emission spectrometry

A method for the determination of barium in sea water was investigated using inductively coupled plasma emission spectrometry, and sea water samples from the Japan Sea and the Pacific Ocean were directly analyzed by this method. Artificial sea water was used to prepare matrix matched standard solutions to overcome the problem of physical interference. The detection limit (signal/noise ratio=2) for barium in deionized and distilled water was 0.08µg l^?1 and in sea water, 0.12µg l^?1. The reproducibilities in the purified water and in the sea water at the 10µg l^?1 level were 0.7% a#FFFFFFnd 0.5%, respectively. The barium concentration in both the Japan Sea and the Pacific Ocean increased with depth and ranged between 5.5–10.0µg l^?1 and 4.1–18.4µg l^?1, respectively.     

Heat influx and exhumation of the Shimanto accretionary complex: Miocene fission track ages from the Kii Peninsula, southwest Japan

Abstract   To determine how local geological events contributed to the evolution of accretionary complexes and eventual exposure of rocks with different structural levels, geochronological mapping was carried out using fission track (FT) analysis at the Kii Peninsula, southwest Japan. At this site, the original zonal structure of Cretaceous accretionary complexes parallel to the subduction zone is disturbed by the northward projection of the Shimanto accretionary complex. Twenty-six zircon FT ages were obtained from an area of ∼12 km in an east–west direction and ∼15 km in a north–south direction, and classified into three groups: (i) ages ∼15 Ma (range ∼10–20 Ma), which are distributed along the northwest–southeast valley; (ii) ages of ∼50 Ma in the northwest of the study area; and (iii) ages older than those in Groups 1 and 2. Based on results from eight zircon FT length distributions, the Miocene ages appear to be the result of spatial variations in heat influx and cooling after the regional exhumation of the area, as recorded by FT ages of ∼50 Ma.     

Triaxial stress state deep in orogenic belts: an example from Turkey

A rare metachert pebble containing amphibole grains with microboudin structures in a wide range of orientations provides an opportunity to perform stress analysis in two orthogonal orientations on the foliation surface. The sample was analysed by the microboudin method to infer the triaxial stress state during microboudinage. Stress parameters proportional to the far-field differential stress were determined for sodic amphibole grains in the two orientations. The ratio of the stresses in the two orthogonal orientations (σ₁−σ₂)/(σ₁−σ₃) was calculated to be 0.64, indicating that σ₂ lies closer to the midpoint between σ₁ and σ₃ than to σ₃.     

Petrology,geochemistry and geodynamic setting of Eocene-Oligocene alkaline intrusions from the Alborz-Azerbaijan magmatic belt,NW Iran

The Kaleybar, Razgah and Bozqush (KRB) intrusions were studied to better understand subduction-related Eocene-Oligocene alkaline magmatism in NW Iran. The bulk of intrusions mainly consist of Si-undersaturated rocks including foid-bearing monzonite and syenite (nepheline syenite, pseudoleucite syenite) with some foid-bearing diorite and gabbro. In addition, they are spatially associated with Si-saturated rocks ranging in composition from monzo-diorite to syeno-granite. The main mafic rock-forming minerals of the studied rocks are olivine (Fo₄₄Fa₅₆), clinopyroxene (diopside to augite), biotite (Mg-biotite through Fe-biotite), amphibole (ferro-pargasite and magnesio-hastingsite with Mg#<0.55), and garnet (Ti-andradites). Based on whole rock geochemistry, the foid-syenites and associated rocks show mildly alkaline (shoshonitic) affinity. The content of SiO₂, K₂O?+?Na₂O, and K₂O/Na₂O ratio ranges from 47.8 to 60.7?wt.%, 5.31 to 16.33?wt.%, and 0.6 to 3.2, respectively. The intrusions are commonly metaluminous, with an aluminum-saturation index (ASI) ranging from 0.66 to 1.01. Almost all the rocks display similar arc-related geochemical features characterized by the enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE) together with the depletion in high field strength elements (HFSE). The chondrite-normalized REE patterns show no to marked negative Eu anomaly (Eu/Eu*?=?0.55 to 1.12), (La/Yb)_N?=?8.16 to 31, (La/Sm)_N?=?2.80 to 10.59, and (Tb/Yb)_N?=?0.84 to 2.40. The evaluation of the REE patterns for the KRB magmas and the comparison of the trace element ratios with experimental studies indicate a chemically enriched lithospheric mantle source composed of garnet-spinel-lherzolite that have underwent a low degree of partial melting <5% to generate the KRB intrusions. Based on the present data, we infer that the mantle source was contaminated by a subduction component and the melting of the mantle lithosphere occurred by local extension in an overall convergent regime in NW Iran. The extension regime during the Eocene is proposed to be the result of the Neo-Tethys slab roll-back and the Sevan-Akera-Qaradagh (SAQ) slab break-off.     

Rockfall hazard in the Daisekkei Valley, the northern Japanese Alps, on 11 August 2005

This paper describes a rockfall event in the Daisekkei Valley of Mount Shirouma-dake (2,932 m), the northern Japanese Alps. The rockfall occurred on a steep cliff comprising well-jointed felsites and produced debris of ≥8,000 m³. Most debris was deposited on an elongated snowpatch located immediately beneath the cliff, and it caused casualties among people who were trekking along a trail on the snowpatch. Additionally, a large rock block slipped 1 km on the snowpatch. The rockfall could have been due to the differential retreat of the rockwall, which contains areas of high- and low-density joints. Seasonal and diurnal freeze–thaw activities and snow avalanches and wash appear to be important factors responsible for the retreat. Although some rock blocks that can collapse further remain on the rockwall, the position of the mountain trail in the Daisekkei Valley is fixed. Fundamental reform of tourism systems for climbers, including education on natural hazards, is required.     

Measurement of small ions and condensation nuclei over the sea near the land

Summary To study the ionization equilibrium, simultancous measurements of the concentration of small ions (n), concentration of condensation nuclei (Z), and the diffusion coefficient of condensation nuclei (D) have been carried out over the sea. If we take the variation ofD into consideration, the correlation among them was found to be well expressed by the simple formula;q=n Z. The dependence of the effective attachment coefficient of small ions () upon the size of nuclei (2r) were also studied, and was found to correlate well withD orr. Slight differences of the dependence of uponD orr over the sea from that over the land seem to be well explained by the difference of charged states of nuclei over the sea and land.

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Zusammenfassung Zur Untersuchung des Ionisationsgleichgewichts wurden gleichzeitige Messungen der Konzentration schneller Ionen (n), der Konzentration der Kondensationskerne (Z) und des Diffusions-Koeffizienten der Kondensationskerne (D) über dem Meere ausgefürt. Unter Berücksichtigung des Diffusions-Koeffizienten (D) konnte der Zusammenhang zwischen den beiden anderen Grössen recht gut durch eine einfache Formel ausgedrückt werden:q=n Z. Die Abhängigkeit des wirksamen Anlagerungskoeffizienten für schnelle Ionen () von der Grösse der Kondensationskerne (2r) wurde ebenfalls untersucht, und es wurde gefunden, dass recht gut mitD oderr korreliert. Kleinere Unterschiede in der Abhängigkeit von vonD oderr, welche bei einem Vergleich der Messungen über See und über Land festgestellt wurden, liessen sich gut durch den Unterschied der geladenen Zustände der Kondensationskerne über See und Land erklären.

     

Evidence for a late thermal event of unequilibrated enstatite chondrites: A Rb-Sr study of Qingzhen and Yamato 6901 (EH3) and Khairpur (EL6)

Abstract— The Rb-Sr whole rock and internal systematics of two EH3 chondrites, Qingzhen and Yamato 6901, and of one EL6 chondrite, Khairpur, were determined. Sulfides were separated using a stepwise dissolution technique. The mineral species in each fraction were estimated based on the chemical analyses of 12 major elements. The internal Rb-Sr systematics of the EH3 chondrites are highly disturbed. Fractions corresponding to sulfide phases show excess ⁸⁷Sr, while other fractions corresponding to silicate phases produce a linear trend on a Rb-Sr evolution diagram. If these linear relations are interpreted as isochrons, the ages of the silicate phases are 2.12 ± 0.23 Ga and 2.05 ± 0.33 Ga with the initial Sr isotopic ratios of 0.7112 ± 0.0018 and 0.7089 ± 0.0032, for Qingzhen and Yamato 6901, respectively. The process of the isotopic disturbance probably involved the breakdown of the major K-bearing sulfide (djerfisherite), and a lack of isotopic exchange between sulfide and silicate phases indicates moderate temperatures of reheating. Although a complete Sr isotopic re-homogenization among silicate phases was not attained, we interpret the Rb-Sr results as indicative of a late thermal event about 2 Ga ago on the parent bodies of these EH3 chondrites. These ages agree well with previously published K-Ar ages. An older isochron age of 4.481 ± 0.036 Ga with a low initial Sr isotopic ratio of 0.69866 ± 0.00038 was obtained for the data from silicate fractions of Khairpur, indicating early petrological equilibration on the parent body of EL6 chondrites.