Middle miocene deduction and late miocene beginning of collision registered in the hengchun peninsula: Geodynamic implications for the evolution of Taiwan

Taiwan is located in the axis of the Manila Trench. It results from an oblique collision between the northernmost part of the Luzon arc and the Chinese passive margin. This active collision follows the subduction of the Oligocene-Miocene oceanic crust of the South China Sea along the Manila Trench. The tectonized Chinese margin emerged in the Hengchun peninsula (South Taiwan). Gentle folds which are delineated by the Quaternary reefal limestones demonstrate Recent deformations. These folds deformed a thick detrital sequence of Miocene age (Ssuchung Chi series) which was previously strongly folded and thrust westward (axis NS-N20) upon the Renting mélange of Latest Miocene age. These main deformations, sealed by the Middle Pliocene, are the evidence for the onset of collision in this part of Taiwan at the end of the Miocene. Because of its obliquity, the collision started already in the northern part of Taiwan during the Late Miocene (6-7-8 Ma ?).The Ssuchung Chi series, a sequence of proximal turbidites, has contained, since the Middle Miocene (NN 6~13 Ma), fragments of an Oligocene to Lower Miocene oceanic crust. This ophiolitic material is very similar to the East Taiwan Ophiolite of the Coastal Range. It originated most probably from a slice of South China Sea crust obducted in Middle Miocene times (13–14 Ma) upon the Chinese margin (North of the Hengchun peninsula). This obduction occurred 7 to 8 Ma before the beginning of collision. These results make it possible to propose an evolutionary model for Taiwan from the Oligocene to the Recent, with the different phases of a collision between a volcanic arc and a passive margin.     

Evolution estivale de la turbidité dans le lac de Neuchâtel

Some turbiditic measures carried out by a limnological diffusiometer along with the physico-chemical determinations of the Lake of Neuchatel have permitted to subdivide the water column in 4 distinct layers: the Epilimnium, the Clear Water Layer, the Pelagic Nepheloid Layer and the Benthic Nepheloid Layer.      

A new method for sampling and analyzing volcanic sublimates — application to Merapi volcano, Java

A new method for the sampling of sublimates from high-temperature volcanic gases has been used at Merapi volcano, Java, in 1978. The sublimates were collected on the inner walls of silica tubes introduced into fumarolic vents. Volcanic gases were allowed to move freely through the tubes and as they cooled, a fraction of the volatile components condensed on the inner walls of the tubes along the temperature gradient. The sublimates were then analyzed by a combination of light microscopy, scanning electron microscopy, electron microprobe and X-ray diffraction.Six successive zones of different compositions and mineralogical associations have been identified along the covered range of temperatures (900° to around 400°C). From the high to the low temperatures, these zones are composed of: (1) cristobalite, magnetite, hercynite; (2) molybdenite; (3) acmite; (4) halite, sylvite; (5) sphalerite, pyrite; and (6) galena. Equilibrium calculations show that these crystalline phases are stable for pS₂, pC₁, and pO₂, values typical of magma-buffered gases that have not been contaminated by atmospheric oxygen.The deposits observed in the tubes may be useful in aiding the understanding of the mechanisms acting during the cooling of the gaseous phase on its way to the surface and before its emission into the atmosphere.     

Ilmenite composition in the Tellnes Fe–Ti deposit,SW Norway: fractional crystallization,postcumulus evolution and ilmenite–zircon relation

Major and trace element XRF and in situ LA-ICP-MS analyses of ilmenite in the Tellnes ilmenite deposit, Rogaland Anorthosite Province, SW Norway, constrains a two stage fractional crystallization model of a ferrodioritic Fe-Ti-P rich melt. Stage 1 is characterized by ilmenite-plagioclase cumulates, partly stored in the lower part of the ore body (Lower Central Zone, LCZ), and stage 2 by ilmenite-plagioclase-orthopyroxene-olivine cumulates (Upper Central Zone, UCZ). The concentration of V and Cr in ilmenite, corrected for the trapped liquid effect, (1) defines the cotectic proportion of ilmenite to be 17.5 wt% during stage 1, and (2) implies an increase of D _V^Ilm during stage 2, most likely related to a shift in fO₂. The proportion of 17.5 wt% is lower than the modal proportion of ilmenite (ca. 50 wt%) in the ore body, implying accumulation of ilmenite and flotation of plagioclase. The fraction of residual liquid left after crystallization of Tellnes cumulates is estimated at 0.6 and the flotation of plagioclase at 26 wt% of the initial melt mass. The increasing content of intercumulus magnetite with stratigraphic height, from 0 to ca. 3 wt%, results from differentiation of the trapped liquid towards magnetite saturation. The MgO content of ilmenite (1.4–4.4 wt%) is much lower than the expected cumulus composition. It shows extensive postcumulus re-equilibration with trapped liquid and ferromagnesian silicates, correlated with distance to the host anorthosite. The Zr content of ilmenite, provided by in situ analyses, is low (<114 ppm) and uncorrelated with stratigraphy or Cr content. The data demonstrate that zircon coronas observed around ilmenite formed by subsolidus exsolution of ZrO₂ from ilmenite. The U-Pb zircon age of 920 ± 3 Ma probably records this exsolution process. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

An analytical solution to multi-component NAPL dissolution equations

This note presents a novel method for determining the changing composition of a multi-component NAPL body dissolving into moving groundwater, and the consequent changes in the aqueous phase solute concentrations in the surrounding pore water. A canonical system of coupled non-linear governing equations is derived which is suitable for representation of both pooled and residual configurations, and this is solved. Whereas previous authors have handled such problems numerically, it is shown that these governing equations succumb to analytical solution. By a suitable substitution, the equations become decoupled, and the problem collapses to a single first-order equation. The final result is expressed implicitly, with time as a function of the number of moles of the least soluble component, m₁. The number of moles of each other component is expressed explicitly in terms of m₁. It is shown that the time-m₁ relationship has a well behaved inverse. An example is given in which the analytic solution is verified against traditional finite difference analysis, and its computational efficiency is shown.