Low-temperature thermochronology of fault zones

<p>Thermal signatures as well as timing of fault motions can be constrained by thermochronological analyses of fault-zone rocks (e.g., Tagami, 2012, 2019).  Fault-zone materials suitable for such analyses are produced by tectocic and geochemical processes, such as (1) mechanical fragmentation of host rocks, grain-size reduction of fragments and recrystallization of grains to form mica and clay minerals, (2) secondary heating/melting of host rocks by frictional fault motions, and (3) mineral vein formation as a consequence of fluid advection associated with fault motions.  The geothermal structure of fault zones are primarily controlled by the following three factors: (a) regional geothermal structure around the fault zone that reflect background thermo-tectonic history of studied province, (b) frictional heating of wall rocks by fault motions and resultant heat transfer into surrounding rocks, and (c) thermal influences by hot fluid advection in and around the fault zone.  Geochronological/thermochronological methods widely applied in fault zones are K-Ar (<sup>40</sup>Ar/<sup>39</sup>Ar), fission-track (FT), and U-Th methods.  In addition, (U-Th)/He, OSL, TL and ESR methods are applied in some fault zones, in order to extract temporal information related to low temperature and/or recent fault activities.  Here I briefly review the thermal sensitivity of individual thermochronological systems, which basically controls the response of each method against faulting processes.  Then, the thermal sensitivity of FTs is highlighted, with a particular focus on the thermal processes characteristic to fault zones, i.e., flash and hydrothermal heating.  On these basis, representative examples as well as key issues, including sampling strategy, are presented to make thermochronological analysis of fault-zone materials, such as fault gouges, pseudotachylytes and mylonites, along with geological, geomorphological and seismological implications.  Finally, the thermochronological analyses of the Nojima fault are overviewed, as an example of multidisciplinary investigations of an active seismogenic fault system.</p><p> </p><p>References:</p><ol><li>Tagami, 2012. Thermochronological investigation of fault zones. Tectonophys., 538-540, 67-85, doi:10.1016/j.tecto.2012.01.032.</li> <li>Tagami, 2019. Application of fission track thermochronology to analyze fault zone activity. Eds. M. G. Malusa, P. G. Fitzgerald, Fission track thermochronology and its application to geology, 393pp, 221-233, doi: 10.1007/978-3-319-89421-8_12.</li> </ol>

The geological characteristics and quality of feldspar mines in Tay Nguyen area and its applications of the ceramic production

The article presents a summary of the geological characteristics of the feldspar mines in Tay Nguyen area. The collecting data from the reseached area showed that most feldspar mines in Tay Nguyen area had source of pegmatite. They were established with a high to average temperature and associated by metamorphic process and granitoid of area. The feldspar mines were mineral vein and penetrate to grantioid with a length of hundred meter and a with of 2-20 meters. This feldspar had a white to yellow color and very high alkalinity (14–16 %), silice oxide (61–64 %). Its is suitable for VN 6598:2000 standard applied for ceramic. It’s necessary to have further research on technological characteristics in order to orient to the exploitation and the efficient use in future of feldspar mones in Tay Nguyen area.

Polymetallic mineralization in Ediacaran sediments in the Żarki-Kotowice area, Poland

In one small mineral vein in core from borehole 144-Ż in the Żarki-Kotowice area, almost all of the ore minerals known from related deposits in the vicinity occur. Some of the minerals in the vein described in this paper, namely, nickeline, hessite, native silver and minerals of the cobaltite-gersdorffite group, have not previously been reported from elsewhere in the Kraków-Lubliniec tectonic zone. The identified minerals are chalcopyrite, pyrite, marcasite, sphalerite, Co-rich pyrite, tennantite, tetrahedrite, bornite, galena, magnetite, hematite, cassiterite, pyrrhotite, wolframite (ferberite), scheelite, molybdenite, nickeline, minerals of the cobaltitegersdorffite group, carrollite, hessite and native silver. Moreover, native bismuth, bismuthinite, a Cu- and Ag-rich sulfosalt of Bi (cuprobismutite) and Ni-rich pyrite also occur in the vein. We suggest that, the ore mineralization from the borehole probably reflects post-magmatic hydrothermal activity related to an unseen granitic intrusion located under the Mesozoic sediments in the Żarki-Pilica area.

Breaking the surface

The pebble is a small but perfectly integrated part of a metal factory. This factory has produced copper, silver, zinc, lead and gold (real gold, not its iron sulphide facsimile, pyrite). It is about 100 kilometres long and 60 kilometres across, by about 6 kilometres deep. It is called Wales. The metals have sustained, puzzled, frustrated, and finally abandoned many generations of Welsh miners. Many hundreds of generations, indeed, for these metals have been sought, avidly, since at least the Bronze Age, more than 3000 years ago, when shafts were dug through solid rock with little more than hand-held antler bone and rounded cobble. It is no small feat to chase the metal underground, for its path is tortuous, its presence capricious and its surroundings dangerous. The Welsh miners have been celebrated at home in literature and songs, and also in more surprising quarters, as in the Japanese filmmaker Hayao Miyazaki’s portrayal of them in Castle in the Sky (a children’s animé film, perhaps, but deeply serious at core, like everything that Miyazaki has done). So how is a country-sized metal factory created? Tiny fragments of the answer reside within the pebble. A streak of white crosses the pebble, cutting across both the strata and the tectonic cleavage surfaces. Cutting both these fabrics, it must then be younger. Such evidence of what-came-first and what-came-next is at the heart of geology, and has been so since the very beginnings of the science, since before geological time was pinned and measured by the application of atomic clocks and of fossil time-zonations. And for all today’s shiny atom-counting machines and well-stocked libraries and museums, this kind of logic is still the first thing the geologist applies when any new and unfamiliar problem comes into view. But what is it in the pebble that is younger? Peer with the hand lens, and the white streak is resolved as a mineral vein: that is, as a mass of tiny crystals that have grown within a fracture in the rock.

Ferrierite from Tapu, Coromandel Peninsula, New Zealand, and a crystal chemical study of known occurrences

Ferrierite has been found at Tapu, Coromandel Peninsula, New Zealand, as a mineral vein with calcite in altered hornblende andesite lava of the Miocene Beeson's Island Volcanics. The ferrierite is low in SiO2 (63.67%) and high in Al2O3 (13.75%), MgO (3.48%), and BaO(2.35%). The large a axis and cell volume (a 19.236(4), b 14.162(6), c 7.527(3) Å, V 2050 Å3) are consistent with the low SiO2, high Al2O3, high MgO chemistry. Optical orientation and optical sign (a = Z, b = X, c = Y, 2V(-)55°) of the mineral are different from those of the Lake Kamloops ferrierite reported by Graham (1918). Refractive indices α 1.487, γ 1.489, and density 2.136 were measured. Cleavage observed on (100) is perfect and on (001) is imperfect. Using data from eighteen occurrences so far reported including the Tapu mineral, the crystal chemistry of ferrierite has been studied.