Pyroxene Andesite Research Articles

Szolnok – Milléri-holtág part I-II. több korszakú lelőhely őrlőkő leletei archeometriai vizsgálatának előzetes eredményei : Új adatok a domoszlói piroxénandezit nyersanyag régészeti elterjedéséhez

The multi-period archaeological site Szolnok – Milléri-holtág part I-II is located in the north-eastern vicinity of Szolnok, approximately 5 km from the town, on the high bank of the Milléri-holtág. The total excavated area is almost 27 000 m2 . The preventive excavation was performed by the staff of the Hungarian National Museum in two campaigns (in 2014 and 2015) connected with the M4 motorway constructions. Most excavated settlement features belonged to a Middle Iron Age (Scythian Period) and a Late Iron Age (Celtic Period) rural settlement with scattered structures. Besides these, other settlement features were found from the Neolithic, Late Bronze Age and Medieval Period (Árpád Period). It has to be mentioned that in the excavated part of the Scythian Period settlement, only circular and oval structures were found. The rectangular features – typical for other settlements of the period – were absent in Milléri-Holtág part I-II. However, the archaeological finds were typical: ceramic assemblages were characterised by long-lasting forms (pots, bowls) of the Iron Age household ceramics. The assemblages of the Late Iron Age features were very similar to the vessel types of the earlier period. The partition of the artefacts can only be made with the help of some characteristic forms and ornamentations that appeared in a close unit. The ground stone assemblage of the site (primarily fragments of grinding stones) was analysed with petrographic and geochemical methods. Based on these investigations, the finds' most frequent raw material type could be identified with the Domoszló-type pyroxene andesite from the Mátra Mountains, studied intensively in the past few years. Other types of andesite were present in the ground stone assemblage in smaller amounts. The identification of the source areas of these different andesite raw material types needs more exploration, not just in the territory of Hungary, but also in some areas beyond the borders, e.g. Subcarpathia (Zakarpatska Oblast, Ukraine), Eastern-Slovakia, Transylvania (Romania).

Source Determination of Debris Avalanche Deposit based on the Morphology and Distribution of Hummocky Hills on the Northeastern Flank of G. Sundoro and G. Sumbing, Central Java, Indonesia

The presence of hummocky hills as a typical product of debris avalanche deposits is prominently visible in the northeastern flank of G. Sundoro and G. Sumbing, Temanggung, Central Java. In an attempt to better understand the past behavior of both G. Sundoro and G. Sumbing, we identify the source of the debris avalanche deposit. Interpretation is performed on the basis of the assumption of two possible sector collapse sources, i.e., G. Sundoro and G. Sumbing. The Sumbing source scenario is assumed as freely spreading type considering 1) distribution of the hummocky hills are relatively on the northeastern flank of the volcano, and 2) the present crater structure on the summit of the volcano which is opening to the northeast. The Sundoro source scenario is assumed as valley-filling type considering the distribution of the hummocky hills are relatively on the eastern flank of Sundoro extended to the far distal area and bounded by older high topography of G. Sumbing and North Serayu Mountains. The source identification was done on the basis of field observation of the deposit lithological characteristics combined with image analysis, including hummocky hills morphometry, displacement angle, and spatial distribution. Image analysis identifies approximately 645 hummocky hills ranging from 1,851 mz to 623,828 mz and average of 23,482 m2. Petrographic analysis of 5 representative block lava samples shows variation of olivine basalt, pyroxene andesite, to hornblende andesite. The results show that big size hummocky hills dominate the western side, while small size on the east. Displacement angle varied following the valley orientation with typical downslope topography. These suggested that the hummocky hills were originated from G. Sundoro as a valley-filling debris avalanche deposit.

Quaternary Seabed Sediment Characteristics as an indication of VMS-mineral deposits at the South Banda Basin and its surroundings, Indonesia

The South Banda back-arc basin is a morphotectonic environment that is part of the South Banda Basin, characterized by a flat morphology with depths ranging from 5000m to 6000m. The purpose of this paper is to analyze and relate morphometric aspects to the Quaternary seabed sediment deposits deposited in an active tectonic basin in the Banda Sea area, including information on the type of sediment and its distribution as well as its relation to volcanic hosted-massive sulfide (VHMS) or volcanogenic massive sulfide (VMS) mineral deposits. The seabed lithofacies in the Banda Arc area were deposited in several morphotectonic environments. The types of deposits that are deposited are pelagic, and hemipelagic deposits including turbidite and volcanic origin deposits. Volcanic deposits consist of gravel, sand, muddy sand, and silt which are classified very poorly to moderately well sorted. The grain composition is volcanic lithic, feldspar, augite, hypersthene, and enstatite which are commonly found in volcanic arcs and troughs. Groups of volcanic grains composed of pyroxene andesite, pumice, and tuffite or siliceous gravel, distributed in the northern and the middle of the volcanic arc area are interpreted to originate from the Banda volcanic complex and the Seram-Gorong islands.

Magma Evolution of Ngebel Volcano, Ponorogo, East Java, Indonesia

The magma evolution of Ngebel Volcano, both temporally and spatially, is represented by the characteristics of its lava. Ngebel Volcano, located in East Java, is a Quaternary andesitic stratovolcano. This volcano is part of the Wilis Volcanic Complex. The volcanism stage of Ngebel Volcanic Complex can be divided into the Jeding with andesitic basalt (SiO2 49 - 59%), pyroxene andesite Kemlandingan (SiO2 49 - 59%), Manyutan with hornblende andesite (SiO2 49 - 59%), and Ngebel with dacite (SiO2: 49 - 59%). The variation of major elements combined with petrographic features such as plagioclase, pyroxene, hornblende, quartz, and opaque minerals from basaltic andesite to dacite is interesting. The minerals show that the magma differentiation process of Ngebel Volcanic Complex is the results of fractional crystallization of magma. The purpose of this study is to determine the evolution of magma from volcanic rocks of which stratigraphic positions have been determined. The analytical methodology used is petrographic and geochemical analysis. Detailed temporal evolution shows that magma from the Ngebel Volcanic Complex underwent a differentiation process that changed the magma composition from mafic to more felsic.

MORFOLOGI DAN KLASIFIKASI TANAH PADA FORMASI PENIRON BAHAN INDUK ANDESIT PIROKSEN DI DESA PAGEDONGAN, BANJARNEGARA

Rock formation as parent material in Pagedongan Village, Banjarnegara influences the properties of the soil formed. The purpose of this research was to identify the morphology and soil classification according to USDA Taxonomy, National Soil Classifications, and World Reference Base for Soils. This study uses a survey method by determining observation points based on a rock formation, namely Peniron Formation, with pyroxene andesite as parent material for observing soil morphology, physical and chemical of soil in the field, then laboratory analysis included soil texture, bulk density, organic C, soil pH H2O and KCl, exchangeable cations K, Ca, Mg, Na, CEC, and base saturation. The results showed that the soil developed in the Peniron Formation with pyroxene andesite as parent material had morphology with diagnostic horizons of umbric epipedon and argillic endopedon. The results showed that the soil classification according to USDA Taxonomy is Typic Palehumults Isohyperthermic, according to National Soil Classifications is Podsolics Ortoxic, and according to World Reference Base for Soils is Loamic Abruptic Alfisols.

Evolution Magmatism of Nagasari Volcano Dieng, Central Java, Indonesia

Nagasari Volcano, part of the Dieng volcanic complex, is one of the unique volcanoes in Central Java. Around this volcano grow eruption craters, volcanic cones, and pyroclastic flow ridges. There were several 14 eruption centers around Mount Nagasari, so it is necessary to know the development of magmatism evolution. The aims of the research to determine the evolutionary development of magmatism. The methodology used is geological mapping and petrographic analysis. The observations of rocks found in the study area include andesite lava, lapilli-tuff, fallen pyroclastic breccias, and flow pyroclastic breccias. Meanwhile, geological mapping and petrographic observations of volcanic rock samples show that the evolution of magmatism in the study area from the oldest to the youngest is basaltic magma that formed Prau Volcano in the pre-caldera period. On the other hand, magmatism in the post-caldera I period was of the type of pyroxene andesite forming the Gembol to Jimat Volcano group. In contrast, in the post-caldera II period, the hornblende-biotite andesite group formed the Dieng Kulon to Kendil group.

Geological, geophysical, and geochemical constraints on the time-space evolution of Akan composite caldera, Hokkaido, Japan

Some calderas are geometrically complex that may be related not to a single eruption, magma body, or structure. In order to reveal their forming processes, multidisciplinary methods should be applied. Akan volcano has E-W elongated and irregular-shaped caldera (24 × 13 km), implying a complex mechanism of formation. Akan caldera results from successive explosive eruptions from 1.4 to 0.1 Ma. On the basis of duration of dormancy and petrological features (mainly whole-rock major element compositions) of juvenile materials, these eruptions have been grouped into 17 eruptive groups (Ak1–Ak17), each of which consists of a single or a sequential phase. In order to investigate the processes of caldera formation, we focus on the younger eruptive groups (Ak1–Ak7: 0.8 to 0.2 Ma) that have relatively large magnitudes (>10 km3) and likely control the present caldera shape. We performed component analysis of lithic fragments from pyroclastic fallout deposits, whole-rock trace element analysis of juveniles, and gravitational survey of the caldera. We grouped Ak1–Ak7 into three types, namely, type A (Ak1, Ak2), type B (Ak3–Ak5), and type C (Ak6, Ak7), based on the lithic componentry, most of which are accessary and accidental fragments from vent and conduit areas. The characteristic lithic component in each type is as follows: altered rock in type A, aphyric dacite in type B, and pyroxene andesite in type C. These data suggest that explosive eruptions of each type are derived from distinct sources. The whole-rock composition of juvenile materials of each type also shows distinct trends on Harker diagrams. These three chemical trends are nearly parallel, suggesting that three different magma systems were active. This is consistent with the lithic componentry showing three spatially distinct vent sources. The geological and petrological evidence is supported by a Bouguer anomaly map. Akan caldera is characterized by three circular closed minima, indicative of three depressed segments that correspond to the source regions, each of which possibly discharged the three types of magma. Caldera-forming eruptions of Akan caldera occurred from at least three distinct sources with distinct magma systems. In conclusion, Akan caldera is a composite caldera, and its shape reflects the distribution of multiple source regions. The case study of Akan caldera shows a possible time-space evolutionary pathway for a caldera complex where several smaller calderas are nested.

Crust–mantle interaction recorded by Early Cretaceous volcanic rocks within the southern margin of the North China Craton

This study presents new geochronological and geochemical data for Early Cretaceous volcanic rocks in the southern margin of the North China Craton (NCC), to discuss the crust–mantle interaction. The studied rocks include pyroxene andesites from Daying Formation, hornblende andesites and andesites from Jiudian Formation, and rhyolites from a hitherto unnamed Formation. These rocks formed in Early Cretaceous (138–120 Ma), with enrichment in light rare earth elements (REE), depletion in heavy REE and arc-like trace elements characteristics. Pyroxene andesites show low SiO2 contents and enriched Sr–Nd–Pb–Hf isotopic compositions, with orthopyroxene phenocryst and Paleoproterozoic (2320–1829 Ma) inherited zircons, suggesting that they originated from lithospheric mantle after metasomatism with NCC lower crustal materials. Hornblende andesites have low SiO2 contents and high Mg# (Mg# = 100 Mg/(Mg + Fe2+)) values, indicating a lithospheric-mantle origin. Considering the distinct whole-rock Sr isotopic compositions we divide them into two groups. Among them, the low (87Sr/86Sr)i andesites possess amount inherited Neoarchean to Neoproterozoic (2548–845 Ma) zircons, indicating the origin of lithospheric mantle with addition of Yangtze Craton (YC) and NCC materials. In comparison, the high (87Sr/86Sr)i andesites, with abundant Neoarchean–Paleozoic inherited zircons (3499–261 Ma), are formed by partial melting of lithospheric mantle with incorporation of NCC supracrustal rocks and YC materials. Rhyolites have extremely high SiO2 (77.63–82.52 wt.%) and low total Fe2O3, Cr, Ni contents and Mg# values, combined with ancient inherited zircon ages (2316 and 2251 Ma), suggesting an origin of NCC lower continental crust. Considering the presence of resorption texture of quartz phenocryst, we propose a petrogenetic model of ‘crystal mushes’ for rhyolites prior to their eruption. These constraints record the intense crust–mantle interaction in the southern margin of the NCC. Given the regional data and spatial distribution of Early Cretaceous rocks within NCC, we believe that the formation of these rocks is related to the contemporaneous far-field effect of the Paleo-Pacific Plate.

Pore structure evolution in andesite rocks induced by freeze–thaw cycles examined by non-destructive methods

In this paper, we compare the values of petrophysical properties before and after 100 freeze–thaw (F–T) cycles, as well as recorded length change behaviour and temperature development on a vacuum-saturated fractured andesite rock sample taken from the Babina Quarry in Slovakia using a specially-constructed thermodilatometer, VLAP 04, equipped with two HIRT-LVDT sensors. We also used non-destructive visualization of the rock pore network by µCT imaging in order to study the development of the pore structure and fracture network in pyroxene andesites during the freeze–thaw process. The results show that the andesite rock samples, due to good fabric cohesion, low porosity, and low pore interconnection, showed good resistance against frost-induced damage. However, it must be stated that the main process causing disintegration of this type of rock is fracture opening, which is caused by internal stresses induced by water–ice phase transition. The overall residual strain recorded after 100 F–T cycles was not significant, however, the increase of 31 pp in volume of the fracture showed us that repeated freezing and thawing can lead to long term deterioration in terms of subcritical crack growth in brittle-elastic solids like pyroxene-andesite rocks.

Mineralogy, chronology and formation process of the epithermal gold–silver vein deposits in the historical Togi mine, Noto Peninsula, Japan

AbstractTo determine local deposit features in the vein‐type gold–silver ore deposit of the historical Togi mine, Noto Peninsula, central Japan, we investigated the occurrence and chemical compositions of ore minerals, especially silver‐ and/or gold‐bearing minerals, and wall‐rock alteration in the Togo No. 3 tunnel, a major tunnel of the Urukami mining area of the Togi mine. In the tunnel, the stockwork veins which are generally 0.1–1.5 m wide runs in Neogene pyroxene andesite. In the ore‐bearing quartz vein, in addition to the sulfides such as sphalerite, pyrite and chalcopyrite, the following Au and/or Ag ore minerals were identified: electrum with <49.3 mol% Ag, uytenbogaardtite, fischesserite, silver‐rich minerals of the Ag2S–Ag2Se solid solution series, and Se‐rich pearceite. Gangue minerals in the quartz veins are quartz and adularia. The wall rock is silicified, chloritized, and sericitized pyroxene andesite. Multiple generations of adularia grown on quartz suggest that adularia has grown by repeatedly passing the hydrothermal solution through the vein. Based on the characteristic occurrence of the Ag and/or silver‐rich ore minerals such as electrum, fischesserite, and Se‐rich pearceite and a gangue mineral, adularia, and on the wall‐rock alteration characterized by chlorite, sericite, and calcite, the Togi deposit is classified as a Se‐type and low‐sulfidation epithermal gold vein deposit. The K‐Ar ages of illite/smectite mixed‐layer minerals from the altered outcrop and plagioclase from a fresh andesite sample are 17.68 ± 0.41 and 17.52 ± 0.43 Ma, respectively, in agreement with published data of the Besshodake andesite. These results indicate that the hydrothermal fluids generated by the Miocene andesitic magma activity infiltrated the fissures relating to the formation of the Togi‐gawa Nangan Fault at the northern boundary of the Togi mining area, and Au and/or Ag‐rich ore minerals were formed from the hydrothermal fluid with decreasing temperature at the shallow level.

Limestone Facies Change of Jonggrangan To Sentolo Formation in The Western Part of Yogyakarta-Central Java Basin

The research location is in the western of Yogyakarta-Central Java Basin, where limestone of Jonggrangan and Sentolo Formation are found with the same age but have different depositional facies characteristics. These differences will be interesting to study the historical process of its formation. The research was conducted through a series of methods. Starting from geological mapping to determine the order of rock stratigraphy, the depiction of outcrop profiles, and limestone sampling for petrographic analysis. Eventually, the depositional environment of the two rock formations was discovered. Field observation results and laboratory analysis were further integrated to determine the rock facies that make up the two formations. The rock units in the study area from old to young are the pyroxene andesite breccia unit of Upper Oligocene age and limestone. The bioclastic limestone and layered limestone units are deposited by interfingering, unconformity over the pyroxene andesite breccia unit. The Middle Miocene bioclastic limestone unit is equivalent to Jonggrangan Formation in the inner shelf environment (Restricted Lagoon and Open Lagoon facies environment). Whereas layered limestone of Middle Miocene age is equivalent to the Sentolo Formation in the lower slope environment (Restricted Lagoon, Open Lagoon, and Open Sea Shelf) facies.

Fluorapophyllite-(NH4), NH4Ca4(Si8O20)F⋅8H2O, a new member of the apophyllite group from the Vechec quarry, eastern Slovakia

AbstractThe new mineral fluorapophyllite-(NH4), ideally NH4Ca4(Si8O20)F⋅8H2O, was found at the Vechec andesite quarry located near Vechec village, Vranov nad Topľou Co., Prešov Region, Slovak Republic. It occurs in cavities of quartz–illite–saponite–tobelite xenolith embedded in pyroxene andesite. Fluorapophyllite-(NH4) is associated with calcite, tridymite, pyrite, chabazite-Ca and heulandite-Ca. It forms clusters, aggregates or crystalline crusts consisting of individual, well-developed crystals up to 4 mm in size, exhibiting the forms {110}, {101} and {001}. The mineral is colourless to light pink and translucent with white streak and vitreous to pearly lustre; it is non-fluorescent under ultraviolet radiation. The Mohs hardness is ~4½ to 5, tenacity is brittle, fracture is irregular, and there is perfect cleavage on {001}. The calculated density is 2.325 g cm–3. Fluorapophyllite-(NH4) is optically uniaxial (+) with ω = 1.5414(5) and ɛ = 1.5393(8) (λ = 589 nm). It is non-pleochroic. The empirical formula (based on 29 O + F apfu) is [(NH4)0.55K0.32Na0.07Ca0.06]Σ1.00(Ca4.01Mg0.02)Σ4.03Si7.97O20[F0.84(OH)0.16]Σ1.00⋅8H2O. Fluorapophyllite-(NH4) is tetragonal, space groupP4/mnc,a= 8.99336(9) Å,c= 15.7910(3) Å,V= 1277.18(3) Å3andZ= 2. The seven strongest X-ray powder diffraction lines are [dobsin Å,(I,%)(hkl)]: 7.897(32)(002), 7.812(13)(101), 4.547(14)(103), 3.946(100)(004), 2.985(39)(105), 2.4841(11)(215) and 1.5788(12)(00.10). The crystal structure of fluorapophyllite-(NH4), refined toR1= 0.0299 for 743 unique (I> 3σI) observed reflections, confirmed that the atomic arrangement is very similar to that of the other members of the apophyllite group. The new mineral is named according to the current nomenclature scheme for apophyllite-group minerals and is an NH4dominant analogue of fluorapophyllite-(K), fluorapophyllite-(Na) and fluorapophyllite-(Cs).

Terrain genetic unit for spring-based regional development in mountains in Indonesia

This research was carried out in the Mount Mandalawangi region of West Java Province. The research objective is to explore the potential sources of springs in supporting the development of the region so as to encourage the economic potential of the community. The methodology used was geological mapping, spatial mapping, mapping of socio-economic conditions, mapping of water demand levels, which were evaluated using the Terrain Genetic Unit method. The area around Mount Mandalawangi is a relatively fertile area has ±36 points of springs, the discharge ranges from 0.00003 m3/sec-0.587 ltr/sec. The dominant lithology is the Mandalawangi (Qmm) Mountain consisting of glass tuffs containing pumice, and lava composed of pyroxene andesite to basalt. The results of the study using the Terrain Genetics Unit method there are 3 zones that have the potential to develop springs based on the region, Andesite Plateau, Corrugated Hills of Lapili Volcano and Corrugated Hills of Tuff Breccia Interference. The analysis is that regional development can be planned to the maximum by prioritizing the source of spring with a note that there needs to be an arrangement for the source of existing springs.

The Geology and Lamongan Volcanic Rocks Case Study at Ranu Pakis, Klakah, Lumajang, East Java Province, Indonesia

Lamongan volcano is one of the unique volcanoes in the Sunda Volcano. This volcano has side eruption centers or on the slopes of the volcano. The morphology of parasitic eruptions in this volcanoes complex includes maars and boccas. There are about 64 parasitic eruption centers consisting of 37 volcanic cones (bocca) and 27 ranu (maar).
 The purpose of this research is to study the characteristics of lithology and petrogenesis of this volcano complex, especially in Ranu Pakis and surrounding areas. The analytical method used is to do geological mapping and petrographic analysis.
 The lithology found in this research area consists of magmatic and phreatomagmatic eruption deposits. Genetically this lithology includes pyroclastic flow, pyroclastic fall (scoria fall and phreatomagmatic scoria fall/accretionary lapili), tuff (phreatic) and basaltic lava. In some pyroclastic deposits, especially in maar there are fragments of accretionary lapilli, while in bocca there are basaltic lavas. Other fragments present in pyroclastic deposits are basalt scoria blocks and bombs embedded in the groundmass of volcanic ash. The results of petrographic analysis indicate that the volcanic rocks in the study area are calc alkaline affinity consisting of pyroxene andesite, basalt and pyroxene basalt lava. The pyroxene basalt lava is composed by plagioclase, clinopyroxene and little olivine embedded in the volcanic glass. Lavas are structured scoria and textured porphyritic, intersertal, trachytic, aphyric and pilotaxitic. Trachytic texture is found in the basalt fragments of pyroxene from the pyroclastic fall deposits in Ranu Pakis and Ranu Wurung. While pyroxene andesite lavas composed by plagioclase, clinopyroxene embedded in the volcanic glass. Lavas are structured scoria and textured porphyritic, intergranular, pilotaxitic and aphyric.

Geochronological and geochemical feature of the Cenozoic adakites in Hoh Xil, Tibetan Plateau

The volcanic rocks in the Tibetan Plateau have undergone complex evolution, as the collision between the Indian and Eurasian Plates proceeds. The volcanic rock samples collected from a volcanic edifice in the Hoh Xil, Tibetan Plateau, are studied in this paper. The geochemistry and zircon U-Pb chronology of the volcanic rock samples are determined. Our results indicate that the volcanic rocks in this area are mostly alkali-rich intermediate-acidic ones, and consist of quartz trachyandesite, andesite, pyroxene andesite, and andesitic tuff. Geochemically, these rocks feature high light rare earth elements and large-ion lithophile elements concentration, with low Nb, Ta, and Ti concentration, and significant Pb positive anomaly. Based on our analysis, we conclude that the volcanic rocks are adakites. The eruption ages of the volcanic rocks in this area are determined for the first time in the literature: 45.23 ± 0.35 Ma for the hornblende trachyandesite; 41.36 ± 0.45 Ma for the biotite trachyandesite; and 42.97 ± 0.23 Ma for the biotite-quartz trachyandesite. This suggests that the volcanic rocks studied in this paper were formed in the Lutetian (Eocene). It is further concluded that the volcanic rocks originated from a mantle provenance that have assimilated large amount of crustal materials. The formation of the volcanic rocks is attributable to the breakoff of oceanic lithospheric slab.

Genesis of the Meishan iron oxide–apatite deposit in the Ningwu Basin, eastern China: Constraints from apatite chemistry

The Meishan iron oxide–apatite deposit is located in the Ningwu volcanic basin in eastern China. The deposit comprises massive and brecciated ores in the main orebody, located at the contact between a gabbro–diorite porphyry and biotite–pyroxene andesites, and sub‐economic stockwork and disseminated ores. Among the four stages of alteration and mineralization, apatite coexists with magnetite, andradite, and quartz in massive magnetite ore and occurs in disseminated magnetite ore, coexisting with magnetite, siderite (after diopside), and quartz for Stage 2 iron mineralization. Apatite is also present in the altered gabbro–diorite porphyry. The apatites from the massive and disseminated magnetite–apatite ores are fluor‐ and hydroxyl‐ variety. Those from the altered gabbro–diorite porphyry show extensive solid solution between the hydroxyl‐apatite, fluor‐apatite, and chlor‐apatite end members. The apatites at Meishan record oxidized states during formation of the mineral deposit. The SO3 contents of apatite in the Meishan deposit mostly vary from 0.4 to 1.2 wt%, with the highest value of 4.97 wt%. MnO contents in apatites from our study are less than 0.17 wt%, and most values are below detection limit, indicating that the apatite formed in a high ƒO2 magmatic–hydrothermal fluid. The strong Eu depletion in apatites at Meishan resulted from the fractionation of plagioclase. The gabbro–diorite porphyry, magnetite, and apatite show similar LREE‐enriched patterns with significant negative Eu anomalies for apatite and magnetite, and no Eu anomaly for the gabbro–diorite porphyry. The gabbro–diorite porphyry and Stage 2 apatite associated with iron mineralization have also similar primitive mantle‐normalized trace element patterns, suggesting that the mineralization was related to gabbro–diorite porphyry. The REE pattern with significant negative Eu anomalies in apatite from the Meishan deposit is comparable with that of other Kiruna‐type deposits elsewhere in the world.

Structure of the shallow magma chamber of the active volcano Mt. Zao, NE Japan: Implications for its eruptive time scales

Zao volcano is one of the representative active stratovolcanoes in northeast Japan, having many historical eruption records, as the last one occurred in 1940. Since 2013 to present, precursory phenomena, such as volcanic tremors and deformation of the summit area, have been detected in this volcano; thus, it is urgently necessary to thoroughly characterize the magma feeding system beneath the volcano. Our aim is to understand the magma chamber structure and dynamics associated with the recent activity (ca. ~2 ka) of Zao volcano in NE Japan. We conducted petrological and geochemical studies in the representative pyroclastic products and youngest lavas of its recent activity. The products are divided into the GSN (Goshikidake-nanbu) pyroclastics, GST (Goshikidake-tobu) pyroclastics and GS lavas (Furikodaki lava and Goshikidake-nanpo lava and associated pyroclastic deposits).The rock samples are calc-alkaline olivine-bearing pyroxene andesites originated as the result of mixing between felsic (containing Mg-poor pyroxenes + anorthite (An)-poor plagioclases) and mafic (containing forsterite (Fo)-rich olivines + An-rich plagioclases magmas). Thermodynamic modelling indicates that the temperature (T)–pressure (P)–water activity (H2O) conditions of the felsic (ca. 60–61 wt% SiO2, 968–1000 °C, 1.6–2.0 kbar and 1.8–2.2 wt% H2O) and the mafic (ca. 48.0–50.5 wt% SiO2, 1113–1170 °C, <2.4 kbar and 1.0–2.2 wt% H2O) end–members are similar between the GSN, GST pyroclastics and GS lavas.Compositional zoning of orthopyroxene phenocrysts suggests the formation of two mixed magmas, namely the main mixed and the Mg-rich mixed ones. The mafic magma from a deeper source entered repeatedly into a shallower felsic magma chamber. As a result, the main mixed magma developed within the chamber. The Mg-rich-mixed magma tentatively developed by the injection and simultaneous mixing of both the main mixed magma and the injected mafic one, merging later on into the main mixed magma.The Fe-Mg diffusion modelling on orthopyroxenes reveal that the injections occurred from <60 days to 1.7 years for thin-darker-zone types, and multiple injections of mafic magma occurred from 2.5 years to 150 years for broad-darker-zone types until the eruptions. The thin-darker-zone type orthopyroxene phenocrysts are abundant in the GSN and GST pyroclastics but rare in the GS lavas. Instead, the broad-darker-zone type orthopyroxenes are rare in the GSN and GST pyroclastics and abundant in the GS lavas. Thus, the main mixed layer was more evolved for the GS lavas than for the GSN and GST pyroclastics. The injected mafic magmas for the GS lavas were merged more extensively than the GSN and GST pyroclastics, resulting in a larger release of volatile components that triggered the effusive episodes. Given that local precursory phenomena have been currently detected in Zao volcano, we are confident that any research to thoroughly characterize the magma feeding system under this active volcano is essential for society to better react to any potential volcanic hazard in the near future.

The magma evolution sequence and geodynamic setting in the Qibaoshan ore area, Wulian County, Shandong Province, China

The Qibaoshan ore area is located in Wulian town, Shandong Province, which is an important polymetallic metallogenic zone containing gold, copper, lead, and zinc. The polymetallic mineralization is mostly related to the Qibaoshan complex. The Qibaoshan complex is composed mainly of pyroxene diorite, andesitic porphyrite, pyroxene andesite porphyrite, amphibole andesite porphyrite, diorite porphyrite, and granodiorite porphyry, among which granodiorite–porphyry is the main wall rock of gold and copper ore body, whereas lead and zinc mineralization is closely related to diorite porphyrite. A combined study of laser ablation–inductively coupled plasma–mass spectrometry zircon U–Pb dating and geochemical analyses (major and trace elements) for 5 Mesozoic plutons from the Qibaoshan complex was carried out to determine their ages, petrogenesis, and tectonic setting. The U–Pb zircon ages measured by laser ablation–inductively coupled plasma–mass spectrometry indicate that the Qibaoshan complex was emplaced in 3 stages, represented by the ~175 Ma pyroxene diorite, ~129 Ma andesitic porphyrite/ porphyrite, ~125 Ma granodiorite‐porphyry, and ~112 Ma diorite porphyrite. Systematic diagenetic chronology and rock geochemistry show that formation of ~175 Ma pyroxene diorite in Qibaoshan ore‐concentrated area is possibly related to the transformation environment from compression to extension of the Sulu orogenic belt and/or of the subduction of the Pacific Plate, whereas the formation of the Early Cretaceous subvolcanic rock has a volcanic arc affinity related to subduction of the Pacific Plate. Based on the previous studies, this paper argues that the metallogenic age of Qibaoshan polymetallic ore‐concentrated area is 125–105 Ma, which is formed in the volcanic arc dynamics environment of the Pacific Plate subduction in the Late Yanshanian. In addition, a small amount of 610–799 Ma and 1.8 Ga was developed in the samples of the pyroxene diorite and andesitic porphyrite, suggesting their source may have great affinities with South China.

The Discovery of Young Dacite Lava in Akusekijima Island, Tokara Islands, Japan

A hitherto unreported dacite lava was found on Akusekijima Island, Tokara Islands, Japan. The lava, named Omune Lava, is 100 m thick. K-Ar dating of the lava by the sensitivity method considering mass fractionation of initially trapped atmospheric argon, shows it to be less than 0.08 Ma. The surface of the lava is much less dissected than surrounding areas, and is not covered by any tephra layer. It suggests an eruption even as recent as the Holocene. The range of SiO 2 wt.% of andesites (two pyroxene andesites) is between 56 and 63%. On the other hand, Omune Lava (hornblende dacite) contains 68-69% SiO 2 . Two trends are recognized with only a small difference among Akusekijima rocks. Our results show that dacite magma, instead of andesitic magma, concerned the latest volcanic activity in Akusekijima Island.

B40 島原半島地域の第四紀火山活動発達史 : 玄武岩・輝石安山岩質単成火山群から雲仙火山へ

B40 島原半島地域の第四紀火山活動発達史 : 玄武岩・輝石安山岩質単成火山群から雲仙火山へ