Identification of the source caldera for the Middle Miocene ash-flow tuffs in the Kii Peninsula based on apatite trace-element composition

A large caldera cluster consisting of at least four calderas (Omine, Odai, Kumano-North and Kumano calderas) existed in the central–southern part of the Kii Peninsula approximately 14–15 Ma. On the other hand, thick Middle Miocene ash-flow tuffs, referred to as the Muro Ash-flow Tuff and the Sekibutsu Tuff Member, are distributed in the northern part of the Kii Peninsula. Although these tuffs are considered to have erupted from the caldera cluster in the central-southern Kii Peninsula, identifying the source caldera in the cluster has been controversial because of similarities in the petrological characteristics and identical radiometric ages of the volcaniclastic rocks of these calderas. We successfully discriminated the characteristics of the eruptive products of each caldera in the caldera cluster based on the apatite trace-element compositions of the pyroclastic dikes and ash-flow tuffs of the calderas. We also demonstrated that the source caldera of at least the lower main part of the Muro Ash-flow Tuff and the Sekibutsu Tuff Member was the Odai Caldera, which is located in the central Kii Peninsula. Our findings show possible correlations among the pyroclastic conduits and ash-flow tuffs of the caldera-fill and/or outflow deposits, even in cases where they have been densely welded and diagenetically altered. This method is useful for the study of deeply eroded ancient calderas.     

Methodological studies on luminescence dating of volcanic ashes

We report here the results of a feasibility study of luminescence dating of polymineralic volcanic ash. Of the several possible protocols that used different emission bands and different IR stimulation regimes, the post infrared-infrared stimulated luminescence (pIR-IRSL) signal (detected using a violet-blue emission window with stimulation temperature in the region 260–320 °C) provided the most stable signal. This involved, i) identification of the most suitable temperature for pIR-IRSL read out, ii) determination of alpha efficiency and, iii) estimation of anomalous (athermal) fading rate. Anomalous fading rate (g-value in %/decade) of pIR-IRSL signal at 300 °C was 0.0–1.6%/decade and it ranged from 2.4 to 5.2%/decade for IRSL at 50 °C, both preheated to 320 °C. Thus, though more stable, pIR-IRSL signals may fade in nature, and even during laboratory extended irradiation. Of the models for fading correction by Huntley and Lamothe (2001) and Kars et al. (2008), the Kars et al. (2008) model performed better as the natural luminescence intensity was closer to the onset of saturation in the luminescence dose response curve. Our measurements suggest that alpha efficiencies of the pIR-IRSL signals are higher than that of IRSL. Fading corrected pIR-IRSL single aliquot regeneration (SAR) protocol based ages on three of the five volcanic ash beds are in agreement with the expected ages of ∼74 ka, based on geochemical association of the present samples to be the Youngest Toba Tuff (YTT). Other ash samples that gave ages of <24 ka and <37 ka, were inferred to have been in their secondary context, reworked from their original depositional sites. The onset of saturation dose of the pIR-IRSL signal (D₀) was ∼330 Gy and this implied a maximum measurable equivalent dose of 660 Gy. The minimum detectable dose was ∼5 Gy. These dose limits correspond to a typical age range of 1–150 ka using the pIR-IRSL signal for volcanic ashes.     

四川绿豆岩提取钾肥及其综合利用新工艺试验研究

绿豆岩是一种富钾火山凝灰岩，因含有硅质豆粒，颜色鲜艳成绿色，故俗称绿豆岩。绿豆岩按后生变化结果可分力富钾凝灰岩（脱玻后的玻屑凝灰岩）和绿鳞石粘土岩。绿鳞石粘土岩经酸浸分解，析出非晶态二氧化硅，游离出钾、镁、铝等离子，按化工工艺流程生产出硫酸铵钾（俗称钾氮肥）、七水硫酸镁、氢氧化铝等产品。     

新疆苏普特背斜花岗岩和变安山质凝灰岩LA-ICP-MS锆石U-Pb年代学特征及意义

阿尔泰南缘古生代康布铁堡组火山岩系是许多铁矿、铜锌矿以及铅锌矿的赋矿围岩,但该赋矿地层目前还缺乏精确的同位素年代学资料。通过对变安山质凝灰岩和花岗岩LA-ICP-MS锆石U-Pb定年,获得阿尔泰南缘苏普特背斜花岗岩的年龄为412.7±0.78 Ma,安山质凝灰岩的年龄为411.2±3.4 Ma,表明阿尔泰南缘苏普特背斜内泥盆纪早期存在着强烈的火山活动,与区内广泛发育的火山岩属于同一事件的产物,具有相同的动力学背景。为研究阿尔泰南缘古生代构造演化及苏普特背斜异常区提供了重要的理论依据。     

Physical-chemical and electrochemical characterization of Fe-exchanged natural zeolite applied for obtaining of hydrogen peroxide amperometric sensors

This work demonstrates that a Fe-exchanged zeolitic volcanic tuff from Cepari (Fe/CV) (Bistrita-Nasaud County, Romania) is suitable for the amperometric detection of H₂O₂, using new modified carbon paste electrodes based on this material (Fe/CV-CPEs). The physical-chemical characterization of natural (CV) and modified (Fe/CV) forms was realized using chemical analysis, optical microscopy, scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), energy dispersive X-ray spectroscopy (EDX) and Fourier transformed infrared (FTIR) spectroscopy. The resulting electrodes (Fe/CV-CPEs) were investigated using cyclic voltammetry and chronoamperometry measurements. The new electrodes showed good electrocatalytic activity toward H₂O₂ reduction. The calibration curve for H₂O₂ determination was linear up to 0.1 mM, with a detection limit (signal to noise ratio of 3) of 20 μM.     

中国东部中新生代火山—碎屑—凝灰岩储层研究综述

主要论述了中国东剖中新生代火山储层的发育状况及赋方式，对这些储层进行了区域对比，讨论了火山岩储层的发育规律，并在此基础上详细了讨论了火山岩储层的研究状况，，包括火山岩储层的孔隙研究，相带研究及其与油气关系。     

扬子北缘元古宇马槽园群时代归属新证据 ——对地层对比和古地理格局的启示

马槽园群是华南前寒武纪地层中的重要单元,其沉积特征及时代归属对建立和完善扬子北缘地层格架、认识和恢复当时的古地理格局有重要意义.通常认为,扬子北缘马槽园群(下部八里垭组,上部火烧尖组)是一套角度不整合于中元古界神农架群之上的新元古代磨拉石建造.取自该群下部八里垭组上部的同沉积凝灰岩样品的高精度离子探针(SHRIMP)锆石U-Pb年龄为(1165±14)Ma.该年龄数据表明,马槽园群沉积地层的形成时代应为中元古代,而不是新元古代.野外调查与沉积相分析表明,马槽园群沉积地层中滑塌包卷、正粒序等重力流沉积构造发育,主体为一套斜坡相碳酸盐岩重力流沉积,而非磨拉石建造.结合前人研究结果认为,马槽园群无论是在沉积特征还是时代归属上都不能与华南新元古代裂谷系地层进行对比,而应该属于裂谷系之下的基底地层.     

辽西义县组基性、中基性火山岩内沉凝灰岩层的发现及其意义

义县组岩性以基性、中基性火山岩、火山碎屑岩为主，局部发育有富含“热河生物群”化石的沉积层。在这些沉积层之下、义县组复成分底砾岩之上，发现有 4个沉凝灰岩层，与基性、中基性火山岩呈互层状产出，其岩性以沉凝灰岩或含砾凝灰质粉砂岩为主。这些凝灰岩层厚度虽小，但分布较广泛，走向延伸稳定。根据辽西地区中生代火山岩活动的基本规律，沉凝灰岩层与基性、中基性火山岩的空间展布特征及野外地质综合研究将义县组早期火山活动划分出 5个火山作用旋回，并确认四合屯、黄半吉沟、尖山沟、以及上园、大康堡、河夹心等地富含“热河生物群”化石的沉积层均属于同一火山旋回（第五旋回）的产物。这一发现极大地丰富了辽西地区中生代陆相盆地火山—沉积作用的研究内容，并将促进火山活动与生物灭绝事件方面的研究工作。     

Growth and evolution of an emergent tuff cone: Considerations from structural geology, geomorphology and facies analysis of São Roque volcano, São Miguel (Azores)

The syn-eruptive and post-eruptive history of São Roque tuff cone, its geological setting and volcanological features were studied in detail to understand the role played by the different factors that contributed to the morphological evolution of this relatively simple and small volcanic edifice.In addition, attention was also focused on the series of natural changes that affected the tuff cone during the course of the years and that finally led to its structural disassembly. A novel model is proposed to explain this process.The São Roque volcanic centre, located on the island of São Miguel (Azores), consists of two well-consolidated bodies and numerous small islets that formed more than 4700 years ago during the hydromagmatic activity that took place along an intruding dyke, whose NNW–SSE trend is in agreement with the regional tectonic pattern. The eruptive vents probably migrated progressively from SSE to NNW, forming small edifices through the rapid accumulation of sediments during alternating phases of “dry” and “wet” magmatic emissions. Syn-eruptive partial collapses greatly modified the original morphological structure of these edifices, probably allowing sea water to continuously flow into the vents. The complex interaction of these factors controlled the depth of magma fragmentation, producing different types of deposits, in which the ash-lapilli ratio varies considerably. The high-water saturation degree of these deposits caused syn-eruptive and post-eruptive remobilization which resulted in collapses and some small-scale landslides.Post-eruptive, WNW–ESE trending transtensional and extensional tectonic activities operated during the initial dissection of the cone, generating instability. Furthermore, the rapid accumulation of “wet” tephra, and its following consolidation, caused selective collapses that favoured the fragmentation of the deposit and caused the formation of numerous islets separated by radially-arranged channels. Collapses also involved the lava units emplaced in more recent times around the tuff cone, which show that brittle deformation has been significant in the area for a prolonged period.