东昆仑早石炭世火山岩的地球化学特征及其构造背景

东昆仑早石炭世火山岩主要沿昆中缝合带及其旁侧分布,岩性以玄武岩为主,之后亦有安山岩和英安岩产出,先后形成于洋脊、洋岛和岛弧构造环境。洋脊玄武岩Ｋ２Ｏ、Ｐ２Ｏ５、ＳｉＯ２、ＲＥＥ含量和ＦｅＯ／ＭｇＯ比值低,钙、铁、镁高,轻重稀土元素分馏差。岛弧玄武岩硅、碱、铝和ＲＥＥ含量以及ＬＲＥＥ／ＨＲＥＥ比值高,镁、铁质低。洋岛玄武岩ＴｉＯ２和Ｐ２Ｏ５高,Ｋ２Ｏ低,ＲＥＥ和ＬＲＥＥ／ＨＲＥＥ介于前二者之间。火山岩的构造背景表明,早石炭世昆中断裂带以“开”为主,形成洋脊玄武岩和洋岛玄武岩;早石炭世末转为“合”,形成岛弧型玄武岩、安山岩和英安岩。洋脊玄武岩的识别,对于研究区域构造及其演化甚为重要。     

The Extraordinary Rainfall over the Eastern Periphery of the Tibetan Plateau in August 2020※

A large amount of accumulated precipitation was recorded over the Eastern Periphery of the Tibetan Plateau (EPTP) in August 2020. Using hourly rain gauge records and the ERA5 reanalysis dataset, we analyzed the unique characteristics of rainfall in August and the accompanying circulation conditions and conducted a comparison with previous data. This record-breaking amount of accumulated rainfall was centered on the northern slope of the EPTP. This location was in contrast with the historical records of the concentration of rainfall over the middle and southern slopes. The hourly rainfall in August 2020 was both more frequent and more intense than the climatological mean rainfall. An amplification effect of the topography was observed, with the precipitation over the EPTP showing a more significant change with terrain height in August 2020. A circulation analysis showed that cold (warm) anomalies existed over the north (south) of approximately 35°N compared with those in the years when the southern EPTP received more rain. The western Pacific subtropical high was more intense and extended to the west, and the low-level cold air from the north was more active. The enhanced low-level southerly winds on the periphery of the subtropical high injected warm, moist air further north than the climatological mean. These winds became easterly near the northern EPTP and were forced to ascend by the steep terrain.     

Duration of Eo-Alpine metamorphic events obtained from multicomponent diffusion modeling of garnet: a case study from the Eastern Alps

Rocks from the Micaschist–Marble Complex of the Wölz Tauern, which are part of the middle Austroalpine unit, contain large (up to 2 cm) garnet crystals that show clear evidence of multistage growth. Isotopic dating indicates that a Variscan (～270 Ma) garnet core was overgrown by new garnet formed during Eo-Alpine metamorphism at Cretaceous times. P-T paths for the Eo-Alpine metamorphism were obtained using the method of pseudosections (Powell and Holland in Metam Geol 16:309–343, 1998) and are consistent with earlier results from independent thermobarometry. Due to the large size of the garnets, growth zoning was preserved during amphibolite facies metamorphism at both Variscan and Alpine times. Full multicomponent diffusion modeling of compositional zoning at the interface of the Alpine and Pre-Alpine garnets in conjunction with the retrieved P-T paths allow average subduction/exhumation as well as heating/cooling rates to be retrieved. The modeling suggests that a minimum subduction/exhumation rate of ～4 cm/a and heating/cooling rates on the order of 100–260°C/Ma for a 60°C subduction angle are required to preserve the observed compositional zoning overall while modifying the zoning at the interface between two garnets to the extent observed. Such rapid rates of burial/exhumation are consistent with the results of direct GPS measurements of convergence rates at several orogenic belts as well as with inferred rates from modeling in the Alps and other areas. In combination, this indicates that such rapid rates are commonplace during metamorphism in collisional orogens and places important constraints on the rheological behavior of crustal blocks in such orogens.     

奥地利东阿尔卑斯山地区杂砂岩带中赋存于碳酸盐岩中的晶质菱镁矿床

奥地利东阿尔卑斯山地区Austroalpine杂砂岩带中的石炭纪Veitsch逆冲推覆体是"Veitsch型"晶质菱镁矿化的典型地区。几十年来,对其成因的解释一直是人们争论的焦点。为了解决这一长久以来的问题,本文对Veitsch推覆体的地质学、矿物学和地球化学制约条件进行了论述。菱镁矿仅仅存在于Veitsch推覆体之中,而其它推覆体中的碳酸盐岩岩层中则无菱镁矿。赋存于Veitsch推覆体中的碳酸盐岩石中的菱镁矿以不规则的岩株状、透镜状和层状产出。块状和厚层状的菱镁矿总是被白云岩包裹。在Veitsch推覆体中,沉积作用开始于晚维宪期的后造山的类磨拉石海相建造,并晚于内部基底带的变形和变质作用("Bretonic期")形成,该基底带位于现代的东阿尔卑斯山地区。沉积序列研究表明,演化从浅海大陆架开始,有时还穿插有高盐度的泻湖和透镜状生物礁,发展到海退的海岸线伴随有发育强烈的三角洲沉积的分支海湾和河流。由于成矿作用有好几个期次,所以对地球化学数据的解释相当复杂。 在Hohentauern／Sunk矿床中,石膏和硬石膏层在菱镁矿质沉积主岩中互层,其δ34S值分别为 17.6±0.2‰和 17.2±0.2‰,表现出石炭纪海水的特征。白云岩和菱镁矿的REE浓度要高于石灰质主岩。在Hohentauern／Sunk矿床中,球形白云岩中的白云岩球体和白云质基质     

Alkaline intrusion in a granulite ensemble in the eastern ghats belt,India: Shear zone pathway and a pull-apart structure

The alkaline complex of Koraput, Orissa, India, is one of several bodies in the high-grade Eastern Ghats belt, but this one is an integral part of the high-grade belt and remote from the western boundary against the Bastar craton. The Koraput complex forms a lozenge-shaped intrusion into the metapelitic granulites and is bounded by shear zones. The combined effect of movement along these shear zones, is a northeasterly elongated sygmoidal cavity with maximum width along the northwesterly trending Reidel shear. Thus the Koraput alkaline complex can be considered to have been emplaced in a pull-apart structure, developed in the granulitic country rocks. Moreover, in view of the fact that the western margin of the high-grade Eastern Ghats belt bears clear evidence of collisional features, rather than that of rifting or break-up, the rift-valley model for the alkaline magmatism in this high-grade belt appears untenable.     

Fish Biodiversity in the Vermetid Reef Of Shiqmona (Israel)

Abstract. A study of the structure of the fish community associated with a vermetid reef at Shiqmona, Israel, revealed the highest fish biodiversity (36 species) of any habitat along the Mediterranean coast of Israel. Despite the prevalence of fish of Erythrean origin in the Levantine littoral, the benthic fish community at the site is entirely autochthonous. The families richest in members were the Blenniidae and the Gobiidae. Eighteen species are benthic, sixteen supra-benthic and two pelagic.     

1981-2012年西北东部夏季降水不同强度雨日变化及其环流特征的对比分析

利用1981-2012年中国西北东部198个台站的逐日气象观测数据和ERA-Interim再分析资料,分析了近32年中国西北东部夏季不同强度降水的雨日和雨量的变化特征,并对比了产生不同强度降水的大气环流系统的异同。结果表明,西北东部夏季降水以小雨和中雨为主,二者占夏季雨日的90%以上、占夏季雨量的70%左右。小雨日数占总雨日的比率在空间上自东南向西北递增;中雨、大雨、暴雨和（特）大暴雨日数的比率自东南向西北递减。夏季小雨、中雨日数和降水量均呈减少的趋势,21世纪初的减少速率慢于20世纪80-90年代;暴雨则呈略微增多的趋势。通过对1981和2003年的个例分析发现,乌拉尔山阻塞高压、蒙古气旋和西北太平洋副热带高压增强西伸时,有利于北方干冷气流和南方暖湿气流在西北东部交汇,降水较多;反之则降水较少。在冷、暖空气均增强的背景下,若冷、暖气团的交界线偏南,西北东部主要受北方冷气团控制,南边界的水汽输送较微弱,易发生小雨;若冷、暖气团的交界线偏北,西北东部主要受到南方暖湿气团的影响,南边界的水汽输送和辐合较强,多出现强降水,降水强度取决于水汽的强度和上升运动的高度。     

U-Pb and Pb-Pb zircon dating of the older orthogneiss suite in the Silvretta nappe,eastern Alps: Cadomian magmatism in the upper Austro-Alpine realm

Two orthogneiss suites dominate the Silvretta nappe. Primary crystallization of the larger suite (younger orthogneisses) is assumed to be Ordovician in age. The second, adjacent magmatic suite consists of older, alkaline to calc-alkaline, ultrabasic, basic to intermediate and granitic rocks known as older orthogneisses. U-Pb data of multigrain zircon fractions, as well as single zircon stepwise evaporation ²⁰⁷Pb/²⁰⁶Pb results suggest a latest Proterozoic to early Cambrian intrusion age for the protoliths of the older orthogneisses as both dating methods yield early Cambrian crystallization ages of 526±7 and 519±7 Ma for an alkaline granite gneiss; similar results were obtained for two neighbouring calc-alkaline orthogneisses (²⁰⁷Pb/²⁰⁶Pb ages of 533 ± 4 and 568 ± 6 Ma, respectively). The crystal habitus corresponds to P5, S19 and S9 zircons of magmatic origin. Whole-rock initial Sr isotope ratios indicate a primitive source. The igneous protoliths of these older orthogneisses represent a fragment of a Cadomian (Pan-African) crust found in places within the basement of the European Hercynides.     

Geochemical and stratigraphic indicators of late Holocene coastal evolution in the Gythio area, southern Peloponnese, Greece

The study of past changes in sea level, and of historical and pre-historical coastal evolution, using coastal sediment stratigraphies is well-established over a range of geographic areas, in both seismic and aseismic settings. In the eastern Mediterranean, however, such studies are less common, and, notably, the use of sediment geochemistry, and its combination with lithostratigraphic studies to analyze palaeoenvironmental and palaeo-sea-level change, has not been explored to any significant extent, despite the fact that geochemical data have been successfully used elsewhere to aid in the identification of sea-level changes. Here, we use a combined geochemical, stratigraphic and microfossil approach to reconstruct late Holocene coastal evolution and sea-level change at two sites near Gythio in the southern Peloponnese, Greece. The sites show stratigraphic and geochemical evidence of the presence in Late Helladic times (ca. 1500 BC) of barrier-protected coastal lagoonal/wetland environments, which have gradually infilled over the last ca. 3500 yr. Archaeological remains and ceramic and charcoal-bearing horizons within the sediment sequences indicate Late Roman occupation of the area, although there is no sedimentary evidence of significant pre-Roman activity at the study sites. An apparent brackish wetland peat deposit at − 3.4 m (overlain by anoxic lagoonal clays) at Kamares (Kato Vathi) Bay shows a calibrated radiocarbon age of 1640–1440 BC, suggesting a relative sea-level rise of 0.8–1 mm/yr in this area over the past 3500 yr, in good agreement with previous archaeological and sea-level modelling studies. There is no evidence, based on the stratigraphic, microfossil or geochemical record, of sudden marine flooding events related to local or regional seismic activity, despite the presence of the area in a seismically active zone known to be subject to periodic earthquakes and tsunami. The data highlight the utility of combining geochemical and stratigraphic studies in the reconstruction of coastal evolution and the study of palaeo-sea-level changes, particularly in sequences (such as those described here) where microfossils are poorly preserved.     

Principal Modes and Related Frequencies of Sea Surface Temperature Variability in the Pacific Coast of North America

We examined monthly time-series (1950 to 1999) of sea surface temperature (SST) anomalies in 47 quadrants (2° × 2°) along the Pacific coast of North America. Correlation, clustering and principal components analyses were applied to identify the spatial structure in coastal SST. The resulting modes and the individual series were investigated using spectral analysis to identify the most significant time-scales of variability, and the propagation of the main signals was explored by computing the wavenumber-frequency spectrum of each spatial mode. Results showed that coastal SST variability in the northeast Pacific conformed to three main geographical modes. A tropical mode extends from the equator to about the entrance to the Gulf of California. This mode appears related to two low frequency components of the El Niño-Southern Oscillation of about 3 and 5 years. The SST anomaly related to these signals propagates poleward, seemingly at low speeds (≈0.08 m s^?1). A temperate (or transitional) mode, which includes the coastal areas along the California Current System, also shows the 5-year signal plus a decadal-scale component (periods between 10–17 years). Finally, a subarctic mode includes the coastal areas along the Gulf of Alaska and is dominated by the interdecadal variability that is characterized by the Pacific Decadal Oscillation.