Effects of eruption and lava drainback on the H2O contents of basaltic magmas at Kilauea Volcano

 Lava drainback has been observed during many eruptions at Kilauea Volcano: magma erupts, degasses in lava fountains, collects in surface ponds, and then drains back beneath the surface. Time series data for melt inclusions from the 1959 Kilauea Iki picrite provide important evidence concerning the effects of drainback on the H₂O contents of basaltic magmas at Kilauea. Melt inclusions in olivine from the first eruptive episode, before any drainback occurred, have an average H₂O content of 0.7±0.2 wt.%. In contrast, many inclusions from the later episodes, erupted after substantial amounts of surface degassed lava had drained back down the vent, have H₂O contents that are much lower (≥0.24 wt.% H₂O). Water contents in melt inclusions from magmas erupted at Pu'u 'O'o on the east rift zone vary from 0.39–0.51 wt.% H₂O in tephra from high fountains to 0.10–0.28 wt.% H₂O in spatter from low fountains. The low H₂O contents of many melt inclusions from Pu'u 'O'o and post-drainback episodes of Kilauea Iki reveal that prior to crystallization of the enclosing olivine host, the melts must have exsolved H₂O at pressures substantially less than those in Kilauea's summit magma reservoir. Such low-pressure H₂O exsolution probably occurred as surface degassed magma was recycled by drainback and mixing with less degassed magma at depth. Recognition of the effects of low-pressure degassing and drainback leads to an estimate of 0.7 wt.% H₂O for differentiated tholeiitic magma in Kilauea's summit magma storage reservoir. Data for MgO-rich submarine glasses (Clague et al. 1995) and melt inclusions from Kilauea Iki demonstrate that primary Kilauean tholeiitic magma has an H₂O/K₂O mass ratio of ∼1.3. At transition zone and upper mantle depths in the Hawaiian plume source, H₂O probably resides partly in a small amount of hydrous silicate melt. Received: 31 March 1997 / Accepted: 17 November 1997     

Shallow seismicity beneath Ruapehu Crater Lake: results of a 1994 seismometer deployment

 Virtually all the seismicity within Ruapehu Volcano recorded during a 2-month deployment in early 1994, with 14 broadband seismographs around the Tongariro National Park volcanoes in the North Island of New Zealand, was associated with the active vent and occurred within approximately 1 km of Ruapehu Crater Lake. High-frequency volcano-tectonic earthquakes and low-frequency events (similar to bursts of 2 Hz volcanic tremor) were both found to have sources in this region. The high-frequency events, which often consisted of a smaller precursor event followed approximately 2 s later by the main event, had sharp onsets and were locatable using standard techniques. The depth of these events ranged from the surface down to approximately 1500 m below Crater Lake. The low-frequency events did not have sharp onsets and were located by phase-correlation methods. Nearly all occurred under a small region on the east side of Crater Lake, at depths from 200 to 1000 m below the surface. This low-frequency earthquake source region, in which no high-frequency events occurred, may be the steam zone within the actual vent of Ruapehu Volcano. Received: 30 June 1996 / Accepted: 16 February 1998     

Vent distribution and its relation to regional tectonics, Cappadocian Volcanics, Turkey

The distribution of polygenetic and monogenetic volcanoes of the Neogene-Quaternary Cappadocian Volcanic Province (CVP) is analyzed to investigate the relationship between vent location and regional tectonic lineaments. Two fault systems exist in the province. One system (Miocene-Quaternary Tuzgölü–Ecemiş system) is oblique, whereas the other system (late Miocene–Pliocene CVP system) is parallel to the long axis of the CVP. The polygenetic volcanoes are aligned parallel to the second system but concentrate around the major faults of the first system. Regional offsets are proposed along the first fault system based on the distribution of the polygenetic volcanoes. The monogenetic volcanoes group into five geographically distinct clusters. In the western part of the CVP, the monogenetic cones are aligned parallel to the CVP system, whereas in the central part the cones are fed by dikes injected along the recent fractures of the Tuzgölü–Ecemiş system. In the eastern part, the monogenetic cones form along the radial fractures of the Erciyes composite volcano.     

论澜沧老厂银铅多金属矿床成矿特征

澜沧老厂系受燕山期构造控制由上部灰岩与下部火山岩组成统一矿化体的银铅多金属大型矿床。深部钻孔揭露花岗斑岩与矽卡岩铜矿化,说明其成因与隐伏酸性岩体有关。历史遗留由灰岩型矿石提银后的富铅炉渣,其含铅金属量加上灰岩型矿石已探明的铅金属量,相当火山岩型矿石已探明铅金属量的２．５倍。说明灰岩型矿体是矿床的主体。只研究火山岩型而忽略灰岩型铅锌矿的研究,或以火山岩型矿体的成矿特征来说明老厂矿床的整体特征,都是不全面的。     

Sulphur dioxide,particle and elemental emissions from Mount Etna,Italy during July 1987

Sulphur dioxide emission rates were measured at Mount Etna, Italy during July 1987 while the volcano was undergoing relatively quiet activity. The SO₂ flux averaged 930 ± 587 (1) Mg/d, excluding 19 July when the flux was 3200 ± 1730 (1) Mg/d. Rising magma and/or an influx of less degassed magma could explain the increased SO₂ flux. The high SO₂ flux did not correlate with changes in observed volcanic activity. This suggests that SO₂ monitoring may be useful as an indicator of shallow magmatic activity, but not as a predictor of future eruptions of Mount Etna.Particles emitted from the two active craters, Bocca Nuova and Southeast Crater (SE), were composed of silicates, sulphates and dithionites. Chloride species were only observed in particles from SE. Different eruptive styles probably produced the differences in particle compositions emitted from each crater.Vapour — magma enrichment factors were calculated for many elements from both craters. Cl, Br and S were the most enriched elements in the sampled fumes. Similar enrichment factors at both craters suggest a common magma supply.Cl, S and F have the largest elemental fluxes emitted from Mount Etna. During quiet activity, the Cl flux represents 27% of the global anthropogenic emissions, but its effect is limited to the local region due to atmospheric removal processes. Mount Etna also exhaled significant amounts of Zn, Br, Mo, F and Cu compared with regional anthropogenic emissions.     

树轮密度对气候的响应及重建研究进展

树轮密度是重建过去气候变化的重要代用指标。过去几十年,国内外学者针对树轮密度开展了大量的研究工作,取得了丰硕的成果。论文收集了国内外有关树轮密度的研究文献,从树轮密度对气候变化的响应和气候重建等方面进行了概述。尽管树轮密度对气候变化的响应可能受到样点的地理位置、地形(如海拔、坡向等)、树种等因素的影响,但湿冷地区树轮晚材最大密度能较好地反映生长季或生长季末期温度变化;而干旱地区的早材平均密度能揭示生长季早期的降水变化。因此,目前大多数研究以重建生长季或生长季末期温度为主,也有重建降水量、海平面气压变化的案例。此外,重建方程的方差解释量存在空间和树种间的差异,但这些差异需要更多的研究工作加以验证。最长的重建序列来自于欧洲,长达2018 a;国内基于树轮密度重建的最长温度序列来自于西南地区,长达449 a。另外,树轮密度序列在对温度响应的分异性问题以及评估强火山喷发的降温效应方面还存在争议。其争议源于树轮密度与温度关系还受到其他环境变量与人为因素的影响,因此今后研究还需关注树轮密度与降水、光照等其他气候变量的关系,同时也要注重树种、海拔、实验方法等非气候因子的影响。     

新疆阔尔真阔拉金矿—带火山岩形成时代及地球化学特征

阔尔真阔拉金矿产于基性、中酸性火山岩及酸性次火山岩中．该套火山岩为钙碱性岩石，具低FeO、MgO、Zr、Nb及Rb／Sr,稀土总量偏低，∑REE=42．81—85．82，具正Eu异常(基性岩)和不明显负Eu异常(中性、中酸性及酸性次火山岩)．由基性应中性及酸性次火山岩，稀土总量有所增加，δEu有所降低，但中性岩至酸性次火山岩的变化规律不明显．其地球化学特征表明为岛弧环境，形成时代为早石炭世(347—343Ma)，是由亏损地幔岩经部分熔融形成．     

麻栗坡杨万火山喷流沉积-热液改造型铜矿

杨万铜矿床位于八布裂陷槽中。矿床位于中三叠统杨万明下段（T2y^a），受层位、岩性、构造及火山活动控制。围岩蚀变发育，绿泥石化、绿帘石化、硅化、碳酸盐化、类石墨化等与矿化关系密切。矿床成困应为海相火山喷流（溢）沉积－热液改造铜矿型。     

镜泊湖全新世火山空降碎屑剖面和喷发历史

镜泊湖全新世火山群 10余座火山分成 5个小的喷发中心位居西南和东北两区 ,每个喷发中心由 2～ 4个火山组成。西南区包括“火山口森林”、“大干泡”、“五道沟”和“迷魂阵”等 4个喷发中心 ,东北区仅“蛤蟆塘”1个喷发中心。火山喷发的产物主要包括熔岩流、溅落堆积和空降堆积 ,火口的锥体主要由溅落堆积的火山渣、火山弹、熔岩饼和薄层熔岩流组成。在“大干泡”和“蛤蟆塘”两处的空降碎屑堆积可达数米厚。镜泊湖全新世火山岩分布面积近 5 0 0km2 ,岩浆主要源自“火山口森林”的1号和 4号火口。文中通过“火山口森林”4号火口空降碎屑实测剖面及其碳化木14 C定年 ,纠正了以往的14 C定年资料 ,认为镜泊湖全新世火山的喷发活动主要在距今 5 2 0 0～ 5 5 0 0a,相继由多次喷发形成 10余座火山。研究认为 ,镜泊湖地区全新世期间不存在以千年计的 3期火山喷发活动     

The Sanfandila earthquake sequence of 1998, Queretaro, Mexico: activation of an undocumented fault in the northern edge of central Trans-Mexican Volcanic Belt

A sequence of small earthquakes occurred in Central Mexico, at the northern edge of the Trans-Mexican Volcanic Belt (TMVB) in the State of Queretaro, during the first 3 months of 1998. Medium to large events in the continental regime of central Mexico are not common, but the seismic history of the region demonstrates that faults there are capable of generating destructive events. The sequence was analyzed using data from a temporary network with the goals of identifying the causative fault and its relation to regional tectonics. Employing a waveform inversion scheme adapted from a method used for regional studies, we found that the source mechanisms conform to the style of faulting (i.e. extension in the E–W direction) representative of the Taxco–San Miguel Allende Fault system. This system has been proposed as the southernmost extension of the Basin and Range (BR) Province. The spatial distribution of hypocenters and source mechanisms indicate that the seismogenic segment was a fault with an azimuth of approximately 334° with almost pure dip slip. Since events which occurred just south from this region show features which are consistent with TMVB tectonics (i.e. extension in an N–S direction), the sequence may mark the boundary between the TMVB and BR stress domains.