腾格里沙漠西南缘土门剖面微量元素记录的MIS3高分辨率季风环境变化

对位于腾格里沙漠西南边缘的土门剖面中时代为MIS3的TMS3层段进行序列分析与14C和释光测年,并在此基础上对沉积层进行系统的微量元素地球化学分析。结果表明：TMS3是由沙丘砂与其他5类沉积相（黄土状亚砂土、砂黄土、湖沼相、水成黄土和古土壤）构成的相互叠覆的沉积,形成14.5个“沉积旋回”。TMS3微量元素Mn、P、Sr、Rb、V、Zn、Cr、Ni、Cu和Nb在沙丘砂中含量低,在其他5类沉积相中含量高;Rb/Sr比值则呈现相反的变化趋势。在剖面上,随着沙丘砂与这5类沉积相的交替,元素含量、Rb/Sr比值表现出明显的峰（高值）谷（低值）波动,并形成基本上与沉积旋回数量一致的“元素旋回”——ECY1—ECY14.5。该层段14.5个元素旋回揭示了相同数量的腾格里沙漠东亚冬夏季风演变的“旋回”——MCY1—14.5,包括14次冬季风事件和15次夏季风事件,每个季风旋回的持续时间平均约2.48 ka;TMS3元素记录的15次夏季风事件与GRIP冰芯和葫芦洞石笋MIS3-δ18O曲线的间冰阶具有相同的发生次数,也与邻近的古浪黄土MIS3中的间冰阶可以进行很好的对比。土门剖面TMS3的地球化学迁聚...     

Continuous monitoring of volcanic eruption dynamics: a review of various techniques and new results from a frequency-modulated radar Doppler system

 In situ measurement of volcanic eruption velocities is one of the great challenges left in geophysical volcanology. In this paper we report on a new radar Doppler technique for monitoring volcanic eruption velocities. In comparison with techniques employed previously (e.g., photographic methods or acoustic Doppler measurements), this method allows continuous recordings of volcanic eruptions even during poor visibility. Also, radar Doppler instruments are usually light weight and energy efficient, which makes them superior to other Doppler techniques based on laser light or sound. The proposed new technique was successfully tested at Stromboli Volcano in late 1996 during a period of low activity. The recorded data allow a clear distinction between particles rising from the vent and particles falling back towards the vent. The mean eruption velocity was approximately 10 m/s. Most of the eruptions recorded by radar were correlated to seismic recordings. The correlation between the magnitude of the volcanic shocks and the eruption force index defined in the paper may provide new insights into magma transport in the conduit. Received: 15 May 1998 / Accepted: 15 December 1998     

Physical volcanology and structural development of Cerro Azul Volcano, Isabela Island, Galápagos: implications for the development of Galápagos-type shield volcanoes

3 ) erupted from circumferential vents near the summit. These flows are nearly an order of magnitude smaller in volume than the predominantly aa flows erupted from radial eruptive fissures near the break in slope (0.06–0.1 km³). The differences in volume and flow morphology with altitude are due to slower eruption rates from summit vents than from flank vents, which, in turn, are attributable to the different heights the magmas must ascend from shallow reservoirs. These observations support the contention that the steep upper flanks were constructed by the buildup of short lava flows rather than by the structural deformation of originally gently dipping flanks. In addition to the higher eruption rates, a subdued lower flank geometry is promoted by the deposition of lava deltas onto the shallow Galápagos platform on the western, northern, and eastern flanks of the volcano. ⁴⁰Ar/³⁹Ar geochronology and volume estimates show that, despite their morphologic differences, the growth of the western Galápagos shields has been nearly synchronous, precluding an evolutionary model for their development. The wide variations in elevation, volume, area, and the distribution of slope angles among the western volcanoes can be linked instead to different long-term eruption rates and, to a lesser degree, the position of each volcano relative to the edge of the Galápagos platform. Received: 24 September 1998 / Accepted: 7 August 1999     

库伦地区早白垩世义县组(K_1y)火山碎屑流相堆积物特征及火山喷发类型

库伦地区早白垩世义县组火山岩广泛分布 ,经 1∶ 5万区域地质填图及剖面详细研究 ,将义县组上段 ( K1 y2 )火山碎屑流相堆积物自下而上划分为三个亚相 ,即地涌流堆积亚相、碎屑流堆积亚相、灰云浪堆积亚相 ;在横向上据堆积物特点及其距火口远近程度划分出近源亚相、中源亚相和远源亚相。在此基础上 ,探讨了火山喷发类型——为普林尼型喷发柱式爆发     

云南金平勐拉峨眉山玄武岩型铜矿矿化规律

赋矿的峨眉山玄武岩系以爆发相角砾状玄武岩为底,沉积相凝灰岩为顶,可明显划分为三大火山喷发旋回和三岩性段,每一喷发旋回分别对应Ⅰ、Ⅱ、Ⅲ铜矿化层,喷发旋回与铜矿(化)体(层)间存在明显的对应关系,工业矿体由后期含矿构造热液叠加再富集而成。     

火山通道岩浆流动动力学模型在天池火山喷发过程中的应用

在圆柱形火山通道的下部,岩浆上升速度与岩浆粘度、密度及压力有关。这时的流体动力学过程可以应用一般的牛顿流体模型。火山通道中部气泡化岩浆上升时,液相和气相的转化符合质量守恒方程,混合相总体符合动量守恒方程。其中气泡形成与生长过程符合达西定律与数密度方程。在火山通道靠上部的碎屑化带里,不同组分符合质量守恒方程,混合相总体符合动量守恒方程。天池火山千年大喷发时,通道直径是62m。岩浆房内的岩浆含有约3%体积百分数的气泡,气泡体积在65%时岩浆破碎,颗粒离开通道时的速度是145ms~(-1),而气体离开通道时的速度是170ms~(-1)。气体颗粒分散相出口压力是12.2MPa。在破火山口塌陷之前,岩浆房内气泡体积可高达30%～40%。与此同时,碎屑化发生时岩浆的孔隙度也增加到70%～75%左右。这时的出口压力降低至7～8MPa,出口气体速度增加到180ms~(-1)。气象站碱流质寄生火山喷发对应的喷发通道直径是40m,喷发以气体出口速度15～25ms~(-1)的弱爆破性喷发和侵出式喷发为特征。这时浮岩的孔隙度比千年大喷发的孔隙度低,为48%～61%,而浮岩密度高,为1.01～1.35gcm~(-3)。在侵出相喷发时最高释放率可以达到42m~3s~(-1)(致密岩石当量 DRE),孔隙度变化范围是70%～80%。     

滇西腾冲中更新世英安质岩浆的爆发机制

本文对腾冲马站钻孔的中酸性火山岩进行了岩相学、锆石SIMS U-Pb年代学及地球化学研究,确定其岩石类型、形成时代及岩浆喷发前的岩浆状态,从而揭示腾冲火山喷发机制。根据矿物组成将腾冲钻孔的中酸性火山岩分为两层:上层灰白色角闪熔岩(矿物组合:单斜辉石+斜方辉石+角闪石+黑云母+斜长石+钾长石+钛磁铁矿+磁铁矿+石英);下层黑色辉石熔岩(矿物组合:单斜辉石+斜方辉石+斜长石+钛磁铁矿+磁铁矿)。腾冲钻孔中酸性火山岩的锆石均呈半自形-自形,振荡环带明显,为岩浆成因。测年结果表明,灰白色角闪熔岩的结晶年龄为0.7Ma,黑色辉石熔岩中最年轻的锆石为0.6Ma;结合上覆中更新世粗面岩,我们推断其喷发时代为中更新世。地球化学显示角闪熔岩和辉石熔岩都为高钾钙碱性英安岩。相似的全岩和斑晶核部的地化特征,指示角闪英安岩和辉石英安岩来自同一个岩浆房。综合斑晶的地化特征及平衡结晶的温压条件,我们认为早期的岩浆房经历一次基性岩浆补给事件,导致火山爆发产生黑色辉石英安岩,后期岩浆房又经历一次酸性岩浆补给事件,导致火山爆发产生灰白色角闪英安岩。两次岩浆补给事件是导致火山爆发的直接原因。     

Vesiculation path of ascending magma in the 1983 and the 2000 eruptions of Miyakejima volcano, Japan

The vesiculation of magma during the 1983 eruption of Miyakejima Volcano, Japan, is discussed based on systematic investigations of water content, vesicularity, and bubble size distribution for the products. The eruption is characterized by simultaneous lava effusion and explosive sub-plinian (‘dry’) eruptions with phreatomagmatic (‘wet’) explosions. The magmas are homogeneous in composition (basaltic andesite) and in initial water content (H₂O = 3.9±0.9 wt%), and residual groundmass water contents for all eruption styles are low (H₂O <0.4 wt%) suggestive of extensive dehydration of magma. For the scoria erupted during simultaneous ‘dry’ and ‘wet’ explosive eruptions, inverse correlation was observed between vesicularity and residual water content. This relation can be explained by equilibrium exsolution and expansion of ca. 0.3 wt% H₂O at shallow level with different times of quenching, and suggests that each scoria with different vesicularity, which was quenched at a different time, provides a snapshot of the vesiculation process near the point of fragmentation. The bubble size distribution (BSD) varies systematically with vesicularity, and total bubble number density reaches a maximum value at vesicularity Φ ∼ 0.5. At Φ  ∼ 0.5, a large number of bubbles are connected with each other, and the average thickness of bubble walls reaches the minimum value below which they would rupture. These facts suggest that vesiculation advanced by nucleation and growth of bubbles when Φ < 0.5, and then by expansion of large bubbles with coalescence of small ones for Φ > 0.5, when bubble connection becomes effective. Low vesicularity and low residual water content of lava and spatter (Φ  < 0.1, H₂O  < 0.1 wt%), and systematic decrease in bubble number density from scoria through spatter to lava with decrease in vesicularity suggest that effusive eruption is a consequence of complete degassing by bubble coalescence and separation from magma at shallow levels when magma ascent rate is slow.

Tree-ring crossdates for a First Millennium AD advance of Tebenkof Glacier, southern Alaska

Tree-ring crossdates from glacially killed logs show that Tebenkof Glacier advanced into a forefield forest in the AD 710s and 720s. Recession from this First Millennium AD (FMA) advance occurred before the 950s, after which the ice margin readvanced in the 1280s to 1320s at the start of the Little Ice Age (LIA). A more extensive LIA advance was underway from the 1640s to 1670s, and the terminus stayed at or near its LIA maximum until the 1890s. These are the first absolute tree-ring crossdates for a FMA glacier advance in North America and support growing evidence from northwestern North America and Europe for a significant cool interval in the centuries around AD 500.     

A quantitative look at the demise of a basaltic vent: the death of Kupaianaha,Kilauea Volcano,Hawai'i

 The Kupaianaha vent, the source of the 48th episode of the 1983-to-present Pu'u 'O'o–Kupaianaha eruption, erupted nearly continuously from July 1986 until February 1992. This investigation documents the geophysical and geologic monitoring of the final 10 months of activity at the Kupaianaha vent. Detailed very low frequency (VLF) electromagnetic profiles across the single lava tube transporting lava from the vent were used to determine the cross-sectional area of the molten lava within the tube. Combined with measurements of lava velocity, these data provide an estimate of the lava output of Kupaianaha. In addition, lava temperatures (calculated from analysis of quenched glass) and bulk-rock chemistry were obtained for samples taken from the tube at the same site. The combined data set shows the lava flux from Kupaianaha vent declining linearly from 250 000 m³/day in April 1991 to 54 000 m³/day by November 1991. During that time surface breakouts of lava from weak points along the tube occurred progressively closer to the vent, consistent with declining efficiency in lava transport. There were no significant changes in lava temperature or in bulk MgO content during this period. Another eruptive episode (the 49th) began uprift of Kupaianaha on 8 November 1991 and erupted lava concurrently with Kupaianaha for 18 days. Lava flux from Kupaianaha decreased in response to this new episode, but the response was delayed by approximately 1 day. After 14 November 1991, lava velocities were no longer measurable in the tube because the lava stream beneath the skylight had crusted over; however, the VLF-derived electrical conductances documented the decreasing flux of molten lava through the tube. Kupaianaha remained active, but output continued to decrease until early February 1992 when the last active surface flows were seen. In November 1991 we used the linearly decreasing effusion rate to accurately predict the date for the death of the Kupaianaha vent. The linear nature of the decline in lava tube conductance and the delayed and slow response of the Waha'ula tube conductances to the 49th eruptive episode led us to speculate that (a) the Kupaianaha vent shut down because of a decrease in driving pressure and not because of a freeze-up of the vent, and (b) that Pu'u 'O'o, episode 49, and Kupaianaha were fed nearly vertically from a source deep within the rift zone. Received: 29 September 1995 / Accepted: 21 November 1995