...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Geosphere >Pleistocene hydrothermal activity on Brokeoff volcano and in the Maidu volcanic center, Lassen Peak area, northeast California: Evolution of magmatic-hydrothermal systems on stratovolcano...
【24h】

Pleistocene hydrothermal activity on Brokeoff volcano and in the Maidu volcanic center, Lassen Peak area, northeast California: Evolution of magmatic-hydrothermal systems on stratovolcano...

机译：在Brookoff火山和Maidu Volcanic Centre，Lassen Peak区，加利福尼亚州的山羊峰面积：岩浆 - 热水系统的演变 - Stratovolcano ......

获取原文
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Partially eroded stratovolcanoes worldwide, notably Mounts Rainier and Adams in the Cascades and several volcanoes in Japan, record episodic periods of eruption and geothermal activity that produce zones of hydrothermal alteration. The partly eroded core of late Pleistocene Brokeoff volcano on the south side of Lassen Peak exposes the upper 1 km of multiple ancient (ca. 410–300 ka) magmatic-hydrothermal alteration zones in a 3.5 by 5 km area that allows characterization of the three-dimensional hydrothermal evolution of the volcano. Both acid- and neutral-pH hydrothermal solutions produced distinctive alteration mineral assemblages in close proximity. Early hydrothermal activity is characterized by alunite-rich alteration that is temporally and spatially related to shallow intrusions in the center of the volcano. Younger acid alteration and a large area of neutral-pH alteration formed along the volcano’s flanks. The neutral-pH alteration is vertically zoned over 1000 m from shallow zeolite ± adularia through intermediate argillic (smectite-pyrite ± illite) to deep propylitic (chlorite-calcite-albite-illite) alteration. Pleistocene alteration is partly overprinted by surficial, steam-heated alteration related to Lassen’s modern hydrothermal activity. A large (～3.5 km 2 ), shallow (≤300 m), ca. 1.5 Ma alunite-rich magmatic-hydrothermal alteration zone is exposed on the northeast flank of the nearby Maidu volcanic center. Hydrothermal activity occurred just prior to, or at the beginning of, major eruptive periods on both volcanoes. Fluid flow and hydrothermal alteration were controlled by primary permeability (lateral fluid flow driven by paleotopographic ground-water gradients in volcaniclastic rocks), steeply dipping fractures in more deeply exposed parts of alunite-rich alteration zones, and inferred basement structures. Stable-isotope data indicate hydrothermal fluids were mixtures of variably exchanged meteoric and magmatic waters. Variations in types of hydrothermal alteration and fluid compositions may reflect a temporal increase in depth of magma emplacement and degassing that resulted in increased interaction with and neutralization by wall rocks during ascent of magmatic gases. Alteration zones on both volcanoes are not strongly mineralized, probably reflecting relatively low amounts of magmatic acid, sulfur, and chlorine consistent with degassing of small volumes of pyroxene andesite magma compared to large dacite and/or granodiorite batholiths that form significant epithermal and porphyry deposits.
机译：全世界部分侵蚀的划分的划分的划分，特别是在日本的瀑布和几座火山中升温和亚当斯山脉，记录了产生水热改变区域的喷发和地热活动的集体时期。 Lassen Peak南侧的晚期更新世的近期渗透火山的部分被侵蚀的核心在3.5到5公里的区域中沿着古代（CA.410-300 ka）Magmatic-Hymerothermal改变区的较高的1公里处。允许表征三个 - 火山的二维水热进化。酸和中性pH水热溶液均产生紧密接近的独特改变矿物组件。早期的水热活性的特征在于富含少量的改变，其在时间上和空间上与火山中心的浅侵入性有关。沿火山侧翼形成的酸改变和大面积的中性pH变化。通过中间体（蒙脱石 - 硫铁矿±illite）在深丙基（亚氯酸酯 - 燃烧层 - illite）改变中，中性-PH改变从浅沸石±亚特征垂直划出1000μm以上超过1000μm。优质化改变部分通过与Lassen的现代水热活动有关的表现，蒸汽加热的改变部分叠印。大（〜3.5公里2），浅（≤300米），加利福尼亚州。 1.5马尼亚特丰富的岩浆 - 水热改变区暴露在附近的Maidu火山中心的东北侧面。在两股火山上的主要喷发时期之前发生水热活动。通过初级渗透率（由火山岩石中的古图谱地下水梯度驱动的横向流体流动来控制流体流动和水热改变，在更深入的富有的富有的Alunite的改变区域中陡峭浸渍骨折，并推断出地下室结构。稳定同位素数据表示水热流体是可变交换的陨石和岩石水的混合物。水热改变和流体组合物类型的变化可以反映岩浆施加和脱气深度的时间增加，导致壁岩在岩浆气体中壁岩之间的相互作用增加。与大型曲线和/或细菌岩底溶质相比，两个火山上的改变区可能反映了相对较少量的岩浆酸，硫和氯，其含量与小体积的氨基钼酸盐均一致。

著录项

相似文献

  • 外文文献
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号