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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Seismicity and fluid geochemistry at Lassen Volcanic National Park, California: Evidence for two circulation cells in the hydrothermal system
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Seismicity and fluid geochemistry at Lassen Volcanic National Park, California: Evidence for two circulation cells in the hydrothermal system

机译：加利福尼亚州拉森火山国家公园的地震活动和流体地球化学：热液系统中两个循环单元的证据

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摘要

Seismic analysis and geochemical interpretations provide evidence that two separate hydrothermal cells circulate within the greater Lassen hydrothermal system. One cell originates south to SW of Lassen Peak and within the Brokeoff Volcano depression where it forms a reservoir of hot fluid (235-270 ℃) that boils to feed steam to the high-temperature fumarolic areas, and has a plume of degassed reservoir liquid that flows southward to emerge at Growler and Morgan Hot Springs. The second cell originates SSE to SE of Lassen Peak and flows southeastward along inferred faults of the Walker Lane belt (WLB) where it forms a reservoir of hot fluid (220-240 ℃) that boils beneath Devils Kitchen and Boiling Springs Lake, and has an outflow plume of degassed liquid that boils again beneath Terminal Geyser. Three distinct seismogenic zones (identified as the West, Middle, and East seismic clusters) occur at shallow depths (<6 km) in Lassen Volcanic National Park, SW to SSE of Lassen Peak and adjacent to areas of high-temperature (≤161 ℃) fumarolic activity (Sulphur Works, Pilot Pinnacle, Little Hot Springs Valley, and Bumpass Hell) and an area of cold, weak gas emissions (Cold Boiling Lake). The three zones are located within the inferred Rockland caldera in response to interactions between deeply circulating meteoric water and hot brittle rock that overlies residual magma associated with the Lassen Volcanic Center. Earthquake focal mechanisms and stress inversions indicate primarily N-S oriented normal faulting and E-W extension, with some oblique faulting and right lateral shear in the East cluster. The different focal mechanisms as well as spatial and temporal earthquake patterns for the East cluster indicate a greater influence by regional tectonics and inferred faults within the WLB. A fourth, deeper (5-10 km) seismogenic zone (the Devils Kitchen seismic cluster) occurs SE of the East cluster and trends NNW from Sifford Mountain toward the Devils Kitchen thermal area where fumarolic temperatures are ≤123 ℃. Lassen fumaroles discharge geothermal gases that indicate mixing between a N_2-rich, arc-type component and gases derived from air-saturated meteoric recharge water. Most gases have relatively weak isotopic indicators of upper mantle or volcanic components, except for gas from Sulphur Works where δ~(13)C-CO_2, δ~(34)S-H_2S, and δ~(15)N-N_2 values indicate a contribution from the mantle and a subducted sediment source in an arc volcanic setting.
机译：地震分析和地球化学解释提供了证据，表明两个独立的热液单元在更大的拉森热液系统中循环。一个单元格起源于拉森峰西南部，并在Brokeoff火山洼地内，形成一个热流体（235-270℃）的储层，沸腾后可将蒸汽供入高温的富马酸区域，并具有羽状脱气的储层液体向南流动，出现在Growler和Morgan Hot Springs。第二个单元格起源于拉森峰的东南部，并沿Walker Lane带（WLB）的推断断层向东南流，在那里形成热流体（220-240℃）的储层，该流体沸腾在魔鬼厨房和沸腾泉湖下面，并具有脱气液体的流出羽流再次在终端间歇泉下方沸腾。拉森火山国家公园的浅深度（<6 km），西南部至拉森峰的上证所以及与高温（≤161℃）相邻的三个浅层地震区（分别为西，中和东地震带）出现）的富马活动（硫磺工程，中学生尖峰峰，小温泉谷和邦帕斯地狱）以及一个寒冷而微弱的气体排放区域（冷沸腾湖）。这三个区域位于推断的罗克兰火山口中，以响应深循环的陨石水和覆盖与拉森火山中心相关的剩余岩浆的热脆性岩石之间的相互作用。地震的震源机制和应力反演主要表明了北向的正断层和东西向伸展，东群中有一些斜断层和右向剪切。东星团的不同震源机制以及时空地震模式表明，WLB内部区域构造和推断的断层影响更大。第四个更深（5-10 km）的地震发生带（魔鬼厨房地震群）出现在东群的东南部，并且从西福德山向迷雾温度≤123℃的魔鬼厨房热区趋势NNW。 Lassen喷气孔排放的地热气体表明富含N_2的弧形成分与源自空气饱和的陨石补给水的气体混合。除了来自硫磺厂的气体，其中δ〜（13）C-CO_2，δ〜（34）S-H_2S和δ〜（15）N-N_2值表明，大多数气体的上地幔或火山成分的同位素指示相对较弱。来自弧火山环境中地幔和俯冲沉积物来源的贡献。

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