Rock-magnetic evidence for the low-temperature emplacement of the Habushiura pyroclastic density current, Niijima Island, Japan
Rock-magnetic evidence for the low-temperature emplacement of the Habushiura pyroclastic density current, Niijima Island, Japan
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日本新岛羽布什浦火山碎屑密度流低温侵位的岩石磁证据
DOI：
10.1144/sp396.7
复制
发表时间：
2014
影响因子：
5.4
通讯作者：
K. Suzuki
中科院分区：
文献类型：
--
作者：
Reina Nakaoka;K. Suzuki
摘要利用岩石磁学分析方法，估算了哈布什瓦火山碎屑密度流(PDC)矿床中偶然碎屑和年轻碎屑的侵位温度。Habushiura PDC形成于公元886年日本新岛岛海底岩浆喷发早期的沿海或浅海地区。我们采集了11个岩层的160个样品，包括3种岩相类型：块状火山灰凝灰岩(A相)、分级和/或扩散分层的火山灰凝灰岩(B相)和大浮岩群(C相)。A相和C相的幼年样品的侵位温度范围很广，从低于150°C到300°C，而B相的侵位温度低于150°C。火山灰成分的形态特征和逐步热退磁后古地磁方向的随机变化表明，低温侵位是通过熔融岩浆喷发和湍流摄取环境空气而发生的。意外碎片的侵位温度高达380℃，高于幼年碎片。它们被认为比幼年碎片冷却得更慢，因为它们的体积比它们的表面积更小。
Abstract The emplacement temperatures of accidental and juvenile fragments in the Habushiura pyroclastic density current (PDC) deposit were estimated using analysis of rock magnetism. The Habushiura PDC was generated in a costal or shallow offshore area during the early stage of the AD 886 phreatomagmatic eruption on Niijima Island, Japan. We collected 160 samples from 11 beds, which include three lithofacies types: a massive lapilli tuff (Facies A); a graded and/or diffusely stratified lapilli tuff (Facies B); and a swarm of large pumice (Facies C). Juvenile specimens from Facies A and C show a wide range of emplacement temperatures, from less than 150 °C up to 300 °C, in contrast with the emplacement temperatures lower than 150 °C of Facies B. Morphological features of the ash components and random changes in palaeomagnetic direction by stepwise thermal demagnetization indicate that low-temperature emplacement occurred by phreatomagmatic eruptions and ingestion of ambient air by the turbulent current. The emplacement temperatures of accidental fragments were up to 380 °C, which is higher than juvenile fragments. They are thought to have cooled more slowly than juvenile fragments due to the smaller surface area with respect to their volume.
DOI：
10.1098/rspa.1953.0064
发表时间：
1953-01-01
影响因子：
--
作者：
FISHER, R
通讯作者：
FISHER, R