Stratigraphy, paleomagnetism, geochronology and structure of silicic volcanic rocks, Waiotapu/Paeroa range area, New Zealand
Stratigraphy, paleomagnetism, geochronology and structure of silicic volcanic rocks, Waiotapu/Paeroa range area, New Zealand
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地层学、古地磁学、地质年代学和硅质火山岩结构，怀奥塔普/派罗瓦山脉地区，新西兰
DOI：
10.1016/0375-6505(94)90014-0
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发表时间：
1994
期刊：
影响因子：
--
通讯作者：
B. Kohn
中科院分区：
文献类型：
--
作者：
G. Grindley;T. Mumme;B. Kohn
长期以来，Waiotapu 地热田下方的改变的熔结岩序列一直与暴露在西部的 Ngapouri 和 Paeroa 断层悬崖中未改变的熔结岩序列相关。最近的年龄测定（裂变径迹和 K-Ar）和磁极性研究表明这种相关性是无效的。Paeroa Scarp 部分包括三种主要的熔凝岩（Paeroa、Te Weta 和 Te Kopia），它们在 0.34 Ma 和 0.38 Ma 之间从当地火山口源喷发。火山口边界断层 (CBF) 标志着派罗瓦火山口的东部边界，穿过怀奥塔普和怀基特地热区之间的派罗瓦山脉北部。 CBF 以东，Ngapouri 陡坡段由 Waiotapu 熔凝灰岩 (0.58 ± 0.03 Ma) 不整合覆盖在松山晚期熔凝灰岩 (Akatarewa A) 和表碎凝灰岩 (X 单元) 的反向磁化层序上，并被流纹岩 (Ngapouri 流纹岩) 侵入。火山口的间歇性崩塌将外来的怀奥塔普熔凝岩和 Ngapouri 流纹岩剥落到火山口中，在两片派罗瓦熔凝岩之间形成不连续层。 Akatarewa 火成岩 (A,B) 被覆盖在截头安山岩锥体 (Ngakoro 安山岩) 上的碎屑凝灰岩 (Y 单元) 和更古老的未命名火成岩 C 分隔开；所有这些都属于晚松山时代，可能可以追溯到 Jaramillo 亚纪元。较年轻的 Rangitaiki (0.35 ± 0.03 Ma)、Matahina (0.28 ± 0.04 Ma)、Ohakuri (0.27 ± 0.03 Ma) 和 Kaingaroa (0.22 ± 0.04 Ma) 熔结岩遍布该地区，后者来自附近 雷波罗阿盆地（火山口）。 Paeroa 和 Ngapouri 倾斜断块的逐渐隆起以及 Reporoa 盆地的进一步下沉使得厚厚的湖床（胡卡群）堆积起来，覆盖了地热储层，这些地热储层最初是由火山口形成而形成的，后来又因火山口的形成而恢复活力。目前的上升流区主要集中在活动断层和突破盖层的断层交汇处。整个怀奥塔普-怀基特地区自封闭浅层储层的热液喷发通常是由切割和连接主要火山口的主要断层上的火山和/或构造事件引发的。
The altered ignimbrite sequence underlying the Waiotapu Geothermal Field has long been correlated with unaltered ignimbrite sequences exposed in the Ngapouri and Paeroa fault-scarps to the west. Recent age-dating (fission-track and K-Ar) and magnetic polarity studies have indicated this correlation is invalid.The Paeroa Scarp section comprises three major ignimbrites (Paeroa, Te Weta and Te Kopia) erupted between 0.34 and 0.38 Ma ago from local caldera sources. The Caldera Boundary Fault (CBF) marking the eastern boundary of the Paeroa Caldera crosses the northern Paeroa Range between the Waiotapu and Waikite thermal areas. East of the CBF, the Ngapouri Scarp section comprises the Waiotapu Ignimbrite (0.58 ± 0.03 Ma) unconformably overlying a reversely magnetised sequence of late Matuyama age ignimbrite (Akatarewa A) and epiclastic tuff (Unit X), intruded by rhyolite (Ngapouri Rhyolite). Episodic caldera collapse has spalled exotic blocks of Waiotapu Ignimbrite and Ngapouri Rhyolite into the caldera, where they form a discontinuous layer between two sheets of Paeroa Ignimbrite.In the Waiotapu Geothermal Field - separated from the Ngapouri Ridge by a younger rhyolite dome - the Waiotapu Ignimbrite is underlain by Akatarewa ignimbrites (A,B) separated by epiclastic tuffs (Unit Y) overlying a truncated andesite cone (Ngakoro Andesite) and an older unnamed Ignimbrite C; all are of late Matuyama age, possibly extending back to the Jaramillo sub-chron.Younger sheets of Rangitaiki (0.35 ± 0.03 Ma), Matahina (0.28 ± 0.04 Ma), Ohakuri (0.27 ± 0.03 Ma) and Kaingaroa (0.22 ± 0.04 Ma) ignimbrite were emplaced across the area, the latter from the nearby Reporoa Basin (caldera). The progressive uplift of the Paeroa and Ngapouri tilted fault-blocks and further subsidence of the Reporoa Basin allowed the accumulation of thick lake beds (Huka Group) which capped geothermal reservoirs, originally established and later rejuvenated by episodic caldera formation. Present-day upflow zones are largely concentrated by active faults and fault intersections breaching the cap-rocks. Hydrothermal eruptions from self-sealed shallow reservoirs throughout the Waiotapu-Waikite area were commonly initiated by volcanic and/or tectonic events on major faults cutting and linking major calderas.