ABSTRACT

The Taupo Volcanic Zone (TVZ) in the central North Island of New Zealand lies across the boundary formed in the late Mesozoic between two major basement regions: the Waipapa and Torlesse composite terranes. However, the precise location of this terrane contact within the TVZ is not well constrained because it is buried beneath Pleistocene volcanic and volcaniclastic sequences locally >3 km thick. Here we report new U-Pb zircon detrital age spectra from basement sandstones and younger Waikora Formation greywacke gravel from five geothermal well core samples and one surface sample. We combine these new data with existing TVZ zircon xenocryst and xenolith age spectra from volcanic host rocks, to correlate these materials with each basement terrane and constrain the likely spatial location and uncertainty of the terrane boundary under the TVZ. Its position with respect to surficial geothermal systems suggests that, at depth, the terrane boundary may have been reactivated by Quaternary extension in the evolving Taupo Rift. Put another way, the past and current position of the Taupo Rift fundamentally may have been controlled by the terrane boundary, which may ultimately be partly responsible for providing enhanced fracture permeability for deep-seated geothermal fluids.

摘要

新西兰北岛中部的陶波火山带 (TVZ) 横跨中生代晚期形成的两个主要基底区域之间的边界：Waipapa 和 Torlesse 复合地体。然而，该地体接触在 TVZ 内的精确位置并没有得到很好的限制，因为它被埋在更新世火山和火山碎屑层序下，局部厚度大于 3 公里。在这里，我们报告了来自五个地热井岩心样品和一个地表样品的基底砂岩和较新的 Waikora 组灰瓦克砾石的新 U-Pb 锆石碎屑年龄谱。我们将这些新数据与来自火山主岩的现有 TVZ 锆石包体和包体年龄谱相结合，将这些材料与每个基底地体相关联，并限制 TVZ 下地体边界的可能空间位置和不确定性。它相对于地表地热系统的位置表明，在深处，地体边界可能已被正在演化的陶波裂谷中的第四纪伸展重新激活。换句话说，陶波裂谷过去和现在的位置从根本上可能受到地体边界的控制，这可能最终是为深层地热流体提供增强的裂缝渗透率的部分原因。