Michael T. Macnaughtan, Ingo A. Pecher, Lorna J. Strachan, Gareth J. Crutchley
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引用次数: 0
摘要
俯冲带是碳回收中心,数百万年来,大量的地质碳通过热成岩气体窗口吸积或俯冲到这里。我们的研究重点是新西兰的查塔姆隆起,它是∼400 Myr活动的东冈瓦纳边缘的化石增生楔残留物。我们对横跨查塔姆海隆西北斜坡的非生中生代沉积序列(MES)和上覆序列 Y 白垩层间进行了基于偏移的振幅变化(AVO)地震分析。通过两期反相位属性分析,解释了不同的反相位 III-IV 级反射异常,这些异常将硅质中生代沉积序列与上覆的 Y 白垩系划分开来。III类异常通过其强烈的负截距振幅统一起来,其绝对振幅随角度的变化而增加,而IV类异常的绝对振幅则随入射角度的变化而减小。同时进行的地震数据反演(AVO)突出显示了 P-阻抗异常的存在,该异常直接位于区域性出现的 Y 顺序白垩系区间的下部。III 类异常被建模并解释为以前未定义的粗粒岩性的结果,含有低饱和度(2%-10%)的游离气体。同时出现的 IV 类反渗透异常被建模为细粒度的上部 MES 提供了证据,孔隙中的游离气体饱和度同样很低。我们推测气体的来源可能来自希库兰芝俯冲边缘、原位古微生物活动或与古东贡得瓦纳俯冲边缘和增生楔有关的新的未确定来源。
Deep Free-Gas Accumulation Beneath the Chatham Rise, New Zealand—An AVO Study
Subduction zones serve as carbon recycling centers, where vast amassments of geologic carbon accrete or subduct through thermogenic gas windows over millions of years. We focus on New Zealand's Chatham Rise, a fossilized accretionary wedge remnant of the ∼400 Myr-active East Gondwanan margin. We undertake an amplitude-variation-with-offset (AVO)-based seismic analysis of the abiogenic Mesozoic sedimentary sequence (MES) and overlying Sequence Y chalk interval, which span the Chatham Rise's northwestern slope. Two-term AVO attribute analysis resulted in the interpretation of distinct AVO Class III–IV reflection anomalies, which demarcate the siliciclastic MES from overlying Sequence Y chalks. Unified through their strong negative intercept amplitudes, Class III anomalies increase in absolute amplitude with angle, while Class IV anomalies decrease in absolute amplitude with angle of incidence. Simultaneous AVO inversion of seismic data highlighted the presence of P-impedance anomalies, which directly underlie the regionally occurring Sequence Y chalk interval. Class III anomalies are modeled and interpreted as the result of a previously undefined coarse-grained lithofacies, bearing low saturations (2%–10%) of free gas. Co-occurring ClassIV AVO anomalies are modeled to provide evidence for a fine-grained upper MES, bearing similarly low saturations of free-gas in pore space. We speculate on the gas' origin, which could be from the Hikurangi subduction margin, in situ ancient microbial activity, or a new undetermined source related to the ancient East Gondwanan subduction margin and accretionary wedge.
期刊介绍:
Geochemistry, Geophysics, Geosystems (G3) publishes research papers on Earth and planetary processes with a focus on understanding the Earth as a system. Observational, experimental, and theoretical investigations of the solid Earth, hydrosphere, atmosphere, biosphere, and solar system at all spatial and temporal scales are welcome. Articles should be of broad interest, and interdisciplinary approaches are encouraged.
Areas of interest for this peer-reviewed journal include, but are not limited to:
The physics and chemistry of the Earth, including its structure, composition, physical properties, dynamics, and evolution
Principles and applications of geochemical proxies to studies of Earth history
The physical properties, composition, and temporal evolution of the Earth''s major reservoirs and the coupling between them
The dynamics of geochemical and biogeochemical cycles at all spatial and temporal scales
Physical and cosmochemical constraints on the composition, origin, and evolution of the Earth and other terrestrial planets
The chemistry and physics of solar system materials that are relevant to the formation, evolution, and current state of the Earth and the planets
Advances in modeling, observation, and experimentation that are of widespread interest in the geosciences.