Fluid flow and origin of a carbonate mound offshore Vancouver Island: Seismic and heat flow constraints
Fluid flow and origin of a carbonate mound offshore Vancouver Island: Seismic and heat flow constraints
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DOI：
10.1016/j.margeo.2007.01.002
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发表时间：
2007-04
期刊：
影响因子：
2.9
通讯作者：
T. He;G. Spence;M. Riedel;R. Hyndman;N. Chapman
中科院分区：
文献类型：
--
作者：
T. He;G. Spence;M. Riedel;R. Hyndman;N. Chapman
在温哥华岛近海俯冲增生沉积棱柱体的中斜坡区，大洋钻探计划（ODP）889号现场和综合大洋钻探计划（IODP）U1327号现场以西3.5 km处，发现了一个长1.5 km、宽1 km、高70-80 m的碳酸盐丘。海底视频图像显示海底碳酸盐和化能合成群落的存在。一次测线间距很小的高分辨率单道地震测量记录了海底下约400米的相干反射率，提供了这一隆起及其下天然气水合物海底模拟反射层的声学图像，据解释，这一隆起是在目前向海斜坡底部形成的一个大型逆断层上盘中形成的一个构造地形高地。断裂带为包括天然气在内的流体向海底迁移提供了通道，在那里成岩碳酸盐形成并胶结了近地表沉积物。为了研究可能向上流动的流体在土丘下面的热效应，在土丘和在邻近地区的热流计算从海底以下的BSR的深度。这些数据与根据以前的多道地震数据计算的更广泛区域的热流相结合。周围4公里乘8公里区域内最平坦部分的热流平均值为74 mW/m2。以该值代表区域或背景热流，一个简单的二维分析方法被用来计算理论热流的变化，由于地形。在整个土丘，大部分的变化是由地形效应，包括当地的6 mW/m2负异常的中央土丘和一个大的20 mW/m2的土丘陡峭的边坡正异常解释。然而，就在土丘南部，在一个2公里长的带中有一个6-7 mW/m2的正异常，该带主要是平坦的海底。这种异常的大部分可能与地形影响无关，而很可能是由于沿着沿着或断裂带向上流动的热流体。
A 1.5 km long, 1 km wide and 70–80 m high carbonate mound was identified on the mid-slope region of the subduction accretionary sedimentary prism offshore Vancouver Island ∼3.5 km west of Ocean Drilling Program (ODP) Site 889 and Integrated Ocean Drilling Program (IODP) Site U1327. Seabed-video images show the presence of seafloor carbonate as well as chemosynthetic communities. A high-resolution single channel seismic survey with close line spacing, recording coherent reflectivity down to about 400 m beneath the seafloor, provided acoustic images of this mound and of the gas hydrate bottom-simulating reflector (BSR) beneath it. The mound is interpreted to have developed as a structural topographic high in the hanging wall of a large reverse fault formed at the base of the current seaward slope. The fault zone provides pathways for fluids including gas to migrate to the seafloor where diagenetic carbonate forms and cements the near-surface sediments. To examine the thermal effect of possible upward fluid flow beneath the mound, heat flow at the mound and in the neighbouring region was calculated from the depth of the BSR below the seafloor. These data were combined with heat flow calculated over a broader region from previous multi-channel seismic data. Heat flow within the flattest portion of the surrounding 4 km by 8 km region averages ∼74 mW/m2. Taking this value to represent the regional or background heat flow, a simple 2D analytical method was used to calculate theoretical heat flow variations due to topography. Across the mound, most of the variability is explained by topographic effects, including a local 6 mW/m2negative anomaly over the central mound and a large 20 mW/m2positive anomaly over the mound steep side slope. However, just south of the mound, there is a 6–7 mW/m2positive anomaly in a 2-km-long band that has predominantly flat seafloor. Most of this anomaly is probably unrelated to topographic effects, but rather likely due to warm upward fluid flow along faults or fracture zones.