首页> 外文期刊>New Zealand journal of geology & geophysics >Upper crustal structure beneath the eastern Southern Alps and the Mackenzie Basin, New Zealand, derived from seismic reflection data
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Upper crustal structure beneath the eastern Southern Alps and the Mackenzie Basin, New Zealand, derived from seismic reflection data

机译:根据地震反射数据得出的南阿尔卑斯山东部和新西兰麦肯齐盆地下方的上地壳结构

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A 65 km seismic reflection transect was shot in 1998 across Mackenzie Basin to Mount Cook Village, South Island, New Zealand, to provide a detailed image of the crustal structure in the central Southern Alps. The first 5 s (two-way time (TWT)) of data were processed separately, with a maximum offset of 14 km for each shot, to image the upper 12-15 km of the crust. Data were processed as one continuous section, although the line was physically segmented due to an area of relatively steep topography with no vehicular access. No major, continuous regional-scale features >10 km are present in the data, but numerous 2-3 km scale reflections and discontinuities occur which are consistent with the known geology of monotonous greywacke sequences overlying schist. Strong, well-defined reflections mark the active Irishman Creek Fault and confirm it to be a southeasterly dipping reverse fault with c. 1300-1700 m of Late Cretaceous-Pleistocene sediments preserved in the footwall and an uplifted greywacke basement "high" in the hanging wall. Some evidence exists for active faults beneath latest Quaternary gravels at the Jollie valley and Tekapo River. Oppositely dipping reflections and discontinuities define a large, c. 15 km wavelength antiform beneath Tasman valley and Mount Cook that is imaged to 10 +- 2 km depths (3.5 s TWT). Two "end-member" interpretations are consistent with the seismic data observations, velocity models, and constraining features of exposed geology, and extend existing geological cross-sections to 10-15 km depth. One interpretation assumes imaged structures are primarily backthrusts developed in response to distributed Cenozoic deformation southeast of the Alpine Fault plate boundary, incorporating features observed in contemporary geodetic strain and numerical plate boundary models. The second interpretation assumes structures are mostly Mesozoic, either reactivated or preserved by late Cenozoic deformation. The main difference between the interpretative cross-sections is the degree to which active structures link into basal detachment and high-strain zones at depth.
机译:1998年,在Mackenzie盆地拍摄了65公里的地震反射样带,直达新西兰南岛的库克山村,以提供南阿尔卑斯山中部地壳结构的详细图像。分别处理了前5 s(双向时间(TWT))数据,每次拍摄的最大偏移量为14 km,以对地壳的上部12-15 km成像。数据被作为一个连续的部分进行处理,尽管由于地形相对陡峭,没有车辆通行,所以对线进行了物理分割。数据中没有大于10 km的主要的,连续的区域尺度特征,但是发生了2-3 km尺度的大量反射和不连续性,这与覆盖片岩的单调性葛瑞克序列的已知地质是一致的。强烈,清晰的反射标志着活动的爱尔兰人溪断层,并确认它是东南倾角为c的反向断层。在底盘中保留了1300-1700 m的晚白垩世-更新世沉积物,在悬挂的壁中保留了一个隆起的灰色瓦克地下室“高”。在佐利谷和特卡波河最新的第四纪砾石下存在活动断层的一些证据。相反地​​,反射和不连续性定义较大的c。塔斯曼河谷和库克山下方的15 km波长反型地物成像到10±2 km深度(3.5 s TWT)。两种“端元”解释与地震数据观测,速度模型和裸露地质的约束特征相一致,并将现有的地质剖面扩展到10-15 km的深度。一种解释认为,成像的结构主要是反冲作用,它是响应于阿尔卑斯断层板块边界东南部分布的新生代形变而形成的,并结合了现代大地应变和数值板块边界模型中观察到的特征。第二种解释假设结构大部分是中生代的,或者由新生代晚期变形而重新激活或保留。解释性横截面之间的主要区别在于,活动结构在深度上连接到基底脱离和高应变区的程度。

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