Oceanic basement structure, sediment thickness, and heat flow near Hole 504B
Oceanic basement structure, sediment thickness, and heat flow near Hole 504B
复制标题
504B 孔附近的海洋基底结构、沉积物厚度和热流
DOI：
--
复制
发表时间：
1998
期刊：
影响因子：
--
通讯作者：
R. Stephen
中科院分区：
文献类型：
--
作者：
S. Swift;G. Kent;R. Detrick;J. Collins;R. Stephen
海洋地壳中最深的钻孔504 B孔周围的一项新的地震反射测量揭示了活动断层、可能的火山中心以及钻孔附近热流和基底结构关系的横向变化。以1公里测线间距在25公里乘25公里网格内收集的单道和多道地震剖面的迁移大大提高了对基底结构和沉积厚度的分辨率。在504 B孔以西，热流在东西向线状基底脊之上较高，而向东的热流在脊之上正常，在两个埋藏的基底丘之上较高。这种差异可能是由于沉积厚度的横向变化。小的、埋藏的基底小山丘很常见，可能是熔岩流的点源。孔504 B位于一个平坦的盆地中，该盆地向西倾斜。504 B孔以南1.1-1.2 km处的最近活动断层由延伸至海底的沉积物反射层不连续面指示。该断层呈东西走向，穿过一个埋藏的火山丘，在那里钻了678 B和896 A孔。从区域上看，504 B孔以北的基底起伏比南部低100至150米，我们将其归因于从最近时间尺度上公布的当地磁异常模式中获得的扩展速率增加。我们发现至少有五个地堑结构类似于失败的裂谷，这可能是由于不对称的扩张或伴随着扩张速率的变化而形成的。基底脊上的南向陡坎和北向陡坎一样常见。沉积物厚度与基底深度高度相关，这是由于地壳年龄为1-2 Ma时在地形低洼处的优先沉积以及后来的风选。
A new seismic reflection survey around Hole 504B, the deepest borehole in ocean crust, reveals active faulting, possible volcanic centers, and a lateral change in the relationship of heat flow and basement structure near the borehole. Migration of single channel and multichannel seismic profiles collected in a 25 by 25 km grid with a 1 km line spacing significantly improved the resolution of basement structure and sediment thickness. West of Hole 504B, heat flow is high above east-west lineated basement ridges, whereas heat flow to the east is normal above ridges and high above two buried basement knolls. The difference is probably due to lateral variations in sediment thickness. Small, buried basement knolls are common and may have been point sources for lava flows. Hole 504B lies in a flat-floored basin that slopes gently upward to the west. A recently active fault 1.1–1.2 km south of Hole 504B is indicated by sediment reflector discontinuities that extend up to the seafloor. The fault strikes east-west and crosses a buried volcanic knoll where Holes 678B and 896A were drilled. Regionally, basement relief north of Hole 504B is 100 to 150 m lower than to the south, which we attribute to an increased spreading rate obtained from dating published local magnetic anomaly patterns with a recent timescale. We find at least five graben structures resembling failed rifts which may have formed in response to asymmetric spreading or to the change in tectonic stress accompanying the spreading rate change. South facing scarps on basement ridges are as common as north facing scarps. Sediment thickness is highly correlated to basement depth due to preferential deposition in topographic lows when the crust was 1–2 Ma old and to later winnowing.