(Table VII, page 92) Elemental chemical analyses of post volcanic deposits recovered from Hudson-70, Phase VII cruise (CNAV Endeavour)

The Dellwood Seamount Area, an area of approximately 10,000 square km., about 185 km. west of the northern tip of Vancouver Island is located at or near the northernmost end of the Juan de Fuca plate. The main purpose of the study was to test the hypothesis that the Dellwood Knolls mark the site of a short spreading segment connected to the Explorer Spreading Segment at one end by a transform fault trending along the southwestern slope of Paul Revere Ridge; and meeting the Queen Charlotte right lateral transform fault at the other end. An analysis of more than 950 km. of continuous seismic reflection profiles, in conjunction with other geophysical data, shows that (i) the Revere -Dellwood fault zone is a dextral transform fault zone connecting the Explorer and Dellwood spreading segments. (ii) The Queen Charlotte transform fault dies out at the southeastern end of the Scott Channel near the northeastern end of the Dellwood Spreading Segment. (iii) In the channel between the Dellwood Knolls (one of two possible locations of the Dellwood Spreading Segment), the sediments and volcanic basement are cut by normal faults, a feature which is characteristic of spreading centres with median valleys. The heat flow in this channel and in the Revere - Dellwood fault zone is high. (iv) The lower continental slope sediments west of Queen Charlotte Sound is faulted and crumpled and may be the northerly extension of the Scott Islands fault, zone and a site of slow contemporaneous or recently ceased subduction. The deformation of the thick turbidite sequence in the Winona Basin may also be due to subduction. Basalt from the area is chemically intermediate between tholeiitic and alkalic types. That from the Northwest Dellwood Knolls, however, is least differentiated and less than 1 myr. old in contrast to basalt from the sediment-draped Southeast Dellwood Knolls, the latter basalt having Mn-coating up to 50 mm. thick and is thus relatively old. This suggests that spreading may be occurring at the Northwest Dellwood Knolls and not in the channel between the knolls. The texture of basalts from the Dellwood Seamount Range vary depending on size of pillow and depth below pillow surface, but the mineralogy is essentially similar. An unusual rock probably best described as a plagio-clase-olivine basalt porphyry was also recovered from the Dellwood Seamount Range. Non-volcanic rocks recovered include glacial erratics, an authigenic sandstone comprising glacial fragments in an iron-rich cement, a laminated limonitic sediment and manganese nodules. The Dellwood Spreading Segment may have originated by left lateral transcurrent offset from the Explorer Spreading Segment, the offset caused by a change in the direction of motion of the Juan de Fuca plate.

德尔伍德海山区域（Dellwood Seamount Area）面积约10000平方千米，地处温哥华岛北端以西约185千米处，位于胡安·德·富卡板块（Juan de Fuca plate）的最北端或其邻近区域。本研究的核心目的是验证下述假说：德尔伍德海丘（Dellwood Knolls）所在区域为一段短扩张段的就位位置，该扩张段一端通过沿保罗·里维尔岭西南坡展布的转换断层（transform fault）与探险家扩张段（Explorer Spreading Segment）相连，另一端则与夏洛特皇后右旋转换断层（Queen Charlotte right lateral transform fault）交汇。对超过950千米的连续地震反射剖面结合其他地球物理数据开展的分析结果显示：（i）里维尔-德尔伍德断裂带（Revere-Dellwood fault zone）为一条右旋转换断裂带，连接了探险家扩张段与德尔伍德扩张段（Dellwood Spreading Segment）。（ii）夏洛特皇后转换断层在斯科特水道（Scott Channel）的东南端，即德尔伍德扩张段东北端附近处终止。（iii）在德尔伍德海丘（德尔伍德扩张段的两处可能位置之一）之间的水道内，沉积物与火山基底被正断层（normal faults）切割，这一特征是带有中央谷（median valleys）的扩张中心（spreading centres）的典型标志。该水道及里维尔-德尔伍德断裂带的热流（heat flow）值较高。（iv）夏洛特皇后湾以西的下大陆坡（lower continental slope）沉积物发生断裂与褶皱，可能为斯科特群岛断裂带（Scott Islands fault zone）的北向延伸带，同时也是缓慢的同期俯冲或近期停止俯冲的区域。威诺纳盆地（Winona Basin）内厚层浊积岩序列（turbidite sequence）的变形也可能由俯冲作用导致。该区域的玄武岩化学成分介于拉斑玄武岩（tholeiitic）与碱性玄武岩（alkalic）之间。不过，西北德尔伍德海丘（Northwest Dellwood Knolls）的玄武岩分异程度最低，且年龄不足1百万年；与之形成鲜明对比的是覆有沉积物的东南德尔伍德海丘（Southeast Dellwood Knolls）的玄武岩，后者的锰涂层厚度可达50毫米，因此相对古老。这一现象表明，扩张作用可能发生在西北德尔伍德海丘，而非海丘之间的水道内。德尔伍德海山山脉（Dellwood Seamount Range）的玄武岩结构随枕状熔岩的尺寸及枕面下深度的不同而变化，但矿物学特征基本一致。研究还从德尔伍德海山山脉中采获了一种特殊岩石，最适宜将其描述为斜长石-橄榄石玄武斑岩（plagio-clase-olivine basalt porphyry）。采获的非火山岩包括冰川漂砾（glacial erratics）、一种以富铁胶结物包裹冰川碎屑的自生砂岩（authigenic sandstone）、层状褐铁矿沉积物以及锰结核（manganese nodules）。德尔伍德扩张段可能源自探险家扩张段的左旋走滑错移（transcurrent offset），该错移由胡安·德·富卡板块运动方向的改变所引发。