(Table 1) Major and trace element composition of basalts from ODP Leg 163 sites and Hole 152-917A@en

During Leg 163, in the Southeast Greenland margin, drilling penetrated a thick succession of volcanic rocks that erupted during breakup of the North Atlantic in the early Tertiary. Samples recovered during Leg 163 supplement the samples recovered during Leg 152 from the transect across the volcanic margin at 63°N. During Leg 163, drilling at Site 989 was intended to recover the oldest part of the continental prebreakup series, and drilling at Site 990 was intended to penetrate the transition zone from synbreakup, compositionally variable volcanic products, to postbreakup volcanics with a limited compositional range and a depleted chemical character similar to mid-ocean-ridge basalts (oceanic character). All the lava flows recovered from Sites 989 and 990, however, have an oceanic chemical character with low contents of incompatible elements and high contents of Sc. A dikelet from Site 990 and a previously drilled dike from Site 917 are likewise oceanic. We consider that the two drilled lava flows from Site 989 were emplaced after breakup despite their setting on the innermost part of the continental margin. The succession at Site 990 consists of 13 units of lava flow that show a slight compositional development upsection with Mg# decreasing from ~62 to ~49. This variation is within the limits known from the slightly younger oceanic succession drilled earlier at Site 918, in which the variation is thought to reflect fractionation in magma chambers in the oceanic crust. The reestablishment of magma chambers after the breakup must have been achieved during the interval that the short, undrilled lava succession between uppermost Site 917 and lowermost Site 990 was deposited. […]在第163航次（Leg 163）中，于格陵兰东南缘开展的钻探作业穿透了一套厚层火山岩系，该套岩系形成于早第三纪北大西洋张裂时期。本航次采集的样品补充了第152航次（Leg 152）在北纬63度跨火山边缘剖面所获取的样品。 第163航次中，989站位（Site 989）的钻探目标为获取张裂前大陆层序的最古老部分；990站位（Site 990）的钻探则旨在穿透从张裂同期、成分多变的火山产物，到张裂后期、成分范围有限且具有类似洋中脊玄武岩（mid-ocean-ridge basalts）贫化地球化学特征的洋型火山岩的过渡带。 然而，从989站位与990站位获取的所有熔岩流均具有洋型地球化学特征：不相容元素含量较低，钪（Sc）元素含量较高。采自990站位的1条细岩脉（dikelet）与此前在917站位（Site 917）钻取的1条岩墙同样具有洋型特征。 我们认为，尽管989站位的2套熔岩流位于大陆边缘最内侧区域，但它们实际是在张裂之后就位的。990站位的层序由13个熔岩流单元组成，其成分随剖面向上呈现轻微演化：镁指数（Mg#）从约62降至约49。该成分变化范围与此前在918站位（Site 918）钻取的略年轻洋壳层序已知的变化范围一致，后者的成分变化被认为反映了洋壳内部岩浆房中的岩浆分异作用。 张裂后岩浆房的重建，必然发生在917站位最顶部与990站位最底部之间那套厚度较薄、未被钻取的熔岩序列沉积的时期。[…]