Secondary mineral assemblages in a volcanic sequence of ODP Hole 104-642E

Mineralogical and geochemical analyses of alteration products from upper and lower volcanic series recovered during ODP Leg 104 reveal variations both in composition and order of crystallization of clay minerals vesicles and voids filling and replacing glass. These results provide information about successive alteration stages of rocks and interlayered volcaniclastic sediments. The first stage, related to initial basalt-seawater interaction, is characterized by development of Fe-smectites, especially Fe-rich saponite. A second stage of intermittently superimposed subaerial weathering is marked by iron-oxides-halloysite-kaolinite formation. The third episode, interpreted as hydrothermal on the basis of O-isotopic data, is defined by postburial coprecipitation of Fe-poor, Mg-rich saponite and celadonite. A distinct final and pervasive hydrothermal stage, occurring mainly in the lower series and dominated by Al-smectites-zeolites assemblage, indicates changes toward a more reducing alteration environment.

Dinoflagellates and pollen of the Brito-Arctic Igneous Province flora, ODP Hole 104-642E

Palynological studies of the intrabasaltic sediment layers in the lower volcanic series from ODP Leg 104 outer Voring Plateau Hole 642E Cores 102 through 109 indicated abundant pollen and rarer dinoflagellate cysts. The dinoflagellates belong to the Apectodinium hyperacanthum Zone and indicate an age equivalent to nannoplankton Zones NP9-lower NP10 around the Paleocene/Eocene boundary. The pollen and spore assemblage found here in 12 of the samples from the lower volcanic series is of well- preserved and distinctive specimens and contains unusual forms of pollen from the Taxodiaceae and the Hamamelidae. It has not been transported far from vegetation that was dominated by conifer forest with some ferns and deciduous arborescent angiosperms. Nearly identical assemblages are found elsewhere in the Brito-Arctic Igneous Province, in intrabasaltic sediments from eastern Greenland, the Faeroe Islands, the Isle of Mull, and Antrim (Northern Ireland), and above basalt at the Rockall Plateau. The assemblage is also present in sediments around the Paleocene/Eocene boundary in Spitsbergen. This pollen and spore flora is also associated with dinoflagellate cysts of the Apectodinium hyperacanthum Zone in the deposits from eastern Greenland, the Rockall Plateau, and Spitsbergen, suggesting that these are correlative. Assemblages of the same age from the North Sea, Denmark, and the London and Paris Basins are different. Paleobotanical evidence suggests a short survival of the intrabasaltic flora, and that all the deposits considered here are of about the same age. We propose that at around the Paleocene/Eocene boundary a distinct flora, named here as the Brito-Arctic Igneous Province (BIP) flora, occurred on the line of volcanicity stretching from Rockall to the Greenland Sea, and even to Spitsbergen. Geophysical evidence supports our view that the Rockall to East Greenland intrabasaltics are more or less contemporaneous, at about the Paleocene/Eocene boundary. However, the comparable pollen and spore assemblage in the Hebridean province, at Mull and Antrim, is from pyroclastics that may be a little older.

Isotope record and major element chemistry of intestitial waters of ODP Leg 104 sites

The variations in major elements and isotope composition (87Sr/86Sr, delta18O, deltaD) of interstitial waters in Leg 104 sediments is most probably caused by the alteration of volcanic matter. A reaction scheme where volcanic glass reacts with pore-water magnesium and potassium to form trioctahedral smectite, phillipsite, and chert is proposed. Model calculations demonstrate that the pore waters may evolve their negative 6180 signatures without recourse to unreasonably large amounts of volcanic detritus or external sources.

Chemical analysis of ODP Hole 104-642E

During Ocean Drilling Program Leg 104 a 900-m-thick sequence of volcanic rocks was drilled at Hole 642E on the Vøring Plateau, Norwegian Sea. This sequence erupted in two series (upper and lower series) upon continental basement. The upper series corresponds to the seaward-dipping seismic reflectors and comprises a succession of about 122 flows of transitional oceanic tholeiite composition. They have been subdivided into several formations consisting of flows related to each other by crystal fractionation processes, magma mixing, or both. Major- and trace-element chemistry indicates affinities to Tertiary plateau lavas of northeast Greenland and to Holocene lavas from shallow transitional segments of the Mid-Atlantic Ridge, such as Reykjanes Ridge. The tholeiitic magmas have been derived from a slightly LREE-depleted mantle source. Two tholeiitic dikes that intruded the lower series derive from an extremely depleted mantle source. Interlayered volcaniclastic sediments are dominantly ferrobasaltic and more differentiated. They appear to come from a LREE-enriched mantle source, and may have been erupted in close vicinity of the Vøring Plateau during hydroclastic eruptions. The two tholeiitic dikes that intruded the lower series as well as some flows at the base of the upper series show evidence of assimilation of continental upper crustal material.

Chemical analysis of ash layers in ODP Leg 104 holes

Numerous fresh ash layers comprise about 0.3% by volume of Neogene to Holocene sediments drilled at Leg 104 Sites 642 and 643 (Vøring Plateau, North Atlantic). Median grain sizes of the ashes are about 100 /µm and maximum grain sizes range up to 1200 µm. Rhyolitic pumice shards dominate, with minor bubble wall shards. Basaltic shards are poorly vesicular and blocky or round. Phenocrystic plagioclase, zircon, and clinopyroxene occur in the rhyolitic, plagioclase, and clinopyroxene phenocrysts and basaltic lithics in the basaltic tephra. Quartz, amphibole, clinozoisite, and rutile are interpreted as xenocrysts. All ash layers are well-sorted and represent distal fallout from major explosive eruptions. Most ashes are rhyolitic (high-K and low-K) in composition, some are bimodal (tholeiitic and rhyolitic). Early Miocene tephra is dominantly basaltic. Iceland is inferred to be the likely source region for most ashes. Late Miocene high-K rhyolites may have originated from the K-rich Jan Mayen magmatic province. One Quaternary layer with biotite and alkali feldspar phenocrysts may have been derived from Jan Mayen Island. Four individual Pliocene to Holocene ash layers from Sites 642 and 643 can be correlated fairly well. Upper Miocene layers are tentatively correlated as a sequence between Sites 642 and 643. Average calculated layer frequencies are about three layers/m.y. through the Pliocene and Pleistocene and five to eight layers per m.y. through the middle and late Miocene, suggesting rather continuous volcanic activity in the North Atlantic. Episodic magmatic activity during Neogene epochs in this part of the North Atlantic, as postulated in the literature, cannot be confirmed.