Investigations on volcanic rocks in sediment core CRP-3 from the Ross Sea, Antarctica

The petrography, mineralogy and geochemistry of volcanic and subvolcanic rocks in CRP-3 core have been examined in detail in order to characterise and to compare them with volcanic and subvolcanic rocks cropping out in the Victoria Land area, and to define the clast provenance or to establish possible volcanic activity coeval with deposition. Clasts with sizes ranging from granule to boulder show geochemical and mineralogical features comparable with those of Ferrar Supergroup rocks. They display a subalkaline affinity and compositions ranging from basalts to dacite. Three different petrographic groups with distinct textural and grain size features (subophitic, intergranular-intersertal, and glassy-hyalopilitic) are recognised and are related to the emplacement/cooling mechanism. In the sand to silt fraction, the few glass shards that have been recognised are strongly altered: however chemical analyses show they have subalkalic magmatic affinity. Mineral compositions of the abundant free clinopyroxene grains found in the core, are less affected by alteration processes, and indicate an origin from subalkaline magmas. This excludes the presence, during the deposition of CRP-3 rocks of alkaline volcanic activity comparable with the McMurdo Volcanic Group. Strong alteration of the magmatic body intruded the Beacon sandstones obliterates the original mineral assemblage. Geochemical investigations confirm that intrusion is part of the Ferar Large Igneous Province.

Chemistry of igneous rocks of DSDP Leg 30 holes

Igneous rock units were encountered at four of the five sites drilled on Leg 30 of the Deep Sea Drilling Project. These units uncluded a diabase sill at Site 285, a basalt underlain by a gabbro at 286, two basalt flows at 287, and a basalt flow at 289. Site 285 is located approximately in the center of the South Fiji Basin, Site 286 is adjacent to a filled portion of the New Hebrides Trench, Site 287 is adjacent to a basement high in the Coral Sea Basin, and Sites 288 and 289 are located on the Ontong-Java Plateau north of the Solomon Islands (Figure 1). Figure 2 presents generalized lithologic columns for the igneous rock units found at these sites. When a unit number is given, e.g., Site 286, Unit 4 basalt, this number conforms with the unit number assigned to it in the overall stratigraphic sequence of that hole as defined in the individual Site Reports in this volume. Unless otherwise stated, depths are given as measured from the sediment-igneous rock contact rather than the mudline.