Geochemistry and ages of rock samples from Kirwanveggen, Antarctica

The basement of southern Kirwanveggen (western Dronning Maud Land) is formed by a SSW-dipping section consisting of (from SW to NE): migmatic gneisses; granitoid; low-grade/prograde meta-pelites, meta-psammites and meta-basalts (= "Polaris Formation"); ortho-gneiss; quartzite mylonite; Polaris Formation; quartzite mylonite; meta-turbidites. These units are (partly) separated by at least four SSW-dipping, NE to N directed major thrusts. Most probably, this thrust system is of Pan-African age. Towards north, the section is followed by the molasse-like Urfjell Group, deposited later than approx. 550 Ma and earlier than 450 Ma. Similarities with the Pan-African of the Shackleton Range (thrusting, molasse) led to the assumption, that the East/West Gondwana suture runs from the Shackleton Range towards Sor Rondane (eastern Dronning Maud Land) passing southern Kirwanveggen at its south-east.

Composition of marine phosphorites and phosphate-bearing sediments

The book deals with behavior of phosphorus and its concentration in oceanic phosphorites. The major stages of marine geochemical cycle of phosphorus including its supply to sedimentary basins, precipitation from sea water, distribution and speciation in bottom sediments, diagenetic redistribution, and relation to other elements are under consideration. Formation of recent phosphorites as a culmination of phosphate accumulation in marine and oceanic sediments is examined. Distribution, structure, mineral and chemical compositions of major phosphorite deposits of various age on continental margins, as well as on submarine plateaus, uplifts and seamounts and some islands are described. A summary of trace element abundances in oceanic phosphorites is presented. Problems of phosphorite origin are discussed.

Grain size composition and geochemistry of volcaniclastic sediments in the Lau Basin

Early Pliocene to Pleistocene volcaniclastic sediments recovered during Ocean Drilling Program Leg 135 from Sites 834 to 839 in the Lau Basin show a wide range of chemical and mineralogical compositions extending the spectrum previously known from the Lau Basin, Lau Ridge and Tofua Arc. The following major types of volcaniclastics have been distinguished: (1) primary fallout ashes originating from eruptions on land, (2) epiclastic deposits that resulted from subaerial and submarine eruptions, (3) subaqueous fallout and pyroclastic flow deposits resulting from explosive submarine eruptions, and (4) hyaloclastites resulting from mechanical fragmentation and spalling of chilled margins of submarine pillow tubes and sheet-lava flows. Vitric shards are mostly basaltic andesitic to rhyolitic and broadly follow two major trends in terms of K2O enrichment: a low-K series (LKS) with about 1 wt% K2O at 70 wt% SiO2, and a very low-K series (VLKS) with only about 0.5 wt% K2O at 70 wt% SiO2. Sites 834 and 835 on "old" backarc basin crust, >4.2 and 3.4 m.y. old, comprise LKS rhyolites >3.3 m.y. old. Calc-alkaline basaltic turbidites originating from the Lau Ridge flowed in at 3.3 Ma. In the period from 3.3 to 2.4 Ma basaltic andesitic to rhyolitic, fine-grained LKS and VLKS volcaniclastics were deposited by turbidity currents and subaerial fallout. Three thin, discrete fallout layers (2.4-3.2 m.y. old) with high-K calc-alkaline compositions probably erupted in New Zealand. Volcaniclastics from Site 836, all <0.6 m.y. old, make up 24% of the sediments and comprise local basaltic andesitic to andesitic hyaloclastites with low Ba/Zr ratios of 0.9 to 1.4 and polymict andesitic sediments with Ba/Zr ratios of up to 5.5, containing clasts altered to lower greenschist facies. In Sites 837-839, drilled on young crust (1.8-2.1 m.y. old), volcaniclastics make up 45%-64% of the total sediment. Glass compositions are often bimodal with a mafic and a rhyolitic population. Large-volume rhyolitic, silt- to lapilli-sized volcaniclastics are interpreted as pyroclastic flows from explosive eruptions on a seamount 25-50 km away from the sites. Ba/Zr ratios are 2 to 4, partially overlapping with some Lau Basin basement lavas that show an "arc" signature, and they can reach values >5 in thin volcaniclastic layers <0.6 m.y. old.

Chemical composition of rocks and minerals from the Doldrums and Arkhangelsky Fracture Zones

The book deals with results of complex geological and geophysical studies in the Doldrums and Arkhangelsky Fracture Zones of the Central Atlantic. Description of the main features of bottom relief, sediments and crustal structure, geomagnetic field, composition of igneous and sedimentary rocks are given in the book. The authors made conclusions on tectonic delamination of the oceanic crust and existence of specific rock complexes forming non-spreading blocks

(page 43), Geochemical composition of a phosphatic manganese nodule from Blake Plateau

Mr. John Murray, to whom the specimens of bottom deposits collected by the "Blake" were sent for examination, looked over the whole and selected some typical specimens. These have been described in detail, and he has added some general notes on the specimens characteristic, 1. of the Coast between the Gulf of Maine and Cape Hatteras; 2. of thee coast between Cape Hatteras and Lat. 31? 48' N.; 3. of the coasts around the greater and lesser Antilles ; and, finally, of the Gulf of Mexico and Straits of Florida.