Age determination on monazite from Forefinger Point granulites, East Antarctica (Table 2.6-1)

Electron microprobe (EMP) dating on monazite in granulite- facies rocks from Forefinger Point, East Antarctica, yielded dominant ages of 500 Ma on matrix monazites.They are associated with secondary cordierite, biotite and sapphirine, formed during nearly isothermal decompression after the high P-T assemblages involving garnet, orthopyroxene and sillimanite. Older ages around 750-1000 Ma are detected in monazite cores and in monazite inclusions in garnet porphyroblast. Combining the available age data and the reaction textures, it becomes evident that the Forefinger Point granulites have been overprinted by a granulite-facies decompressional event of Pan-African age. Moreover, EMP monazite dating imply that the Forefinger Point granulites have experienced at least two stages of metamorphic evolution.

Appendix A: LA-ICP-MS results (Laser-ablation inductively coupled plasma mass spectrometer) from monazite Moacir standard

Three samples of garnet-kyanite paragneiss from the Variscan Ulten Zone (Northern Italy) were studied in detail for U-Th-Pb monazite dating. Monazite in these gneisses is abundant, shows highly variable grain size and occupies different textural positions: within the matrix, as inclusion in garnet and kyanite, within apatite aggregates. Monazite shows different deformation features as a function of the textural position: enclosed (shielded) monazite is generally more fractured than matrix (unshielded) monazite. The integration of textural information with deformation features and in situ U-Th-Pb analyses by LA-ICP-MS indicates that there is no direct correlation between textural site and monazite ages. Old ages of 351-343 Ma, determined on portions of large matrix (unshielded) monazite and on rare domains of monazite shielded by garnet, have been related to a prograde stage of the Variscan metamorphic evolution of the Ulten Zone. Ages of 330-326 Ma, which are related to the thermal peak, are recorded by small matrix monazite, external domains of large matrix monazite, and by (domains of) fractured monazite enclosed in garnet and kyanite. Large, old unshielded grains formed as blasts during the prograde metamorphic history and survived the peak metamorphism during which crystallisation/re-crystallisation partially occurred.

Heavy mineral content of ODP Leg 107 holes

Analyses of rock clasts and of heavy minerals in upper Miocene coarse detrital units drilled along the East Sardinia passive-type continental margin (Sites 654, 653, 652, and 656) reveal that the stretched basement contains quite complex rock suites. Taking also into account previous sampling data, in moving from west to east across the margin, the nature of the basement changes drastically. To the west there are mostly Hercynian basement rocks with their cover, referable to the alpine foreland of the Corsica-Sardinia block. To the east, along the lower margin, where crustal thinning is quite severe, the basement contains rock suites referable to a pre-upper Tortonian orogenized zone with units constituting parts of the Alpine and Apenninic chains (presumably with thickened continental crust prior to stretching). Largest thinning and ocean forming occurred then, in a rather short time, mostly at the expense of unstable crust just thickened by orogenetic/tectogenetic processes.

Holocene sedimentation in the Strait of Otranto, Mediterranean Sea

An extensive radiograph study of 24 undisturbed, up to 206-cm long box and gravity cores from the western part of the Strait of Otranto revealed a great variety of primary bedding structures and secondary burrowing features. The regional distribution of the sediments according to their structural, textural, and compositional properties reflects the major morphologic subdivisions of the strait into shelf, slope, and trough bottom (e.g., the bottom of the northern end of the Corfu-Kephallinia Trough, which extends from the northeastern Ionian Sea into the Strait of Otranto): (1) The Apulian shelf (0 to -170m) is only partly covered by very poorly sorted, muddy sands without layering. These relict(?) sands are rich in organic carbonate debris and contain glauconite and reworked (?Pleistocene) ooids. (2) The slope sediments (-170 to -1,000 m) are poorly sorted, sandy muds with a high degree of burrowing. One core (OT 5) is laminated and shows slump structures. An origin of these slumped sediment masses from older deposits higher on the slope was inferred from their abnormal compaction, color, texture, organic content, and mineral composition. (3) Cores from the northern end of the Corfu-Kephallinia Trough (-980 to -1,060 m) display a few graded sand layers, 2-5 cm (maximum 30 cm) thick with parallel and ripple-cross-laminations, deposited by oceanic bottom or small-scale turbidity currents. They are intercalated with homogeneous lutite. (4) Hemipelagic sediments prevail in the more southerly part of the Corfu-Kephallinia Trough and on the "Apulian-Ionian Ridge", the southern submarine extension of the Apulian Peninsula. Below a core depth of 160 cm, these cores have a laminated ("varved") zone, representing an Early Holocene (Boreal-Atlanticum) "stagnation layer" (14C age approximately 9,000 years). The terrigenous components of the surface sediments as well as those of the deeper sand layers can be derived from the Apulian shelf and the Italian mainland (Cretaceous Apulian Plateau and Gargano Mountains, southern Apennines, volcanic province of the Monte Vulture). Indicated by the heavy mineral glaucophane, a minor proportion of the sedimentary material is probably of Alpine origin. If this portion is considered to be first-cycle clastic material it reaches the Strait of Otranto after a longitudinal transport of 700 km via the Adriatic Sea. The lack of phyllosilicates in the coarse- to medium-grained shelf samples might be explained by the activity of the "Apulian Current" (surface velocities up to 4 knots) which in the past possibly has affected the bottom almost down to depths of the shelf edge. The percentage of planktonic organisms, and also the plankton: benthos ratio in the sediments is a useful indicator for bathymetry (depth zonation).

Heavy mineral abundance of ODP Leg 174A sites

The purpose of this paper is to report the heavy mineral content of Miocene to Pleistocene sequences drilled during Ocean Drilling Program Leg 174A on the New Jersey Shelf. Sandy intervals recovered from Holes 1071A, 1071F, 1072A, and 1073A were sampled for heavy mineral analysis. Because of the low core recovery of the sandy parts of the succession, sampling has been incomplete. In spite of the resulting restriction and because of major variations in heavy mineral assemblages, eight distinct heavy mineral associations could be defined. The data presented thus considerably extend the present knowledge on the lithology of the stratigraphic record as described by Austin, Christie-Blick, Malone, et al. (1998). In this chapter the heavy mineral associations and their assignment to particular sequences are described.

Geochemical analysis of minerals from sediment core CRP-2 in the Ross Sea, Antarctica

Distribution patterns, petrography, whole-rock and mineral chemistry, and shape and fabric data are described for the most representative basement lithologies occurring as clasts (granule to bolder grain-size class) from the 625 m deep CRP-2/2A drillcore. A major change in the distribution pattern of the clast types occurs at c. 310 mbsf., with granitoid-dominated clasts above and mainly dolerite clasts below; moreover, compositional and modal data suggest a further division into seven main detrital assemblages or petrofacies. In spite of this variability, most granitoid pebbles consist of either pink or grey biotite±hornblende monzogranites. Other less common and ubiquitous lithologies include biotite syenogranite, biotite-hornblende granodiorite, tonalite, monzogranitic porphyries (very common below 310 mbsf), microgranite, and subordinately, monzogabbro, Ca-silicate rocks, biotite-clinozoisite schist and biotite orthogneiss (restricted to the pre-Pliocene strata). The ubiquitous occurrence of biotite±hornblende monzogranite pebbles in both the Quaternary-Pliocene and Miocene-Oligocene sections, apparently reflects the dominance of these lithologies in the onshore basement, and particularly in the Cambro-Ordovician Granite Harbour Igneous Complex which forms the most extensive outcrop in southern Victoria Land. The petrographical features of the other CRP-2/2A pebble lithologies are consistent with a supply dominantly from areas of the Transantarctic Mountains facing the CRP-2/2A site, and they thus provide further evidence of a local provenance for the supply of basement clasts to the CRP-2/2A sedimentary strata.

Age determination on rock samples from Svalbard

A linear, N-S-trending belt of elliptical, positive magnetic anomalies occurs in central Nordaustlandet, northeast Svalbard. They extend from the Caledonian and older complexes in the vicinity of Duvefjorden, southwards beneath the western margin of Austfonna and the offshore areas covered by Carboniferous and younger strata, to the vicinity of Edge¯ya. One of the strongest anomalies occurs in inner Duvefjorden where it coincides with a highly magnetic quartz monzonite-granite pluton at Djupkilsodden. U-Pb and Pb-Pb zircon dating of this post-tectonic pluton defines an age of c. 415 Ma, this being based on the Pb-Pb analyses of three specimens (Pb-Pb ages of 414±10 Ma, 411±10 Ma and 408±10 Ma) and a U-Pb discordia with an upper intercept at 417+18/-7 Ma. Neighbouring felsic plutons in central Nordaustlandet, including the Rijpfjorden and Winsnesbreen granites, lack magnetic signatures in their exposed parts, but have a similar Caledonian age. The central Nordaustlandet magnetic anomalies appear to be part of a circa 300 km long linear belt of late Silurian or early Devonian post-tectonic plutonism that characterizes the Caledonian basement of eastern Svalbard. Felsic intrusions of similar age further west in Spitsbergen are likewise both highly magnetic (Hornemantoppen batholith) and largely non-magnetic (Newtontoppen batholiths / Chydeniusbreen granitoid suite). They all appear to have been intruded at the end of the main period of Caledonian terrane assembly of the northwestern Barents Shelf.