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Ancient microbial activity in volcanic glass creates micron-sized cavities that can be regarded as trace fossils. These are common in glassy rims of oceanic pillow lavas and volcanic breccias. Morphologically comparable mineralized traces are also found in (meta)-volcanic glasses from ophiolites and Precambrian greenstone belts. Multiple lines of evidence indicate microbial formation of these borings, although the affinity of the trace maker(s) is poorly constrained. Two broad morphological types have been previously recognized and termed 'granular' and 'tubular' bioalteration textures. Here optical microscopy and SEM observations are used to erect two new ichnogenera: Granulohyalichnus igen. nov. and Tubulohyalichnus igen. nov. Five ichnospecies are also defined: Granulohyalichnus vulgaris isp. nov., a granular species; Tubulohyalichnus simplus isp. nov., an unornamented tubular species: Tubulohyalichnus annularis isp. nov., an annulated tubular species; Tubulohyalichnus spiralis isp. nov., a helicoidal tubular species; Tubulohyalichnus stipes isp. nov., a branched tubular species. This systematic taxonomy is advanced to allow reliable comparisons to be made between new and existing reports of these microbial borings. Moreover, the adoption of a taxonomic framework will aid the development of these ichnofossils as palaeoenvironmental indicators and tracers of microbial evolution.

The transition zone between 100% dykes and high-level plutonic rocks of the Solund-Stavfjord Ophiolite Complex is complex due to the existence of many lithologies with different and variable contact relationships. The rocks of the plutonic complex vary in composition from FeTi basaltic to quartz dioritic, and the grain sizes vary from fine to pegmatitic. Felsic varieties are produced by fractional crystallization of basaltic magma as demonstrated by geochemical evolution and by gradual transition from gabbro to quartz diorite. Patches of fractionated dioritic rocks may show both gradual and intrusive relationships with the surrounding host gabbro. This demonstrates that late-stage liquids commonly left the source region and locally intruded the surrounding parent rocks. The high-level plutonic rocks are thoroughly epidotized and are cut by dykes consisting of granoblastic epidote and quartz. The high-level plutonic complex is associated with irregular bodies of fine- to medium-grained plagioclase-porphyritic diabase of high MgO content. These diabase bodies are intruded by dykes that become progressively more regular in shape. The plutonic complex locally shows intrusive relationships with the overlying 100% dyke complex, but is itself cut by two dyke swarms. The dykes of the first swarm formed while the plutonic complex experienced sinistral shear strain, and the dykes are generally less regular and thinner than the dykes of the second swarm. This indicates that the dykes of the first swarm intruded while the rocks of the plutonic complex were still hot, while the next dyke swarm intruded later when the rock complex was colder. Dykes of both swarms range in composition from slightly to strongly fractionated, suggesting that the magma chambers they were expelled from underwent significant fractionation in between magma replenishment. Numerous dykes of both swarms carry large quantities of glomeroporphyritic aggregates of plagioclase and altered clinopyroxene, indicating that the source area to the dykes very often was a crystal mush.

The Late Proterozoic rocks of the Wadi El-Imra district of the Central Eastern Desert, Egypt, comprise a metagabbro-diorite complex (oldest) and Older and Younger Granitoid complexes. Trace element characteristics show that the basic and granitoid rocks are of calc-alkaline affinity, but some of the Younger Granitoids grade into alkaline granites. The [[Epsilon].sub.Nd] values of the the basic and granitoid rocks range from +8.3 to +4.9, and Nd model ages are younger or rather similar to crystallization ages. These data suggest a predominant depleted mantle derivation, indicating formation by subduction in an oceanic setting. REE patterns of the granitoid rocks suggest different modes of petrogenesis. This, coupled with the occurrence of amphibolite xenoliths in the Older Granitoids, may indicate that some of these rocks represent partial melts from basic rocks that have been amphibolitized at deep crustal levels of the oceanic arc. Keywords: Egypt, Pan-African Orogeny, igneous activity, trace elements, isotopes.

The volcanigenic rocks of the Kaczawa Mts (western Sudetes, Poland), in the eastern Variscides, show changing geological and geochemical evolution during early Palaeozoic time. The lower part of the succession (Cambrian (?)-Ordovician) has three components. 1. Shallow marine to subaerial metabasalts, associated with limestones and volcaniclastics. The lavas are dominantly of a transitional tholeiitic-alkaline type and their trace element patterns typically represent a rift-related environment. They pass laterally (and upwards ?) into more depleted basalts resembling enriched MORB, with Nd-isotopic characteristics indicating contamination by continental crust. 2. Interlayered rhyodacitic lavas and volcaniclastics which show negative Epsilon(sub Nd) values, suggesting formation of the original magma by crustal melting. 3. An overlying alkaline bimodal suite of lavas and volcaniclastic rocks, as well as alkaline metabasites of shallow-intrusive character. The geochemistry of the latter resembles oceanic island volcanics, but they may well have been emplaced in the same evolving rift environment. The upper part of the Kaczawa succession, Ordovician-Silurian (?) in age, comprises a thick and monotonous sequence of deep-marine pillowed and massive metabasalts, associated with black shales and cherts. These lavas exhibit MORB trace element characteristics, with minor evidence of crustal contamination. During this stage of rifting, true oceanic crust probably formed. It is thus suggested that the studied part of the Kaczawa succession developed in a progressively evolving rift, initially within an ensialic environment, and finally reaching the stage of a basin underlain by oceanic-type crust. Together with similar Cambrian-Ordovician volcanic-sedimentary associations, widely distributed in western Europe, from Portugal, through France and Germany, they represent a record of the Early Palaeozoic rifting in the northern periphery of Gondwana.

Alteration of basaltic glass through the entire volcanic sequence of the Troodos ophiolite is partly bio-mediated. The following observations support this conclusion: alteration textures resembling microbes in form and size; altered glass locally shows high carbon concentrations at the alteration front and organic remains. The absence of DNA suggests that the bio-alteration is a fossil process. Temperatures calculated from [[Delta].sup.18]O of carbonate, assumed to have been in equilibrium with seawater, yield 27-65 [degrees] C, and [[Delta].sup.18][O.sub.silicate] versus [H.sub.2]O relationships indicate seawater alteration. These data are consistent with biogenic alteration during an early stage of ocean-floor alteration of the Troodos oceanic crust some 70-90 Ma ago. Keywords: Cyprus, Troodos ophiolite, biodegradation, glass, basalt, stable isotopes.