A macroscopic fold formed during the fourth deformation, D4, in the Robertson River Metamorphics, north Queensland, Australia. Growth of biotite, garnet, staurolite and andalusite porphyroblasts also occurred synchronous with D4. Only biotite porphyroblasts have formed preferred alignments across the fold, and they define two dominant orientations. The more common is parallel to D4 fold axes, which is also parallel to D1 D2 and D4 intersection lineations. The other varies up to 90° from this within the D4 axial plane. Mineral elongation lineations do not reflect the extension direction of the deformation in which they formed (D4), but are a function of pre-existing anisotropics in the rock parallel to intersection lin-eations. Porphyroblast growth is inferred to be a result of microfracturing along favourably oriented linear anisotropics formed by multiple intersection of foliations, as well as parting of the the S1, and S2 foliations.

A mineralogical and 4OAr/39Ar study of 13 amphibole samples in the Kamila Amphibolite Belt and Kamila Shear Zone in northern Pakistan has found a correlation between the degree of greenschist facies alteration and quantity of excess 40Ar. Additionally, there is a north–south divide with amphibole samples from the northern region showing larger degrees of gree schist facies alteration, brittle deformation, and excess 40Ar incorporation compared to the predominantly plastically deformed, less altered, amphibole samples from the Kamila Shear Zone in the south. Acid leaching of two amphiboles from the Kamila Amphibolite Belt indicates that a large proportion of the excess 40Ar is correlated with later greenschist facies alteration hases, and can be easily removed by acid etching, thus revealing acceptable regional 40Ar/39Ar plateau ages.

Oriented samples of the Lower Cambrian Bayan Gol Formation from Salaany Gol, Mongolia, were collected at roughly 5 m stratigraphic intervals for palaeomagnetic analysis. Progressive alternatingfield and thermal demagnetization isolated two magnetic components: a present-field overprint, typically removed by 10 mT fields and ~200°C heating; and a high-coercivity, high-unblocking-temperature (550–600 °C), predominantly single-polarity component that was imparted to the rocks prior to early or middle Palaeozoic deformation. Single-polarity magnetization at Salaany Gol contrasts with results from Lower Cambrian rocks on the Siberian platform, previously considered correlative with the Bayan Gol Formation, which show a prominent change in polarity bias near the top of the Tommotian Stage. Two hypotheses can explain this discrepancy. First, the entire Bayan Gol Formation may correlate with the predominantly reversely polarized, lower half of the Tommotian Stage in Siberia. This model is consistent with plausible interpretations of δ13C profiles for the Zavkhan basin and the Siberian platform. Alternatively, the characteristic magnetic direction from our samples may be a pre-fold overprint. If post-accretionary, then comparison with Siberian palaeomagnetic results suggest a Silurian–Devonian remagnetization age, and existing bioand chemostratigraphic correlations provide the most reliable spatial and temporal links between the Zavkhan basin and the Siberian platform. If the observed magnetic directions are primary or an immediate overprint then they may be used to constrain the early Cambrian palaeogeography of the Zavkhan basin and the Palaeo-Pacific Ocean. Mean inclination of 62 ±4° corresponds to a palaeolatitude of 44 ±5°, several thousand kilometres from the equatorial Siberian craton

Single grain 207Pb/206Pb zircon ages were determined for granitoids and gneisses which constitute the Archaean basement rocks of the Aravalli craton of Rajasthan, northwestern Indian Shield. The protolith ages for two gneisses, collected from east of Udaipur, are ˜3230 Ma and 2887 Ma respectively. The granitoids display an intrusive relationship with the gneisses and yielded ages ranging between 2666 Ma and 2620 Ma. These ages provide the basis for a geochronological model of evolution of the oldest basement of the Aravalli craton.

An early fabric is preserved in pseudomorphs of contact metamorphic cordierite and andalusite found in hornfelsed Dalradian rocks at the NW margin of the Ben Vuirich Granite. As previous work had suggested that this fabric may be of regional tectonic (D1) origin, and taken as evidence that a pre-590 Ma (Neoproterozoic) orogenic event had affected the Dalradian Supergroup, the textures found in the hornfelses and their porphryoblasts are illustrated and described in detail. Three types of hornfels are recorded: unspotted, cordierite-, and andalusite-bearing. Cordierite was altered to mica, garnet, and kyanite, and andalusite pseudomorphed by kyanite, during the subsequent D2 regional metamorphism.

The early fabric is finely spaced and associated with a weak shape fabric, except in the higher grade hornfelses where it is more intensely developed and formed during the deformation of irregularly shaped, cross-cutting granitic veinlets. It is concluded that the hornfels fabric is probably bedding modified by intrusion-related deformation, rather than a D1 fabric parallel to bedding. The implication of this finding is that intrusion of the Ben Vuirich Granite occurred during the Vendian (c.650 Ma) rifting phase, at about the time that the Tayvallich lavas were being deposited, and before any significant deformation of the Dalradian rocks had taken place. There is no unambiguous evidence to show that the early fabric in the hornfels at Ben Vuirich formed during a Precambrian, regional-scale, deformation of the Dalradian block.

Recently, an outcrop with clear evidence for Quaternary faulting has been discovered in the eastern part of Bohemian Massif, 25 km southwest of Brno (Moravia, Czech Republic). Basement serpentinite, fluvial gravels, loess and young scree are affected by a steep NNW–SSE trending fault. The geological situation of the outcrop is described for the first time in this article.

Pb-isotope data on ore galenas from the West Shropshire orefield show a significant spread of 20pb/204pb values, with minor variation in 207Pb/204Pb and 208Pb/204Pb ratios. These indicate that lead was derived from multiple sources, some of them uranium-enriched and incompletely mixed prior to ore deposition. Four possible mineralizing agents are considered: circulating sea-water, metamorphic waters, basinal brines and convecting formation waters. Pb-isotope data exclude a circulating sea-water origin for the mineralization, and best support a convecting formation water mineralizing agent. A model involving a single fluid tapping multiple lead sources is proposed to explain the observed Pb-isotope variation.

The development of a series of internationally acceptable chronostratigraphical units initially grew up through agreed use. Today's requirement of endorsement by the International Commission on Stratigraphy has resulted in the official rejection of names which are perfectly valid and still essential in the parts of the world for which they were introduced. Recognition of this fact is urged, by the acceptance of the Secondary Standards as locally defined chronostratigraphical units pending possible future correlation with the primary standard.

An interpretation of the negative gravity anomaly at Warlingham, Surrey, controlled by a seismic reflection profile and several boreholes, suggest that it may be caused by a wedge-shaped body of lowdensity Upper Palaeozoic rocks. The seismic reflection data suggest that the upper boundary of the body may be thrust-controlled and originated during Variscan compression. The location of the thrusting appears to be controlled by the southern margin of the stable London Platform. Comparison with similar structures of this type elsewhere suggests that the Variscan Front in this area lies just to the north of Warlingham.

Lack of understanding of the graptolite nema and virgula is probably the main cause of the general failure to arrive at a general mode of life theory for planktonic species. The nema and virgula are shown to be different structures. The nema may have had a rhabdosome rotational function at early growth stages; the primary function of the virgula may have been rhabdosomal rotation, whilst a secondary function was as a stipe growth guide. Rotational function would be inapplicable for pseudovirgulae and in synrhabdosomes.

The blueschists of Andros Island consist of a probable Permian-Eocene metasedimentary rock succession (meta-sandstone, marble, chert), containing large bodies of magmatic rock (serpentinized ultra-mafic rocks, gabbros and granodiorite). The development of a layer-parallel foliation and axial plane cleavage, followed by two phases of intense deformation with recumbent folding, almost completely obliterated the primary bedding and stratigraphic relations in the metamorphic complex. The main features of the geological evolution of Andros, that is, the original environment of deposition and the character and direction of tectonic transport, have been hitherto unclear because of this deformation. The present sedimentological and structural study has led to the discovery of preserved relics of primary sedimentary structures, including graded bedding and chaotic sedimentary breccias. Associated turbidite and olistostromic formations can be recognized at three stratigraphic levels in the Andros Island’s reconstructed column. Some layers of the metasedimentary rocks, having preserved clear signs of the layer’s top and bottom, were also used for the identification of the primary anticlines and synclines among widespread developed recumbent folds. This study has shown that the structural style of the last synmetamorphic recumbent folds with northwest vergence is the same, independent of the direction of the present axial plane dips. This data can be interpreted as a result of monovergent tectonic transport in the last metamorphic event. The analysis of structural relations between primary bedding and first synmetamorphic foliation proves that most of the stratigraphic succession has been preserved in a normal stratigraphic position after the first blueschist and before the second greenschist deformation stage.

The blueschists of Andros Island consist of a probable Permian-Eocene metasedimentary rock succession (meta-sandstone, marble, chert), containing large bodies of magmatic rock (serpentinized ultra-mafic rocks, gabbros and granodiorite). The development of a layer-parallel foliation and axial plane cleavage, followed by two phases of intense deformation with recumbent folding, almost completely obliterated the primary bedding and stratigraphic relations in the metamorphic complex. The main features of the geological evolution of Andros, that is, the original environment of deposition and the character and direction of tectonic transport, have been hitherto unclear because of this deformation. The present sedimentological and structural study has led to the discovery of preserved relics of primary sedimentary structures, including graded bedding and chaotic sedimentary breccias. Associated turbidite and olistostromic formations can be recognized at three stratigraphic levels in the Andros Island's reconstructed column. Some layers of the metasedimentary rocks, having preserved clear signs of the layer's top and bottom, were also used for the identification of the primary anticlines and synclines among widespread developed recumbent folds. This study has shown that the structural style of the last synmetamorphic recumbent folds with northwest vergence is the same, independent of the direction of the present axial plane dips. This data can be interpreted as a result of monovergent tectonic transport in the last metamorphic event. The analysis of structural relations between primary bedding and first synmetamorphic foliation proves that most of the stratigraphic succession has been preserved in a normal stratigraphic position after the first blueschist and before the second greenschist deformation stage.