Distribution and abundance patterns of two parapagurid hermit crabs (Crustacea: Decapoda: Anomura) along the west and south coasts of South Africa

A series of over 6 000 research-trawl samples collected along the west and south coasts of South Africa between 1987 and 2014 were analysed for the presence and biomass of two parapagurid hermit crabs, Sympagurus dimorphus and Parapagurus bouvieri. The percentage of trawls that landed S. dimorphus and P. bouvieri and the mean caught biomass were higher on the west than on the south coast for both the more-abundant S. dimorphus (30.59 vs 5.81% success and 287.88 vs 31.37 kg km^–2, respectively) and for the less-abundant P. bouvieri (13.76 vs 3.58% success and 38.56 vs 16.32 kg km^–2, respectively). Very few parapagurids were caught shallower than 150 m; thereafter, the proportion of trawls containing hermit crabs increased, peaking over the depth range 201–250 m for S. dimorphus (54%) and 401–450 m for P. bouvieri (51%), and declining steadily thereafter. On the west coast, the relative caught biomass of S. dimorphus increased significantly from north to south, but there was no apparent latitudinal trend in relative biomass for P. bouvieri. Similarly, there was a significant decline in caught biomass of S. dimorphus with increasing longitude along the south coast, but no apparent trend for P. bouvieri. Although this represents by far the most comprehensive global analyses of distribution and abundance patterns for parapagurids to date, extremely little remains known about the biology and ecological relationships of these species, or indeed of other members of the group.     

Deep seismic reflection profiling in the Archaean northeastern Yilgarn Craton, Western Australia: implications for crustal architecture and mineral potential

Deep seismic reflection data across the Archaean Eastern Goldfields Province, northeastern Yilgarn Craton, Western Australia, have provided information on its crustal architecture and on several of its highly mineralised belts. The seismic reflection data allow interpretation of several prominent crustal scale features, including an eastward thickening of the crust, subdivision of the crust into three broad layers, the presence of a prominent east dip to the majority of the reflections and the interpretation of three east-dipping crustal-penetrating shear zones. These east-dipping shear zones are major structures that subdivide the region into four terranes. Major orogenic gold deposits in the Eastern Goldfields Province are spatially associated with these major structures. The Laverton Tectonic Zone, for example, is a highly mineralised corridor that contains several world-class gold deposits plus many smaller deposits. Other non crustal-penetrating structures within the area do not appear to be as well endowed metallogenically as the Laverton structure. The seismic reflection data have also imaged a series of low-angle shear zones within and beneath the granite–greenstone terranes. Where the low-angle shear zones intersect the major crustal-penetrating structures, a wedge shaped geometry is formed. This geometry forms a suitable fluid focusing wedge in which upward to subhorizontal moving fluids are focused and then distributed into the nearby complexly deformed greenstones.     

The Mesoarchean emergence of modern-style subduction

Well-preserved volcanic sequences span the Paleoarchean to Neoarchean evolution of the Pilbara Craton, in northwestern Australia. This region provides the best physical evidence bearing on the stage of Earth's history when modern-style tectonic processes began. Paleoarchean assemblages in the eastern nucleus of the craton (the 3.51–3.24 Ga Pilbara Supergroup) show few features that can reasonably be interpreted as evidence for modern-style subduction processes. Incompatible trace element-enriched felsic volcanic horizons show geochemical evidence for the interaction between mafic magmas and crust, but this evidence, on its own, can equally well be interpreted in terms of either a subduction-enriched mantle source or local and limited assimilation of felsic crust into the voluminous tholeiitic magmas that dominate the Pilbara Supergroup. Viewed in context within the thick autochthonous and consistently upward-younging Pilbara Supergroup, these felsic units are most likely related to the same plume-dominated processes that formed the basalts that dominate the supergroup. It is very unlikely that modern-style plate tectonic processes played any role in the Paleoarchean evolution of the Pilbara Craton, although some form of non-uniformitarian (e.g. flat) subduction process may have operated.In stark contrast, the Mesoarchean units of the West Pilbara Terrane and the late-tectonic basins that cover that boundary between the West and East Pilbara Terranes, show clear evidence for modern-style convergent margin processes. Igneous rocks in this belt, which flanks the old eastern cratonic nuclei, have enriched geochemical signatures that cannot be accounted for by crustal contamination. This region is also characterised by a linear magmatic and structural fabric, by the presence of lithologically and geochronologically exotic belts, and by the presence of a broad belt of isotopically more juvenile crust. The collective strength of these arguments provides compelling evidence that a modern-style oceanic arc fringed the East Pilbara Terrane at 3.12 Ga and accreted to that terrane by 2.97 Ga. These assemblages mark the minimum age for the birth of modern-style plate subduction process.     

Geodynamics of the eastern Yilgarn Craton

Over the last decade there have been significant advances in our understanding of the stratigraphy, magmatism, deformation, metamorphism and timing of mineralisation, in the eastern Yilgarn Craton (EYC) of Western Australia. The integration of these disciplines has enabled a holistic review of the tectonic history of the EYC which favours a paraautochthonous tectonic model.     

Kīlauea summit overflows: their ages and distribution in the Puna District, Hawai'i

 The tube-fed pāhoehoe lava flows covering much of the northeast flank of Kīlauea Volcano are named the 'Ailā'au flows. Their eruption age, based on published and six new radiocarbon dates, is approximately AD 1445. The flows have distinctive paleomagnetic directions with steep inclinations (40°–50°) and easterly declinations (0°–10°E). The lava was transported ∼40 km from the vent to the coast in long, large-diameter lava tubes; the longest tube (Kazumura Cave) reaches from near the summit to within several kilometers of the coast near Kaloli Point. The estimated volume of the 'Ailā'au flow field is 5.2±0.8 km³, and the eruption that formed it probably lasted for approximately 50 years. Summit overflows from Kīlauea may have been nearly continuous between approximately AD 1290 and 1470, during which time a series of shields formed at and around the summit. The 'Ailā'au shield was either the youngest or the next to youngest in this series of shields. Site-mean paleomagnetic directions for lava flows underlying the 'Ailā'au flows form only six groups. These older pāhoehoe flows range in age from 2750 to <18,000 BP, and the region was inundated by lava flows only three times in the past 5000 years. The known intervals between eruptive events average ∼1600 years and range from ∼1250 years to >2200 years. Lava flows from most of these summit eruptions also reached the coast, but none appears as extensive as the 'Ailā'au flow field. The chemistry of the melts erupted during each of these summit overflow events is remarkably similar, averaging approximately 6.3 wt.% MgO near the coast and 6.8 wt.% MgO near the summit. The present-day caldera probably formed more recently than the eruption that formed the 'Ailā'au flows (estimated termination ca. AD 1470). The earliest explosive eruptions that formed the Keanakāko'i Ash, which is stratigraphically above the 'Ailā'au flows, cannot be older than this age. Received: 10 October 1998 / Accepted: 12 May 1999     

Rotation measure variations for 20 millisecond pulsars

We report on variations in the mean position angle of the 20 millisecond pulsars being observed as part of the Parkes Pulsar Timing Array (PPTA) project. It is found that the observed variations are dominated by changes in the Faraday rotation occurring in the Earth??s ionosphere. Two ionospheric models are used to correct for the ionospheric contribution and it is found that one based on the International Reference Ionosphere gave the best results. Little or no significant long-term variation in interstellar RM was found with limits typically about 0.1 rad?m^?2?yr^?1 in absolute value. In a few cases, apparently significant RM variations over timescales of a few 100 days or more were seen. These are unlikely to be due to localised magnetised regions crossing the line of sight since the implied magnetic fields are too high. Most probably they are statistical fluctuations due to random spatial and temporal variations in the interstellar electron density and magnetic field along the line of sight.     

Who moves into, out of and within London?

Summary Eight variables from the 1991 Census 2% Sample of Anonymised Records are used to classify Greater London's population into ten socio-demographic groups. This provides the basis for examining differences between 'types of people' in the extent to which they changed address in the year before the Census and whether they moved into, out of or within London.