ALBERT

Description: This paper explores, within a historical context, the importance of geoconservation of not only sites but also artefacts, collections and specimens as well as letters and original documents. It sets out the search and finding of sites in northeast Wales and materials thought lost then found and the subsequent nomination of Regionally Important Geological/Geomorphological Sites (RIGS) conservation status of the sites to safeguard them for the future. It is important to note that RIGS can be designated for their historical value alone, which is in contrast to Sites of Special Scientific Interest (SSSIs), which are protected solely for their national scientific and research value. The role of Ethel Woods (nee Skeat) and Margaret Crosfield in developing an understanding of the geological history of northeast Wales had been lost over time. This paper contains biographical sketches of the two women, followed by their Lower Palaeozoic lithological, structural and graptolite research and places it in an historical context. This case study illustrates how female curiosity, perseverance and attention to detail unearthed previously forgotten treasures. The importance of conserving their sites, specimens and sketch field notebooks in our electronic and throw-away age is vital. The role of the North East Wales Regionally Important Geological/Geomorphological Sites (NEWRIGS) in conserving this information is put forward as an example of good practice.

Description: Late Miocene to Quaternary intraplate basaltic volcanism in the Al Ghab and Homs regions, northwestern Syria (the Al Ghab volcanic group and the Homs volcanic group), occurred roughly synchronously with the propagation of the Dead Sea Fault System in these regions. Petrographic evidence as well as major and trace element variations suggest that the basalts have undergone varying amounts of crystal fractionation of olivine ± clinopyroxene ± spinel, with feldspar fractionation only in the most evolved samples. The major and trace element chemistry and Nd–Sr–Pb isotopic variations of the basalts reflect both mantle source heterogeneity and relatively minor crustal contamination. Semi-quantitative assimilation–fractional crystallization modelling suggests that some samples may reflect assimilation of no more than 6% of upper continental crust, probably with Late Proterozoic Arabian Shield characteristics. Amongst the least crustally contaminated and relatively primitive samples, basanites are characterized by marked depletion of K, Rb and Zr relative to other neighbouring incompatible elements on primitive mantle normalized trace element diagrams. This, together with their low SiO 2 and high TiO 2 and Dy/Yb, is consistent with magma genesis involving a large proportion of garnet-bearing hornblendite or similar amphibole-rich metasomatic veins. Associated alkali and tholeiitic basalts with the higher SiO 2 , lower TiO 2 , less negative K, Rb and Zr anomalies, and moderately high Dy/Yb are consistent with melt extraction from a largely peridotitic mantle source. It is suggested that the compositional spectrum from basanite via alkali basalt to tholeiitic basalt can be explained by increasing degrees of metasomatic vein–wall-rock interaction, plus asthenospheric melt assimilation. In agreement with this is the identification of three distinct isotopic and chemical characteristics within the spectrum of mafic lavas, each of which can be referred to a unique mantle source (metasomatic vein, lithospheric wall-rock peridotite mantle and asthenospheric peridotite mantle). A decrease in eruption volume and increase in Si-undersaturation of the lavas from south (Homs) to north (Al Ghab) along the northern Dead Sea Fault System from latest Miocene to Quaternary times suggest a diminishing thermal perturbation and increasing importance of the amphibole-rich veins in magma genesis over time. It is proposed that the genesis of the oldest lavas reflects the arrival of asthenospheric melts beneath the Homs region, which with assimilation of lithospheric metasomatic veins and their wall-rocks produced the parental magmas of the Homs volcanic group. Subsequently, upwelling asthenospheric material could have been channelled northwards at the base of the lithosphere, presumably related to the northward propagation of the Dead Sea Fault System in the Pliocene. Cooling of this channelled asthenospheric material, which did not penetrate the lithosphere during this later period of magma genesis, provided the minimal thermal perturbation necessary for melting of amphibole-rich metasomatic veins and wall-rock peridotite within the lithosphere.

Description: An unusual andesitic suite from the Miocene volcanic arc in Northland, New Zealand, comprises pyroxene andesite and garnet-bearing hornblende–pyroxene, hornblende and biotite–hornblende andesites. Garnet crystals occur as 1–10 mm single crystals or more commonly as two or more annealed crystals and as garnetite lenses. The andesitic rocks also contain enclaves of high-MgO pyroxenite, hornblendite, and pyroxene–hornblende gabbro as well as high-Al 2 O 3 hornblende gabbro, garnet–hornblende gabbro, and anorthosite. Garnet crystals in the andesitic volcanic rocks and in the enclaves show comparable compositional ranges, zoning patterns and inclusions, which indicate that they share a common petrogenetic history. They can be grouped into four distinct types on the basis of mode of occurrence, chemical composition and zoning patterns, which leads to their interpretation as antecrysts rather than orthocrysts. The compositions of the garnets, as well as their included mineral assemblages, reflect a petrogenetic trend from high-temperature pyroxene-bearing high-Mg garnet to low-temperature Fe-rich garnet at relatively constant pressure. Well-preserved zoning patterns, in particular those of the Ca- and Mg-rich garnets, reflect processes within a deep crustal arc environment. Later assimilation is suggested by some zoning patterns that show decreasing Ca and increasing Fe and Mn contents. The garnets are interpreted as being derived by disintegration of discrete but closely related cumulate material that formed at pressures of 8–10 kbar. The host volcanic rocks and their garnet crystals together with the enclaves thus represent a consanguineous mixture of liquid and solid components that developed where subduction-related magmas ponded and interacted at or near the base of the crust. Together they represent a rare snapshot of the processes and components that produce arc-type rocks.

Description: Early–Middle Miocene intraplate basalts from the Aleppo Plateau, NW Syria have been analysed for their platinum-group elements (PGEs). They contain extremely low PGE abundances, comparable with most alkali basalts, such as those from Hawaii, and mid-ocean ridge basalts. The low abundances, together with high Pd/Ir, Pt/Ir, Ni/Ir, Cu/Pd, Y/Pt and Cu/Zr are consistent with sulphide fractionation, which likely occurred during partial melting and melt extraction within the mantle. Some of the basalts are too depleted in PGEs to be explained solely by partial melting of a primitive mantle-like source. Such ultra-low PGE abundances, however, are possible if the source contains some mafic lithologies. Many of the basalts also exhibit suprachondritic Pd/Pt ratios of up to an order of magnitude higher than primitive mantle and chondrite, an increase too high to be attributable to fractionation of spinel and silicate minerals alone. The elevated Pd/Pt, associated with a decrease in Pt but not Ir and Ru, are also inconsistent with removal of Pt-bearing PGE minerals or alloys, which should have concurrently lowered Pt, Ir and Ru. In contrast, melting of a metasomatized source comprising sulphides whose Pt and to a lesser extent Rh were selectively mobilized through interaction with silicate melts, may provide an explanation.