Long-term memory of subduction processes in the lithospheric mantle: evidence from the geochemistry of basic dykes in the Gardar Province of South Greenland

The rift-related magmas of the Proterozoic Gardar Igneous Province were emplaced across the contact between the South Greenland Archaean craton and the Palaeoproterozoic Ketilidian mobile belt. It has been suggested that the geochemistry of Gardar intrusive rocks in the two areas varies across the craton margin and that this reflects a lithospheric control. However, comparison of the geochemical and isotopic signatures of basic and ultrabasic dykes from across the area shows that there is no systematic variation related to the age of the country rock. All the Gardar basic rocks are inferred to have been derived from the mantle, with relatively little crustal contamination. We suggest that the lithospheric mantle beneath the Gardar Province was enriched by slab-derived fluids during the Ketilidian orogeny (c. 1800 Ma). Subsequent melting of this mantle source was promoted during Gardar rifting when volatile-rich, small-degree melts from the asthenosphere were introduced into the lithospheric mantle, forming enriched metasomites. Ultrabasic lamprophyre dykes in the Gardar Province represent melts derived largely from these metasomites, whereas basaltic magmas were formed by larger-scale melting of the lithospheric mantle, inheriting a subductionrelated signature. There is no evidence that the Gardar magmas were derived from a highly enriched lithospheric keel that had existed since craton formation

A reactive assimilation model for regional-scale cordierite-bearing granitoids: geochemical evidence from the Late Variscan granites of the Central Iberian Zone, Spain

Regional scale biotite and cordierite-bearing granites (s.l.) in the Variscan of the Central Iberian Zone (CIZ) are spatially closely associated with cordierite-rich nebulites and cordierite-bearing two-mica granites, and with cordierite-rich high grade hornfelses and cordieritites (>60% cordierite) that are relatively common in the aureoles of these granites. Building on published field evidence, petrological data are presented which, combined with new chemical and isotopic (Sr-Nd) modelling, indicate that the cordierite-bearing granites cannot be derived by simple anatexis of regional sedimenatry protoliths; but the data are consistent with a process of reactive assimilation that involves the interaction of biotite granite magma with high-grade host rocks ranging from cordierite nebulites to andalusite-bearing cordieritites. The contribution of the postulated cordierite-rich contaminants to the diversity of cordierite granite compositions is modelled using the compositions of regional Lower Cambrian-Upper Neoproterozoic metasedimentary rocks that are generally chemically mature (CaO very rarely exceeds 1.4%). These rocks include specific horizons in which extreme chemical alteration is attributable to sediment reworking during eustatic falls in sea level. Such compositions may account for the presence of the high concentrations in Al that later produced cordieritites. Fractional crystallisation is also important, particularly in generating the more evolved cordierite granite and cordierite biotite muscovite granite compositions. Although assimilation in situ is normally regarded as a minor contributor volumetrically to evolving plutons, in this instance the emplacement of large volumes of granite magma into a high-T-low-P environment significantly increased the potential for reactive assimilation

⁸⁷Sr/⁸⁶Sr chemostratigraphy of Neoproterozoic Dalradian limestones of Scotland and Ireland: constraints on depositional ages and time scales

New calcite <sup>87</sup>Sr/<sup>86</sup>Sr data for 47 limestones from the metamorphosed and deformed Neoproterozoic-Cambrian Dalradian Supergroup of Scotland and Ireland are used to identify secular trends in seawater <sup>87</sup>Sr/<sup>86</sup>Sr through the Dalradian succession and to constrain its depositional age. Dalradian limestones commonly have Sr greater than 1000 ppm, indicating primary aragonite and marine diagenesis. Low Mn, Mn/Sr less than 0.6, ë<sup>18</sup>O and trace element data indicate that many <sup>87</sup>Sr/<sup>86</sup>Sr ratios are unaltered since diagenesis despite greenschist- to amphibolite-facies metamorphism, consistent with the documented behaviour of Sr and O during metamorphic fluid-rock interaction. Thus, the <sup>87</sup>Sr/<sup>86</sup>Sr data are interpreted largely to reflect <sup>87</sup>Sr/<sup>86</sup>Sr of coeval seawater. Currently available data show that Neoproterozoic seawater <sup>87</sup>Sr/<sup>86</sup>Sr rose from c. 0.7052 at 850-900 Ma to c. 0.7085 or higher in the latest Neoproterozoic. Temporal changes at c. 800 Ma and c . 600 Ma bracket the range in <sup>87</sup>Sr/<sup>86</sup>Sr values of calcite in Grampian. Appin and lowest Argyll Group (c.0.7064-0.7072) and middle and uppermost Argyll Group (c. 0.7082-0.7095) limestones, consistent with a rise in seawater <sup>87</sup>Sr/<sup>86</sup>Sr around 600 Ma. <sup>87</sup>Sr/<sup>86</sup>Sr data are consistent with the sedimentary affinity of the Islay Subgroup with the underlying Appin Group, and with a possible time interval between deposition of Islay and Easdale Subgroup rocks. They indicate that the Dalradian, as a whole, is younger than c. 800 Ma

The transition from Calc-alkaline to Potassic Volcanism in the Aeolian Islands, Southern Italy

The geochemical and petrological variations of a range of lavas from the Aeolian Islands volcanic arc, southern Italy are investigated and compared with potassic and ultra-potassic volcanism in the Roman region, and with subduction related basalts from throughout the world. Aeolian Islands lavas range from calc-alkaline basalts and andesites, typified by lavas from the island of Salina, to potassium rich shoshonites and tephrites found at Stromboli and Vulcano. Variations within individual lava series may be largely explained by fractional crystallisation, however the differences between the series are not due to this process and the various series are thought to originate from a range of parental magmas with quite different K2O content. Potassic lavas from Vulcano are characterised by incompatible element ratios typical of subduction related volcanism, and by relatively low 87Sr/86Sr ratios (0.70432-0.70494) similar to those of calc-alkaline lavas from Salina (0.70411-0.70466). In contrast at Stromboli, potassic lavas have relatively high Nb and Ta contents and elevated 87Sr/86Sr (0.7050-0.7075) A three component mixing model is proposed to explain the geochemistry of the Aeolian Islands lavas, this involves mantle wedge, a subduction related component thought to originate by dehydration of the subducting lithosphere, and a component derived from subducted sedimentary material. In addition some heterogeneity of the mantle wedge is indicated by within-plate style trace element enrichment in Stromboli lavas. A similar mixing model is applicable to Roman province lavas and also to subduction related basalts throughout the world. Evidence is presented to suggest that variations in certain incompatible element ratios may result from the involvement of small degree partial melting in the genesis of island arc basalts. However it is clear that such a process is not solely responsible for the anomalous trace element geochemistry of subduction related magmatism

142Nd/144Nd Inferences on the nature and origin of the source of high 3He/4He magmas

High-precision measurements of 142Nd/144Nd in picrites from the Baffin Bay region that contain the highest 3He/4He ratios yet measured in terrestrial mantle-derived rocks are indistinguishable from the value measured in the terrestrial standard and other modern mantle-derived rocks. The Baffin Island lavas are distinguished from other hotspot lavas by their unusually high 3He/4He and 182W/184W ratios, but their Sr, 142Nd, 143Nd, Hf, and Pb isotopic signatures overlap the values measured in North Atlantic MORB. These features imply either that the mantle source region of high 3He/4He magmas carries the lithophile isotopic signatures of incompatible element depletion, or that the He isotope signature of this source is decoupled from the lithophile isotope tracers in the magmas. The coupled 142Nd–143Nd data are consistent with the magma source acquiring the incompatible element depletion during, or shortly after, Earth formation if the bulk-Earth has a 142Nd/144Nd ratio more similar to the average measured for enstatite chondrites than modern terrestrial rocks. If Earth's initial 142Nd/144Nd was higher than the average of enstatite chondrites, the data are consistent with the traditional interpretation that the depleted-mantle reservoir was formed through the extraction of an incompatible-element-rich reservoir, such as continental crust, after the circa 4 Ga extinction of 146Sm. This explanation, however, fails to account for the high 3He/4He. The Nd isotopic composition of the picrites could reflect a dominant contribution from the incompatible element depleted source of North Atlantic MORB, overprinted by a small (10–20%) contribution from a mantle source with He concentrations at least ten times higher than the depleted mantle along with W isotopic compositions substantially higher than typical of mantle-derived rocks

Representations of love in the novels of Jeanette Winterson from 1985 to 2000

"What a strange world it is where you can have as much sex as you like but love is taboo. I'm talking about the real thing, the grand passion, which may not allow affection or convenience or happiness. The truth is that love smashes into your life like an ice floe, and even if your heart is built like the Titanic you go down." (TP 51) This reference from Jeanette Winterson's "The Powerbook" typifies the value that love is given in her seven main novels. Love is idealised. It is also depicted as unavoidable, as unavoidable as the ice floe and as potentially destructive. Idealised, inevitable love is the thread that connects Winterson's writing together.Winterson's representations of love and the paradox at the heart of these representations are the primary concerns of this thesis. On the one hand love provides the opportunity for searching for freedom and for crossing barriers of sexuality in her work. This freedom is sought through the questioning of the dominance of heterosexuality in Western discourses of love. Winterson's writing takes pleasure in the concept of the forbidden fruit and challenges the discourses that have legitimised heterosexuality and unhappy marriages. It is understood in her work that normative practices have traditionally been a weapon to marginalise. On the other hand, she posits that love and the effect of loving are transcendent. Love surpasses the everyday. It is special. By suggesting the possibility of transcendence Winterson is enabling the maintenance of hierarchical thinking. Winterson's paradoxical position surfaces when love is heightened as a transcendent emotion. This is a political, material paradox because by allowing for hierarchical thinking her work ultimately maintains rather than deconstructs binary oppositions, whilst simultaneously urging that love should be available to all regardless of sex or sexuality

Cocoa flavanol interactions with intestinal sugar metabolism

The interaction between cocoa polyphenols and sugars was investigated in the Caco-2 cell model. Previous investigations have suggested a link between sugar content of a food/meal and epicatechin bioavailability. To investigate this hypothesis further, the effect of sucrose, glucose and fructose on epicatechin absorption across the Caco-2 monolayer was studied, and is presented here. Apical to basolateral transport of epicatechin was enhanced by co-incubation with sucrose, but not glucose or fructose. It is proposed that sucrose-induced cell signalling stimulated activity of the sodium-dependent glucose transporter SGL T1, which lead to widening of tight junction pore size. Consequently paracellular permeability of epicatechin was enhanced. The presence of glucose or fructose, but not sucrose, reduced the total concentration of methylated epicatechin produced by Caco-2 cells. Decreased formation of methylated epicatechin is hypothesised to be a consequence of catechol-O-methyl transferase inhibition (COMT). COMT requires a magnesium cation cofactor, which is also required by some glycolytic enzymes. It is suggested that competition for the magnesium (11) cofactor leads to reduced epicatechin methylation. Flavanol-rich dark chocolate extract also reduced total methylation of epicatechin. It is proposed that flavanols with a degree of polymerisation greater than monomer compete with epicatechin for methylation

Representations of love in the novels of Jeanette Winterson from 1985 to 2000

"What a strange world it is where you can have as much sex as you like but love is taboo. I'm talking about the real thing, the grand passion, which may not allow affection or convenience or happiness. The truth is that love smashes into your life like an ice floe, and even if your heart is built like the Titanic you go down." (TP 51) This reference from Jeanette Winterson's "The Powerbook" typifies the value that love is given in her seven main novels. Love is idealised. It is also depicted as unavoidable, as unavoidable as the ice floe and as potentially destructive. Idealised, inevitable love is the thread that connects Winterson's writing together. Winterson's representations of love and the paradox at the heart of these representations are the primary concerns of this thesis. On the one hand love provides the opportunity for searching for freedom and for crossing barriers of sexuality in her work. This freedom is sought through the questioning of the dominance of heterosexuality in Western discourses of love. Winterson's writing takes pleasure in the concept of the forbidden fruit and challenges the discourses that have legitimised heterosexuality and unhappy marriages. It is understood in her work that normative practices have traditionally been a weapon to marginalise. On the other hand, she posits that love and the effect of loving are transcendent. Love surpasses the everyday. It is special. By suggesting the possibility of transcendence Winterson is enabling the maintenance of hierarchical thinking. Winterson's paradoxical position surfaces when love is heightened as a transcendent emotion. This is a political, material paradox because by allowing for hierarchical thinking her work ultimately maintains rather than deconstructs binary oppositions, whilst simultaneously urging that love should be available to all regardless of sex or sexuality