Kingsley Dunham Center

Keyworth, United Kingdom

Kingsley Dunham Center

Keyworth, United Kingdom
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Riley T.R.,British Antarctic Survey | Millar I.L.,Kingsley Dunham Center
Antarctic Science | Year: 2014

The recognition of a Mesoproterozoic large igneous province (LIP) across large parts of southern Africa has been strengthened by recent geochronology, geochemistry and petrology. The c. 1100 Ma Umkondo province has been recognized across parts of Botswana, Zimbabwe, South Africa and Mozambique where tholeiitic sills, dykes and rare lava flows have been correlated into a single magmatic province emplaced in the interval 1108-1112 Ma. The extension of the province into the Dronning Maud Land region of Antarctica has been suggested by several workers, but detailed analyses of geochemistry and petrogenesis are lacking, as are comparative studies. This study investigates 25 dykes and sills of the Borgmassivet intrusions which include several of the major diorite sills of the province, up to 300 m in thickness. The dykes and sills are also considered to be c. 1100 Ma and they were emplaced, in part, synchronously with the Ritscherflya Supergroup sedimentary sequence. The Borgmassivet intrusions are characterized by geochemical signatures that suggest the magmas were either extensively contaminated by continental crust or derived from an enriched lithospheric mantle source, where the enrichment was related to earlier subduction. The limited geochemical range of the Borgmassivet and Umkondo intrusions are probably not consistent with significant levels of crustal contamination. Furthermore, the trace element ratios indicate a source in the sub-lithospheric mantle, followed by gabbroic fractionation and interaction with lithospheric wall rocks. © Antarctic Science Ltd 2014.

Fowler M.,University of Portsmouth | Millar I.L.,Kingsley Dunham Center | Strachan R.A.,University of Portsmouth | Fallick A.E.,Scottish Universities Environmental Research Center
Lithos | Year: 2013

The Neoproterozoic (c. 870. Ma) West Highland Granitic Gneiss, exposed in the Northern Highlands Terrane of Scotland, has elemental characteristics that are strikingly similar to those of the host Moine metasediments, which are thus consistent with an origin involving major Moine melting. Most of the constituent bodies have compositions significantly removed from minimum melts of pelites, and trace element constraints suggest variable but significant restite entrainment leading to less silicic bulk compositions with enhanced REE, Zr and Y. However, initial Nd and Hf isotope ratios are not coincident with contemporary Moine and imply a significant juvenile contribution. Close association with a regional suite of metabasites prompts consideration of mafic magma input, for which binary mixing models offer qualitative support. Quantitative difficulties with typical Moine metasediments are eased with radiogenic pelites or by partial melting of the mafic component. A possible alternative is currently unexposed Grenvillian felsic crust. Subsequent interaction of the granitic gneisses with meteoric water has significantly perturbed the oxygen and Sr isotope systems, the timing of which is equivocal but probably occurred during Caledonian events.The elemental characteristics of the West Highland Granitic Gneiss show many similarities with Scandinavian (rift-related?) granites of the same age, but since their geochemistry is largely inherited from the protolith it would be unwise to pursue palaeotectonic attribution on this basis. However, the probable incorporation of significant mantle-derived mafic magma of MORB-like affinity is consistent with an extensional setting. © 2013 Elsevier B.V.

Horak J.M.,National Museum of Wales | Evans J.A.,Kingsley Dunham Center
Geological Magazine | Year: 2011

Limestone megaclasts up to hundreds of metres in size are present within the Gwna Group mélange, North Wales, UK. The mélange has been interpreted as part of a Peri-Gondwanan fore-arc accretionary complex although the age of deposition remains contentious, proposals ranging from Neoproterozoic to Early Ordovician. This paper uses strontium isotope chemostratigraphy to establish the age of the limestone blocks and thus provide a maximum age constraint on mélange formation. Results show that, although the carbonates are locally dolomitized, primary 87Sr/86Sr ratios can be identified and indicate deposition sometime between the late Tonian and earliest Cryogenian. This age is older than that suggested by stromatolites within the limestone and indicates that the limestone did not form as cap carbonate deposits. © Cambridge University Press 2010.

Palin R.M.,University of Oxford | Searle M.P.,University of Oxford | Waters D.J.,University of Oxford | Parrish R.R.,Kingsley Dunham Center | And 5 more authors.
Journal of Metamorphic Geology | Year: 2013

The Red River shear zone (RRSZ) is a major left-lateral strike-slip shear zone, containing a ductilely deformed metamorphic core bounded by brittle strike-slip and normal faults, which stretches for >1000 km from Tibet through Yunnan and North Vietnam to the South China Sea. The RRSZ exposes four high-grade metamorphic core complexes along its length. Various lithologies from the southernmost core complex, the Day Nui Con Voi (DNCV), North Vietnam, provide new constraints on the tectonic and metamorphic evolution of this region prior to and following the initial India-Asia collision. Analysis of a weakly deformed anatectic paragneiss using P-T pseudosections constructed in the MnO-Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-O (MnNCKFMASHTO) system provides prograde, peak and retrograde metamorphic conditions, and in situ U-Th-Pb geochronology of metamorphic monazite yields texturally controlled age constraints. Tertiary metamorphism and deformation, overprinting earlier Triassic metamorphism associated with the Indosinian orogeny and possible Cretaceous metamorphism, are characterized by peak metamorphic conditions of ~805 °C and ~8.5 kbar between c. 38 and 34 Ma. Exhumation occurred along a steep retrograde P-T path with final melt crystallizing at the solidus at ≥~5.5 kbar at ~790 °C. Further exhumation at ~640-700 °C and ~4-5 kbar at c. 31 Ma occurred at subsolidus conditions. U-Pb geochronological analysis of monazite from a strongly deformed pre-kinematic granite dyke from the flank of the DNCV provides further evidence for exhumation at this time. Magmatic grains suggest initial emplacement at 66.0 ± 1.0 Ma prior to the India-Asia collision, whereas grains with metamorphic characteristics indicate later growth at 30.6 ± 0.4 Ma. Monazite grains from a cross-cutting post-kinematic dyke within the core of the DNCV antiform provide a minimum age constraint of 25.2 ± 1.4 Ma for the termination of fabric development. A separate and significant episode of monazite growth at c. 83-69 Ma is suggested to be the result of fluid-assisted recrystallization following the emplacement of magmatic units. © 2012 Blackwell Publishing Ltd.

Vaughan A.P.M.,British Antarctic Survey | Leat P.T.,British Antarctic Survey | Dean A.A.,British Antarctic Survey | Millar I.L.,Kingsley Dunham Center
Lithos | Year: 2012

Subduction-related Mesozoic mafic dykes in eastern Palmer Land, Antarctic Peninsula, record the development of an intra-oceanic arc terrane, the Dyer Arc, probably of late Permian-Triassic age, represented by a tholeiitic dyke group. Arc rocks were deformed in late Triassic-early Jurassic and mid-Cretaceous times on the Gondwana margin. Eruption of syn- to post-mid-Cretaceous orogenesis magmatism is represented by a calc-alkaline group of dykes. The tholeiitic dykes intruded immature granitic crust of the Eastern Zone sub-terrane of the Central Domain, one of the magmatic terranes of the Pacific margin of Gondwana. The calc-alkaline dykes straddle the major tectonic boundary between the Central Domain and the continental margin Eastern Domain. 132 dykes were studied, 82 of which are calc-alkaline, 48 tholeiitic and two shoshonitic, across an area of approximately 4000km 2. Tholeiitic dykes strike broadly NNW-SSE, transposed into parallelism with the strike of the tectonic boundary during Cretaceous orogenesis whereas calc-alkaline dykes strike tightly ESE-WNW at a high angle to the boundary. The tholeiites pre-date late Triassic deformation and metamorphism, and are interpreted as dominantly Triassic in age, whereas Ar-Ar dated calc-alkaline dykes are younger (~100Ma and ~97Ma) and field relations indicate that they overlap with the waning phase of the mid-Cretaceous Palmer Land Event. The tholeiites have trace element abundances similar to, but more depleted than, those of modern intra-oceanic arcs, as recorded by Zr/Hf ratios. Nb/Yb versus TiO 2 */Yb and Sm/Yb versus La/Sm plots are used to model depths of partial melting. The tholeiites were mostly generated at shallow depths corresponding to 2.5 and certainly less than 3.0GPa in largely garnet-free mantle. The calc-alkaline magmas were generated at pressures greater than 3.0 to possibly >3.5GPa, in the garnet zone. The deepening of the mantle source, and onset of calc-alkaline magmatism are interpreted to have been caused by deformation of the intra-oceanic arc terrane on the Gondwana margin, and lithospheric thickening during the Palmer Land Event. © 2012 Elsevier B.V.

Palin R.M.,University of Oxford | Searle M.P.,University of Oxford | Waters D.J.,University of Oxford | Horstwood M.S.A.,Kingsley Dunham Center | Parrish R.R.,Kingsley Dunham Center
Journal of Metamorphic Geology | Year: 2012

Petrographic analysis of peraluminous metapelites from two separate regions of the Karakoram metamorphic complex, North Pakistan, has produced new insights into the P-T-t evolution of the deep crust along the south Asian margin before and after the India-Asia collision. Average P-T estimates and pseudosection construction in the MnO-Na 2O-CaO-K 2O-FeO-MgO-Al 2O 3-SiO 2-H 2O-TiO 2-Fe 2O 3 (MnNCKFMASHTO) system using THERMOCALC have provided prograde and peak metamorphic conditions and U-Pb geochronology of metamorphic monazite has provided age constraints. Two new events in the tectonothermal evolution of the Hunza Valley have been documented; an andalusite-grade contact metamorphic event at 105.5±0.8Ma, at unknown P-T conditions, associated with the widespread subduction-related granite magmatism before the India-Asia collision, and a kyanite-grade overprint of sillimanite-grade rocks with peak P-T conditions of ~7.8kbar, 645°C at 28.2±0.8Ma associated with the ongoing India-Asia collision. A kyanite-grade event observed in the Baltoro region with similar peak P-T conditions (~7.4-8.0kbar, ~640-660°C) is interpreted to have occurred sometime after 21.8±0.6Ma, however, previous studies have suggested that this event commenced in the Baltoro as early as c. 28Ma. A calculated prograde P-T path for this kyanite-grade event in the Baltoro indicates that garnet first nucleated on an initially high geothermal gradient (~30°Ckm -1) and grew during a significant increase in pressure of ~2.6kbar over a temperature increase of ~100°C. This event is thought to represent evidence for conductive heating of the middle crust during early stages of intrusion and lateral migration of the Baltoro batholith, with thermal conditions comparable with tectonic models of magmatic over-accretion. © 2012 Blackwell Publishing Ltd.

Henderson A.L.,Lancaster University | Najman Y.,Lancaster University | Parrish R.,Kingsley Dunham Center | Mark D.F.,Scottish Enterprise | Foster G.L.,UK National Oceanography Center
Earth-Science Reviews | Year: 2011

Deposited within the Indus-Tsangpo suture zone, the Cenozoic Indus Basin sedimentary rocks have been interpreted to hold evidence that may constrain the timing of India-Eurasia collision, a conclusion challenged by data presented here. The Eurasian derived 50.8-51. Ma Chogdo Formation was previously considered to overlie Indian Plate marine sedimentary rocks in sedimentary contact, thus constraining the timing of collision as having occurred by this time. Using isotopic analysis (U-Pb dating on detrital zircons, Ar-Ar dating on detrital white mica, Sm-Nd analyses on detrital apatite), sandstone and conglomerate petrography, mudstone geochemistry, facies analysis and geological mapping to characterize and correlate the formations of the Indus Basin Sedimentary rocks, we review the nature of these contacts and the identification and correlation of the formations. Our results reveal that previously interpreted stratigraphic contacts identifying Chogdo Formation unconformably overlying Indian plate sedimentary rocks are incorrect. Rather, we suggest that the inaccuracy of previous interpretations is most likely a result of Formation misidentification and thus cannot be used to constrain the timing of India-Asia collision. © 2011 Elsevier B.V.

Dickson A.J.,University College London | Leng M.J.,Kingsley Dunham Center | Maslin M.A.,University College London | Rohl U.,University of Bremen
Quaternary Science Reviews | Year: 2010

Variations in the strength of coastal upwelling in the South East Atlantic Ocean and summer monsoonal rains over South Africa are controlled by the regional atmospheric circulation regime. Although information about these parameters exists for the last glacial period, little detailed information exists for older time periods. New information from ODP Site 1085 for Marine Isotope Stages (MIS) 12-10 shows that glacial-interglacial productivity trends linked to upwelling variability followed a pattern similar to the last glacial cycle, with maximums shortly before glacial maxima, and minimums shortly before glacial terminations. During the MIS-11/10 transition, several periodic oscillations in productivity and monsoonal proxies are best explained by southwards shifts in the southern sub-tropical high-pressure cells followed by abrupt northwards shifts. Comparison to coeval sea-surface temperature measurements suggests that these monsoonal cycles were tightly coupled to anti-phased hemispheric climate change, with an intensified summer monsoon during periods of Northern (Southern) Hemisphere cooling (warming). The timing of these events suggests a pacing by insolation over precession periods. A lack of similar regional circulation shifts during the MIS-13/12 transition is likely due to the large equatorwards shift in the tropical convection zone that occurred during this extreme glaciation. © 2010 Elsevier Ltd.

Schofield D.I.,British Geological Survey | Millar I.L.,Kingsley Dunham Center | Wilby P.R.,British Geological Survey | Evans J.A.,Kingsley Dunham Center
Geological Magazine | Year: 2010

A new high precision U-Pb zircon age of 710.8 ± 1.5 Ma for granophyric granitic rock from the Stanner Hanter Complex of the Welsh Borderland lies just within error of an older Rb-Sr isochron age. Nd values of -0.3 and -1.2 combined with TDM of 1394 Ma and 1468 Ma indicate that the magma incorporated an older crustal source component. The Nd data highlight differences with western Avalonia, the widely considered Late Neoproterozoic north American counterpart to southern Britain, and point toward a closer similarity with other Peri-Gondwanan terranes that incorporate older, cratonic source material. Copyright © Cambridge University Press 2009.

Meek A.,British Museum | Henderson J.,University of Nottingham | Evans J.,Kingsley Dunham Center
Journal of Analytical Atomic Spectrometry | Year: 2012

Glass is one of several early modern industries where the development from small-scale workshop to large-scale industry offers a valuable insight into wider socio-economic trends. Previously, medieval and early modern forest (wood ash) glass has been studied using a range of analytical techniques. However, characterisations of production centres and exchange systems for forest glasses are difficult to verify, in part because very few examples of raw glass from furnace sites have been investigated. Compositional analysis can provide evidence for the raw materials used and can sometimes provide compositional groupings specific to sites. However, strontium and neodymium isotope determinations can actually provenance the glass by linking the geological ages, or sources, of raw materials to production sites. Using EPMA fifty-six raw glass samples from four sites in two English production areas in operation during the 14 th and 16 th centuries have been analysed. These analyses have shown that the main products of these sites were potash-rich, wood or bracken ash glasses. However, the chemical composition does not provide sufficient resolution to identify differences between the two English regions or the sites within these regions. A subset of five raw glass samples from each of these sites have also been analysed using TIMS to determine strontium and neodymium concentration and isotope ratios. The results allow glasses produced in each region to be differentiated, and can even be used to divide glass production sites within the regions. © 2012 The Royal Society of Chemistry.

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