Hawkins T.,University of Brighton |
Hawkins T.,Natural History Museum in London |
Smith M.P.,University of Brighton |
Herrington R.J.,Natural History Museum in London |
And 4 more authors.
Ore Geology Reviews | Year: 2017
The magnetite deposits of the Turgai belt (Kachar, Sarbai and Sokolov), in the Valerianovskoe zone of the southern Urals, Kazakhstan, contain a combined resource of over 3 Gt of iron oxide ore. The deposits are hosted by carbonate sediments and volcaniclastic rocks of the Carboniferous Valerianovka Supergroup, and are spatially related to the gabbroic to granitoid composition intrusive rocks of the Sarbai–Sokolov intrusive series. The magnetite deposits are developed dominantly as metasomatic replacement of limestone, but also, to a lesser extent, of volcanic rocks. Pre-mineralisation metamorphism and alteration resulted in the formation of wollastonite and the silicification of limestone. Magnetite mineralisation is associated with the development of a high temperature skarn assemblage of diopside, grossular–andradite garnet, actinolite, epidote and apatite. Sub-economic copper-bearing sulphide mineralisation overprints the magnetite mineralisation and is associated with deposition of hydrothermal calcite and the formation of an extensive sodium alteration halo dominated by albite and scapolite. Chlorite formation accompanies this stage and further later stage hydrothermal overprints. The replacement has in places resulted in preservation of primary features of the limestone, including fossils and sedimentary structures in magnetite, skarn calc-silicates and sulphides. Analysis of Re–Os isotopes in molybdenite indicates formation of the sulphide mineral assemblage at 336.2 ± 1.3 Ma, whilst U–Pb analyses of titanite from the skarn alteration assemblage suggests skarn alteration at 326.6 ± 4.5 Ma with re-equilibration of isotope systematics down to ~ 270 Ma. Analyses of mineral assemblages, fluid inclusion microthermometry, O and S isotopes suggest initial mineralisation temperatures in excess of 600 °C from hypersaline brines (45–50 wt.% NaCl eq.), with subsequent cooling and dilution of fluids to around 150 °C and 20 wt.% NaCl eq. by the time of calcite deposition in late stage sulphide-bearing veins. δ18O in magnetite (− 1.5 to + 3.5‰) and skarn forming silicates (+ 5 to + 9‰), δ18O and δ13C in limestone and skarn calcite (δ18O + 5.4 to + 26.2‰; δ13C − 12.1 to + 0.9‰) and δ34S in sulphides (− 3.3 to + 6.6‰) and sulphates (+ 4.9 to + 12.9‰) are all consistent with the interaction of a magmatic-equilibrated fluid with limestone, and a dominantly magmatic source for S. All these data imply skarn formation and mineralisation in a magmatic–hydrothermal system that maintained high salinity to relatively late stages resulting in the formation of the large Na-alteration halo. Despite the reported presence of evaporites in the area there is no evidence for evaporitic sulphur in the mineralising system. These skarns show similarities to some members of the iron oxide–apatite and iron oxide–copper gold deposit classes and the model presented here may have implications for their genesis. The similarity in age between the Turgai deposits and the deposits of the Magnitogorsk zone in the western Urals suggests that they may be linked to similar magmatism, developed during post-orogenic collapse and extension following the continent–continent collision, which has resulted in the assembly of Laurussian terranes with the Uralide orogen and the Kazakh collage of the Altaids or Central Asian Orogenic Belt. This model is preferred to the model of simultaneous formation of very similar deposits in arc settings at either side of an open tract of oceanic crust forming part of the Uralian ocean. © 2015 Elsevier B.V.
Starkey N.A.,Open University Milton Keynes |
Jackson C.R.M.,Carnegie Institution of Washington |
Greenwood R.C.,Open University Milton Keynes |
Parman S.,Brown University |
And 6 more authors.
Geochimica et Cosmochimica Acta | Year: 2016
Measurements of Xe isotope ratios in ocean island basalts (OIB) suggest that Earth's mantle accreted heterogeneously, and that compositional remnants of accretion are sampled by modern, high-3He/4He OIB associated with the Icelandic and Samoan plumes. If so, the high-3He/4He source may also have a distinct oxygen isotopic composition from the rest of the mantle. Here, we test if the major elements of the high-3He/4He source preserve any evidence of heterogeneous accretion using measurements of three oxygen isotopes on olivine from a variety of high-3He/4He OIB locations. To high precision, the δ17O value of high-3He/4He olivines from Hawaii, Pitcairn, Baffin Island and Samoa, are indistinguishable from bulk mantle olivine (δ17OBulk Mantle-δ17OHigh 3He/4He olivine=-0.002±0.004 (2×SEM)‰). Thus, there is no resolvable oxygen isotope evidence for heterogeneous accretion in the high-3He/4He source. Modelling of mixing processes indicates that if an early-forming, oxygen-isotope distinct mantle did exist, either the anomaly was extremely small, or the anomaly was homogenised away by later mantle convection.The δ18O values of olivine with the highest 3He/4He ratios from a variety of OIB locations have a relatively uniform composition (~5‰). This composition is intermediate to values associated with the depleted MORB mantle and the average mantle. Similarly, δ18O values of olivine from high-3He/4He OIB correlate with radiogenic isotope ratios of He, Sr, and Nd. Combined, this suggests that magmatic oxygen is sourced from the same mantle as other, more incompatible elements and that the intermediate δ18O value is a feature of the high-3He/4He mantle source. The processes responsible for the δ18O signature of high-3He/4He mantle are not certain, but δ18O-87Sr/86Sr correlations indicate that it may be connected to a predominance of a HIMU-like (high U/Pb) component or other moderate δ18O components recycled into the high-3He/4He source. © 2016 Published by Elsevier Ltd.
Kirkbride M.,University of Dundee |
Everest J.,British Geological Survey |
Benn D.,UNIS |
Gheorghiu D.,SUERC |
Dawson A.,University of Aberdeen
Holocene | Year: 2014
We present 17 cosmogenic 10Be ages of glacial deposits in Coire an Lochain (Cairngorm Mountains), which demonstrate that glacial and nival deposits cover a longer timescale than previously recognised. Five ages provide the first evidence of a late-Holocene glacier in the British Isles. A previously unidentified moraine ridge was deposited after c. 2.8 kyr and defines a small slab-like glacier with an equilibrium line altitude (ELA) at c. 1047 m. The late-Holocene glacier was characterised by rapid firnification and a dominance of sliding, enabling the glacier to construct moraine ridges in a relatively short period. Isotopic inheritance means that the glacier may have existed as recently as the 'Little Ice Age' (LIA) of the 17th or 18th century ad, a view supported by glacier-climate modelling. Nine 10Be ages confirm a Younger Dryas Stadial (YDS) age for a cirque-floor boulder till, and date the glacier maximum to c. 12.3 kyr when the ELA was at c. 963 m altitude. Both glaciers existed because of enhanced accumulation from wind-blown snow, but the difference in ELA of only c. 84 m belies the YDS-LIA temperature difference of c. 7°C and emphasises the glacioclimatic contrast between the two periods. Three 10Be ages from till boulders originally deposited in the YDS yield ages <5.5 kyr and indicate snow-avalanche disturbance of older debris since the mid-Holocene, as climate deteriorated towards marginal glaciation. © The Author(s) 2013.
Kinnaird T.C.,SUERC |
Sanderson D.C.W.,SUERC |
Woodward N.L.,University of Aberdeen
Earth and Environmental Science Transactions of the Royal Society of Edinburgh | Year: 2011
Luminescence methods were used to date a palaeoenvironmental coastal exposure on Stronsay, Orkney. The section consists of glacial sediments that are overlain by intercalated peats and windblown sands, implying varying past environmental conditions. Rapid luminescence characterisation was undertaken using screening methods in combination with quantitative dating of selected samples, providing information on depositional processes and chronology. A temporal discontinuity between the glacial sediments and later peats encompasses the period associated with an important Mesolithic site located inland, and implies erosional episodes. The onset of blanket bog formation on Stronsay dates to 3760±330 yrs BP, consistent with observations elsewhere in Orkney and northern Scotland. Periods of enhanced aeolian activity on Stronsay occurred in the late Bronze Age (2700±265 yrs BP) and at the beginning of the Little Ice Age (650±75 yrs BP). Recent periods of sand deposition in the 19th and 20th centuries (AD 1865±20 and 1960±5) correspond to periods of known historic storminess. These results add to an expanding catalogue of data on sand movements throughout the Holocene in Orkney, and set a framework to interpret the evolution of nearby archaeological and natural landscapes from prehistoric to modern times. Copyright © Royal Society of Edinburgh 2012.
Torres Acosta V.,University of Potsdam |
Bande A.,University of Potsdam |
Sobel E.R.,University of Potsdam |
Parra M.,University of Sao Paulo |
And 4 more authors.
Tectonics | Year: 2015
The cooling history of rift shoulders and the subsidence history of rift basins are cornerstones for reconstructing the morphotectonic evolution of extensional geodynamic provinces, assessing their role in paleoenvironmental changes and evaluating the resource potential of their basin fills. Our apatite fission track and zircon (U-Th)/He data from the Samburu Hills and the Elgeyo Escarpment in the northern and central sectors of the Kenya Rift indicate a broadly consistent thermal evolution of both regions. Results of thermal modeling support a three-phased thermal history since the early Paleocene. The first phase (~65-50 Ma) was characterized by rapid cooling of the rift shoulders and may be coeval with faulting and sedimentation in the Anza Rift basin, now located in the subsurface of the Turkana depression and areas to the east in northern Kenya. In the second phase, very slow cooling or slight reheating occurred between ~45 and 15 Ma as a result of either stable surface conditions, very slow exhumation, or subsidence. The third phase comprised renewed rapid cooling starting at ~15 Ma. This final cooling represents the most recent stage of rifting, which followed widespread flood-phonolite emplacement and has shaped the present-day landscape through rift shoulder uplift, faulting, basin filling, protracted volcanism, and erosion. When compared with thermochronologic and geologic data from other sectors of the East African Rift System, extension appears to be diachronous, spatially disparate, and partly overlapping, likely driven by interactions between mantle-driven processes and crustal heterogeneities, rather than the previously suggested north-south migrating influence of a mantle plume. © 2015. American Geophysical Union. All Rights Reserved.
McMahon S.,University of Aberdeen |
Parnell J.,University of Aberdeen |
Ponicka J.,University of Aberdeen |
Hole M.,University of Aberdeen |
Astronomy and Geophysics | Year: 2013
Sean McMahon, John Parnell Joanna Ponicka, Malcolm Hole and Adrian Boyce argue that cavities in martian volcanic rocks are a good place to look for microbial life on Mars. © 2013 Royal Astronomical Society.
Glasser N.F.,Aberystwyth University |
Davies B.J.,Aberystwyth University |
Carrivick J.L.,University of Leeds |
Rodes A.,SUERC |
And 3 more authors.
Quaternary Science Reviews | Year: 2014
Predicting the future response of the Antarctic Ice Sheet to climate change requires an understanding of the ice streams that dominate its dynamics. Here we use cosmogenic isotope exposure-age dating (26Al, 10Be and 36Cl) of erratic boulders on ice-free land on James Ross Island, north-eastern Antarctic Peninsula, to define the evolution of Last Glacial Maximum (LGM) ice in the adjacent Prince Gustav Channel. These data include ice-sheet extent, thickness and dynamical behaviour. Prior to ~18ka, the LGM Antarctic Peninsula Ice Sheet extended to the continental shelf-edge and transported erratic boulders onto high-elevation mesas on James Ross Island. After ~18ka there was a period of rapid ice-sheet surface-lowering, coincident with the initiation of the Prince Gustav Ice Stream. This timing coincided with rapid increases in atmospheric temperature and eustatic sea-level rise around the Antarctic Peninsula. Collectively, these data provide evidence for a transition from a thick, cold-based LGM Antarctic Peninsula Ice Sheet to a thinner, partially warm-based ice sheet during deglaciation. © 2013.
News Article | October 9, 2015
Researchers from the Scottish Universities Environmental Research Centre (SUERC) found a new way to determine the outcome of stored carbon dioxide (CO2) emissions. The increasing levels of global warming continue to pose risks such as massive wildfires and extensive droughts. CO2 byproduct from coal burning and other energy generation processes add to the accumulative global warming rate and its effects. Carbon capture and storage (CCS) refers to the process of storing CO2 in abandoned gas and oil fields. Deep aquifers - water-bearing rocks found underground - were also identified as an alternative storage unit. Trapping CO2 emissions underground will help prevent the greenhouse gas from getting to the atmosphere. Scientists claim that a general usage of CCS in the next few years will help in the reduction of CO2 emission levels and, ultimately, slow down global warming. The research team used gas samples from the wells at the Cranfield enhanced oil recovery field in Mississippi in southern America. They focused on samples taken in 2009 and 2012. A 'fingerprinting' process enables the scientists to study 'unique signatures' from noble gasses such as neon, helium and argon to monitor potential CO2 movement. The paper's co-author, Professor Finlay Stuart from SUERC University of Glasgow, expressed that the research proved how the noble gases in the injected CO2 can be used as fingerprints. The finding is first of its kind. By looking at the gases' unique signatures, scientists can then monitor the CO2 and how it was disposed. Stuart explained the huge potentials of CCS as a CO2 mitigation method. However, before CCS can develop into a widespread CO2 storage process, further research is needed to determine the effectivity of stowing the greenhouse gas underground. Noble gases such as neon, helium and argon are chemically inactive. Its interaction with water and rocks will have no effect in its activity. This level of inactivity can help identify the physical procedures that altered CO2 and determine its fate. The study's co-author Dr. Stuart Gilfillan from the University of Edinburgh, expressed that the findings is beneficial to large-scale fingerprints in future CCS projects. "This study now shows that these fingerprints can be used to track the movement and fate of injected CO₂ over much shorter periods relevant to CCS," said Gilfillan. The research was funded by the Engineering and Physical Sciences Research Council in the United Kingdom. Researchers published their paper in the International Journal of Greenhouse Gas Control on Sep. 29, 2015. The University of Glasgow released the study findings online on Oct. 5, 2015.
Muir G.K.P.,Scottish Universities Environmental Research Center |
Cook G.T.,Scottish Universities Environmental Research Center |
MacKenzie A.B.,Scottish Universities Environmental Research Center |
MacKinnon G.,Scottish Universities Environmental Research Center |
Radiocarbon | Year: 2015
During the period from 1995 to 2011, radiocarbon measurements from the coast around Hartlepool in NE England have revealed anomalous enrichments in seawater, sediment, and marine biota. These cannot be explained on the basis of atomic weapons testing or authorized nuclear industry discharges, including those from the nearby advanced gas-cooled reactor. Enhanced 14C-specific activities have also been observed since 2005 in biota during routine monitoring at Hartlepool by the Food Standards Agency, but are reported as “likely” originating from a “nearby non-nuclear source.” Studies undertaken in Hartlepool and Teesmouth during 2005 and 2011 suggest that the 14C discharges are in the vicinity of Greatham Creek, with activity levels in biota analogous to those measured at Sellafield, which discharges TBq activities of 14C per annum. However, if the discharges are into Greatham Creek or even the River Tees, it is proposed that they would be much smaller than those at Sellafield and the high specific activities would be due to much smaller dilution factors. The discharge form of the 14C remains unclear. The activity patterns in biota are similar to those at Sellafield, suggesting that initial inputs are dissolved inorganic carbon (DI14C). However, the mussel/seaweed ratios are more akin to those found around Amersham International, Cardiff, which is known to discharge 14C in an organic form. 14C analysis of a sediment core from Seal Sands demonstrated excess 14C to the base of the core (43–44 cm). 210Pb dating of the core (0–32 cm) produced an accumulation rate of 0.7 g cm–2 yr–1, implying that 14 C discharges have occurred from the 1960s until the present day. © 2015 by the Arizona Board of Regents on behalf of the University of Arizona.
Palamakumbura R.N.,James Hutton Institute |
Robertson A.H.F.,James Hutton Institute |
Kinnaird T.C.,SUERC |
International Journal of Earth Sciences | Year: 2016
This study focuses on the younger of a series of Quaternary terraces along the flanks of the Kyrenia Range in northern Cyprus, specifically the Kyrenia (Girne) and the Koupia terraces. The Kyrenia (Girne) terrace is tentatively correlated with oxygen isotope stage 5 (125 Ka), and the Koupia terrace with oxygen isotope stage 3 (<50 Ka). Along the northern flank of the range, the Kyrenia (Girne) terrace deposits (5–20 m above modern sea level) typically begin with a basal lag conglomerate and then pass upwards into shallow-marine calcarenites and then into variable aeolianites, paleosols and fluvial deposits (up to 20 m thick). In contrast, the Koupia terrace (<2 m above modern sea level) consists of aeolianites and shallow-marine calcarenites (up to 8 m thick). The equivalent deposits along the southern flank of the range are entirely non-marine fluvial mud, sands and conglomerates. The marine to continental terrace systems can be tentatively correlated based on mapping, height above modern sea level and sedimentary facies. However, variable preservation and patchy exposure require such correlations to be independently tested. To achieve this, a portable optically stimulated luminescence (OSL) reader was used to determine the luminescence characteristics of the two terrace systems. Luminescence profiles show major differences in luminescence characteristics between the two terrace depositional systems, which can be related to sedimentary processes, provenance and age. These features allow sections in different areas to be effectively correlated. Individual sections show luminescence properties that are generally consistent with an expected up-sequence decrease in age. However, the younger Koupia terrace deposits show higher luminescence intensities compared with the older Kyrenia (Girne) terrace deposits. This can be explained by multiple phases of reworking of the Kyrenia (Girne) terrace deposits, which changed the luminescence characteristics of the sediment. The use of the portable OSL reader is therefore an effective means of correlating Late Quaternary terrace deposits in northern Cyprus and probably also elsewhere. © 2015, Springer-Verlag Berlin Heidelberg.