Lamproites as indicators of accretion and/or shallow subduction in the assembly of south‐western Anatolia,Turkey

The geochemistry and mineralogy of lamproites from south‐western Anatolia can be used as a snapshot of the lithospheric composition beneath the Menderes Massif. High and near‐constant K₂O contents, the presence of mantle xenocrystic phlogopite and olivine, highly magnesian olivine phenocrysts and Cr‐rich spinel inclusions all indicate that the lithospheric mantle was phlogopite‐bearing ultradepleted harzburgite at the time of lamproite eruption (20–4 Ma). This mantle assemblage most probably originated in a complex multistage process, including (intra‐oceanic) supra‐subduction zone depletion during the final stages of southern Neotethyan ocean closure, and accretion of the forearc oceanic lithosphere as shallowly subducted material to the already assembled Anatolia. The data presented here support shallow subduction of the oceanic lithosphere as a cause of the uplift of the Menderes Massif, in contrast to the traditional core‐complex model. Terra Nova, 00, 000–000, 2010     

Phase relations and fractionation sequences in potassic magma series modelled in the system CaMgSi2O6-KAlSiO4-Mg2SiO4-SiO2-F2O−1 at 1 bar to 18 kbar

Liquidus phase relations in the system diopside–kalsilite–forsterite–quartz with 3 wt% F were examined at 1 bar and the locations of important invariant points were determined at 18 kbar. At all pressures within this range a large liquidus field for fluorphlogopite (Phl) exists, and has a large influence on both melting and fractionation processes. One eutectic point was found to the silica-rich side of the plane Lc–Fo–Di at Di₁Ks₃₀Fo₂Qz₆₇, where a melt coexists with San, Qz, Phl and Di at 840 °C and 1 bar. Another eutectic point must exist in the silica-poor part of the system because the phase topology determines that thermal barriers must exist. At this point a feldspathoid, either Lc or Ks, must coexist with Fo, Phl and a Ca-bearing phase such as Di. The exact location and phase assemblage were not determined, but the equilibrium melt must have a composition rich in Di (>29 wt%) and extremely poor in Qz (<8 wt%). The composition of the first eutectic moves towards lower SiO₂ contents with increasing pressure (Di₃Ks₄₀Fo₁Qz₅₆ at 18 kbar), whereas the second does not exist at 18 kbar due to the disappearance of Lc as a stable liquidus phase. Liquids which coexist with mafic minerals such as En, Fo, Phl and Di are important for the genesis of potassium-rich mafic rocks by partial melting in the mantle and for the early stages of fractional crystallisation. The equilibrium melt at the invariant point Fo + En + Phl + Di + L at 1125 °C is very poor in Fo and Di components at atmospheric pressure (Di₅Ks₃₇Fo₅Qz₅₃), whereas at 18 kbar the melt contains large amounts of Fo and Di (Di₁₉Ks₃₁- Fo₂₈Qz₂₁), and has a composition close to that of natural lamproites. Kamafugites do not correspond to melts in this system under any of the studied conditions, and appear to require CO₂ in the source. Fractionation processes from primitive potassic basanite melts are controlled principally by the size (and not the mere presence) of the liquidus phase field for phlogopite: at high pressures where the Phl field is large, olivine is eliminated early from the fractionating assemblage and Cpx + Phl fractionation may lead to relatively silica-rich rock differentiates such as trachytes. At low pressures, extensive olivine and restricted Phl crystallisation prevents silica enrichment in the melt, resulting in phonolitic differentiates. Later crystallisation of alkali feldspar accentuates the trends laid down in the early stages of fractionation. Received: 2 February 1999 / Accepted: 14 October 1999     

MicroRaman spectroscopy of diamond and graphite in Almahata Sitta and comparison with other ureilites

This work is the first detailed study of carbon phases in the ureilite Almahata Sitta (sample #7). We present microRaman data for diamond and graphite in Almahata Sitta, seven unbrecciated ureilites, and two brecciated ureilites. Diamond in Almahata Sitta was found to be distinct from that in unbrecciated and brecciated ureilites, although diamond in unbrecciated and brecciated ureilites is indistinguishable. Almahata Sitta diamond shows a peak center range of 1318.5–1330.2 cm^?1 and a full width at half maximum (FWHM) range of 6.6–17.4 cm^?1, representing a shock pressure of at least 60 kbar. The actual peak shock pressure may be higher than this due to postshock annealing, if shock synthesis is the source of ureilite diamonds. Diamond in unbrecciated and brecciated ureilites have peak center wave numbers closer to terrestrial kimberlite diamond, but show a wider range of FWHM than Almahata Sitta. The larger peak shift observed in Almahata Sitta may indicate the presence of lonsdaleite. Alternatively, the lower values in brecciated ureilites may be evidence of an annealing step either following the initial diamond‐generating shock or as a consequence of heating during reconsolidation of the breccia. Graphite in Almahata Sitta shows a G‐band peak center range of 1569.1–1577.1 cm^?1 and a G‐band FWHM range of 24.3–41.6 cm^?1 representing a formation temperature of 990 ± 120 °C. Amorphous carbon was also found. We examine the different theories for diamond formation in ureilites, such as chemical vapor deposition and shock origin from graphite, and explore explanations for the differences between Almahata Sitta and other ureilites.     

Climate change response in Europe: what’s the reality? Analysis of adaptation and mitigation plans from 200 urban areas in 11 countries

Urban areas are pivotal to global adaptation and mitigation efforts. But how do cities actually perform in terms of climate change response? This study sheds light on the state of urban climate change adaptation and mitigation planning across Europe. Europe is an excellent test case given its advanced environmental policies and high urbanization. We performed a detailed analysis of 200 large and medium-sized cities across 11 European countries and analysed the cities’ climate change adaptation and mitigation plans. We investigate the regional distribution of plans, adaptation and mitigation foci and the extent to which planned greenhouse gas (GHG) reductions contribute to national and international climate objectives. To our knowledge, it is the first study of its kind as it does not rely on self-assessment (questionnaires or social surveys). Our results show that 35 % of European cities studied have no dedicated mitigation plan and 72 % have no adaptation plan. No city has an adaptation plan without a mitigation plan. One quarter of the cities have both an adaptation and a mitigation plan and set quantitative GHG reduction targets, but those vary extensively in scope and ambition. Furthermore, we show that if the planned actions within cities are nationally representative the 11 countries investigated would achieve a 37 % reduction in GHG emissions by 2050, translating into a 27 % reduction in GHG emissions for the EU as a whole. However, the actions would often be insufficient to reach national targets and fall short of the 80 % reduction in GHG emissions recommended to avoid global mean temperature rising by 2 °C above pre-industrial levels.     

A comment on: ‘TitaniQ under pressure: the effect of pressure and temperature on the solubility of Ti in quartz’, by Jay B. Thomas,E. Bruce Watson,Frank S. Spear,Philip T. Shemella,Saroj K. Nayak and Antonio Lanzirotti

Trace concentrations of Ti in quartz are used to indicate the pressure and temperature conditions of crystallization in the ‘TitaniQ’ geothermobarometer of Thomas et al. (Contrib Miner Petrol 160:743–759, 2010). It utilises the partitioning of Ti into quartz as an indicator of the pressures and/or temperatures of crystal growth. For a given value of TiO₂ activity in the system, if temperatures are inferred to ±20 °C, pressure is constrained to ±1 kbar and vice versa. There are significant contrasts, however, between the conclusions from TitaniQ and those for natural quartz (as well as other mineral phases) in volcanic rocks. Application of the TitaniQ model to quartz from the 27 ka Oruanui and 760 ka Bishop high-silica rhyolites, where the values of T, P and TiO₂ activity are constrained by other means (Fe–Ti oxide equilibria, melt inclusion entrapment pressures in gas-saturated melts, melt and amphibole compositions), yields inconsistent results. If realistic values are given to any two of these three parameters, then the value of the third is wholly unrealistic. The model yields growth temperatures at or below the granite solidus, pressures in the lower crust or upper mantle, or TiO₂ activities inconsistent with the mineralogical and chemical compositions of the magmas. CL imagery and measurements of Ti (and other elements) in quartz are of great value in showing the growth histories and changes in conditions experienced by crystals, but direct linkages to P, T conditions during crystal growth cannot be achieved.     

The early differentiation history of Mars from W-Nd isotope systematics in the SNC meteorites

We report here the results of an investigation of W and Nd isotopes in the SNC (Shergottite-Nakhlite-Chassignite (martian)) meteorites. We have determined that ε¹⁸²W values in the nakhlites are uniform within analytical uncertainties and have an average value of ∼3. Also, while ε¹⁸²W values in the shergottites have a limited range (from 0.3-0.7), their ε¹⁴²Nd values vary considerably (from −0.2-0.9). There appears to be no correlation between ε¹⁸²W and ε¹⁴²Nd in the nakhlites and shergottites. These results shed new light on early differentiation processes on Mars, particularly on the timing and nature of fractionation in silicate reservoirs. Assuming a two-stage model, the metallic core is estimated to have formed at ∼12 Myr after the beginning of the solar system. Major silicate differentiation established the nakhlite source reservoir before ∼4542 Ma and the shergottite source reservoirs at 4525 Ma. These ages imply that, within the uncertainties afforded by the ¹⁸²Hf-¹⁸²W and ¹⁴⁶Sm-¹⁴²Nd chronometers, the silicate differentiation events that established the source reservoirs of the nakhlites and shergottites may have occurred contemporaneously, possibly during crystallization of a global magma ocean. The distinct ¹⁸²W-¹⁴²Nd isotope systematics in the nakhlites and the shergottites imply the presence of at least three isotopically distinct silicate reservoirs on Mars, two of which are depleted in incompatible lithophile elements relative to chondrites, and the third is enriched. The two depleted silicate reservoirs most likely reside in the Martian mantle, while the enriched reservoir could be either in the crust or the mantle. Therefore, the ¹⁸²W-¹⁴²Nd isotope systematics indicate that the nakhlites and the shergottites originated from distinct source reservoirs and cannot be petrogenetically related. A further implication is that the source reservoirs of the nakhlites and shergottites on Mars have been isolated since their establishment before ∼4.5 Ga. Therefore, there has been no giant impact or efficient global mantle convection to thoroughly homogenize the Martian mantle following the establishment of the SNC source reservoirs.     

High U/Th partitioning by clinopyroxene from alkali silicate and carbonatite metasomatism: an origin for Th/U disequilibrium in mantle melts?

Clinopyroxene/melt pairs in strongly potassic silicate and carbonatite melts exhibit unusually high U/Th partitioning ratios of ˜ 3 and ˜ 2, respectively. These values are much higher than those found for aluminous clinopyroxenes in peridotite, and have the potential to cause significant (²³⁰Th)/(²³⁸U) isotope enrichment in volcanics. The potassic silicate (lamproite) and carbonatite melts correspond closely to the main agents of mantle metasomatism, indicating that clinopyroxene in metasomatized regions of the mantle may greatly affect U/Th disequilibria. Recycling of alkali pyroxenite veins in the oceanic lithosphere formed by solidification of melt in the extremities of the MORB melting region presents an alternative to eclogite recycling in MORB and OIB genesis.     

Comparison of the climate simulated by the CCM3 coupled to two different land-surface models

We present results from a coupled atmosphere-biosphere model CCM3/IBIS (the Community Climate Model coupled to the Integrated BIosphere Simulator), which is designed to study the dynamic interactions between climate and vegetation and the global carbon cycle. We analyze the climate simulated by CCM3/IBIS with fixed vegetation conditions and we compare it to the climate simulated by the standard CCM3, which includes the LSM (land surface model) land-surface package. Important differences between the two models include simple parametrizations of lakes, wetlands and crops in CCM3/LSM not taken into account in CCM3/IBIS. CCM3/IBIS and CCM3/LSM share common biases (compared to observations) in the temperature field in boreal winter and in the precipitation field annually, making the atmospheric model the most probable cause of those biases. The models differ in the temperature field and surface energy balance in the Sahara annually and in the mid-to high latitudes from spring through fall. CCM3/IBIS simulates global annual air temperatures that are on average 1.7 °C higher than CCM3/LSM and 0.5 °C higher than the observed climatology. Differences in albedo and/or snow parametrization explain most of the Sahara and high-latitude temperature disagreement. Our sensitivity study with CCM3/LSM shows that the presence of lakes and wetlands in CCM3/LSM can account for about half of the difference in temperature in summer over the lake and wetland regions of the mid-latitudes. A second sensitivity study shows that higher surface roughness length in CCM3/IBIS can also explain part of the difference in summer surface temperature in the mid-latitudes. Surface roughness length affects the surface temperature through a feedback mechanism linking surface wind speed, planetary boundary layer height, low level cloudiness and radiation