Extension of sea surface temperature unpredictability

Ocean Dynamics - The sea surface temperature (SST) variability is clearly affected by global climate patterns, which involve large-scale ocean-atmosphere fluctuations similar to the El...     

Regional gravimetric quasi-geoid model and transformation surface to national height system for Turkey (THG-09)

Turkish regional geoid models have been developed by employing a reference earth gravitational model, surface gravity observations and digital terrain models. The gravimetric geoid models provide a ready transformation from ellipsoidal heights to the orthometric heights through the use of GPS/leveling geoid heights determined through the national geodetic networks. The recent gravimetric models for Turkish territory were computed depending on OSU91 (TG-91) and EGM96 (TG-03) earth gravitational models. The release of the Earth Gravitational Model 2008 (EGM08), the collection of new surface gravity observations, the advanced satellite altimetry-derived gravity over the sea, and the availability of the high resolution digital terrain model have encouraged us to compute a new geoid model for Turkey. We used the Remove-Restore procedure based on EGM08 and applied Residual Terrain Model (RTM) reduction of the surface gravity data. Fast Fourier Transformation (FFT) was then used to obtain the residual quasigeoid from the reduced gravity. We restored the individual contributions of EGM08 and RTM to the whole quasi-geoid height (TQG-09). Since the Helmert orthometric height system is adopted in Turkey, the quasi-geoid model (TQG-09) was then converted to the geoid model (TG-09) by making use of Bouguer gravity anomalies and digital terrain model. After all we combined a gravimetric geoid model with GPS/leveling geoid heights in order to obtain a hybrid geoid model (THG-09) (or a transformation surface) to be used in GPS applications. The RMS of the post-fit residuals after the combination was found to be ± 0.95 cm, which represents the internal precision of the final combination. And finally, we tested the hybrid geoid model with GPS/leveling data, which were not used in the combination, to assess the external accuracy. Results show that the external accuracy of the THG-09 model is ± 8.4 cm, a precision previously not achieved in Turkey until this study.     

Multi-disciplinary earthquake researches in Western Turkey: Hints to select sites to study geochemical transients associated to seismicity

Warm and hot spring water as well as soil gas radon release patterns have been monitored in the Aegean Extensional Province of Western Turkey, alongside regional seismic events, providing a multi-disciplinary approach. In the study period of 20 months, seven moderate earthquakes with M _L between 4.0 and 4.7 occurred in this seismically very active region; two earthquakes with magnitude 5.0 also occurred near the study area. Seismic monitoring showed no foreshock activity. By contrast, hydro-geochemical anomalies were found prior to these seismic events, each lasting for weeks. The anomalies occurred foremost in conjunction with dip-slip events and seem to support the dilatancy and water diffusion hypothesis. Increased soil gas radon release was recorded before earthquakes associated with strike-slip faults, but no soil radon anomalies were seen before earthquakes associated with dip-slip faults. Geochemical anomalies were also noticeably absent at some springs throughout the postulated deformation zones of impending earthquakes. The reason for this discrepancy might be due to stress/strain anisotropies.     

Hydrogen and oxygen isotope evidence for fluid–rock interactions in the Menderes massif, western Turkey

The Menderes Massif comprises an inner crystalline core with gneissic rocks and an outer surrounding schist belt with predominantly metasedimentary rocks. Both units have a complex metamorphic history including a late Alpine overprint. Temperatures inferred from oxygen isotope compositions of coexisting minerals increase from 420 to 600°C from the rim to the center. More positive '¹⁸O values in all minerals from the schist belt may reflect a higher abundance of sedimentary precursor material, whereas biotites and muscovites in core and rim are indistinguishable in hydrogen isotope composition. 'D values of muscovites range from -35 to -60‰, whereas 'D values of biotites range from -65 to -125‰, indicating normal values for muscovite but anomalously negative values for some biotites. For muscovite the trend can be interpreted in terms of increasing loss of water with rising metamorphic temperature. For biotite the 'D values decrease with increasing H₂O content and decreasing Na₂O+K₂O content, which provides evidence for alteration processes or exchange of K and Na with water from interlayers of biotite forming hydro-biotite. The data suggest isotopic resetting of pre-Alpine characteristics during Alpine metamorphism. The hydrogen isotope composition of biotite was later disturbed, probably during extensional neotectonic movements in this region, as this allowed infiltration of and exchange with D-depleted meteoric water; however, the muscovites retained its Alpine characteristics.     

Geochemical and isotopic (Sr,C, O) data from the alkaline complex of Grønnedal-ĺka (South Greenland): evidence for unmixing and crustal contamination

The alkaline intrusion of Grønnedal-ka (South Greenland) is the oldest of the ten major rift-related plutonic complexes of southern Greenland that intruded during the Gardar period between 1330 and 1150 Ma into the 2.6-Ga-old gneisses and metasediments of the Ketilidian basement. The Grønnedal-ka alkaline intrusion consists of carbonatites, silicocarbonatites, transitional carbonatites and nepheline-bearing syenites. The silicocarbonatites exhibit locally ocellar textures that are typical for immiscibility processes. A ⁸⁷Sr/⁸⁶Sr initial ratio of about 0.703184 major and trace element compositions—including REE and C-, and O-isotope data from 15 carbonatite, 12 silicocarbonatite, 10 transitional carbonatite and 8 syenite and samples—provide evidence for minor crustal contamination of the mantle-derived magma that generated by unmixing carbonatites, silicocarbonatites and syenites. A scatter in major and trace element contents and isotope ratios is related to late- to post-magmatic alteration processes. The Grønnedal-ka silicocarbonatites are one of the rather rare cases in which unmixing of a highly alkaline mantle-derived magma into an alkalisilicate and a carbonatitic magma-fraction under plutonic conditions is well documented by textural and geochemical data.     

Petrochemistry and petrology of I-type granitoids in an arc setting: the composite Torul pluton, Eastern Pontides, NE Turkey

The Upper Cretaceous Torul pluton, located in the Eastern Pontides, is of sub-alkaline affinity and displays features typical of volcanic arc granitoids. It is a composite pluton consisting of granodiorite, biotite hornblende monzogranite, quartz monzodiorite, quartz monzonite and hornblende biotite monzogranite. The oldest syenogranite (77.9 ± 0.3 Ma) and the youngest quartz diorite form small stocks within the pluton. Samples from the granodiorites, biotite hornblende monzogranites, quartz monzodiorites, quartz monzonites and hornblende biotite monzogranites have SiO₂ between 57 and 68 wt% and display high-K calc-alkaline, metaluminous to peraluminous characteristics. Chondrite-normalized REE patterns are fractionated (La_cn/Lu_cn = 6.0?14.2) with pronounced negative Eu anomalies (Eu/Eu* = 0.59–0.84). Initial ?_Nd(i) values vary between ?3.1 and ?4.1, initial ⁸⁷Sr/⁸⁶Sr values between 0.7058 and 0.7072, and δ¹⁸O values between +4.4 and +7.3‰. The quartz diorites are characterized by relatively high Mg-number of 36–38, low contents of Na₂O (2.3–2.5 wt%) and SiO₂ (52–55 wt%) and medium-K calc-alkaline, metaluminous composition. Chondrite-normalized REE patterns are relatively flat [(La/Yb)_cn =  2.8–3.3; (Tb/Yb)_cn =  1.2] and show small negative Eu anomalies (Eu/Eu* = 0.74–0.76). Compared to the other rock types, radiogenic isotope signatures of the quartz diorites show higher ⁸⁷Sr/⁸⁶Sr (0.7075–0.7079) and lower ?_Nd(i) (–4.5 to –5.3). The syenogranites have high SiO₂ (70–74 wt%) and display high-K calc-alkaline, peraluminous characteristics. Their REE patterns are characterized by higher La_cn/Lu_cn (12.9) and Eu/Eu* (0.76–0.77) values compared to the quartz diorites. Isotopic signatures of these rocks [?_Nd(i) =  ?4.0 to ?3.3; ⁸⁷Sr/⁸⁶Sr_(i) =  0.7034?0.7060; δ¹⁸ O =  + 4.9 to + 8.2] are largely similar to the other rock types but differ from that of the quartz diorites. Fractionation of plagioclase, hornblende, pyroxene and Fe–Ti oxides played an important role in the evolution of Torul granitoids. The crystallization temperatures of the melts ranged from 800 to 900°C as determined from zircon and apatite saturation thermometry. All these characteristics, combined with low K₂O/Na₂O, low Al₂O₃/(FeO_T + MgO + TiO₂), and low (Na₂O + K₂O)/(FeO_T + MgO + TiO₂) ratios suggest an origin through dehydration melting of mafic lower crustal source rocks.     

Petrological study and radiometric age determination of the migmatites in the Penninic rocks of the Zillertaler Alpen (Tyrol/Austria)

Summary Migmatites are very common in the Penninic Zentralgneis series of the Western Tauern Window. Nebulitic migmatites occurring near the Berliner Hütte (Zillertaler Alpen) have been studied by petrological and geochronological methods in order to determine the conditions and time of their formation. These migmatites occur in an area in which Alpine metamorphism attained its highest grade.An Rb/Sr isochron for the migmatites yielded a Hercynian age of 283±28 m.y. This age probably corresponds to the climax of Hercynian metamorphism in the Penninic area of the Tauern Window. Rb/Sr age determinations on the phengites and biotites of these migmatites give ages of 21 and 14 m.y., respectively. These ages are the result of cooling of the rocks below 500°C and 300°C, respectively, during Alpine times.From the chemical composition of the migmatites a solidus temperature of about 670°C at 4 kb is inferred. Consideration of oxygen isotope and mineral stability data for minerals formed during high grade Alpine metamorphism indicates that these P-T conditions were not achieved during Alpine times. This also supports a pre-Alpine age for the migmatization.

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Petrologische Studie und radiometrische Altersbestimmung an penninischen Migmatiten der Zillertaler Alpen (Tirol, Österreich)

Zusammenfassung In den penninischen Zentralgneisarealen des westlichen Tauernfensters treten weit verbreitet Migmatite auf. Für die Migmatisation wurde sowohl ein prä-alpidisches als auch ein alpidisches Alter angenommen. Zur Festlegung des Alters der Migmatisation wurden die in der Nähe der Berliner Hütte auftretenden nebulitischen in-situ gebildeten Migmatite petrologisch untersucht und ihr Bildungsalter geochronologisch bestimmt. Diese Migmatite liegen in dem Gebiet höchstgradiger alpidischer Metamorphose. Eine Rb/Sr-Isochrone ergab für diese Gesteine ein herzynisches Bildungsalter von 283±28 m.y. Dieses Alter entspricht wahrscheinlich dem Höhepunkt der herzynischen Metamorphose. Rb/Sr-Altersbestimmungen an den Phengiten und Biotiten ergaben für die Abkühlung dieser Gesteine unter 500 bzw. 300°C ein alpidisches Alter von ca. 21 bzw. 14 m.y.Aus der chemischen Zusammensetzung der Migmatite und einer Druckabschätzung für die herzynische Metamorphose von ca. 4 kb ergibt sich für das Leukosom der Migmatite eine Solidustemperatur von ca. 670°C.Aus den Stabilitätsbeziehungen alpin gebildeter Minerale, den¹⁸O/¹⁶O Temperaturen und der Soliduskurve des Leukosoms der Migmatite ergibt sich, daß eine alpidische Migmati sation selbst unter den Bedingungen der höchstgradigen alpidischen Metamorphose nicht möglich ist.

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With 8 Figures     

Pb-Sr-Nd isotopic compositions and trace element geochemistry of megacrysts and melilitites from the Tertiary Urach volcanic field: source composition of small volume melts under SW Germany

 The Urach volcanic field is unique within the Tertiary–Quaternary European volcanic province (EVP) due to more than 350 tuffaceous diatremes and only sixteen localities with extremely undersaturated olivine melilitite. We report representative Pb-Sr-Nd isotopic compositions and incompatible trace element data for twenty-two pristine augite, Cr-diopside, hornblende, and phlogopite megacryst samples from the diatremes, and seven melilitite whole rocks. The Pb isotopic compositions for melilitites and comagmatic megacrysts have very radiogenic ²⁰⁶Pb/²⁰⁴Pb ratios of 19.4 to 19.9 and plot on the northern hemisphere mantle reference line (NHRL). The data indicate absence of an old crustal component as reflected in the high ²⁰⁷Pb/²⁰⁴Pb ratios of many basalts from the EVP. This inference is supported by ²⁰⁶Pb/²⁰⁴Pb ratios of ∼17.6 to 18.3 and ɛ_Nd of ∼−7.8 to +1.6 for five phlogopite xenocryst samples reflecting a distinct and variably rejuvenated lower Hercynian basement. The ⁸⁷Sr/⁸⁶Sr ratios of 0.7033 to 0.7035 in the comagmatic megacrysts are low relative to their moderately radiogenic Nd isotopic compositions (ɛ_Nd +2.2 to +5.1) and consistent with a long-term source evolution with a low Rb/Sr ratio and depletion in light rare-earth elements (LREE). The melilitite whole-rock data show a similar range in Nd isotopic ratios as determined for the megacrysts but their Sr isotopic compositions are often much more radiogenic due to surface alteration. The REE patterns and incompatible trace element ratios of the melilitites (e.g. Nb/Th, Nb/U, Sr/Nd, P/Nd, Ba/Th, Zr/Hf) are similar to those in ocean island basalts (OIB); negative anomalies for normalized K and Rb concentrations support a concept of melt evolution in the lithospheric mantle. Highly variable Ce/Pb ratios of 29 to 66 are positively correlated with La/Lu, La/K₂O, and Ba/Nd and interpreted to reflect melting in the presence of residual amphibole and phlogopite. The data suggest an origin of the melilitites from a chemical boundary layer very recently enriched by melts from old OIB sources. We suggest that the OIB-like mantle domains represent low-temperature melting heterogeneities in an upwelling asthenosphere under western Europe. Received: 9 March 1995/Accepted: 24 July 1995     

Measuring streambank erosion due to ground water seepage: correlation to bank pore water pressure,precipitation and stream stage

Limited information exists on one of the mechanisms governing sediment input to streams: streambank erosion by ground water seepage. The objective of this research was to demonstrate the importance of streambank composition and stratigraphy in controlling seepage flow and to quantify correlation of seepage flow/erosion with precipitation, stream stage and soil pore water pressure. The streambank site was located in Northern Mississippi in the Goodwin Creek watershed. Soil samples from layers on the streambank face suggested less than an order of magnitude difference in vertical hydraulic conductivity (K_s) with depth, but differences between lateral K_s of a concretion layer and the vertical K_s of the underlying layers contributed to the propensity for lateral flow. Goodwin Creek seeps were not similar to other seeps reported in the literature, in that eroded sediment originated from layers underneath the primary seepage layer. Subsurface flow and sediment load, quantified using 50 cm wide collection pans, were dependent on the type of seep: intermittent low‐flow (LF) seeps (flow rates typically less than 0·05 L min^?1), persistent high‐flow (HF) seeps (average flow rate of 0·39 L min^?1) and buried seeps, which eroded unconsolidated bank material from previous bank failures. The timing of LF seeps correlated to river stage and precipitation. The HF seeps at Goodwin Creek began after rainfall events resulted in the adjacent streambank reaching near saturation (i.e. soil pore water pressures greater than ?5 kPa). Seep discharge from HF seeps reached a maximum of 1·0 L min^?1 and sediment concentrations commonly approached 100 g L^?1. Buried seeps were intermittent but exhibited the most significant erosion rates (738 g min^?1) and sediment concentrations (989 g L^?1). In cases where perched water table conditions exist and persistent HF seeps occur, seepage erosion and bank collapse of streambank sediment may be significant. Copyright © 2007 John Wiley & Sons, Ltd.