F. F. Slejko

The 87Sr/86Sr strontium isotopic systematics applied to Glera vineyards: A tracer for the geographical origin of the Prosecco

Glera vineyards from the Prosecco wine district in northern Italy have been characterised in terms of the (87)Sr/(86)Sr isotope-ratio of musts from the 2010, 2011 and 2012 vintages, coupled with the isotopic analysis of Sr in the labile fraction of the soils of provenance. For a single vineyard, detailed Sr isotopic analyses were carried out in sequentially extracted soil fractions at three different depths, and in the grape components (skin, seeds, must and stem), in order to verify the lack of Sr isotopic fractionation within the plant. The (87)Sr/(86)Sr in must, seeds and stem overlaps within experimental uncertainties; skins are shifted towards a lower Sr isotopic composition. A large range of Sr isotopic compositions ((87)Sr/(86)Sr between 0.70706 and 0.71215) characterizes musts from the different vineyards, notwithstanding the relatively limited extension of the investigated geographic area. A statistically significant correspondence between the soil labile fraction and must is observed.

Geochemistry and isotope geochemistry of the Monfalcone thermal waters (northern Italy): inference on the deep geothermal reservoir

Geochemical investigations were carried out to define the origin of the low- to moderate-temperature thermal waters feeding the Monfalcone springs in northern Italy. Chemical data indicate that waters approach the composition of seawater. Mixing processes with cold low-salinity waters are highlighted. The δ18O and δD values are in the range −5.0 to −6.4 ‰, and −33 to −40 ‰, respectively, suggesting the dilution of the saline reservoir by karst-type freshwaters. A surplus of Ca2+ and Sr2+ ions with respect to a conservative mixing is ascribed to diagenetic reactions of the thermal waters with Cretaceous carbonates at depth. The measured Sr isotopic composition (87Sr/86Sr ratio) ranges between 0.70803 and 0.70814; after correction for the surplus Sr, a 87Sr/86Sr ratio indicating Miocene paleo-seawater is obtained. The dissolved gases indicate long-lasting gas–water interactions with a deep-originated gas phase of crustal origin, dominated by CO2 and marked by a water TDIC isotopic composition in the range −5.9 to−8.8 and helium signature with 0.08 < R/Ra < 0.27, which is a typical range for the crust. A possible scenario for the Monfalcone thermal reservoir consists of Miocene marine paleowaters which infiltrated through the karstic voids formed within the prevalently Cretaceous carbonates during the upper Eocene emersion of the platform, and which were entrapped by the progressive burial by terrigenous sediments.RésuméDes investigations géochimiques ont été effectuées pour définir l’origine des températures basses à modérées des eaux thermales qui alimentent les sources de Monfalcone dans le Nord de l’Italie. Les données chimiques indiquent que les eaux approchent la composition de l’eau de mer. Les processus de mélange avec de l’eau froide de faible salinité sont mis en lumière. Les valeurs de δ18O et δD varient de −5.0 à −6.4 ‰, et −33 à −40 ‰, respectivement, suggérant une dilution du réservoir salé par de l’eau douce de type karstique. Un excédent d’ions Ca2+ et Sr2+ par rapport à un mélange conservatif est attribué aux réactions diagénétiques des eaux thermales avec les carbonates du Crétacé en profondeur. La composition isotopique mesurée du Sr (rapport 87Sr/86Sr ) s’étend entre 0.70803 et 0.70814; Après correction pour l’excédent de Sr, un rapport 87Sr/86Sr représentatif d’une paléo eau de mer Miocène est obtenu. Les gaz dissous indiquent des interactions eau-gaz de longue durée avec un phase gazeuse d’origine profonde (crustale), dominée par le CO2 et marquée par une composition isotopique TDIC de −5.9 à −8.8 et une signature hélium avec 0.08 < R/Ra < 0.27, qui est typique de la croute. Un scénario possible pour le réservoir thermal de Monfalcone considère des eaux anciennes marines miocènes qui se sont infiltrées par les vides karstiques formés dans les carbonates crétacés durant l’emersion éocene de la plateforme, et qui ont été rendues prisonnières du fait de l’ensevelissement progressif par les sédiments terrigènes.ResumenSe llevaron a cabo investigaciones geoquímicas para definir el origen de la baja a moderada temperatura de aguas termales que alimentan a los manantiales de Monfalcone en el norte de Italia, Los datos químicos indican que las aguas se aproximan a la composición del agua de mar. Se destacan los procesos de mezcla con aguas frías de baja salinidad. Los valores de δ18O y δD están en el rango de −5.0 a −6.4 ‰, y −33 a −40 ‰, respectivamente, sugiriendo la dilución del reservorio salino por agua dulces de tipo kárstico. Un exceso de los iones Ca2+ y Sr2+ con respecto a una mezcla conservativa se atribuye a reacciones diagenéticas de las agua termales con carbonatos del Cretácico en profundidad. La composición medida del isótopo Sr (relación 87Sr/86Sr) varía entre 0.70803 y 0.70814; después de haber corregido por los excesos de Sr, relación 87Sr/86Sr obtenida indica paleoaguas marinas del Mioceno. La presencia de gases disueltos indica las interacciones gas – agua de larga duración con una fase gaseosa originada en profundidad de origen cortical, dominada por CO2 y marcada por una composición isotópica del agua TDIC en el rango de −5.9 a −8.8 y vestigios de helio con 0.08 < R/Ra < 0.27, que es un intervalo típico para la corteza. Un escenario posible para el reservorio termal de Monfalcone consiste en paleoaguas marinas del Mioceno las cuales se infiltraron a través de huecos kárstico formados dentro de los carbonatos prevalentes del Cretácico durante la emersión de la plataforma en el Eoceno superior, y que fueron entrampados por un enterramiento progresivo debido a sedimentos terrígenos.摘要地球化学调查界定了意大利北部Monfalcone(蒙法尔科内)低-中温温泉水的来源。化学数据显示,水的成分与海水相同。很明显,与寒冷的低盐度水的混合过程十分明显。δ18O 和 δD值分别在–5.0至-6.4‰ 和–33到40‰。这一现象表明地下卡斯特淡水河对盐水储层的稀释作用。剩余的Ca2+ 和 Sr2+离子归因于热水域与白垩纪碳酸盐在深度的成岩反应的结果。检测到的Sr 同位素成分(87Sr/86Sr 比率) 在0.70803和0.70814之间。修正后,剩余的Sr, 87Sr/86Sr的比率现实出来自中新世的古海水。溶解的气体显示,持续的源于地壳的二氧化碳与水的相互作用,主要由水中的TDIC 同位素成分在-5.9到-8.8和氦0.08 < R/Ra < 0.27。这是典型的源于地壳数值。蒙法尔科内热储层极有可能是由中新世的古海水渗入在上始新世形成的碳酸盐平台,被连续的陆源沉积物截流形成的。SažetakGeokemijska istraživanja provedena su kako bi se utvrdilo porijeklo termalnih voda niskih do srednjih temperatura koje napajaju Monfalconske izvore u sjevernoj Italiji. Kemijski podatci pokazuju da se sastav voda približava sastavu morske vode. Istaknuti su procesi miješanja sa hladnim vodama niskog saliniteta. Vrijednosti δ18O i δD u rasponu su od −5.0 do −6.4 ‰ odnosno −33 to −40 ‰, sugerirajući razrjeđivanje slanog rezervoara slatkim vodama krškog tipa. Višak iona Ca2+ i Sr2+ s obzirom na konzervativno miješanje pripisuje se diagenetičkim reakcijama termalnih voda s krednim karbonatima u dubini. Izmjereni izotopni sasatav (omjer 87Sr/86Sr) varira između 0.70803 i 0.70814, nakon ispravka za suvišan Sr, pokazujući paleo morsku vodu iz Miocena. Otopljeni plinovi pokazuju dugoročne interakcije plinova i voda s plinovitom fazom dubokog krustalnog porijetla s dominirajućim CO2 i istaknutim izotopnom kompozicijom TDIC-a u rasponu −5.9 do −8.8 i helija sa 0.08 < R/Ra < 0.27, što je tipičan raspon za koru. Mogući scenarij za Monfalkonski termalni spremnik sastoji se od miocenskih morskih paleo voda koje prodiru kroz krške šupljine formirane u pretežno krednim karbonatima tijekom izdizanja platforme u gornjem Eocenu koje su zatočene od strane progresivnog pokopavanje terestičkim sedimenatima.ResumoRealizaram-se investigações geoquímicas com o fim de identificar a origem de águas termais de baixa a moderada temperatura que alimentam as nascentes de Monfalcone, no norte de Itália. Os dados químicos indicam que a água tem composição próxima da água do mar. Salienta-se a existência de processos de mistura com águas de baixas temperatura e salinidade. Os valores de δ18O e δD apresentam-se entre −5.0 a −6.4 ‰ e −33 a −40 ‰, respetivamente, o que sugere a diluição das águas marinhas por águas continentais de origem cársica. Um excesso de iões de Ca2+ e Sr2+ relativamente a uma mistura conservativa é atribuída a reações diagenéticas com águas termais cretácicas profundas. As composições isotópicas analisadas de Sr (relação 87Sr/86Sr) variam entre 0.70803 e 0.70814; no entanto, após a correção do excesso de Sr, a relação 87Sr/86Sr aponta para a presença de uma água fóssil de idade miocénica. Os gases dissolvidos indiciam um longo período de interações gás-água, com uma fase gasosa de origem crustal profunda dominada por CO2 e marcada por uma água com valores de carbono inorgânico dissolvido total entre −5.9 e −8.8 e uma assinatura de hélio com 0.08 < R/Ra < 0.27, a qual corresponde a um intervalo típico de origem crustal. Um cenário possível para o reservatório termal de Monfalcone consiste em paleoáguas marinhas miocénicas infiltradas através de cavidades cársicas formadas no seio das rochas carbonatadas do Cretácico durante a emersão da plataforma no Eocénico superior, as quais foram aprisionadas pelo progressivo preenchimento das cavidades por sedimentos terrígenos.IzvlečekNa termalnih vodah izvira pri Tržiču v severni Italiji, ki imajo od nizke do zmerne temperature, so bile opravljene geokemijske preiskave za določitev njihovega izvora. Kemijski podatki te termalne vode kažejo značilnosti, ki so podobne tistim morske vode. Poudarjeni so tudi procesi mešanja s hladno vodo nizke slanosti. Vrednosti δ18O in δD so v intervalu od −5.0 do −6.4 ‰ prve in od −33 do −40 ‰ druge in kažejo torej na redčenje slanega rezervoarja s sladkimi vodami kraškega značaja. Diagenetske reakcije in interakcije s karbonatno matriko so povzročile presežek ionov Ca2 + in Sr2 + v primerjavi z binarnim konzervativnim postopkom mešanja, kar kaže na globoke procese interakcije s karbonati iz obdobja Krede. Izmerjena izotopska sestava Sr ( razmerje 87Sr/86Sr ) se giblje med 0.70803 and 0.70814; po korekciji za presežek Sr, razmerje 87Sr/86Sr nakazuje paleo-morsko vodo iz Miocena. Raztopljeni plini nakazujejo dolgotrajne interakcije plin-voda s plinsko komponento globokega izvora v zemeljski skorji. V komponenti prevladuje CO2, vrednosti izotopske sestave vode TDIC so v intervalu od −5.9 do −8.8 in helij je med 0.08 < R/Ra < 0.27, kar je tipično v zemeljski skorji. Možni scenarij za termalni rezervoar v Tržiču je torej prisotnost paleo-morske vode iz Miocena, ki je prodrla skozi kraške votline, ki so predhodno nastale v karbonatih iz pretežno obdobja Krede, v času nastajanja celine v Zgornjem Eocenu in ki je bila ujeta in zaprta v karbonatih od naknadnega prekritja s terigeni sedimenti.

Mineral chemistry and Nd isotopic composition of two anorthositic rocks from the Kunene complex (South Western Angola)

Abstract Two anorthositic rocks from the Kunene complex (South Western Angola) were analyzed for their mineral compositions, major element chemistry and Nd isotopes. The two rocks were sampled from the northern and southern parts of the complex with respect to a NE–SW-aligned belt of granitoids. In addition to cumulus plagioclase and intercumulus olivine, the sample from the south is characterized by the presence of biotite and rare clinopyroxene, while orthopyroxene and minor clinopyroxene occur in the sample from the north. Plagioclase in the two rocks shows a different composition, Ab-rich in the sample from the south (average An 48 ) and significantly more calcic in the sample from the north (average An 65 ). Diffractometric analyses indicate that plagioclase in anorthosite from the south of the complex equilibrated at lower temperature compared to those from the north. The late-magmatic biotite in the sample from the south is characterized by a relatively high Ti content and plots within the field of biotites from calc-alkaline suite in the FeO * –MgO–Al 2 O 3 diagram, suggesting the contribution of a crust-derived component. The clinopyroxene–orthopyroxene pairs in the sample from the north give equilibration temperatures of about 880 °C at pressures of 3–5 kbar. The above observations are interpreted as reflecting a different cooling and crystallization path for the two samples. The whole-rock major element chemistry and textural features indicate that these rocks are cumulates. The Nd isotopic composition of whole rocks computed back to the emplacement age (1.37 Ga) gives e Nd values of −6.36 and −5.72 for the sample from the south and the north, respectively, indicating the time-integrated enriched character of the magmas with respect to CHUR, attributable to assimilation of Archean crust. In particular, the more negative e Nd value for the sample from the south could indicate a major role of crustal assimilation. The data suggest the existence of distinct magmas which underwent distinct cooling histories and crustal assimilation in a multi-pulse anorthositic intrusion.

Petrology of potassic alkaline ultramafic and carbonatitic rocks from Planalto da Serra (Mato Grosso State), Brazil

The Planalto da Serra igneous rocks form plugs, necks and dykes of carbonate-rich ultramafic lamprophyres (aillikites and glimmerites with kamafugitic affinity) and carbonatites (alvikites and beforsites). Phlogopite and/or tetraphlogopite, diopside and melanitic garnet are restricted to aillikitic rock-types, whereas pyroclore occurs only in carbonatites. Aillikites and carbonatites are altered to hydrotermalites, having chlorite and serpentine as dominant minerals. Planalto da Serra igneous rock association has kamafugitic affinity (i.e. effusive, ultrapotassic. High LREE/HREE fractionation, incompatible elements data and Sr-Nd isotopes, suggest that the K-ultramafic alkaline and carbonatite rocks originated from a variably metasomatized mantle source enriched in radiogenic Sr. Crustal contamination is negligible or absent. Age values of 600 Ma rule out the geochronological relationship between the investigated intrusions and the Mesozoic alkaline bodies from the Azimuth 125° lineament. The TDM model ages allow to conclude that Planalto da Serra magma is derived from the partial melting of a mantle source metasomatised by K-rich carbonatated melt during the Early to Late Neoproterozoic. On the basis of alkaline magmatism repetitions at 600 Ma and 90–80 Ma we question the subsistence of a stationary mantle plume for so long time.