Sr Signatures Research Articles

Gold-hosting high Ba-Sr granitoids in the Xincheng gold deposit, Jiaodong Peninsula, East China: Petrogenesis and tectonic setting

The Xincheng deposit is the only large gold deposit with a proven reserve of >200t gold hosted by the Early Cretaceous granitoids in northwest Jiaodong Peninsula, East China. The granitoids hosting this ore deposit comprise an inner medium- to fine-grained quartz monzonite and an outer medium- to coarse-grained monzogranite with distinctive K-feldspar megacrysts. LA–ICP–MS zircon dating yields U–Pb ages of 128±1 to 132±1Ma and 127±2 to 129±1Ma, for the quartz monzonite and the monzogranite, respectively. The Early Cretaceous ages obtained in our study are comparable with the 126–130Ma age range reported for the Guojialing granitic suite. The monzogranites, typical high Ba–Sr granites, possess high SiO2 (70.89–73.35%), K2O (3.85–4.32%), total alkalis (K2O+Na2O=8.08–8.68%), Sr (634–888ppm), Ba (1395–2111ppm) and LREE (59.43–145.88), with low HREE and HFSE contents and insignificant Eu anomalies. The rocks display markedly high Sr/Y (114–297) and (La/Yb)N (20–79) ratios. They have low MgO (0.23–0.62%), Cr (0.4–8.33ppm) and Ni (0.47–2.92ppm) contents. The typical high Ba–Sr signatures of the outer acidic monzogranites are also shared by the inner intermediate-acidic quartz monzonites, with a relatively higher abundance of these elements. The plagioclases in the quartz monzonites and monzogranites are oligoclase–andesine with An contents of 11.7–44.5%, and oligoclase with An contents of 12.9–29.3%, respectively, which both show the reverse zoning texture. The quartz monzonites have zircon εHf(t) values of −21.3 to −13.9 (average −18.7), which are less negative and show larger variations than those of the monzogranites (εHf(t)=−24.7 to −18.1, average −19.5). Detailed elemental, mineralogical and isotopic data suggest that the high Ba–Sr quartz monzonites and monzogranites were most likely generated by partial melting of the basement rocks of the Jiaobei terrane accompanied by crustal assimilation, with minor addition of the intermediate magma derived from the partial melting of juvenile mafic lower crust formed by the earlier underplating of mantle magma, and the quartz monzonites may represent the path of intermediate magma inputting into felsic magma. In combination with previous investigations, we suggest subduction of the paleo-Pacific slab beneath the North China Craton (NCC) and associated asthenosphere upwelling were most likely the mechanism associated with the generation of the high Ba–Sr granites.

Widening the market. Strontium isotope analysis on cattle teeth from Owslebury (Hampshire, UK) highlights changes in livestock supply between the Iron Age and the Roman period

87Sr/86Sr isotopic analysis was performed on 95 cattle teeth from the Iron Age and Roman rural site of Owslebury (Hampshire). This constitutes one of largest strontium (Sr) isotopic projects in Roman archaeology and the first ever dealing with Iron Age cattle. The Sr isotopic signal of Middle Iron Age cattle is consistent with a local Sr signature, while in the Late Iron Age and, even more so, in both Roman phases cattle were introduced to the site from a greater variety of geographic areas. Although it is not possible to track down the exact origin of these introduced cattle, some must have travelled substantial distances (70 km and more). The widening of the market illustrated by our study is consistent with artefactual evidence from the site, indicating an increase in trade in the Late Iron Age, which is further emphasised in the Roman period.

The geographic distribution of Sr isotopes from surface waters and soil extracts over the island of Bornholm (Denmark) – A base for provenance studies in archaeology and agriculture

In this paper we report the Sr isotope signatures, and Sr, Al and Na concentrations of 30 surface waters (lakes/ponds and rivers/creeks) and 19 soil sample extracts from the island of Bornholm (Denmark) and present a categorized 87Sr/86Sr value distribution map that may serve as a base for provenance studies, including archaeological migration and authenticity proof for particular food products. The Sr isotopic compositions of surface waters range from 87Sr/86Sr=0.7097–0.7281 (average 0.7175±0.0049; 1σ), whereas 0.1M HNO3, 0.05M HNO3, and 0.01M CaCl2 soil extracts range from 87Sr/86Sr=0.7095–0.7197 and define somewhat lower but statistically indistinguishable averages of 0.7125±0.003 (1s). These compositions are lower than the values expected from the Precambrian granitoid basement (87Sr/86Sr=0.758–0.944), and from the overlying, mainly clastic Paleozoic sediments. Combined Sr isotope composition vs. Sr, Na and Al concentration relationships of soil extracts imply that lowering of the isotopic composition of leachable Sr on Bornholm results as a consequence of significant admixture to this fraction of Sr deposited as marine salts (aerosols), and that rainwater only has a minor influence on the Sr budget of the surface waters. Positively correlated Al/Na and [1/Sr] vs. 87Sr/86Sr relationships in soil extracts and surface waters indicate that the surface run-off on Bornholm is characterized by two predominant sources, namely marine aerosols (sea salts) with high Sr and low 87Sr/86Sr values, and a source with lower [Sr] delivering radiogenic Sr to the surface waters, which we equate with Sr leached from the products of mineral weathering (soils).A feasibility study for using Sr isotopic compositions of surface waters and soil extracts as a proxy for bioavailable Sr signatures was performed with a few samples collected in the vicinity of the eleventh century AD Ndr. Grødbygård cemetery site in SW Bornholm, from where Sr isotope compositions of modern fauna samples and tooth enamel of humans buried in the cemetery have been reported. Waters and soil extracts studied herein from around this site range from 87Sr/86Sr=0.7104–0.7166 and correspond to Sr compositions extracted from snail shells in this area which span a range of 87Sr/86Sr=0.7095–0.7160. Some human tooth enamel is characterized by more radiogenic values (87Sr/86Sr up to 0.718) which points to a possible provenance of these humans from the granite–gneiss terrain in the north of the island and/or to immigration of these humans in their childhood from other places (for example from mainland Sweden) to Bornholm. If the total compositional range of 87Sr/86Sr=0.709–0.718 (n=44) recorded in human enamel from the Ndr. Grødbygård site is considered representative for the variation of bioavailable Sr on Bornholm, then our soil leachate and surface water data entirely covers this range. We therefore propose that the combination of Sr isotope analyses of surface waters and soil leachates are an easy, fast and relatively cost efficient way to characterize a local bioavailable 87Sr/86Sr signature, and consequently propose that the overall average of 87Sr/86Sr=0.7153±0.0048 (1σ; n=50) can be taken as a band for bioavailable Sr fractions suitable to discriminate between local and non-local signatures in provenance studies in the field of archaeology and for food and plant authenticity control in agricultural applications.

Early and late Neoproterozoic C, O and Sr isotope chemostratigraphy in the carbonates of West Congo and Mbuji-Mayi supergroups: A preserved marine signature?

The carbon, oxygen and strontium isotope geochemistry is the most widely applied chemostratigraphic tool in the reconstruction of paleoenvironments and indirect regional or global correlations for the Neoproterozoic times. Relatively good preserved carbonate rocks of the West Congo Supergroup, i.e. the Schisto-Calcaire Subgroup of the Democratic Republic of Congo and Gabon, and the Mbuji-Mayi Supergroup, i.e. the BII group from the Democratic Republic of Congo, make these Neoproterozoic successions unique for chemostratigraphical studies. In this paper, we propose to discuss on the fidelity of δ13Ccarb and Sr signatures in Neoproterozoic carbonates on the basis of a severe diagenetic control, using trace and major geochemistry, combined with C and O stable isotope analysis. Our result highlights that the δ13Ccarb fluctuations of the Schisto-Calcaire Subgroup reflect (i) facies variations, (ii) exchanges between isotopically light carbon in meteoric waters and carbonate during lithification and early diagenesis, and/or (iii) regional metamorphism grades rather than temporal signals of ocean chemistry, while in the unmetamorphosed carbonates of the Mbuji-Mayi Supergroup, reported to the Bitter Springs anomaly (~810Ma), the use of δ13C ratios are worldwide applicable for inter-basin correlations.

Sasanian glass from Veh Ardašīr investigated by strontium and neodymium isotopic analysis

A collection of 31 glass fragments, dated to the 3rd to 7th century AD and excavated in Veh Ardašīr, (modern Iraq), were analysed for their Sr and Nd isotopic compositions with the aim of deepening our knowledge on glass circulating within central Mesopotamia during Sasanian times and to highlight the merits of isotope ratios for the definition of the production scenery. Based on the elemental composition of the samples, two groups related to the exploitation of different plant ashes were previously distinguished, and also a change in the silica source in the course of the 4th century AD emerged. The determination of isotopic distributions of Sr and Nd offers a deeper insight. The 87Sr/86Sr isotope ratio, together with the Sr elemental concentration, confirms this use of different plant ashes, and permits one to distinguish distinct glass batches, although the isotopic Sr signature does not allow us to highlight evidences of different provenances for the samples of different composition. Moreover, the 143Nd/144Nd isotope ratio suggests the use of sands belonging to a common geological area, and also allows the identification of a set of samples that were possibly produced exploiting a further different sand source. As a whole, Sr and Nd isotope ratio values for the samples considered, i.e. 87Sr/86Sr = 0.70833 to 0.70916 and ɛNd = −8.69 to −4.98, differ from the published isotopic data on middle Eastern glass samples and can therefore define a characteristic Sr–Nd signature for plant-ash Sasanian glass excavated in Veh Ardašīr.

Tectonic and climate history influence the geochemistry of large-volume silicic magmas: New δ18O data from the Central Andes with comparison to N America and Kamchatka

New δ18O data from magmatic quartz, plagioclase and zircon crystals in Neogene large-volume, rhyodacitic ignimbrites from the Central Andean Ignimbrite Province reveal uniformly high-δ18O values (δ18O(Qtz) from +8.1 to +9.6‰ — 43 analyses from 15 ignimbrites; δ18O(Plag) from +7.4 to +8.3‰ — 10 analyses from 6 ignimbrites; δ18O(Zrc) from +6.7 to +7.8‰ — 5 analyses from 4 ignimbrites). These data, combined with crustal radiogenic isotopic signatures of Sr, Nd and Pb, imply progressive contamination of basaltic magmas with up to 50vol.% upper crust in these large volume silicic systems. The narrow range of δ18O values also demonstrate that surprising homogeneity was achieved through space (100's km) and time (~10Ma to recent) in these large-volume magmas, via residence in their parental middle to upper crustal bodies. Low-δ18O values of many large volume (>10km3) silicic magmas in North America and Kamchatka, discussed here for comparison, reflect the influence of meteoric-hydrothermal events and glaciations in lowering these δ18O values via the assimilation of hydrothermally-altered crustal material. Conversely, there is a scarcity of a low-δ18O signature in the Central Andes and subduction-related or influenced systems in North America, such as the Oligocene Great Basin of Nevada and Utah, the Southern Rocky Mountain Volcanic Field of Colorado, and the SW Nevada volcanic field system. In these regions, the generally heavy-δ18O magmatic signature is interpreted as a reflection of how a broadly compressional regime, high elevation, aridity and evaporation rates limit availability and infiltration of large amounts of surface meteoric water and hydrothermal alteration of the shallow crust. This leads us to speculate that the δ18O values of large volume silicic magmas in these areas record a paleoelevation and paleoclimate signal. If this is the case, δ18O values of ignimbrites can potentially be used to track the effects of a meteoric-hydrothermal derived δ18O signature from upper crustal rocks that are subsequently assimilated to produce these magma types.

Mafic dykes intrusive into Pre-Cambrian rocks of the São Luís cratonic fragment and Gurupi Belt (Parnaíba Province), north–northeastern Brazil: Geochemistry, Sr–Nd–Pb–O isotopes, 40Ar/39Ar geochronology, and relationships to CAMP magmatism

Dykes of diabase and microgabbro intruded into Pre-Cambrian rocks of the São Luís cratonic fragment and Gurupi Belt, which are tectonic and erosive windows of the Parnaíba Basin in north–northeastern Brazil. Ar–Ar ages were determined, and major, trace element, and Nd–Sr–Pb–O isotopic compositions of these dykes were measured to provide insights into their age, and into the nature of their mantle sources and petrogenetic processes. The data have also been used to compare the chemical and isotopic signatures of the dykes with those of the Central Atlantic Magmatic Province (CAMP). Four chemical groups of mafic dykes have been identified. These comprise two subtypes of high-Ti rocks (i) HTi-1 (TiO2<2.3wt.%; SiO2>47 wt.%), (ii) HTi-2 (TiO2>2.7wt.%; SiO2>47wt.%), in addition to (iii) evolved high-Ti (TiO2>4wt.%; SiO2 of ~46wt.%) and (iv) low-Si (TiO2>2.2wt.%; SiO2<45wt.%) rocks. 40Ar/39Ar geochronology of plagioclase returned ages of 201±4 Ma and 193±10 Ma for the HTi-2 subtype, and of 201±2 Ma and 207±9Ma for the evolved high-Ti group. The HTi-1 and low-Si groups presented highly disturbed age spectra, and did not allow the definition of their emplacement ages. The Argon data indicate an age >200Ma for the low-Si group and are dubious with respect to the age of theHTi-1 subtype, if coeval with (i.e., ~200Ma), or older than, the HTi-2 and evolved high-Ti types. All groups present δ18O values of pyroxene that are compatible with uncontaminated mantle-derived magmas. The HTi-1 subtype (average 143Nd/144Nd200=0.512644; 87Sr/86Sr200=0.7035; 206Pb/204Pb of 17.86) shows the less enriched and less fractionated (more primitive) trace element distribution of all groups. The HTi-2 subtype shows enriched trace element pattern and depleted Nd–Sr signature (143Nd/144Nd200=0.512610; 87Sr/86Sr200=0.7037) and average 206Pb/204Pb ratios of 17.23. The evolved high-Ti chemical group shows average ratios of 143Nd/144Nd200=0.512558, 87Sr/86Sr200=0.7035, and 206Pb/204Pb of 16.88, and the more enriched trace-elements signature among the four groups. The chemical and isotopic compositions and trends of the HTi-1/HTi-2/EHTi types are consistent with their derivation from an asthenosphere-derived parental magma further modified by differentiation and minimal crust contamination (higher in the HTi-2 and EHTi types), and by the derivation of one type from another via fractional crystallization. These high- and evolved high-TiO2 types show ages and some chemical and isotopic features that are consistent with those of the CAMP magmatism. Some differences found are ascribed to petrogenetic processes, such as magma differentiation. A combination of warming of the mantle and edge-driven convection beneath the Pangea supercontinent after the closure of the Neoproterozoic (Brasiliano/Pan-African) orogenies in the Ediacaran–Cambrian boundary might have triggered the magmatic event. The low-Si type shows paired Ta–Nb and Zr–Hf depletions, and depleted Sr–Nd (average 143Nd/144Nd200=0.512687; 87Sr/86Sr200=0.703) and enriched Pb (206Pb/204Pb of 18.66) isotopic compositions that may be interpreted to result either from interaction of a subcontinental lithospheric mantle with products of an earlier subduction or by contamination of the mantle-derived magma during ascent and emplacement in the continental crust. It is hypothesized that these dykes were emplaced in the Ediacaran–Cambrian boundary, after the Neoproterozoic orogeny that built up the Gurupi Belt and in the early extensional stages that preceded the formation of the Parnaíba Basin.

The geochemical and Sr[sbnd]Nd isotopic characteristics of Paleozoic fractionated S-types granites of north Queensland: Implications for S-type granite petrogenesis

Moderately to strongly fractionated S-type granites crop out extensively (>2500km2) in the central and eastern parts of the Hodgkinson Province, north Queensland, Australia. The granites have been subdivided in two major supersuites: the garnet-bearing Whypalla and cordierite-bearing Cooktown Supersuites; and a number of minor suites—including the extremely fractionated Wangetti and Mount Alto Suites. Early formed magmatic tourmaline is a feature of the Wangetti and Mount Alto granites. Almost all of the S-type granites contain metasedimentary enclave material, while microdioritic enclaves are mostly notably absent. The S-type granites are felsic with a moderate SiO2 range (68–77%). Most elements are negatively correlated with increasing differentiation, including TiO2, FeOtot, MgO, CaO, Ba, Sr, Th, LREE, Eu, Zr, Hf, and ratios such as K/Rb; many decrease to very low levels. There are very few positively correlated elements: Rb, U, and to some extent Na2O. Geochemical differences between supersuites include higher CaO, Ba, Sr, Pb, and lower Rb, Sn, B, V in the Whypalla Supersuite. Geochemical variation within the granites is largely due to extensive crystal fractionation. Some of the S-type granites have FeO* and MgO contents of 2.5–3.0% or more indicating they do not represent simple sedimentary melts, but rather represent the presence of both cumulate and restitic material. Variable Nd and Sr signatures (εNd between −2 and −6.5; initial Sr ratios between 0.709 and 0.715), suggest multiple components. The S-type granites intrude a very extensive, siliciclastic turbidite sequence that is isotopically evolved (e.g., εNd mostly −12.0 to −15.0 at 270Ma), and generally too mature (too CaO poor) to produce S-type granites. Isotopic and chemical modeling show that although magma-mixing is permissible, the levels permissible (<ca. 20–25% basaltic input), are not large enough to explain the signature of the granites. Instead the data suggest that the S-type granites were derived from unexposed metasedimentary source rocks at depth, consistent with the geology and accretionary tectonic models for the region. Comparison of the S-type granites with nearby similarly extensively fractionated Carboniferous I-type granites shows contrasting geochemical behaviour which appears to relate to ASI-driven changes in solubility of accessory phases. Fractionating peraluminous magmas, like the North Queensland S-type granites, are characterised by increasing ASI, P2O5 and strongly decreasing Th, LREE, HREE, Zr and Y. In contrast, P2O5 strongly decreases while ASI, Th, LREE, HREE, Zr and Y increase or are constant within the I-type granites. These differences, which are also observable between I- and S-type granites elsewhere, provide evidence of how the nature of the source can control the behaviour of even the most fractionated granites.

Life history of Coilia nasus from the Yellow Sea inferred from otolith Sr:Ca ratios

The habitat use and migratory patterns of the estuarine tapertail anchovy, Coilia nasus, from three sites near- or off-shore of the Yellow Sea, were studied by examining the environmental signatures of Sr and Ca in otoliths using electron probe microanalysis (EPMA). All the samples analyzed were offsprings of typical anadromous C. nasus. The fish grew in freshwater habitat nearly for 1 year, and then entered the brackish and sea water which could be as far as ca. 300 km from the Chinese coast line. The Sr:Ca ratios at the edge of otoliths appeared to correlated with water salinities in sampling sites.

Estuarine dependency in a marine fish evaluated with otolith chemistry

Life-long strontium patterns in otoliths of the sciaenid Micropogonias furnieri caught in the southwestern Atlantic Ocean were examined to evaluate estuarine dependency and habitat use. Otolith Sr concentrations were on average 820 ± 55 μg g−1 for freshwater, 1,751 ± 101 μg g−1 for estuarine, and ranged from 2,000 to over 4,000 μg g−1 for marine waters. The examination of life-long otolith Sr revealed that 71 % of the marine-sampled fish moved toward brackish waters from age 0 to age 1, and that estuarine egress ranged from ages 2.1 to 4.1 years depending on the sampling area. Three different long-term patterns of Sr accumulation were observed and inferred to be the result of ontogeny and habitat shifts. Given that an estuarine Sr signature was consistently present in all sampled fish, M. furnieri is suggested to be a true estuarine-dependent species during its early life history.

Methane seeps as ammonite habitats in the U.S. Western Interior Seaway revealed by isotopic analyses of well-preserved shell material

Methane seep deposits are common in the Upper Cretaceous Pierre Shale of the U.S. Western Interior. They contain a rich fauna including ammonites, bivalves, gastropods, sponges, corals, echinoids, crinoids, and fish. In an effort to understand the role of ammonites in these ecosystems, we examined a seep from the upper Campanian Didymoceras cheyennense Zone in Custer County, South Dakota, that contains molluscs with well-preserved shell material permitting isotopic analyses. Values of δ13C of the micritic limestone at the seep range from −46.94‰ to −11.49‰, confirming the influence of anaerobic oxidation of methane on the isotopic composition of the dissolved inorganic carbon reservoir. The ammonites also consistently display light values of δ13C ranging from −13.71‰ to 0.68‰. These values are generally lighter than those in nonseep specimens from age-equivalent rocks elsewhere in the basin (–1.75‰ to 3.42‰). In a single specimen of Baculites corrugatus from the seep, light δ13C values occur throughout ontogeny. These data suggest that ammonites incorporated isotopically light methane-derived carbon in their shells and lived near the vent fluids and methane-oxidizing bacteria. Both juvenile and adult specimens are present, implying that these ammonites spent their entire lives at the seep and formed an integral part of an interwoven community. The values of 87Sr/86Sr in the limestone and well-preserved fossils at the seep (0.707690–0.707728) are higher than that of the open ocean at this time (0.707659). These elevated values suggest that the seep fluids were imprinted with a radiogenic Sr signature, perhaps derived from equilibration with granitic deposits at depth during the initial uplift of the Black Hills.

Stratiform barite deposits hosted in metamorphic assemblages of Dinek and surrounding regions, Isparta, Turkey

The area of Dinek (Isparta, Turkey) hosts stratiform barite deposits that have been mined for sixty years. These deposits are extensive and contain over 90% BaSO4 in some places. Dinek deposits are thus economically significant, and represent a major portion of Turkey’s barite production. This paper describes the depositional, geochemical and origin characteristics of the Dinek and surrounding regions barite deposits. This information can help establish links with other barite deposits in Turkey, and help inform mining policy in Turkey. The 300km2 study area was mapped in detail and some 300 samples were analyzed for petrography, bulk chemistry and sulfur and strontium isotopes. The most voluminous barite deposits occur in Lower Cambrian – Ordovician carbonate and pelitic rocks. Barites generally conform to host rock stratigraphy and display their own conformable stratiform morphology. Following deposition, host rock sections were deformed and rotated by regional metamorphism and tectonics. Barite deposits bear the signature of advanced diagenesis and show secondary veins, brecciation and fractured structure. Measured δ34S values for barite samples ranged from 3‰ to 31‰. Relatively high radiogenic Sr87/Sr86 values were observed for the northwestern (>0.71445) and southeastern sections (>0.71451) sections of the deposit, as well as for the host rocks (>0.71504). The relatively heavy sulfur isotopic ratios and radiogenic Sr signatures are inconsistent with a crustal magmatic or mantle derived source for the sulfate. These values instead indicate that barite sulfate derived from a primary marine source, while Ba cations may have been supplied by Ba-bearing host rocks. Numerous sedimentary structures, as well as the petrologic and geochemical character of the deposit indicate a dominantly sedimentary, diagenetic origin.

Calymmian (1.50–1.45 Ga) magmatic records in Votuverava and Perau sequences, south-southeastern Brazil: Zircon ages and Nd–Sr isotopic geochemistry

Abstract The main aim of this work is to present and discuss the U–Pb zircon ages and Nd–Sr isotopic data from the metabasic rocks that occur within the metamorphosed Votuverava and Perau volcano sedimentary sequences, located in the Apiai Terrane, south-southeastern Brazil. The geochemical pattern of most of these metabasic rocks is similar to those of tholeiitic basalts, suggesting an extensional environment. The U–Pb zircon ages obtained around ca. 1480 Ma characterize an important basic magmatism during the Mesoproterozoic in south-southeastern Brazil. Nd model ages and ɛ Nd / ɛ Sr signatures suggest the Mesoproterozoic as the main period of mantle/crust differentiation for the crustal precursors of these metabasic rocks. It is quite possible that the Mesoproterozoic extentional events that caused the opening of large sedimentary basins in southern-southeastern Brazil have been underestimated. Possible regional correlations between the Votuverava-Perau basin (PR), the Betara and Agua Clara sequences (PR–SP) and the Serra do Itaberaba Group (SP) demonstrate the magnitude of the extensional process associated with the break-up of the preexisting continental masses.

The geographic distribution of strontium isotopes in Danish surface waters – A base for provenance studies in archaeology, hydrology and agriculture

Abstract In this paper Sr isotope signatures are reported for 192 surface water (lakes/ponds and rivers/creeks) samples from within Denmark and an isotope distribution map is presented that may serve as a base for provenance applications, including archaeological migration studies, ground water – surface water – seawater interaction/contamination monitoring, and potentially for agricultural applications, including cases of authenticity proof for particular food products. The Sr isotopic compositions of surface waters range from 87Sr/86Sr = 0.7078 to 0.7125 (average 0.7096 ± 0.0016; 2σ). This average value lies above the range of 87Sr/86Sr values between 0.7078 and 0.7082 expected from Late Cretaceous to Early Tertiary (Oligocene) limestones which form the dominant bedrock type in a NW–SE trending belt in Denmark. The elevated 87Sr/86Sr signatures >∼0.7095 are explained by additions to the surface waters of radiogenic Sr predominantly derived from the near-surface weathering and wash-out of Quarternary glaciogenic tills and soils deposited and formed during and after the last two ice age stages (Saale and Weichsel). The Sr isotopic compositions and concentrations of the surface waters can, therefore, best be modeled by a two-component mixing involving carbonaceous bedrock and glaciogenic cover sediments as the two predominant Sr sources. A feasibility study for using Sr isotopic compositions of surface waters as a proxy for bio-available Sr signatures was conducted in a representative test area on Zealand (Land of Legends, Lejre) where there is no use and application of commercial fertilizers. It is demonstrated that the Sr isotopic signatures of lake waters from within this area are slightly higher (but statistically still indistinguishable) from the average value defined by snail shells and soil leachates considered to characterize the true bio-available Sr. In combination with results from other studies, this is interpreted to reflect the wash-out of Sr with a higher 87Sr/86Sr signature released by weathering in the topsoils into the saturated water tables, a component which is consequently not readily transferred into the shallow-rooting plants and into small herbivores feeding on them. Since drinking water is a likely important source of Sr uptake of humans and larger animals, the contention is that a surface water isotopic composition can potentially characterize the bio-available component relevant for human and carnivorous large animals. Spline functions and ordinary linear kriging were used for modeling the geographic distribution of bio-available Sr isotopes over territorial Denmark. As expected, based on the two-source mixing scenario, the water 87Sr/86Sr ratio contour maps (with some notable exceptions) neither mirror the pre-Quarternary bedrock geology nor a (Pleistocene) soil-type distribution map of Denmark. As a conservative suggestion, the use of the average 87Sr/86Sr ratio of 0.7096 ± 0.0015 (2σ) is recommended as an average for bio-available Sr from within Denmark (Bornholm excluded) for human and larger animals and as a confidence band for distinguishing “local” from “non-local” signatures in archaeological provenance studies. The study also reveals that the average 87Sr/86Sr ratio of ∼0.7088 defined from soil extracts and small herbivores lies approximately 0.15% lower than that defined by the surface waters. The authors recommend using this lower value as a “local”–“non-local” discriminator for food and plant authenticity control in agricultural applications.

Discrimination and origin of the sanukitoid series: Geochemical constraints from the Neoarchean western Karelian Province (Finland)

Neoarchean late to post-tectonic sanukitoid intrusions are found in the western part of the Karelian Province in Finland. Variable-sized, even-grained to K-feldspar porphyritic intrusions form a series of diorites, tonalites, and granodiorites, that are calc-alkaline to alkali-calcic, magnesian, and mostly peraluminous. The major and trace element geochemistry of the intrusions show typical sanukitoid affinities: a mantle signature (high content of Mg, Ni, Cr and high Mg#) and enrichment in LILE (especially K, Ba, and Sr). The intrusions form a distinctive series that can be distinguished from the TTG series of the Karelian Province by their high Ba–Sr signature, low Na 2O/K 2O ratio, and uniform HREE pattern. The sanukitoid series can be compositionally constrained as follows: SiO 2 = 55–70 wt.%, Na 2O/K 2O = 0.5–3, MgO = 1.5–9 wt.%, Mg# = 45–65, K 2O = 1.5–5.0 wt.%, Ba + Sr > 1400 ppm, and (Gd/Er) N = 2–6. The probable source was enriched subcontinental lithosphere mantle with high LILE concentrations in phlogopite and/or sanidine. The accumulation of K, Ba, and Sr in the mantle source may have occurred as a consequence of two separate metasomatic events: 1) by subduction-related fluids/melts and 2) by metasomatism related to asthenospheric mantle upwelling caused by slab breakoff. The slab breakoff at the end-stage of subduction is also a viable trigger for the sanukitoid magmatism.

Sr isotopic and elemental characteristics of calcites in the Chinese deserts: Implications for eolian Sr transport and seawater Sr evolution

Calcite content, Sr concentrations, and isotopes of calcites in the Chinese deserts are systematically studied in this paper. Calcite contents, which are calculated according to acid-soluble Ca contents in the deserts, are generally higher in the sandy deserts than in the sandy lands and decrease roughly from northwest to northeast of China. Acid-soluble Sr is well correlated with calcite in the Chinese deserts, implying acid-soluble Sr comes mainly from the calcite dissolution. Sr concentrations in calcites, calculated on the basis of calcite contents and acid-soluble Sr concentrations in the deserts, have an inverse relation to calcite contents, essentially mirroring the degree of Sr substitution for Ca in the calcite development. Desert calcites have regional variations in Sr isotopic ratios. Calcite Sr isotopic ratios depend on geological settings and chemical weathering. The Badain Jaran, and Tengger deserts are probably affected by additional factors such as the remote groundwater cycle or overturning of underlying sand deposits. Only four deserts (Taklimakan, Qaidam, Badain Jaran, and Tengger) appear to be potential sources of eolian deposits in the Chinese Loess Plateau (CLP). Isotopic signatures of calcite Sr and silicate Nd further indicate that the Tengger desert was not an important source for eolian deposits in the CLP. Eolian calcite was probably enriched due to wind sorting from the potential sources to the CLP and suffered weathering–leaching after it accumulated in the CLP. Sr isotopic compositions and Ca/Sr molar ratios of calcites are different between the deserts and the Lingtai profile, due to the integrated effect of wind sorting and weathering–leaching. It is essential to calculate accurately the 87Sr/ 86Sr ratio and Sr concentration of eolian calcite entering the oceans according to geochemical data of the Chinese deserts, because of the importance of the Chinese deserts in the global dust cycle. The calculated Sr concentration and 87Sr/ 86Sr ratio of eolian calcite entering the North Pacific Ocean, are 11.75 μmol/g and 0.71032, respectively. The calculated values in this study are close to the recommended values by Jacobson [Jacobson A. D. (2004) Has the atmospheric supply of dissolved calcite dust to seawater influenced the evolution of marine 87Sr/ 86Sr ratios over the past 2.5 million years? Geochem. Geophys. Geosyst. 5(12), 1–9, Q12002. doi: 10.1029/2004GC000750]. Using the same model as that of Jacobson (2004), the effect of Asia dust on the evolution of seawater Sr isotopes is evaluated. ( 87Sr/ 86Sr) seawater increases by 0.3 × 10 −5 if the lower dust flux of 2.34 × 10 8 mol Sr/yr is used in the model, suggesting the little effect of Asian dust on the seawater Sr record in the Quaternary. The increase in ( 87Sr/ 86Sr) seawater is 1.5 × 10 −5 if the higher value of 1.17 × 10 9 mol Sr/yr is used, as observed in the Quaternary Sr record. These results further support the suggestions of Jacobson (2004).

Nature and timing of multiple metasomatic events in the sub-cratonic lithosphere beneath Labait, Tanzania

Petrography, mineral major- and trace element analyses and Rb–Sr and Sm–Nd systematics of xenoliths from Labait volcano, north-central Tanzania, document multiple metasomatic events after initial depletion of the Archaean sub-lithospheric mantle. Four distinct metasomatic phases occurred during the 2.8–3.2 Ga history of the mantle section of the Tanzanian craton. 1) Garnet and Cr-diopside in two depleted lherzolites record LREE enrichment in an early cryptic metasomatic event (~ 2 Ga) resulting in unradiogenic ε Nd (− 6.6) and relatively radiogenic Sr signature ( 87Sr/ 86Sr = 0.7049); 2) Four texturally equilibrated peridotites contain phlogopite and Cr-diopside inferred to be introduced by a hydrous melt/fluid that produced LREE enrichment related to the subduction and collision during the 650 Ma Pan-African Orogeny; 3) Fe-enrichment is observed in many garnet-free wehrlites and dunites having low Mg# olivines. Timing of this enrichment event remains poorly defined; and 4) One spinel lherzolite records orthopyroxene replacing clinopyroxene due to recent infiltration of a rift-related H 2O poor, K-alkaline silicate melt. This ongoing metasomatic reaction caused by rift-related magmatism would result in the conversion of lherzolite to orthopyroxene-rich harzburgite. The reaction possibly represents the mechanism involved in the formation of orthopyroxene-rich sub-continental lithospheric mantle below the Kaapvaal and Siberian cratons. Generally, the rift-related metasomatism beneath Tanzania has caused formation of interstitial clinopyroxene, melt veins and melt pockets and new rims of phlogopite, all of which are in chemical disequilibrium with the original xenolith mineralogy.

Ancient Coastlines in the Continental Shelf of the State of Ceará, Northeast Brazil: Evidence from Sediment Chemistry and Stable Isotopes

Continental shelf sediments from the state of Ceará, northeastern Brazil, have been studied to investigate meteoric diagenesis of marine sediments of previously defined ancient coastal lines. Major elements for 131 samples of carbonate sediments and C and O isotopes for 51 carapace samples of benthonic foraminifers of the Amphistegina radiata and Peneroplis planatus species were analyzed. Geochemical signatures of δ13C, δ18O, SiO2 (stoichiometrically calculated as quartz %), Sr and Mn, and XRD document the impact of meteoric diagenesis on relict sediments from current depths of 25-30 m, 45 m, and 80 m. Morphologies of the marine shelf at these depths, interpreted from previous bathymetric profiles, correspond to holocenic marine terraces. Despite a recent sedimentary cover, it was possible to confirm that these terraces possess relict detrital, biogenic, and continental material, that resulted from erosional reworking of ancient coastlines during the Flandrian transgression.

Petrogenesis of high Ba–Sr plutons from the Northern Highlands Terrane of the British Caledonian Province

A variety of high Ba–Sr granites and syenites is intruded into the Caledonian terrane of the Northern Highlands of Scotland. Volumetrically rather small, the plutons display a considerable range of compositions from ultramafic and mafic to granitic and syenitic. Most intrude Proterozoic Moine metasediments, though some are exposed within the Moine Thrust Zone in the west, beyond which lies the Archaean Lewisian foreland. Although it is generally agreed that they are related in some way to the subduction of Iapetus Ocean crust beneath Laurentia, their petrogenesis is much debated, especially the enigmatic relationship between alkaline syenites and calc-alkaline granites. New isotope (Sr–Nd–O) data suggest that both may be derived from mantle sources that include small fractions of subducted pelagic sediment. Juvenile material is volumetrically dominant, although subsequent fractionation involved contamination with local continental crust. Direct derivation from a mafic underplate is unlikely given the absence of pronounced HREE and Y depletion, the major element dissimilarity with adakitic magmas, and the presence of coeval and geochemically-contiguous mantle-derived rocks. The parent magmas were derived from a Caledonian Parental Magma Array (CPMA) that extended from isotopically depleted to significantly enriched compositions, with high δ 18O in the latter. The oxygen isotope values and the high Ba–Sr signature in particular strongly suggest that mantle contamination with subducted pelagic carbonates generated the CPMA, and Nd–Sr isotopes constrain the sediment contribution to less than 10%. Differentiation of the parent magmas proceeded by fractional crystallisation and variable concurrent assimilation of small magma batches, involving different crystallising assemblages and different continental reservoirs. Caledonian syenites evolved by extensive pyroxene-dominated fractionation sometimes involving contamination with Lewisian granulites. On the other hand, the granites fractionated amphibole and plagioclase, during which most were contaminated with local Moine metasediment. The extended time interval over which the syenites were intruded (30 Ma) accords with continuing Iapetus subduction beneath the Laurentian margin, while the late pulse of isotopically-variable appinites and granites at about 425 Ma sits comfortably with Scandian slab breakoff. However, the high Ba–Sr granites studied here represent small-volume assimilation-fractionation products of mantle-derived appinitic magmas, rather than the voluminous melts of lamprophyre-underplated crust also predicted by slab breakoff, which are absent from the Northern Highland Terrane.

Diffusion versus recrystallization processes in Rb–Sr geochronology: Isotopic relics in eclogite facies rocks, Western Gneiss Region, Norway

Rb–Sr and U–Pb isotopic data for granulite facies rocks, forming textural relics with respect to eclogite facies metamorphism in the Western Gneiss Region (WGR) of Norway, highlight the importance of textures and mineral reaction kinetics for the interpretation of geochronological data. Studied rocks from Bårdsholmen, southern WGR, were subjected to granulite facies metamorphism at 955±3Ma (U–Pb, zircon). Later on, they experienced a subduction-related, kinetically stranded eclogitization (T>650°C at ∼20kbar) at 404±2Ma (Rb–Sr multimineral internal isochron data), followed by exhumation through amphibolite facies conditions. Full conversion of granulite to eclogite was restricted to zones of fluid infiltration and deformation. Despite the fact that metamorphic temperatures vastly exceeded the commonly assumed ‘closure temperature’ for Rb–Sr in submillimeter-sized biotite for several Ma during eclogite facies overprint, Sr-isotopic signatures of relic biotite have not been fully reset. Large biotite crystals nearly record their Sveconorwegian (Grenvillian) crystallization age. Sr signatures of other granulite facies phases (feldspar, pyroxenes, amphibole) remained unchanged, with the exception of apatite. The results imply that isotopic signatures much closer correspond to the P, T conditions of formation recorded by a dated phase and its paragenesis, than to a temperature history. In texturally well-equilibrated high-grade rocks which experienced no mineral reactions and remained devoid of free fluids during exhumation, like granulites or eclogites, isotopic resetting during cooling is either kinetically locked, or restricted to sluggish intermineral diffusion which demonstrably does not lead to full isotopic homogenization. In texturally unequilibrated rocks, textural relics are likely to represent isotopic relics. It is shown that for both high-grade rocks and for rocks with textural disequilibria, geologically meaningful isotopic ages based on isochron methods can only be derived from sub-assemblages in isotopic equilibrium, which have to be defined by analysis of all rock-forming minerals. Conventional two-point ‘mica ages’ for such rocks are a priori geochronologically uninterpretable, and valid multimineral isochron ages a priori do not record cooling but instead date recrystallization-inducing processes like fluid–rock interaction.