Global correlation for strontium isotope curve in the Late Cretaceous of Tibet and dating marine sediments

87Sr/86Sr ratios of marine carbonate samples collected from a sedimentary section of the Late Cretaceous in the south of Tibet were measured. Based on the absence of cathodo-luminescence and a very low Mn/Sr ratio (average 0.06) of the samples, it is thought that they contain information on the original seawater strontium isotope composition. The strontium isotope evolution curve of the Late Cretaceous in Tibet we established here, is consistent with other coeval curves from Europe, North America and Antarctica, supports the notion that the strontium isotope composition of seawater is governed by global events, which provides a new approach for the inter-continental and inter-basinal correlations of Late Cretaceous in the area and is a complementarity for biostratigraphy. In addition, we attempt to determine the age of the boundaries for Campanian/Santonian and Maastrichtian/Campanian by 87Sr/86Sr ratios for Gamba section in southern Tibet. The two boundaries are located in the thickness of 217 m (83.5 M     

Characterization of sulfate mineral deposits in central Thailand

In this paper we present petrographic and geochemical data of sulfate mineral deposits in northeast Nakhon Sawan, central Thailand, and provide new constraints on their age. The deposits are made up mainly of strongly deformed nodular and massive gypsum in the upper part, and less deformed layered anhydrite in the lower part. They are intruded by andesitic dikes that contain Middle Triassic zircons (ca 240 Ma). These dikes are probably part of the regional magmatic activity of the Sukhothai Arc during the Early to Middle Triassic. Sulfur (δ³⁴S) and strontium (⁸⁷Sr/⁸⁶Sr) isotopic compositions of the sulfates range from 15.86 ‰ to 16.26 ‰ and from 0.70810 to 0.70817, respectively. Comparisons with the Phanerozoic seawater isotopic evolution curve indicate that those values are best explained by precipitation of the sulfates from Carboniferous seawater, in particular seawater of late Mississippian age (ca 326 Ma), and this would be consistent with previous studies of calcareous fossils in the limestones that crop out around this site. Our interpretation is that evaporitic gypsum was originally precipitated from hypersaline seawater on a shallow lagoon or shelf on the Khao Khwang Platform during the Serpukhovian, and that this gypsum changed to anhydrite during early burial. The anhydrite was then cut by andesitic dikes during the Middle Triassic, and more recently the upper part of which was rehydrated during exhumation to form secondary gypsum near the surface.     

87Sr enrichment of ophiolitic sulphide deposits in Cyprus confirms ore formation by circulating seawater

The hypothesis that seawater was the source of the hydrothermal fluid which formed the Upper Cretaceous ophiolitic cupriferous pyrite ore desposits of the Troodos Massif (Cyprus) has been tested by analysing the strontium isotopic composition of thirteen mineralized samples from four mines. Initial⁸⁷Sr/⁸⁶Sr ratios range from 0.7052 ± 0.0001 to 0.7075 ± 0.0002, the latter value being indistinguishable from that of Upper Cretaceous seawater at 0.7076 ± 0.0006 (2σ). Hence, the mineralized metabasalt samples have been contaminated with⁸⁷Sr, relative to initial magmatic strontium isotope ratios of the Troodos ophiolitic complex (0.70338 ± 0.00010 to 0.70365 ± 0.00005).Since seawater was the only source of strontium available during formation of the Troodos Complex which was isotopically relatively enriched in⁸⁷Sr, the data confirm that seawater was the source of the hydrothermal oreforming fluid.     

The geological significance of Rb-Sr whole-rock isochrons of polymetamorphic Archaean gneisses,Fiskenaesset area,southern West Greenland

Rb-Sr whole-rock isochron ages of gneisses from the Fiskenaesset area are considerably lower (2600–2800 m.y.) than U-Pb zircon ages for the same rocks (2880–2950 m.y.). There is a significant correlation between the isochron ages and the range in Rb/Sr ratios of the samples involved. Higher ages (and lower initial⁸⁷Sr/⁸⁶Sr ratios) are obtained for sample collections with a wide range in Rb/Sr ratios. Lower ages (and higher initial ratios) are obtained for sample collections with a narrow range in Rb/Sr ratios. This relationship is explained by a model of local metamorphic Sr isotope homogenisation in restricted rock volumes. This model implies that the individual isochron ages do not date specific geological events. There is a significant inverse correlation between the isochron ages and the corresponding initial ratios. It is probable that the igneous precursors of the gneisses intruded with initial⁸⁷Sr/⁸⁶Sr ratios well below 0.701.     

The strontium isotopic composition of seawater,and seawater-oceanic crust interaction

The⁸⁷Sr/⁸⁶Sr ratio of seawater strontium (0.7091) is less than the⁸⁷Sr/⁸⁶Sr ratio of dissolved strontium delivered to the oceans by continental run-off (～0.716). Isotope exchange with strontium isotopically lighter oceanic crust during hydrothermal convection within spreading oceanic ridges can explain this observation. In quantitative terms, the current⁸⁷Sr/⁸⁶Sr ratio of seawater (0.7091) may be maintained by balancing the continental run-off flux of strontium (0.59 × 10¹² g/yr) against a hydrothermal recirculation flux of 3.6 × 10¹² g/yr, during which the⁸⁷Sr/⁸⁶Sr ratio of seawater drops by 0.0011. A concomitant mean increase in the⁸⁷Sr/⁸⁶Sr ratio of the upper 4.5 km of oceanic crust of 0.0010 (0.7029–0.7039) should be produced. This required⁸⁷Sr enrichment has been observed in hydrothermally metamorphosed ophiolitic rocks from the Troodos Massif, Cyprus.The post-Upper Cretaceous increase in the strontium isotopic composition of seawater(～0.7075–0.7091) covaries smoothly with inferred increase in land area. This suggests that during this period the main factor which has caused variability in the⁸⁷Sr/⁸⁶Sr ratio of seawater strontium could have been variation in the magnitude of the continental run-off flux caused by variation in land area. Variations in land area may themselves have been partly a consequence of variations in global mean sea-floor spreading rate.     

87Sr/86Sr ratios in hydrothermal waters and deposits from the East Pacific Rise at 21°N

⁸⁷Sr/⁸⁶Sr ratios of three hydrothermal waters collected on the East Pacific Rise at 21°N define a mixing line between seawater and a hydrothermal end-member at 0.7030 which is derived by seawater-basalt interaction at ca. 350°C and water/rock ratio of about 1.5. Sr concentrations are not affected in the process while Mg uptake from seawater is almost complete. Up to2/3 of this hydrothermal component is involved in anhydrite precipitation while the Sr isotopic ratio in sulfides (chalcopyrite + sphalerite) cannot be distinguished from that of sulfate. It is estimated that ca. 1 × 10¹⁰ moles of strontium are yearly cycled in the hydrothermal systems of mid-oceanic ridges, thereby affecting the⁸⁷Sr/⁸⁶Sr budget of seawater. Mass balance between river runoff, limestone precipitation and ridge basalt alteration suggests that the⁸⁷Sr/⁸⁶Sr ratios of the river runoff are in the range 0.7097–0.7113, and are largely dominated by limestone alteration.     

Strontium isotopic identification of water-rock interaction and ground water mixing

87Sr/86Sr ratios of ground waters in the Bighorn and Laramie basins' carbonate and carbonate-cemented aquifer systems, Wyoming, United States, reflect the distinctive strontium isotope signatures of the minerals in their respective aquifers. Well water samples from the Madison Aquifer (Bighorn Basin) have strontium isotopic ratios that match their carbonate host rocks. Casper Aquifer ground waters (Laramie Basin) have strontium isotopic ratios that differ from the bulk host rock; however, stepwise leaching of Casper Sandstone indicates that most of the strontium in Casper Aquifer ground waters is acquired from preferential dissolution of carbonate cement. Strontium isotope data from both Bighorn and Laramie basins, along with dye tracing experiments in the Bighorn Basin and tritium data from the Laramie Basin, suggest that waters in carbonate or carbonate-cemented aquifers acquire their strontium isotope composition very quickly--on the order of decades. Strontium isotopes were also used successfully to verify previously identified mixed Redbeds-Casper ground waters in the Laramie Basin. The strontium isotopic compositions of ground waters near Precambrian outcrops also suggest previously unrecognized mixing between Casper and Precambrian aquifers. These results demonstrate the utility of strontium isotopic ratio data in identifying ground water sources and aquifer interactions.     

Strontium isotope ratios in volcanic rocks from the South Sandwich Islands

⁸⁷Sr/⁸⁶Sr ratios in the island-arc tholeiite series from the South Sandwich Islands cluster about a value of 0.7040. There is no apparent correlation of strontium isotope values with any major chemical component or with Rb/Sr ratios. The uniformity of the⁸⁷Sr/⁸⁶Sr values is consistent with the fractional crystallization relationship previously proposed for this suite. Though higher than values reported for ocean-floor tholeiites they are not significantly different from ratios reported for calc-alkaline island-arcs.     

Carbon isotope composition and comparison of Lower Triassic marine carbonate rocks from Southern Longmenxia section in Guang’an,Sichuan Basin

The Early Triassic was a period of ecological restoration for the earth's system after the end-Permian mass extinction.Geochemical records linked to the variations in marine ecosystems during this period have attracted the interest of geologists for many years.Based on petrographic analysis of samples and evaluations of their reliability as proxies for original seawater,this study investigated the carbon and oxygen isotopic compositions of 350 carbonate rock samples from the Lower Triassic(and adjacent strata)in the southern Longmenxia section of Guang'an,eastern Sichuan Basin.The results indicate that the Triassic carbonate rocks from the southern Longmenxia section favorably preserved the original seawater'sδ~(13)C signal.Furthermore,carbon and oxygen isotopic compositions are found to be poorly correlated,with a determination coefficient as low as 0.0205 and only 44 rock samples show results of Mn/Sr2 and/orδ~(18)0-6.5‰.The complete carbon isotopic curve for the Lower Triassic is established using the data from the remaining 306 samples with Mn/Sr2 and/orδ~(18)O-6.5‰.This curve presents favorable comparability on a global scale,specifically in theδ~(13)C minima near the Permian-Triassic boundary,at the top of the Jia1 and within the the Jia3,as well as in theδ~(13)C maxima at the tops of the Ye1 and Ye4,at the base of the Jia2 and at the top of the Ye3.The peaks and troughs corresponding to these maxima and minima all reflect global signals.By comparing these results to previous research on coeval carbon isotopic curves established within the chronostratigraphic framework,the ages of these critical evolution points are determined.The results show that the Ye1 roughly corresponds to the Griesbachian substage;the Ye2 through Ye4 correspond to the Dienerian substage;Jial corresponds to the Smithian substage;from the Jia2 to the lower part of the Jia4 correspond to the Spathian substage;and the middle and upper parts of the Jia4 belongs to the Aegean Substage of the Middle Triassic.Around the boundary between the Jial and Jia2(which represents the Smithian-Spathian boundary(SSB)),the value ofδ~(13)C increases rapidly from-0.911‰to 3.679‰.The span during which the seawater's carbon isotope experiences this drastic change may be less than36 kyr.The oxygen isotope,which is more sensitive to sedimentary environmental changes,exhibits changes prior to the carbon isotope near the SSB,indicating a significant increase in the salinity of the seawater before a sharp rise in the carbon isotope;this event leads to the formation of evaporites and dolomites.     

Effect of sea water interaction on strontium isotope composition of deep-sea basalts

Analyses of rim-to-interior samples of fresh tholeiitic pillow basalts, deuterically altered holocrystalline basalts, and older, weathered tholeiitic basalts from the deep sea indicate that ⁸⁷Sr/⁸⁶Sr ratios of the older basalts are raised by low temperature interaction with strontium dissolved in sea water. ⁸⁷Sr/⁸⁶Sr correlates positively with H₂O in these basalts; however, there is little detectable modification of the strontium isotope composition in rocks with H₂O contents less than 1%. The isotope changes appear to be a function of relatively long-term, low-temperature weathering, rather than high-temperature or deuteric alteration. Strontium abundance and isotopic data for these rocks suggest that strontium content is only slightly modified by interaction with sea water, and it is a relatively insensitive indicator of marine alteration. Average Rb-Sr parameters for samples of apparently unaltered basalt are: Rb= 1.11ppm; Sr= 132ppm; ⁸⁷Sr/⁸⁶Sr= 0.70247.     

Strontium and oxygen isotopic composition of some basalts from Hole 504B,Costa Rica Rift,DSDP Legs 69 and 70

Seventeen whole-rock samples, generally taken at 25–50 m intervals from 5 to 560 m sub-basement in Hole 504B, drilled in 6.2 m.y. old crust, were analysed for⁸⁷Sr/⁸⁶Sr ratios, Sr and Rb concentrations, and¹⁸O/¹⁶O ratios. Sr isotope ratios for 8 samples from the upper 260 m of the hole range from 0.70287 to 0.70377, with a mean of 0.70320. In the 330–560 m interval, 5 samples have a restricted range of 0.70255–0.70279, with a mean of 0.70266, the average value for fresh mid-ocean ridge basalts (MORB). In the 260–330 m interval, approximately intermediate Sr isotopic ratios are found.δ¹⁸O values (‰) range from 6.4 to 7.8 in the upper 260 m, 6.2–6.4 in the 270–320 m interval, and 5.8–6.2 in the 320–560 m interval. The values in the upper 260 m are typical for basalts which have undergone low-temperature seawater alteration, whereas the values for the 320–560 m interval correspond to MORB which have experienced essentially no oxygen isotopic alteration.The higher⁸⁷Sr/⁸⁶Sr and¹⁸O/¹⁶O ratios in the upper part of the hole can be interpreted as the result of a greater overall water/rock ratio in the upper part of the Hole 504B crust than in the lower part. Interaction of basalt with seawater(⁸⁷Sr/⁸⁶Sr=0.7091) increased basalt⁸⁷Sr/⁸⁶Sr ratios and produced smectitic alteration products which raised whole-rock δ¹⁸O values. Seawater circulation in the lower basalts may have been partly restricted by the greater number of relatively impermeable massive lava flows below about 230 m sub-basement. These flows may have helped to seal off lower basalts from through-flowing seawater.     

Strontium and neodymium isotopic evidence for the heterogeneous nature and development of the mantle beneath Afar (Ethiopia)

Neodymium isotope and REE analyses of recent volcanic rocks and spinel lherzolite nodules from the Afar area are reported. The¹⁴³Nd/¹⁴⁴Nd ratios of the volcanic rocks range from 0.51286 to 0.51304, similar to the range recorded from Iceland. However, the⁸⁷Sr/⁸⁶Sr ratios display a distinctly greater range (0.70328–0.70410) than those reported from the primitive rocks of Iceland. Whole rock samples and mineral separates from the spinel lherzolite nodules exhibit uniform¹⁴³Nd/¹⁴⁴Nd ratios (ca. 0.5129) but varied⁸⁷Sr/⁸⁶Sr ratios in the range 0.70427–0.70528.The SrNd isotope variations suggest that the volcanic rocks may have been produced by mixing between two reservoirs with distinct isotopic compositions. Two possible magma reservoirs in this area are the source which produced the “MORB-type” volcanics in the Red Sea and Gulf of Aden and the anomalous source represented by the nodule suite. The isotopic composition of the volcanics is compatible with mixing between these two reservoirs.It is shown that the anomalous source with a high⁸⁷Sr/⁸⁶Sr ratio cannot have been produced by simple processes of partial melting and mixing within normal mantle. Instead the high⁸⁷Sr/⁸⁶Sr is equated with a fluid phase. A primitive cognate fluid, subducted seawater or altered oceanic lithosphere may have been responsible for the generation of the source with a high⁸⁷Sr/⁸⁶Sr ratio.     

Neodymium-strontium isotopic evidence for extreme contamination in a layered basic intrusion

Neodymium and strontium isotopic analyses from the Kalka layered basic intrusion, central Australia, are arrayed parallel to the Sr-axis of a Nd-Sr isotopic correlation diagram and are removed from the normal basaltic field. Initial¹⁴³Nd/¹⁴⁴Nd ratios are almost constant and typical of continental basalts, whereas initial⁸⁷Sr/⁸⁶Sr ratios vary greatly and range to high values (0.7049–0.7088). Acidic granulites from the country rock lie upon the continuation of the Kalka trend at higher⁸⁷Sr/⁸⁶Sr ratios outlining a mixing system between granulite and normal basaltic magma. If average granulite acted as a contaminant, isotope dilution calculations show that amounts assimilated reached as high as 25%. Bulk contamination is confirmed petrologically by the abundance of orthopyroxene, particularly as basal orthopyroxenites and the restriction of olivine to less-contaminated levels. Analogies between Kalka and several other major layered intrusions, such as the Bushveld Complex, suggest that large-scale contamination was a significant aspect of their genesis.     

Subaqueous volcanism in the Paleo-Pacific Ocean based on Jurassic basaltic tuff and pillow basalt in the Raohe Complex,NE China

On-land records of subaqueous explosive volcanic eruptions are rarely reported.To understand this phenomenon and discuss its global significance,we studied the geochronology and geochemistry of basaltic tuff and pillow basalt in the Raohe Complex,NE China.The basaltic tuff consists of well-sorted vitreous,crystal(mostly clinopyroxene),and minor lithic fragments.It is characterized by a high Mg O(15.7–15.9%)content and zero Eu anomalies(Eu/Eu~*=99–102).The tuff erupted at 172±1 Ma based on SHRIMP zircon U-Pb dating,coeval with the previously reported age of the pillow basalt.The pillow basalt has intermediate Mg O content and weakly negative Eu anomalies(Eu/Eu~*=90–99).Based on immobile trace element discrimination,the basaltic tuff and pillow basalt belong to alkali basalt displaying an OIB-type trace element pattern,and consistent Nd isotope signatures ofε_(Nd)(t)=4.4–6.2,indicating an identical mantle source.The pillow basalt has coupled Sr-Nd isotopic values,whereas the basaltic tuff has significantly higher initial~(87)Sr/~(86)Sr values that are similar to synchronous seawater.This indicates that the elemental exchange between the mantle-derived material and seawater most likely occurred in a subaqueous explosive volcanic eruption,rather than in an effusive eruption.Detailed calculations suggest that the high efficiency of the Sr-isotope exchange between seawater and the mantle-derived material triggered by a subaqueous explosive volcanic eruption is likely one of the main reasons for the rapid decrease of the global seawater~(87)Sr/~(86)Sr value.     

Sr fluxes and isotopic compositions of the eleven rivers originating from the Qinghai-Tibet Plateau and their contributions to <Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr evolution of seawater

To evaluate influence of chemical weathering of the Qinghai-Tibet Plateau (QTP) on seawater ⁸⁷Sr/⁸⁶Sr variation, river water and sediment samples were collected, and their Sr concentrations and isotopic compositions analyzed, from the seven large rivers that originated from the QTP. By combining these with the data of the Ganges, Brahmaputra, Indus and Irrawaddy originated in the southern QTP, the total Sr flux of the eleven rivers reaches 3.47×10⁹ mol·a⁻¹, which accounts for 10.2% of the total Sr flux transported by the global rivers. The weighted mean ⁸⁷Sr/⁸⁶Sr is 0.71694, higher than the average value of the global rivers. The ⁸⁷Sr_ex (⁸⁷Sr flux in excess of the seawater ⁸⁷Sr/⁸⁶Sr ratio) of the Chinese seven rivers is 1.55×10⁶ mol·a⁻¹, only accounting for about 6% of the value of the eleven rivers originated from QTP, and the Ganges-Brahmaputra system accounts for 86%. We assume that the QTP rivers have no strontium contributions to the oceans before ∼40 Ma and the Sr fluxes of the global rivers, except the QTP eleven rivers, are constant, then a maximum linear increase in Sr fluxes of the QTP rivers from zero to the modern value in response to tectonic uplift can explain ∼69% increase of seawater ⁸⁷Sr/⁸⁶Sr over the past ∼40 Ma and the remainder of 31% is perhaps provided from other factors. Supported by National Natural Science Foundation of China (Grant Nos. 40473009, 40331001, 40873001)     

Strontium and its isotopic composition in interstitial waters of marine carbonate sediments

The concentrations and isotopic compositions of strontium in interstitial waters from several DSDP sites, where sediments consist chiefly of carbonate oozes and chalks, are used as indicators of carbonate diagenesis by reference to a recently-produced curve showing detailed variations in the⁸⁷Sr/⁸⁶Sr ratio of seawater with time. Carbonate sediments of the Walvis Ridge show increases in interstitial Sr²⁺ concentrations in the upper carbonate-ooze sections with the highest concentrations near the ooze-chalk boundary where maximum rates of carbonate recrystallization occur. Below this, in situ production of Sr²⁺ diminishes and there is a diffusive flux of Sr to an underlying sink, presumably volcanogenic sediments or basalts, leading to Sr isotopic disequilibrium between carbonates and interstitial waters. In some other sites, however, there is no apparent Sr sink at depth and isotopic equilibrium is retained. Overall, diffusive smoothing of profiles exerts an important control on the⁸⁷Sr/⁸⁶Sr ratios, although lower ratios than contemporaneous seawater values in the carbonate oozes often correlate with zones of Mg²⁺ loss and reflect a combination of a flux of Sr²⁺ from the zone of maximum recrystallization rates together with a contribution from the in situ alteration of volcanic matter.     

The strontium isotopic composition of interstitial waters from sites 245 and 336 of the Deep Sea Drilling Project

Measurements of ⁸⁷Sr/⁸⁶Sr ratios of interstitial waters from leg 25, site 245 and leg 38, site 336 of the Deep Sea Drilling Project show that the enrichment of Sr²⁺ with depth is caused both by the alteration of volcanic material and by the introduction of strontium derived from calcium carbonate. ⁸⁷Sr/⁸⁶Sr ratios range from 0.70913 to 0.70794 at site 245 and from 0.70916 to 0.70694 at site 336. The low ratios compared with contemporaneous seawater reflect the release of Sr from a volcanic source having, according to material-balance calculations, a ⁸⁷Sr/⁸⁶Sr ratio of about 0.7034 at site 336. At this site the source appears to be volcanic ash and not basaltic basement which acts as a sink for Sr²⁺ during in situ low-temperature weathering. The volcanic contribution to the strontium enrichment in the basal interstitial waters varies from <10% at site 245 to >50% at site 336. The remaining Sr²⁺ is derived from Sr-rich biogenic carbonate during diagenetic recrystallization to form Sr-poor calcite.     

“Mantle” Rb/Sr and 87Sr/86Sr ratios for clinopyroxenes from Norwegian garnet peridotites and pyroxenites

Clinopyroxenes separated from garnetiferous ultramafic rocks in the core zone of the Norwegian Caledonides have rubidium concentrations of 0.008 to 0.064 ppm, strontium concentrations of 23.5 to 421 ppm, and ⁸⁷Sr/⁸⁶Sr ratios of 0.7011 to 0.7029. The very low Rb/Sr ratios of the clinopyroxenes (less than 0.0004) suggest that their ⁸⁷Sr/⁸⁶Sr values have not varied significantly over geologic time and may approximate the initial ⁸⁷Sr/⁸⁶Sr of the eclogite-facies ultramafic mineral assemblages at their time of formation. The ultramafic rocks occur in a basement complex that yields Rb-Sr whole-rock and U-Pb zircon ages of about 1800 m.y. Garnetiferous ultramafic rocks are apparently lacking in younger (Sveconorwegian or Caledonian) sialic sequences, raising the possibility that the eclogite-facies metamorphism may have occurred at least 1800 m.y. ago. The Rb/Sr and ⁸⁷Sr/⁸⁶Sr ratios of the clinopyroxenes are as predicted for the ancient upper mantle under most evolutionary models. However, the data do not preclude the possibility that the eclogite-facies metamorphism occurred in the crust. The garnetiferous ultramafic rocks are generally enclosed by large volumes of dunite which could have shielded the eclogite-facies assemblages from contamination by fluids from the country rock during metamorphism.     

Lead and strontium isotopes in Cretaceous kimberlites and mantle-derived xenoliths from Southern Africa

Concentrations of lead, uranium and thorium and isotopic compositions of lead are reported for twelve Cretaceous kimberlites and five Cretaceous nucleated autoliths. The samples are from Lesotho and from the area around Kimberley (Cape Province, South Africa). In the case of the autoliths potassium, rubidium and strontium concentrations and⁸⁷Sr/⁸⁶Sr ratios were also measured.Work reported on clinopyroxenes from mantle-derived xenoliths in kimberlites includes lead isotopes for twelve samples and strontium isotopes for nine of these.The autoliths have initial⁸⁷Sr/⁸⁶Sr ratios between 0.7035 and 0.7095. A large spread in initial lead isotope ratios (²⁰⁶Pb/²⁰⁴Pb: 17.6–20;²⁰⁸Pb/²⁰⁴Pb: 37.7–39.5) was found in the matrix kimberlites and autoliths. In the²⁰⁷Pb/²⁰⁴Pb vs.²⁰⁶Pb/²⁰⁴Pb plot, the initial lead isotope ratios of the kimberlite and autolith samples roughly define a slope of 0.10, corresponding to an age of 1575 m.y. With respect to the spread of initial ratios as well as with respect to this slope, the kimberlite and autolith lead isotopic pattern is comparable to patterns obtained from carbonatites and ocean island volcanics.The xenoliths studied include coarse-granular and porphyroclastic material from the Kimberley area and coarse-granular samples from Lesotho. Their⁸⁷Sr/⁸⁶Sr ratios are generally between 0.704 and 0.706 but a value of 0.713 was found in one sample. They show a surprisingly large spread in lead isotope ratios (²⁰⁶Pb/²⁰⁴Pb: 17.5–20;²⁰⁸Pb/²⁰⁴Pb: 37.3–39.4).The isotopic patterns of the xenolithic material and of the kimberlites and autoliths are considered to provide a strong indication that the upper mantle beneath Southern Africa is isotopically heterogeneous on a regional scale.     

Marine87Sr/86Sr ratios from the Jurassic to Pleistocene: evidence from groundwaters in Israel

Oceanic⁸⁷Sr/⁸⁶Sr ratios during Jurassic to Pleistocene have been determined by analysing fresh waters from marine limestone and dolomite aquifers. The results are in good agreement with published data from well preserved fossil material. The⁸⁷Sr/⁸⁶Sr ratios obtained are 0.7070 for Lower to Middle Jurassic, 0.7075 for Late Cretaceous, 0.7080 for Lower to Middle Eocene and 0.7087 for Pleistocene aquifer waters. The value of⁸⁷Sr/⁸⁶Sr for the Eimer and Amend isotopic standard was 0.7082.