Terms Of Sr Research Articles

Geochronology and petrogeochemistry of Miocene porphyries from the Beimulang deposit, western Gangdese copper belt

The Beimulang deposit, a newly discovered large porphyry copper deposit, containing 1.3 Mt @ 0.38% Cu, prominently features mineralized orebodies and hydrothermal alteration in the monzogranite porphyry. Zircon U-Pb dating reveals ages of 14.4–14.0 Ma for the monzogranite porphyry and 11.2–11.0 Ma for the granite porphyry. A consistent Re-Os age of 14.1 ± 0.4 Ma from molybdenite suggests a possible link between mineralization and the monzogranite porphyry. The Beimulang Miocene porphyries are rich in SiO2 (70.01–72.81 wt%) and Sr (217–864 ppm) and have high Sr/Y ratios (26–139), which were originated from partial melting of the subduction-modified Tibetan juvenile lower crust. The Beimulang Miocene porphyries show high log w(Fe2O3/FeO) values (>0) in whole rock and high δEu values (mostly > 0.3), high ΔFMQ (4.32–6.43) in zircons, suggesting a high oxidation state. The Beimulang Miocene porphyries show high V/Sc ratios in whole rock and high 10,000 × (δEu)/Y, high (Ce/Nd)/Y, low Dy/Yb ratios (i.e., mostly > 13, > 4, > 0.02 and < 0.3, respectively) in zircons, indicating they are notably hydrated. The granite porphyry has lower εNd (t) (0.70849 – 0.70996) values and higher (87Sr/86Sr)i (-9.3 – -7.8) in whole rock, lower εHf (t) (-5.25 – -2.70) and higher U/Yb (6.0–18.3), δ18O (6.42–7.57‰) in zircon than the monzogranite porphyry (εNd(t) = -5.52 – -4.45; (87Sr/86Sr)i = 0.70744–0.70818; εHf (t) = -3.24 – -0.92; U/Yb = 2.62–8.96; δ18O = 6.10–7.53‰), indicating that the granite porphyry contains fewer juvenile materials compared to the monzogranite porphyry. The high-Mg dioritic rocks in the Beimulang-Zhunuo area reveal significant correlations with monzogranite porphyry rather than granite porphyry in terms of Sr, Sr/Y, Dy/Yb, δEu and SiO2 contents. Taking into account the contemporaneous presence of high-Mg dioritic rocks with the monzogranite porphyry, which are not contemporaneous with the granite porphyry at Beimulang, it can be inferred that these diorite magmas played a significant role in forming the Miocene monzogranite porphyry rather than granite porphyry. Accordingly, the low fertility of the granite porphyry is possibly due to the limited contribution of juvenile melts and lack of the dioritic magmas.

Minerals of the apatite group from ultramafic lamprophyres of the Zima alkaline-ultramafic carbonate complex (Urik-Iya graben, Eastern Sayan region)

Research subject. This paper presents the results of a study of minerals of the apatite group from aillikites of the Zima alkaline-ultramafic carbonatite complex. Aim. To determine the composition of apatites to characterize the studied rocks and to elucidate the patterns of element distribution in the magma of aillikites in the late crystallization stages. Materials and Methods. Minerals of the apatite group from 6 samples (4 from dikes of the Bol'shetagninsky massif, 1 from the Bushkanai dike, 1 from the Beloziminskaya pipe) were studied. The samples showed similar textural-structural features, differing in the mineral composition of the groundmass. Results. Minerals of the apatite group are widespread in the groundmass of all the studied rocks. They are characterized by idiomorphic, subidiomorphic crystals of homogeneous composition, 10-100 microns in size. Minerals of the apatite group were identified as fluorapatite and hydroxyapatite characterized by a significant SiO2 content (up to 5 wt %), low SrO content (up to 1.5 wt %) and REE2O3 (up to 2 wt %). The studied apatites also include MgO, FeO, Na2O, SO4, and CO3. Fluorapatites from dyke aillikites are characterized by a higher silicon content as compared to apatites from the Beloziminskiy pipe. Apatites from fresh aillikites of the Bushkanai dyke have a relatively higher content of Sr, REE, and F than minerals from serpentinized samples. Conclusions. The composition of the studied apatites has a lower Sr and Ba content than orangeite and lamproite apatites. In terms of Sr, Si and REE contents, the studied apatites are similar to kimberlite and ailikite apatites. Such a difference allows minerals of the apatite group to be used as an indicator mineral for classification of kimberlites and related rocks, but only in combination with petrography and composition of other minerals of the groundmass.

FEATURES OF MYOCARDIA DEFORMATION PROPERTIES IN PATIENTS WITH ARTERIAL HYPERTENSION

Objective: Determination of myocardium deformation properties depending on degree of arterial hypertension and the presence/absence of left ventricular hypertrophy (LVH) in patients with arterial hypertension. Design and method: 74 patients of both sexes, with I–III degrees of AH (ESC/ESH, 2018) were studied. Average age of patients was 58.72 ± 11.9 years; AH duration was 10.8 ± 7.2 years. Speckle-tracking EchoCG was performed to obtain an objective and quantitative assessment of global and regional myocardial function using the ACUSON x 700 PV 2.0 manufactured by SIEMENS. Among the parameters for assessing the longitudinal deformation of the left ventricle, we have chosen: global longitudinal strain -GLS (%); Strain Rate-SR. To study the segmental LV contractility, analyzed the apical 4-chamber, 3-chamber and 2-chamber section. Results are presented as M±SD. Results: The patients were divided into 3 groups: I- patients with AH I degree, n = 21 (28.4%); II n = 28 patients with II degree of AH (37.8%); III n = 25 (33.8%) patients with III degree of AH. A comparative analysis of groups showed that in patients with grade III AH, the indicators of GLS and the rate of myocardial deformation are significantly lower than in groups of patients with grades I and II of AH. The index of GLS in group III was: 10.3±3.6%, while in group I - 18.1±4.4% and in group II - 11.8% (p = 0.000). The same was noted in terms of SR: 1.0±0.3 s-1 versus 1.5±0.6 s-1 and 1.1±0.5 s-1, respectively (p = 0.001). To study the deformation properties of the myocardium, patients were divided into 2 groups: patients with LVH and without LVH. In 1st group, the GLS index was lower, 14.9±5.8%, than in 2nd group – 17.9±6.1% (p&lt;0.05); the SR index in the group of patients with LVH was also lower- 1.64±0.75 s-1, than in the group of patients without LVH - 1.87±0.81 s-1 (p&lt;0.05). Conclusions: Thus, significant violations of the deformation properties of LV are formed in patients with AH with an increase of degree of AH and the presence of LVH.

An iron isotope perspective on back-arc basin development: Messages from Mariana Trough basalts

The geology and magmatism of the northern Mariana Trough (NMT) represent a type example for the development of a back-arc basin (BAB). It is a mature spreading center in the south and propagating northward via rifting of arc and rear arc lithosphere in response to trench retreat and overriding plate extension in space and time. It is thus essential to fully characterize its tectonomagmatic processes that are potentially of global significance. For this reason, we carried out a comprehensive geochemical study on basaltic samples (glasses) from the NMT axis from 17 to 23°N by analyzing a full suite of major and trace elements, Sr–Nd–Pb–Hf radiogenic isotopes and stable Fe isotopes. The Fe isotopes, in particular, have the potential to offer novel perspectives beyond the aforementioned geochemical variables. From south to north, the δ56Fe of the NMT basalts (NMTB) decrease systematically, varying from a MOR-like value of +0.12‰ to an arc-like value of 0.00‰. Importantly, incompatible element abundances and Sr–Nd–Pb–Hf isotope compositions of the NMTB also show systematic along-latitude variations. Positively correlated with δ56Fe, the abundances of fluid-insoluble elements (e.g., Nb, Ta, Zr, Hf, Ti and heavy rare earth elements) show the south-to-north decrease, suggesting that the NMTB δ56Fe systematics are inherited from the magma source variation. The source variation is most consistent with an asthenosphere source in the south and progressively more depleted harzburgitic lithosphere source of prior melt depletion towards north. On the other hand, there are scattered but significant enrichment trends towards north in terms of Sr–Nd–Pb–Hf radiogenic isotopes and fluid-soluble incompatible elements (e.g., Ba, Rb, Cs, Th, U, K, Pb, Sr and light rare earth elements), which is consistent with south-to-north increase in slab material (e.g., slab fluids, sediments etc.) contribution. These north-to-south magma source systematics defined by the NMTB can be readily understood as a tectonic response to the back-arc basin development with time from initial arc-magmatism dominated by sub-arc lithospheric mantle melting with significant slab material contributions to back-arc rifting and to back-arc spreading center magmatism characterized by increasing asthenospheric mantle melting, decreasing slab material contribution and diminishing sub-arc lithospheric mantle participation. This tectonic-magma source evolution in space and time is manifested by the snapshot of the NMTB magmatism in terms of the geology, petrology and geochemistry.The NMTB δ56Fe values and fluid-insoluble incompatible element abundances are unaffected by slab materials, but controlled by the harzburgitic residues of previous melt extraction depleted in these elements with low δ56Fe at the early arc-magmatism stage in the north and by the asthenosphere of MORB mantle characteristics in the south with well-developed back-arc spreading system. Importantly, these observations affirm the understanding that compositionally depleted and physically buoyant lithosphere is prerequisite as the overriding plate for subduction initiation at its edges.

Phase equilibria constraints on crystallization differentiation: insights into the petrogenesis of the normally zoned Buddusò Pluton in north-central Sardinia

Abstract The Buddusò Pluton in NE Sardinia (Italy) is a normally zoned intrusion composed of three units with chemical composition ranging from hornblende-bearing tonalites (SiO 2 ∼ 65 wt%) to leucocratic monzogranites (SiO 2 ∼ 76 wt%). Zircon crystals in the pluton are dated at 292.2 ± 0.7 Ma and have ε Hf values ranging from −4 to −8, with no systematic differences observed between the units. The pluton, which is isotopically homogeneous at the whole-rock scale in terms of Sr and Nd isotopes, shows textural evidence indicating local crystal–melt segregation. In this paper, we have implemented a novel approach based on path-dependent phase-equilibria modelling to test the hypothesis that the internal chemical variability of the pluton was generated by crystallization differentiation of a homogeneous parental magma. Our modelling indicates that this hypothesis is valid if the mechanism by which this occurs is compaction in a rheologically locked crystal-rich magma and if the separation occurs at 0.3 GPa from a tonalitic magma with water content &gt;2 wt%. Finally, a subset of the magmatic enclaves in the pluton are considered to be autoliths, formed by the disruption of the compacted crystal mush and interaction between these cumulates and the felsic melt.

Open-system magma evolution and fluid transfer at Campi Flegrei caldera (Southern Italy) during the past 5 ka as revealed by geochemical and isotopic data: The example of the Nisida eruption

We have carried out a detailed petrological investigation on products of the poorly understood Nisida eruption, one of the most recent volcanic events (~4ka BP) at Campi Flegrei caldera. We present major oxide contents and Sr–Nd isotopic data determined on bulk rock, groundmass and separated phenocrysts, along with major and volatile elements (H2O Cl, S and CO2) content of clinopyroxene-hosted melt inclusions from pumice fragments representative of the eruption. We use these to elaborate the role of magmatic evolution processes and fluid transfer prior to, and during, the Nisida eruption.The results indicate that the eruption was triggered by the arrival of a volatile-rich, shoshonite–latite magma. This magma was similar in terms of Sr and Nd isotopes (87Sr/86Sr ~0.70730; 143Nd/144Nd ~0.51250) to the Astroni 6 magmatic component. We infer that emplacement of this magma triggered resurgence of the caldera floor, and fed a large part of the volcanic activity at Campi Flegrei caldera during the past 5ka. The new data on the Nisida eruption and other recent eruptions at Campi Flegrei, together with published data, suggest that fractional crystallization, and potentially fluid transfer from deep to shallow depths may account for most of the chemical variability of the erupted melt. Additional processes, such as magma mingling/mixing, and/or entrapment of antecrysts into the magma prior to the Nisida eruption are required to explain the large isotopic variation displayed by the analyzed products.The Nisida eruption occurred in the eastern sector of the resurgent Campi Flegrei caldera. In this sector, presently affected by an extensional stress regime, previous studies suggest that a Nisida-like eruption would be likely if the level of activity in the caldera were to intensify. In an area with such structural conditions, the ascent of a volatile-rich magma such as that which erupted at Nisida should generate geophysical and geochemical signals detectable by an efficient monitoring network. The results of this investigation should inform the study of other active calderas worldwide that are experiencing persistent unrest, such as Rabaul, Aira, Iwo-Jima, Santorini, Long Valley and Yellowstone.

Miocene adakitic intrusions in the Zhongba terrane: Implications for the origin and geochemical variations of post-collisional adakitic rocks in southern Tibet

Post-collisional adakitic rocks (26–9Ma) have been recognized in southern Tibet for almost 20years; however, their origins and geodynamics remain highly controversial. This paper reports geochronological and geochemical data for the Lasa intrusion exposed in the Zhongba terrane and proposes implications for the origins of the Miocene adakitic rocks in southern Tibet. The Lasa intrusion consists of granite and granodiorite porphyries with zircon U–Pb ages of ca. 16Ma. The porphyries have high SiO2 (65.14–67.61wt.%), Al2O3 (15.13–16.10wt.%), K2O (2.87–3.54wt.%), and Sr (727–1046ppm) contents and low Y (9–13ppm) and Yb (0.82–1.19ppm) contents. They are enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs). The porphyries display relatively low MgO contents (1.39–1.98wt.%), high Sr/Y (65–98) and (La/Yb)N (18.8–25.5) ratios, initial (87Sr/86Sr)i ratios of 0.70912–0.70805, εNd(t) values of –6.4 to –7.9, (206Pb/204Pb)t ratios of 18.7108–18.7665, (207Pb/204Pb)t ratios of 15.6837–15.7118, and (208Pb/204Pb)t ratios of 39.1600–39.3034. These signatures indicate that the Lasa porphyries are adakitic rocks derived from the partial melting of a thickened lower crust. The Miocene adakitic rocks in the Zhongba terrane have similar Sr–Nd isotopic compositions to those of western Lhasa and the Himalaya terrane, which differ from coetaneous adakitic rocks of the eastern Lhasa terrane in terms of Sr–Nd isotopic compositions. Based on the spatial distributions and isotopic features of the post-collisional adakitic rocks in southern Tibet, we suggest that all of the adakitic rocks were derived from the partial melting of thickened lower crust and that their geochemical variations are mainly caused by the heterogeneity of lower crust.

Mantle dynamics and generation of a geochemical mantle boundary along the East Pacific Rise – Pacific/Antarctic ridge

A large-scale mantle compositional discontinuity was identified along the East Pacific Rise (EPR) and the Pacific–Antarctic Ridge (PAR) with an inferred transition located at the EPR 23°S–32°S. Because of the EPR–Easter hotspot interactions in this area, the nature of this geochemical discontinuity remains unclear. IODP Sites U1367 and U1368 drilled into the ocean crust that was accreted at ∼33.5 Ma and ∼13.5 Ma, respectively, between 28°S and 30°S on the EPR. We use lavas from Sites U1367 and U1368 to track this mantle discontinuity away from the EPR. The mantle sources for basalts at Sites U1367 and U1368 represent, respectively, northern and southern Pacific mantle sub-domains in terms of Sr–Nd–Pb–Hf isotopes. The significant isotopic differences between the two IODP sites are consistent with addition of ancient subduction-processed ocean crust to the south Pacific mantle sub-domain. Our modeling result shows that a trace element pattern similar to that of U1368 E-MORB can be formed by melting a subduction-processed typical N-MORB. The trace element and isotope compositions for Site U1368 MORBs can be formed by mixing a HIMU mantle end-member with Site U1367 MORBs. Comparison of our data with those from the EPR–PAR shows a geochemical mantle boundary near the Easter microplate that separates the Pacific upper mantle into northern and southern sub-domains. On the basis of reconstruction of initial locations of the ocean crust at the two sites, we find that the mantle boundary has moved northward to the Easter microplate since before 33.5 Ma. A model, in which along-axis asthenospheric flow to where asthenosphere consumption is strongest, explains the movement of the apparent mantle boundary.

Effect of remineralization/demineralization cycles on mineral profiles of Fuji IX Fast in vitro using electron probe microanalysis

There have been cononcerns about the dissolution of conventional glass ionomer cement (GIC) and its possible degradation when exposed to an acidic environment over time. The objective of this study was to investigate the effects of exposure of Fuji IX Fast to the simulated acidic aspects of the oral environment in terms of any change in the elemental composition of strontium (Sr), phosphorus (P), calcium (Ca) and fluorine (F) which resulted at the surface of this material. Sixty-five cylindrical block of Fuji IX Fast were prepared using split moulds. The demineralizing solution was an acetate buffered demineralizing solution at pH 403. The remineralizing solution was a buffered solution containing 1.5 mM Ca, 0.9 mM P and 10 ppm F at pH 7. The blocks of Fuji IX Fast were subjected either to two-day alternating cycles of remineralization and demineralization for up to 24 days (test); 6 two-day cycles of demineralizing or remineralizing solution separately, or deionized distilled water alone (controls) or were left untreated (base line control). Mineral profiles of Ca, P, Sr and F within 100 microm of the material surface were assessed following 8, 16 and 24 days of treatment (test); 4, 8 or 12 days (controls) or for baseline control samples, using electron probe microanalysis (EPMA). There were significant changes in mineral profile in the test specimens in terms of Sr and Ca concentrations. A molecule for molecule exchange of these elements resulted between GIC and eluant solutions. Fluoride loss from the GIC occurredto the level comparable with uptake levels recorded in eluant solutions from previous studies. The ionic exchanges appeared to be the result of dissolution followed by an equilibrium-driven diffusion. These exchanges were superficial though substantial. Simulated exposure of Fuji IX to the oral environment resulted in an exchange of Ca from the bathing solutions into Fuji IX to replace any Sr which was lost to the GIC. Fluorine loss from the GIC followed previously described patterns. The possible clinical significance of this exchange was discussed.

Mixing of asthenospheric and lithospheric mantle-derived basalt magmas as shown by along-arc variation in Sr and Nd isotopic compositions of Early Miocene basalts from back-arc margin of the NE Japan arc

We report trace element and Sr–Nd isotopic compositions of Early Miocene (22–18 Ma) basaltic rocks distributed along the back-arc margin of the NE Japan arc over 500 km. These rocks are divided into higher TiO 2 (> 1.5 wt.%; referred to as HT) and lower TiO 2 (< 1.5 wt.%; LT) basalts. HT basalt has higher Na 2O + K 2O, HFSE and LREE, Zr/Y, and La/Yb compared to LT basalt. Both suite rocks show a wide range in Sr and Nd isotopic compositions (initial 87Sr/ 86Sr (SrI) = 0.70389 to 0.70631, initial 143Nd/ 144Nd(NdI) = 0.51248 to 0.51285). There is no any systematic variation amongst the studied Early Miocene basaltic rocks in terms of Sr–Nd isotope or Na 2O + K 2O and K 2O abundances, across three volcanic zones from the eastern through transitional to western volcanic zone, but we can identify gradual increases in SrI and decreases in NdI from north to south along the back-arc margin of the NE Japan arc. Based on high field strength element, REE, and Sr–Nd isotope data, Early Miocene basaltic rocks of the NE Japan back-arc margin represent mixing of the asthenospheric mantle-derived basalt magma with two types of basaltic magmas, HT and LT basaltic magmas, derived by different degrees of partial melting of the subcontinental lithospheric mantle composed of garnet-absent lherzolite, with a gradual decrease in the proportion of asthenospheric mantle-derived magma from north to south. These mantle events might have occurred in association with rifting of the Eurasian continental arc during the pre-opening stage of the Japan Sea.

Influence of pulse duration and pulse number in selective RPE laser treatment.

The therapeutic effect of laser treatment for macular diseases is related to the damage to the retinal pigment epithelium (RPE) and the subsequent restoration of the defect due to RPE proliferation. In contrast to conventional laser treatment, it is possible to damage the RPE selectively and to spare the photoreceptors by using repetitive microsecond laser pulses. It was the aim of the study to investigate the influence of pulse duration and number of pulses on angiographically and ophthalmoscopically visible retinal damage thresholds in order to optimize treatment modalities. In total, 625 laser lesions with various parameters were applied to the retina in 11 eyes of 6 Chinchilla breed rabbits using an experimental laser system (Nd:YLF at 527 nm). Pulse duration (1.7 microseconds and 200 nanoseconds) and number of pulses (100, 10, and 1 pulses) were varied at a constant repetition rate of 100 Hz. Damage thresholds were determined in terms of ophthalmoscopic and fluorescein angiographic visibility, and the therapeutic window (TW; angiographic ED(50) vs. ophthalmoscopic ED(50)) as well as the safety range (SR; angiographic ED(84) vs. ophthalmoscopic ED(16)) between both thresholds were calculated. Selected laser lesions were evaluated by histology. Generally, the ED(50) radiant exposure for angiographic visibility decreases for shorter laser pulses and with an increase in the number of pulses. The TW for both pulse durations (1.7 microseconds and 200 nanoseconds) was wider with 100 pulses than with single pulses. The widest TW was found for 100 pulses at 200 nanoseconds pulse duration (5.9-fold above the angiographic threshold), and the smallest TW with a factor of 1.6 was found for 1.7 microseconds single pulses. In terms of SR, only irradiation with 100 pulses at 200 nanoseconds pulse duration was associated with a ratio >2. Independently of pulse duration, histological examination of laser sites 1 hour after irradiation revealed widely intact photoreceptors, while the underlying RPE was damaged. Pulse duration and number of pulses have a significant influence on RPE damage thresholds and consecutively on TW and SR. Because fundus pigmentation in humans may vary intra- and interindividually by a factor of 2, a large TW and ideally also a large SR should be ensured in a clinical treatment context. In rabbits, the safety range with 200 nanoseconds pulses is higher than with the pulse duration of 1.7 microseconds currently in clinical use. These findings suggest the need for clinical pilot studies to prove whether these results can be transposed to the situation in humans.

THE HYPABYSSAL 5034 KIMBERLITE OF THE GAHCHO KUE CLUSTER, SOUTHEASTERN SLAVE CRATON, NORTHWEST TERRITORIES, CANADA: A GRANITE-CONTAMINATED GROUP-I KIMBERLITE

We present petrographic, mineralogical, geochemical and isotopic data on the 5034 kimberlite of the Cambrian Gahcho Kue kimberlite cluster (Slave craton, northern Canada). This Group-IA kimberlite is a multiphase intrusion composed of the diatreme-facies magmatic and hypabyssal kimberlite, which intruded in at least four magmatic phases. The dominant hypabyssal phase is composed of macrocrystal monticellite – phlogopite – serpentine kimberlite. Occasional samples with diopside ± melilite may reflect local heterogeneities in the bulk composition or separate intrusive phases. Aphanitic monticellite – serpentine kimberlite forms as early and contemporaneous small-volume magmas and is present in autoliths and in cross-cutting dykes. The subsequent explosive magmatic phase formed tuffisitic kimberlite breccia, which in turn is cut by macrocrystal phlogopite – serpentine kimberlite. The phlogopite in all recognized hypabyssal rock-types has distinct compositional trends, but within a given rock-type, it also varies significantly in response to local chemical heterogeneities and to the composition of minerals adjacent to it. The large variability in phlogopite compositions is due to very local diffusion-controlled crystallization, and not to changes in bulk composition of the magma. All varieties of the 5034 kimberlite show strong evidence of contamination by host granitic rocks. Pectolite, diopside, melilite and phlogopite have replaced and crystallized around partly assimilated granitic xenoliths from a hybrid melt enriched in Si and Na. A high activity of Si may be the major factor controlling the presence of melilite in kimberlites. The mineralogical character of the 5034 kimberlite, which is intermediate between Group-I and Group-II kimberlites, can be explained by its strong contamination by granites. The composition of the kimberlite in terms of Sr and Nd isotopes suggests an asthenospheric origin of the melt and allows for incorporation of no more than 8–12% granitic material into the parental magma.

Geochemistry of mafic and ultramafic xenoliths from Fidra (Southern Uplands, Scotland): implications for lithospheric processes in Permo-Carboniferous times

Several types of xenoliths occur in a Permian basanite sill in Fidra, eastern central Scotland. One group consists of spinel lherzolites, which have geochemical and isotopic characteristics similar to those of lithospheric upper mantle from elsewhere in western Europe, with both LREE-depleted and LREE-enriched compositions. A separate group comprises pyroxenites and wehrlites, some of which contain plagioclase; these have compositions and textures that indicate that they are cumulates from mafic magmas. In terms of Sr and Nd isotope compositions, the pyroxenites closely resemble the host basanite and most likely formed by high-pressure fractionation of Permo-Carboniferous alkaline magmas at lower crustal depths. They also have mantle-like δ 18O values. A third group is composed of granulite xenoliths that vary between plagioclase-rich and clinopyroxene-rich compositions, some of which probably form a continuum with the pyroxenites and wehrlites. They are all LREE-enriched and most have positive Eu anomalies; thus, they are also mostly cumulates from mafic magmas. Many of the granulites also have Sr and Nd radiogenic isotope ratios similar to those of the host basanite, indicating that they have formed from a similar magma. However, several of the granulites show more enriched isotopic compositions, including higher δ 18O values, trending towards an older crustal component. Thus, the pyroxenites and granulites are largely cogenetic and are mainly the product of a mafic underplating event that occurred during the widespread magmatism in central Scotland during Permo-Carboniferous times.

Nd and Sr isotopic compositions of igneous rocks from the Lower Yangtze region in eastern China: constraints on sources

Nd and Sr isotopic data are compiled from literatures for Mesozoic igneous rocks in the Lower Yangtze region, eastern China. These Mesozoic igneous rocks have been classified into three associations: Na-enriched (alkaline mafic) association, K-enriched association which includes shoshonitic series and ultrapotassic rocks, and high potassium calc-alkaline (HKCA) association. The HKCA association has been further divided into three geographical sub-groups: the rocks north to, along and south to the Yangtze River.The Na-enriched mafic rocks show εNd(T) of 1.4 to −9.9 and 87Sr/86Sr(T) of 0.7047 to 0.7077. The K-enriched rock association shows εNd(T) of −1.8 to −9.3 and 87Sr/87Sr(T) of 0.7053 to 0.7092. Low SiO2 in the rocks suggests that they are mantle-derived. These Nd-Sr isotopic variations may represent isotopic feature in the mantle source of these rocks. The Mesozoic mantle of this region is thus enriched to slightly depleted and highly heterogeneous in terms of Sr and Nd isotopic characteristics. The isotopic characters of the Mesozoic mantle of the region can be modeled by mixing between DMM component representing asthenospheric mantle and EM II representing lithospheric mantle. These characters closely resemble those of mafic and ultramafic rocks in the North Dabie terrane north to the region studied. This suggests that processes operating during continental collision and deep subduction in the Dabie orogenic belt might also operate in petrogenesis of mantle-derived rocks of the Lower Yangtze region. However, since the range of initial Sr and Nd isotopic ratios for the mantle-derived rocks in the Lower Yangtze region overlaps that of Mesozoic basalts from the eastern coast of China, it is yet not known if this is a prevalent phenomenon in the Mesozoic basalts from eastern China.The intermediate and acid rocks of the HKCA association were most likely derived from mixing between the mantle-derived mafic magma and different crustal sources. The HKCA rocks occurring in the area north to the Yangtze River have εNd(T) of −13.5 to −15.5 and 87Sr/86Sr(T) of 0.7058 to 0.7067. The low εNd(T) and 87Sr/86Sr(T) suggest that a crustal source of old and depleted in Rb, such as the source of the Mesozoic granites from the Dabie terrain, was involved in the formation of this sub-group of rocks. The HKCA rocks along the Yangtze River show εNd(T) of −7.0 to −16.5 and 87Sr/86Sr(T) of 0.7061 to 0.7101. Old crustal source, such as Archaean Kongling group and Paleoproterozoic Dongling group rocks, was involved in the formation of these rocks. The granitic rocks of the HKCA association in the area south to the Yangtze River show relatively constant εNd(T) of −4.9 to −6.8 but variable 87Sr/86Sr(T) of 0.7081 to 0.7104. The εNd(T) values of this sub-group rocks are very similar to those of the Neoproterozoic Shangxi group of low-grade metamorphic rocks and volcanic rocks in the region, suggesting that such a component is dominant in the source of this sub-group rocks. These data further suggest that the basement rocks possessing different Sr, Nd isotopic ratios and Nd model ages existed in different locations of the region. The basement similar to that of the Dabie terrain underlays in the depth of the area north to the Yangtze River. Existence of the old basement similar to the Kongling and Dongling groups in the depth of the area along the Yangtze River is very likely although only a few outcrops of the old metamorphic rocks were found in the area. However, the basement like the Neoproterozoic Shangxi group is dominant in the depth of the area south to the Yangtze River.

Crustal contaminants in the Permian Oslo Rift, South Norway: constraints from Precambrian geochemistry

During the late Paleozoic Oslo rifting event, the SW part of the Baltic Shield was penetrated by mantle-derived magmas from a depleted lithospheric or sublithospheric source. Along the way to their final emplacement, these magmas may have interacted with a heterogeneous continental crust, consisting of a mosaic of continental terranes, each with its unique composition and internal crustal history. Information on radiogenic isotope ratios and trace element distributions in the Precambrian terranes surrounding the rift can be used to define characteristic crustal components. These components may be used as endmembers in petrogenetic modelling of the Oslo Rift magmatic system. Based on available data, six endmember components can be identified, and (semi) quantitatively characterized in terms of Sr, Nd and Pb isotopes and selected trace elements. Data on the distribution of rock-types along the rift flanks allow estimates to be made of the relative importance of the components in different parts of the rift. Combining these data with petrological information may allow a realistic understanding of crust–magma interaction in the Oslo Rift magmatic system.

Chronology and petrology of the Daikonjima basalt, Nakaumi Lagoon, eastern Shimane Prefecture, Japan.

Basaltic rocks from Daikonjima, a young shield volcano in Nakaumi Lagoon (eastern Shimane Prefecture), have been dated and analysed for a range of whole-rock major, trace element, and isotope data. K/Ar age data indicate a Quaternary eruption age of circa 200 000 years. Chemical data for a range of stratigraphically controlled samples show that they are all fractionated relative to basaltic primary liquids (100 Mg/(Mg+Fe)∼56, Ni 101-160 ppm, Cr 110-226 ppm). In terms of Sr and Nd isotopes, they represent a homogenous reservoir close to bulk earth values. The earliest magma results from a lower degree of partial melting than later magma batches, and variations in chemistry between younger lava flows can probably be attributed to small differences in modal mineralogy, although the possibility of limited crustal contamination cannot be excluded.

Elemental and isotopic (Sr, Nd, and Pb) characteristics of Madeira Island basalts: evidence for a composite HIMU - EM I plume fertilizing lithosphere

The within-plate volcanic island of Madeira is considered a hot-spot originating from a mantle plume. Lavas range from basanites to mugearites. The majority of primitive lavas are nepheline normative and characterized by strongly fractionated rare-earth elements, where (La/Yb)n = 12-25, and by pronounced normalized negative K but positive Nb-Ta anomalies, similar to high 238U/204Pb (HIMU) type basalts. Madeira basalts are highly depleted in terms of Sr- and Nd-isotope ratios, which are negatively correlated and define a trend steeper than the mantle array. Pb-isotope ratios are moderately high (206Pb/204Pb up to 19.582), with almost all samples plotting close to the Northern Hemisphere Reference Line. Radiogenic isotope systematics demonstrate that the mantle source of Madeira basalts is the result of a multicomponent mixture where HIMU and enriched mantle I (EM I) plume components are diluted by a depleted component (DMM) which represents more than 85% of the source volume. The presence of DMM is considered to result from entrainment of asthenospheric depleted material by the plume. There is trace-element evidence for liquids having equilibrated with garnet and amphibole, the presence of the latter mineral reflecting lithospheric involvement in the genesis of the magmas. Such was done via assimilation, by plume (plus entrained asthenosphere) magmas, of melts generated from oceanic lithosphere and leaving amphibole as residue.

Oxygen isotope constraints on the sources of Hawaiian volcanism

We have measured oxygen isotope ratios in 99 separates of olivine and 14 separates of plagioclase or glass from Hawaiian lavas. These data confirm that the source(s) of some Hawaiian basalts are lower in δ18O than peridotite xenoliths and the source region for mid-ocean ridge basalts (MORB). Our data document correlations between oxygen and radiogenic isotope ratios and consistent differences in δ18O between volcanoes. Low values of δ18O are associated with a ‘depleted’ component that is relatively high in 206Pb/204Pb, low in 3He/4He, and anomalously low in 207Pb/204Pb relative to 206Pb/204Pb. This component is preferentially sampled in lavas from the so-called Kea trend volcanoes (Kilauea, Mauna Kea, Kohala and Haleakala).Low δ18O values in the ‘Kea’ component suggest that it is hydrothermally altered oceanic crust. The similarity of the Kea end member to Pacific MORB in terms of Sr, Nd, and Pb isotope ratios further suggests that this component is assimilated from the local Pacific plate in subcrustal magma chambers. Anomalous 206Pb/204Pb-207Pb/204Pb relationships indicate recent enrichment in U/Pb in this component and further support the hypothesis that this component is young ( < 108 yr) Pacific crust. The isotopic distinctions between Loa and Kea trend volcanoes implies a systematic difference in the magma supply and plumbing systems of volcanoes on these two trends.Samples from Lanai and Koolau have ‘enriched’ radiogenic isotope compositions (radiogenic Sr and non-radiogenic Nd and Pb) and higher δ18O than typical upper mantle values, suggesting the incorporation of recycled sediment and/or oceanic crust in their sources. Other isotopic end members to Hawaiian lavas (e.g., high 3He/4He and post-erosional lavas) have δ18O values within the range typical of the upper mantle.

Distribution and origin of diamonds in Brazil: An overview

Brazil was the first western country to produce diamonds from the washing of alluvial deposits found in central Minas Gerais in the early 1700s. For a century the country remained the world's greatest producer, losing its position only after the discovery of the Kimberley field in South Africa. Currently there are placer deposits (garimpos) scattered throughout the majority of the states with official production averaging 1,000,000 ct/y. Mechanized exploitation using modern dredges has succeeded in only two distinct localities: along the Jequitinhonha River (Diamantina) and at the Fazenda Camargo (Mato Grosso). Large diamonds of several hundred carats have been found periodically in the area of the municipalities of Abaeté and Coromandel in western Minas Gerais State. Carbonado, a polycrystalline variety of diamond, was intensively mined in several localities of the Chapada Diamantina in central Bahia State, mainly in the second half of the last century. Kimberlite-type rocks, on the other hand, were discovered only in the late 1960s, first in the Coromandel area in Minas Gerais and later in Goiás, Mato Grosso, Rondônia and Piauí States. Little is yet known about these intrusions, mainly because the discoveries have been made by foreign companies operating in the country. Detailed studies reported during the Kimberlite Conference of Araxá in 1991 revealed that some intrusions of the Coromandel area have mineralogical and petrographical characteristics, as well as major chemical element compositions, similar to worldwide kimberlites. However, their isotopic signatures in terms of Sr and Nd are intermediate between Groups I and II kimberlites of South Africa. As to mineral inclusions, Brazilian diamonds contain the common phases of olivine, garnets, pyroxenes, sulphides and oxides as observed in diamonds elsewhere. Furthermore, diamonds from the São Luis River in northern Mato Grosso contain, in addition to garnet and pyroxene, periclase, ferripericlase, wüstite, nickel, iron-nickel alloy and moissanite. This high-pressure assemblage resembles the mineralogy predicted for depths of ~650 km, thus suggesting an asthenospheric origin for the São Luis diamonds. This paper presents a review of general aspects of the most representative deposits of diamonds in Brazil. Field relationships point to the existence of at least three distinct ages for the secondary source rocks as illustrated by the Upper Proterozoic metaconglomerates of Diamantina, the Permo-Carboniferous diamictites of Tibagi and the Upper Cretaceous conglomerates of the Romaria Mine. The primary sources remain unknown in all localities. Additional comments are provided on the findings of great diamonds, diamond inclusions and on the study of kimberlite-type rocks carried out in the country in the past two decades.