Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The lunar regolith breccia Dhofar 1769, which was found in 2012 as a single 125 g piece in the Zufar desert area of Oman, contains a relatively large, dark‐colored impact melt breccia embedded in a fine‐grained clastic matrix. The internal texture of the fragment indicates the repeated melt breccia formation on the lunar surface, their repeated brecciation, and mixing in second, third, and fourth generations of brecciated rock types. The chemical and mineralogical data reveal the incorporation of a feldspar‐rich subophitic crystalline melt within a feldspar‐rich microporphyritic crystalline melt breccia. This lithic paragenesis itself is embedded within a mafic, crystalline melt breccia. The entire breccia with the three different impact melts has been finally incorporated into the whole rock breccia. The three impact melts are mixtures of different source rocks and impact projectiles, based on the obtained minor and trace element compositions (in particular of Ni and the rare earth elements [REE]) of the impact melt lithologies. For all processes of impact melt formation, additional steps of their brecciation and re‐lithification require a minimum number of seven impact processes.〈/p〉

Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659

Description: This study presents culture experiments of the cold water species Neogloboquadrina pachyderma (sinistral) and provides new insights into the incorporation of elements in foraminiferal calcite of common and newly established proxies for paleoenvironmental applications (shell Mg/Ca, Sr/Ca and Na/Ca). Specimens were collected from sea ice during the austral winter in the Antarctic Weddell Sea and subsequently cultured at different salinities and a constant temperature. Incorporation of the fluorescent dye calcein showed new chamber formation in the culture at salinities of 30, 31, and 69. Cultured foraminifers at salinities of 46 to 83 only revealed chamber wall thickening, indicated by the fluorescence of the whole shell. Signs of reproduction and the associated gametogenic calcite were not observed in any of the culture experiments. Trace element analyses were performed using an electron microprobe, which revealed increased shell Mg/Ca, Sr/Ca, and Na/Ca values at higher salinities, with Mg/Ca showing the lowest sensitivity to salinity changes. This study enhances the knowledge about unusually high element concentrations in foraminifera shells from high latitudes. Neogloboquadrina pachyderma appears to be able to calcify in the Antarctic sea ice within brine channels, which have low temperatures and exceptionally high salinities due to ongoing sea ice formation.

Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659

Description: GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel http://dx.doi.org/10.13039/501100003153

Description: A large, igneous-textured, and 2 cm-sized spherical object from the L5/6 chondrite NWA 8192 was investigated for its chemical composition, petrography, O isotopic composition, and Hf-W chronology. The petrography and chemical data indicate that this object closely resembles commonly found chondrules in ordinary chondrites and is therefore classified as a “macrochondrule.* As a result of metal loss during its formation, the macrochondrule exhibits elevated Hf/W, which makes it possible to date this object using the short-lived 182Hf-182W system. The Hf-W data provide a two-stage model age for metal–silicate fractionation of 1.4 ± 0.6 Ma after Ca-Al-rich inclusion (CAI) formation, indicating that the macrochondrule formed coevally to normal-sized chondrules from ordinary chondrites. By contrast, Hf-W data for metal from the host chondrite yield a younger model age of ~11 Ma after CAIs. This younger age agrees with Hf-W ages of other type 5–6 ordinary chondrites, and corresponds to the time of cooling below the Hf-W closure temperature during thermal metamorphism on the parent body. The Hf-W model age difference between the macrochondrule and the host metal demonstrates that the Hf-W systematics of the bulk macrochondrule were not disturbed during thermal metamorphism, and therefore, that the formation age of such objects can still be determined even in strongly metamorphosed samples. Collectively, this study illustrates that chondrule formation was not limited to mm-size objects, implying that the rarity of macrochondrules reflects either that this process was very inefficient, that subsequent nebular size-sorting decimated large chondrules, or that large precursors were rare.

Description: This study presents culture experiments of the cold water species Neogloboquadrina pachyderma (sinistral) and provides new insights into the incorporation of elements in foraminiferal calcite of common and newly established proxies for paleoenvironmental applications (shell Mg/Ca, Sr/Ca and Na/Ca). Specimens were collected from sea ice during the austral winter in the Antarctic Weddell Sea and subsequently cultured at different salinities and a constant temperature. Incorporation of the fluorescent dye calcein showed new chamber formation in the culture at salinities of 30, 31, and 69. Cultured foraminifers at salinities of 46 to 83 only revealed chamber wall thickening, indicated by the fluorescence of the whole shell. Signs of reproduction and the associated gametogenic calcite were not observed in any of the culture experiments. Trace element analyses were performed using an electron microprobe, which revealed increased shell Mg/Ca, Sr/Ca, and Na/Ca values at higher salinities, with Mg/Ca showing the lowest sensitivity to salinity changes. This study enhances the knowledge about unusually high element concentrations in foraminifera shells from high latitudes. Neogloboquadrina pachyderma appears to be able to calcify in the Antarctic sea ice within brine channels, which have low temperatures and exceptionally high salinities due to ongoing sea ice formation.

Description: Fragments of five Cretaceous cm-size baddeleyite (ZrO2) and two zircon (ZrSiO4) crystals from the Mbuji-Mayi kimberlite (DR Congo) were measured for trace elements by the LA-ICP-MS technique. EPMA was applied adjacent to the laser spots to control Hf, used as internal standard for all LA-ICP-MS measurements. The 22 analyses confirm perfectly identical Hf concentration on the intra and inter-grain scale. Trace elements also yield surprisingly similar over-all patterns, although individual megacrysts have crystallized within magmas generated from differently depleted mantle domains ({varepsilon}Hfi + 5.1 to +10.2). Examined in detail, the trace elements show differences in concentrations being correlated either on the inter or intra-grain scale. The five baddeleyite megacrysts have high Th, U, Ta, and Nb reaching up to 5000 times chondrite concentrations. In intermediate to heavy REE they are by 30-120 times chondrite enriched but strongly depleted in the lightest REE, except Ce showing a positive anomaly (Ce4+ substitutes Zr4+). Corresponding (La/Yb)N range between 0.006 and 0.040. The two zircon megacrysts show trace element patterns similar to those of baddeleyite, also having high Th and U but low Ta and Nb. Intermediate to heavy REE are from 1 to 100 times chondrite enriched and they also show strong depletion in light REE yielding (La/Yb)N at 0.0001. Cerium is again an exception having about 20 times chondrite abundance. Highest trace element concentrations are correlated with the lowest {varepsilon}Hfi of +5.1, and lowest concentrations with the highest {varepsilon}Hfi of +10.2. This corroborates that not only {varepsilon}Hfi but also trace elements, in particular HFSE of the megacrysts reflect the level of trace elements available at the time of partial mantle melting and megacryst growth. Such growth has occurred in the deep mantle at temperatures exceeding 2000 {degrees}C, to explain structural data indicative for the original presence of cubic ZrO2. On their way to the surface cubic baddeleyites were successively transformed to tetragonal and then monoclinic symmetry. These transformations were not accompanied by measurable chemical changes. All megacrysts record (1) ancient time-integrated Lu/Hf-fractionation of their mantle sources, with the differences in {varepsilon}Hfi most likely reflecting the combined effect of different degrees of fractionation and differences in ages, and (2) the Cretaceous kimberlite event, during which the megacryst formed from highly trace element-HFSE enriched magmas. These highly enriched magmas were most likely produced by very small degrees of partial melting of the originally depleted mantle. The important correlation between {varepsilon}Hfi and trace-element abundance of the individual megacrysts rules out any significant earlier re-enrichment of the individual mantle domains, which would have erased this correlation.

Description: A robust method for U-Pb dating of zircon by laser ablation ICP-MS was established using a Thermo-Finnigan Element2 sector field ICP-MS coupled to a New Wave UP193HE ArF Excimer laser system. This included the construction of a low-volume sample cell and the establishment of a data reduction routine. A detailed systematic approach for determining optimal ablation settings and ICP-MS parameters is presented, which is also applicable to other instrument set-ups. Laser induced time-dependent elemental fractionation is corrected using the intercept method, whereas instrument drift, mass bias and elemental fractionation caused by ionisation differences are corrected by applying external standardisation using the matrix-matched reference zircon GJ-1. The isobaric interference of 204Hg on 204Pb is reduced by using a gold trap enabling the application of an accurate common Pb correction. Typical laser craters are 12, 25 or 35 µm in diameter and ca. 20 µm deep. A single analysis takes 65 s and the automated analysis of a measurement sequence ensures optimal efficiency.The performance of the established procedure was assessed by analysing zircon ranging in age from Mesoproterozoic to Miocene. Concordia ages obtained from multiple analyses on the various well-characterised zircons are all within uncertainty of the accepted values, demonstrating the high accuracy of the method. The uncertainty on the individual ages ranges from 1 to 4 % (2s), depending on the absolute age, Pb content and homogeneity of the analysed zircon. These results indicate that the precision and accuracy obtained using the technique presented in this study are similar to those of other LA-ICP-MS laboratories and SIMS analyses.

Description: Quartz, the most common mineral in most sandstones, rarely is used in provenance studies. This study demonstrates the provenance-discriminatory potential of combining cathodoluminescence (CL) color wavelength spectra of quartz with morphology and in situ U-Pb ages of zircon. The Cambrian Meson Group in northwestern Argentina is used for the test of this combined methodology, because it is composed of nonmetamorphosed sandstones with 〉 90% quartz and a dominance of zircon among the heavy minerals. Correlation of the results from the two methods is evident: (1) both CL spectra typical for bright-luminescent quartz (red to blue; 〉 90%) and oscillatory zircon growth zoning (80-90%) indicate a dominance of magmatic detritus. (2) Upsection, diminishing input from euhedral 510-600 Ma zircons (70% at the base) correlates with lower amounts of volcanic quartz (40% red and violet grains at the base). Instead, plutonic quartz and abraded zircons of 550-700 Ma age prevail. The data point to the occurrence of a (nearly) synsedimentary volcanic phase, which has not been known previously. Furthermore, initial short transportation paths from nearby magmatic bodies (100-200 km) can be assumed, because of the low degree of grain abrasion and an age correlation with magmatic bodies in the region, such as the Santa Rosa de Tastil batholith, here dated at 513 +4/-5 Ma. The proximity to the source area at an initial stage indicates first-cycle sand. The maturity was probably reached by intense chemical weathering. The upsection-diminishing young, volcanic input indicates erosion of the volcanic source within a time period of millions of years. At that stage, mainly up to 1000-km-long coast-parallel transport from the Sierras Pampeanas in the south fed the depositional basin. The change in--and expansion of--the main source areas record a change to production of multicycle sand. Hence, the maturity was partly caused by sedimentary recycling. More generally, the provenance-discriminative effect of the CL of quartz, which has been doubted by some researches, can be confirmed. Therefore, the results imply that both quartz and zircon should be taken into account in provenance studies of quartz arenites.

Description: We analyzed in situ the trace-element distributions in the pristine 2-cm-thick spherule-rich Cretaceous-Paleogene (K-Pg) event bed at Ocean Drilling Program (ODP) Leg 207 Site 1259C (Demerara Rise, western Atlantic) using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) with a spot diameter of 235 {micro}m, corresponding to a sample volume of [~]8.6 x 105 {micro}m3. Unparalleled so far, this high resolution pinpoints the fallout of the Chicxulub projectile to the uppermost 2 mm of the K-Pg bed. Most of the Ni is not of extraterrestrial origin, as indicated by low, typical upper-crustal Ni/Cr ratios. Very low Zr/Hf and Nb/Ta ratios are confined exclusively to the K-Pg bed, indicating that storms and flooding spilled highly fractionated supracrustal material off the Guiana craton to reach the seafloor contemporaneously with the now-altered glass spherules. Chicxulub ejecta volumetrically dominate the K-Pg bed but contributed only minimally to the trace-element budget, as indicated by the very low rare earth element concentrations. At the top of the ejecta layer, together with the fallout of Pt from the impactor ([~]0.1 ppm), a pronounced Pb enrichment (up to 1500 ppm) occurs, which is interpreted to derive from the Guiana craton. Both elements obviously were contained in submicrometer-size particles that could only reach the seafloor attached to larger particles, the sedimentation of which may have occurred up to a year after the Chicxulub impact event. Our high-resolution analysis of the K-Pg event bed allows us, for the first time, to differentiate among the contributing components in detail, as well as assess the settling time frame of this geologically important boundary deposit.