Lead isotopes and age of Hawaiian lherzolite nodules

The reaction between enstatite (En_95.3Fs_4.7) and CaCO₃ has been studied at pressures between 23 and 77 kbars and at temperatures between 800° and 1400°C. At 1000°C enstatite and CaCO₃ react to form dolomite and diopside solid solutions at pressures below approximately 45 kbars and magnesite and diopside solid solutions at higher pressures. The curve for the reaction dolomite_ss + enstatite_ss ? magnesite_ss + diopside_ss lies between 40 to 45 kbars at 1000°C and between 45 and 50 kbars at 1200°C. It is very close to the graphite-diamond transition curve. These experimental results indicate that calcite (or aragonite) is unstable in the presence of enstatite, and that dolomite and magnesite are the stable carbonates at high pressures. The forsterite + aragonite assemblage is, however, stable to at least 80 kbars at 800°C. It is suggested that in the upper mantle where enstatite is present, dolomite is stable to depths of about 150 km and magnesite is stable at greater depths in the continental regions, assuming that the partial pressure of CO₂ is equal or close to the total pressure. It is also suggested that carbonate inclusions in pyroxene can be used as an indicator of the depth of their equilibration; dolomite inclusions in enstatite would be formed at depths shallower than 150 km and magnesite inclusions in diopside at greater depths. Eclogite and peridotite inclusions in kimberlite may be classified on this basis.     

Radiocarbon dates of elevated shorelines,Indonesia and Malaysia. Part 1

Four new radiocarbon dates of elevated strandlines in tectonically active areas of eastern Indonesia and East Malaysia indicate average rates of uplift that range between 4.5 and 9 mm annually during the past 24,000 yr. These values are at least three times higher than former estimates from eastern Indonesia. Another radiocarbon date from the south arm of Sulawesi—also tectonically mobile—indicates a rate of uplift of 1.4–2.5 mm per year which corresponds with earlier determinations. This particular case, however, suggests that the sample was probably located close to a north-south axis about which southern Sulawesi was tilted during the Quaternary.     

Composition of the first bulk melt sample from a volcanic region of Mars: Queen Alexandra Range 94201

Abstract— Antarctic meteorite Queen Alexandra Range (QUE) 94201 is a 12 g basaltic achondrite dominated by plagioclase (now maskelynite) and zoned low‐ and high‐Ca pyroxene. Petrologic, geochemical, and isotopic analyses indicate that it is related to previously described basaltic and Iherzolitic shergottites, which are a group of igneous meteorites that are believed to be from Mars. Unlike previous shergottites, however, QUE 94201 represents a bulk melt rather than a cumulate fraction, meaning it can be used to infer magmatic source regions and the compositions of other melts on Mars. This melt has much more Fe and P than basaltic melts produced on Earth and formed at a much lower oxygen fugacity. This has altered the crystallization sequence of the melt, removing olivine from the liquidus to produce a plagioclase and 2‐pyroxene assemblage. If the high‐phosphorus and low‐oxygen fugacity conditions represented by QUE 94201 are common in magmatic regions of Mars, then olivine may be rare in marrian basalts. No solar cosmic ray effects were seen in the concentrations of ¹⁰Be, ²⁶A1, and ³⁶C1 with depth in the meteorite, implying at least 3 cm of ablation during entry to Earth. Significant excesses of neutron capture noble gas isotopes (^80,82Kr and ^128,131Xe) suggest that the QUE 94201 sample came from a depth >22 cm in a meteoroid of at least that radius. The meteorite also has very low ²¹Ne/²²Ne, which would often be interpreted to mean little ablation (contradicting above evidence) but, in this case, appears to reflect a very low abundance of Mg (the principal target element for Ne) in the meteorite, consistent with our bulk chemical analyses. The meteorite has a terrestrial ³⁶C1 age of 0.29 ± 0.05 Myr and a ¹⁰Be exposure age of 2.6 ± 0.5 Myr in a 47π geometry, implying an ejection age of 2.9 ± 0.5 Myr.     

Noble gases and cosmogenic radionuclides in the Gold Basin L4 chondrite shower: Thermal history,exposure history,and pre‐atmospheric size

Abstract— We measured the concentrations of the cosmogenic radionuclides ¹⁰Be, ²⁶Al, ³⁶Cl, and ⁴¹Ca in the stone and metal fractions of 15 fragments of the Gold Basin L4 chondrite shower, as well as noble gases in 18 Gold Basin fragments. A comparison of ¹⁰Be, ²⁶Al, and ⁴¹Ca concentrations with calculated production rates from two different models indicates that the Gold Basin samples came from depths of about 10 cm to more than 150 cm in an object with a radius of 3–5 m. As was predicted by recent model calculations, the noble gases show a reversal of the ²²Ne/²¹Ne ratio at very high shielding. The ²¹Ne/¹⁰Be and ²¹Ne/²⁶Al ratios in most samples are constant and correspond to a 4π exposure age of 18 ± 2 Myr. However, three Gold Basin samples show a 30–120% excess of ²¹Ne implying that they were previously exposed close to the surface of the parent body, whereas the other samples were buried several meters deeper. Concentrations of neutron‐capture ³⁶Ar in most samples are consistent with measured concentrations of neutron‐capture ³⁶Cl and an exposure age of 18 Myr. Large excesses of neutron‐capture ³⁶Ar were found in those samples with an excess of ²¹Ne, providing additional evidence of a first‐stage exposure on the parent body. The excess of spallation‐produced ²¹Ne and neutron‐capture‐produced ³⁶Ar in these samples indicate a first‐stage exposure of 35–150 Myr on the parent body. The radiogenic ⁴He and ⁴⁰Ar concentrations indicate a major impact on the parent body between 300 and 400 Myr ago, which must have preceded the impacts that brought the Gold Basin meteoroid to the surface of the parent body and then expelled it from the parent body 18 Myr ago.     

Cosmic‐ray exposure age and preatmospheric size of the Bunburra Rockhole achondrite

Abstract– Bunburra Rockhole is the first meteorite fall photographed and recovered by the Desert Fireball Network in Australia. It is classified as an ungrouped achondrite similar in mineralogical and chemical composition to eucrites, but it has a distinct oxygen isotope composition. The question is if achondrites like Bunburra Rockhole originate from the same parent body as the howardite‐eucrite‐diogenite (HED) meteorites or from several separate, differentiated parent bodies. To address this question, we measured cosmogenic radionuclides and noble gases in the Bunburra Rockhole achondrite. The short‐lived radionuclides ²²Na and ⁵⁴Mn confirm that Bunburra Rockhole is a recent fall. The concentrations of ¹⁰Be, ²⁶Al and ³⁶Cl as well as the ²²Ne/²¹Ne ratio indicate that Bunburra Rockhole was a relatively small object (R approximately 15 cm) in space, consistent with the photographic fireball observations. The cosmogenic ³⁸Ar concentration yields a cosmic‐ray exposure (CRE) age of 22 ± 3 Myr, whereas ²¹Ne and ³He yield approximately 30% and approximately 60% lower ages, respectively, due to loss of cosmogenic He and Ne, mainly from plagioclase. With a CRE age of 22 Myr, Bunburra Rockhole is the first anomalous eucrite that overlaps with the main CRE peak of the HED meteorites. The radiogenic K‐Ar age of 4.1 Gyr is consistent with the U‐Pb age, while the young U,Th‐He age of approximately 1.4 Gyr indicates that Bunburra Rockhole lost radiogenic ⁴He more recently.     

Development of polygon shift method for generating 3D view map of buildings

The authors have developed a new method termed “Polygon Shift Method” that enables the generation of a 3D view map of a city with tall buildings with a simplified procedure to shift a polygon and check the overlap between the original and shifted polygon. Boolean operations are applied with a newly defined “Fore or Aft” side and a “Depth Distance” that functionally express the visibility criteria or hidden point processing in the 3D view. Since the polygon shift method can be operated with a raster-based structure, the computer processing for generation of a 3D view map of buildings with shadow is simple and efficient.     

Meteoritic and bedrock constraints on the glacial history of Frontier Mountain in northern Victoria Land, Antarctica

In 2001, a small H4 chondrite, Frontier Mountain (FRO) 01149, was found on a glacially eroded surface near the top of Frontier Mountain, Antarctica, about 600 m above the present ice level. The metal and sulphides are almost completely oxidized due to terrestrial weathering. We used a chemical leaching procedure to remove weathering products, which contained atmospheric ¹⁰Be and ³⁶Cl in a ratio similar to that found in Antarctic ice. The FRO 01149 meteorite has a terrestrial age of 3.0 ± 0.3 Myr based on the concentrations of the cosmogenic radionuclides ¹⁰Be, ²⁶Al and ³⁶Cl. This age implies that FRO 01149 is the oldest stony meteorite (fossil meteorites excluded) discovered on Earth. The noble gas cosmic ray exposure age of FRO 01149 is ~ 30 Myr. The meteorite thus belongs to the 33 Myr exposure age peak of H-chondrites.The bedrock surface on which FRO 01149 was found has wet-based glacial erosional features recording a former high-stand of the East Antarctic ice sheet. This ice sheet evidently overrode the highest peaks (> 2800 m a.s.l.) of the inland sector of the Transantarctic Mountains in northern Victoria Land. We argue that FRO 01149 was a local fall and that its survival on a glacially eroded bedrock surface constrains the age of the last overriding event to be older than ~ 3 Myr. The concentrations of in-situ produced cosmogenic ¹⁰Be, ²⁶Al and ²¹Ne in a glacially eroded bedrock sample taken from near the summit of Frontier Mountain yield a surface exposure age of 4.4 Myr and indicate that the bedrock was covered by several meters of snow. The exposure age is also consistent with bedrock exposure ages of other summit plateaus in northern Victoria Land.     

洪湖人类活动的沉积物记录

对洪湖150cm长的沉积物样芯进行了TOC、TN、TP、Ca、硫化物测试和AMS定年,在此基础上对洪湖地区人类活动的湖泊沉积响应进行了讨论.TOC和TN的含量呈现相似的变化规律,它们在样芯顶部和底部都出现显著峰值,而中部变化平坦,表示1500年来洪湖环境变演的三个显著不同的阶段;TP从过去到现在总体呈上升的趋势,但上升的幅度不大,这与磷在沉积物中复杂的循环机制有关;Ca的剖面变化显示为底部含量高上部低,其变化情况较复杂;硫化物在顶部15cm的含量比背景值略高,可能指示了上个世纪人类对铁矿和矿物燃料开采强度的增大.     

A neutron capture study of the Jilin chondrite

Abstract– The isotopic compositions of Sm and/or Gd of nine documented drill core samples of the Jilin H5 chondrite were determined to study the neutron capture records of individual meteorite samples. All the samples showed significant isotopic shifts of ¹⁵⁰Sm/¹⁴⁹Sm and/or ¹⁵⁸Gd/¹⁵⁷Gd corresponding to neutron fluences of (1.3–1.7) × 10¹⁵ n cm^?2. Considering the short 4π irradiation age of 0.32 Ma during the second stage, the 2π irradiation of 7 Ma during the first stage is the main influence on the Sm and Gd isotopic shifts of the Jilin chondrite. Although a depth dependence of the neutron capture effects was expected from the isotopic variations of ¹⁵⁰Sm/¹⁴⁹Sm and ¹⁵⁸Gd/¹⁵⁷Gd in the Jilin chondrite core samples that were possibly drilled perpendicular to the surface of the large object with a radius of >10 m in the 2π‐geometry, no clear evidence was observed in this study. The data from the combination of the isotopic shifts between Sm and Gd defined as ε_Sm/ε_Gd suggest that the neutrons produced in the 2π‐geometry of the Jilin chondrite follow the similar energy spectra as the neutrons in lunar samples, although the present analytical quality is not enough to discuss a critical discussion for the thermalization of the neutron energy levels.     

Exposure history of separated phases from the Kapoeta meteorite

Abstract— The cosmogenic radionuclides, ¹⁰Be, ²⁶Al, ³⁶Cl, and ⁵³Mn were measured in selected clasts and matrix samples from the howardite Kapoeta. Previous measurements of cosmogenic ²¹Ne indicate higher cosmic‐ray exposure ages for bulk samples than for some separated clasts or mineral separates. A possible interpretation for this difference in apparent exposure ages is a complex recent exposure history for Kapoeta. In this scenario some constituents are exposed to cosmic rays in a 2π geometry as part of a larger body immediately preceding its 4π exposure in a smaller body. To test this scenario we measured cosmogenic radionuclides in several clasts from Kapoeta. These measurements are consistent with a simple single‐stage 4π exposure history during which the entire inventory of cosmogenic radionuclides was produced. Taken together, these data are most consistent with a single‐stage 4π exposure lasting ～3 Ma. This scenario is nevertheless consistent with models in which the exposure of some constituents of Kapoeta to energetic particles occurred at an earlier time, as is indicated by ²¹Ne measurements. However, from our data we conclude that insubstantial quantities of cosmogenic radionuclides were inherited from this earlier irradiation; this earlier exposure to energetic particles must have predated the recent exposure by at least ～10 Ma to allow for the decay of the long half‐life cosmogenic radionuclides.