U-Pb isotopic characteristics of lunar meteorites Yamato-793274 and Yamato-86032

U-Pb data from lunar meteorites Yamato (Y)-86032 and Y-793274 confirm that they are of lunar origin, but also indicate that they are not from the same source region on the Moon and experienced different events while residing as lunar regolith. The Pb of both clast and matrix from Y-86032 is the least radiogenic among lunar meteorites thus far analyzed, similar to that of lunar anorthosite 60025,and indicates derivation from a low-^U/^Pb (μ) source, assuming initial lunar Pb compositions were essentially primitive in nature. Whereas the data from Y-86032 plot slightly above the geochron on a ^Pb/^Pb vs. ^Pb/^Pb diagram, data from 60025 and Y-82192 (considered a pare of Y-86032) plot precisely on the geochron. Very small amounts of U, Th, and Pb were leached from Y-86032 using 0.1N HBr; the Pb isotopic compositions of the leaches are essentially modern terrestrial values, indicating that this rock probably did not reside long at the lunar surface and was not exposed to volatile-rich gases expelled during impact event (s). In contrast, large amounts of the three elements (up to five times those of Y-86032) were removed from Y-793274 during leaching, and the Pb isotopic compositions of these leaches are very radiogenic and similar to those of mare basalt and some lunar soils, indicating that this rock was subjected to lunar impactrelated, volatile-rich gases containing radiogenic ^Pb-rich Pb, very similar to typical lunar soils and some breccias containing significant amounts of marederived material. This is the first occurrence of leaches that are more ^Pb-rich than their corresponding residues and indicate that the meteorite may have originated from near a mare region. To compare, the Pb from leaches of Y-791197 clasts (N. NAKAMURA et al.; Mem. Natl Inst. Polar Res., Spec. Issue, 41,106,1986a) was ^Pb-poor, indicating the meteorite may have originated from the lunar highlands. The Pb in residues of Y-793274 is more radiogenic than that of Y-86032 and Y-82192,similar to that in ALHA81005 and lunar anorthositic gabbros 78155 and 15418,and indicate a lunar source region with high-μ (>100 and possibly as high as 300). Corrected U-Pb data indicate a formation age of ∿ 4.4 Ga and a disturbance to the system at ∿ 4.0 Ga

U-Th-Pb isotopic systematics of lherzolitic shergottite Yamato-793605

We have undertaken U-Th-Pb isotopic studies on lherzolitic shergottite, Yamato-793605. Four mineral separates (olivine, plagioclase, and two phases of pyroxene) and a whole-rock sample were leached with dilute acid in order to remove secondary Pb contamination. However, preferential leaching of U and Th over Pb occurred. The Pb isotopic data points of five residue fractions scattered, and a calculated Pb-Pb age does not clearly indicate either crystallization from a melt or a later disturbance to the U-Pb system, in contrast with other shergottites. The chord through U-Pb data points for pyroxene (PXl) leaches and residue intersects concordia at 4439±9 Ma and 212±62 Ma, suggesting a young disturbance event resulting in Pb loss. The later disturbance event partially reset the U-Pb system. The estimated ^U/^Pb (≡μ) value from the whole-rock residue for the source of Y-793605 is about 5,suggesting that Y-793605 was derived from a volatile-rich source environment and confirms a low-μ source for shergottites compared to volcanic rocks of the Earth

Rb-Sr isotopic systematics of lherzolitic shergottite Yamato-793605

We have undertaken a Rb-Sr isotopic study of the lherzolitic shergottite, Yamato (Y)-793605. The acid-leaching experiment designed to remove secondary Pb contamination during previous work with U-Th-Pb systematics did not significantly affect the Rb-Sr systematics. A Rb-Sr internal isochron obtained for combined data of leachates and residues yielded an age of 173±14Ma with an initial ^Sr/^Sr ratio of 0.71042±0.00007,using λ (^Rb)=1.402×10^y^. The Rb-Sr age, initial ^Sr/^Sr ratio and trace element abundance pattern of Y-793605 are all similar to those of lherzolitic shergottites, ALH 77005 and LEW 88516. We favor the 173Ma age for the time of igneous crystallization, because this interpretation is more consistent with characteristics of both the isotopic systematics and mineral chemistry. A minor disturbance of U-Pb systems observed in residue fractions indicate that shock event(s) occurred more recently, without affecting Rb-Sr system

Sm-Nd isotopic systematics of lherzolitic shergottite Yamato-793605

We have undertaken Sm-Nd isotopic studies on Yamato-793605 lherzolitic shergottite. The Sm-Nd internal isochron obtained for acid leachates and residues of whole-rock and separated mineral fractions yields an age of 185±16Ma with an initial εNd value of +9.7±0.2. The obtained Sm-Nd age is, within analytical errors, identical to the Rb-Sr age of this meteorite as well as to the previous Rb-Sr and Sm-Nd ages of Allan Hills-77005 and Lewis Cliff 88516, although the ε_(Nd) values are not identical to each other. Elemental abundances of lithophile trace elements remain nearly unaffected by aqueous alteration on the Martian surface. The isotopic systems of lherzolitic shergottites, thus, are considered to be indigenous, although disturbances by shock metamorphism are clearly observed. "Young ages of ～180Ma" have been consistently obtained from this and previous Rb-Sr, Sm-Nd and U-Pb isotopic studies and appear to represent crystallization events

MPI-Ding reference glasses for in situ microanalysis: New reference values for element concentrations and isotope ratios

We present new analytical data of major and trace elements for the geological MPI-DING glasses KL2-G, ML3B-G, StHs6/80-G, GOR128-G, GOR132-G, BM90/21-G, T1-G, and ATHO-G. Different analytical methods were used to obtain a large spectrum of major and trace element data, in particular, EPMA, SIMS, LA-ICPMS, and isotope dilution by TIMS and ICPMS. Altogether, more than 60 qualified geochemical laboratories worldwide contributed to the analyses, allowing us to present new reference and information values and their uncertainties (at 95% confidence level) for up to 74 elements. We complied with the recommendations for the certification of geological reference materials by the International Association of Geoanalysts (IAG). The reference values were derived from the results of 16 independent techniques, including definitive (isotope dilution) and comparative bulk (e.g., INAA, ICPMS, SSMS) and microanalytical (e.g., LA-ICPMS, SIMS, EPMA) methods. Agreement between two or more independent methods and the use of definitive methods provided traceability to the fullest extent possible. We also present new and recently published data for the isotopic compositions of H, B, Li, O, Ca, Sr, Nd, Hf, and Pb. The results were mainly obtained by high-precision bulk techniques, such as TIMS and MC-ICPMS. In addition, LA-ICPMS and SIMS isotope data of B, Li, and Pb are presented

40Ar/39Ar Geochronology of Magmatic-Steam Alunite from Alunite Ridge and Deer Trail Mountain, Marysvale Volcanic Field, Utah: Timing and Duration of Miocene Hydrothermal Activity Associated with Concealed Intrusions

Porphyry and epithermal deposits are important sources of base and precious metals. Most actively mined deposits have been exhumed such that ore bodies are relatively close to the surface and are therefore locatable and economic to extract. Identifying and characterizing concealed deposits, particularly more deeply buried porphyry deposits, represents a far greater challenge for mineral exploration, and will become progressively more important as near-surface resources are gradually exhausted over time. We report high-precision 40Ar/39Ar dates for coarsely crystalline alunite that precipitated from magmatic steam in open fractures in Oligocene dacitic volcanic rocks, and a SHRIMP 206Pb/238U zircon date for one of several rhyolite dikes present at Alunite Ridge and Deer Trail Mountain, Utah. Both the magmatic-steam alunite and rhyolite dikes are related to concealed intrusions. The rhyolite dike yielded an age of 30.72 ± 0.36 Ma, which is older than a commonly cited 27.1 Ma age estimate for the Three Creeks Tuff Member of the Bullion Canyon Volcanics that is cut by the dike. 40Ar/39Ar data for samples of magmatic-steam alunite and sericite from six mines and prospects provide evidence for at least two periods of episodic hydrothermal activity at ca. 15.7–15.1 Ma and ca. 14.7–13.8 Ma, with the older and younger pulses of activity recorded at the more eastern and western sites, respectively. These two periods of hydrothermal activity are consistent with previous interpretations that Alunite Ridge and Deer Trail Mountain are underlain by two concealed porphyry stocks. 40Ar/39Ar analyses of individual bands in a sample of massive, centimeter-scale banded vein alunite yield indistinguishable ages with a weighted mean of 13.98 ± 0.12 Ma, consistent with a short-lived (≲250 ka) magmatic event with episodic vapor discharge recurring on short timescales (≲36 ka). 40Ar/39Ar geochronology of magmatic-steam alunite is a valuable tool to constrain the timing and duration of magmatic hydrothermal activity associated with unexposed intrusions and potentially porphyry deposits, and therefore may be useful in exploration