[1] Abyssal peridotites, the depleted solid residues of ocean ridge melting, are the most direct samples available to assess upper oceanic mantle composition. We present detailed isotope and trace element analyses of pyroxene mineral separates from Southwest Indian Ridge abyssal peridotites and pyroxenites in order to constrain the size and length scale of mantle heterogeneity. Our results demonstrate that the mantle can be highly heterogeneous to <1 km and even <0.1 m length scales. Examination of Nd isotopes in relation to modal, trace, and major element compositions indicate that the length scales and amplitudes of heterogeneities in abyssal peridotites reflect both ancient mantle heterogeneity and recent modification by melting, melt-rock reaction and melt crystallization. The isotopic and trace element compositions of pyroxenite veins in this study indicate that they are not direct remnants of recycled oceanic crust, but instead are formed by recent melt crystallization. Combined with existing data sets, the results show that the average global isotopic composition of peridotites is similar to that of mid-ocean ridge basalts, though peridotites extend to significantly more depleted 143 Nd/ 144 Nd and 87 Sr/ 86 Sr. Standard isotope evolution models of upper mantle composition do not predict the full isotopic range observed among abyssal peridotites, as they do not account adequately for the complexities of ancient and recent melting processes.

Presented here are the observations and interpretations from a comprehensive analysis of 16 representative particles returned from the C-type asteroid Ryugu by the Hayabusa2 mission. On average Ryugu particles consist of 50% phyllosilicate matrix, 41% porosity and 9% minor phases, including organic matter. The abundances of 70 elements from the particles are in close agreement with those of CI chondrites. Bulk Ryugu particles show higher ' 18 O, " 17 O, and C 54 Cr values than CI chondrites. As such, Ryugu sampled the most primitive and least-thermally processed protosolar nebula reservoirs. Such a finding is consistent with multi-scale H-C-N isotopic compositions that are compatible with an origin for Ryugu organic matter within both the protosolar nebula and the interstellar medium. The analytical data obtained here, suggests that complex soluble organic matter formed during aqueous alteration on the Ryugu progenitor planetesimal (several 10's of km), <2.6 Myr after CAI formation. Subsequently, the Ryugu progenitor planetesimal was fragmented and evolved into the current asteroid Ryugu through sublimation.

Records of micrometeorite collisions at down to submicron scales were discovered on dust grains recovered from near-Earth asteroid 25143 (Itokawa). Because the grains were sampled from very near the surface of the asteroid, by the Hayabusa spacecraft, their surfaces reflect the low-gravity space environment influencing the physical nature of the asteroid exterior. The space environment was examined by description of grain surfaces and asteroidal scenes were reconstructed. Chemical and O isotope compositions of five lithic grains, with diameters near 50 μm, indicate that the uppermost layer of the rubble-pile-textured Itokawa is largely composed of equilibrated LL-ordinary-chondrite-like material with superimposed effects of collisions. The surfaces of the grains are dominated by fractures, and the fracture planes contain not only sub-μm-sized craters but also a large number of sub-μm-to severalμm-sized adhered particles, some of the latter composed of glass. The size distribution and chemical compositions of the adhered particles, together with the occurrences of the sub-μm-sized craters, suggest formation by hypervelocity collisions of micrometeorites at down to nm scales, a process expected in the physically hostile environment at an asteroid's surface. We describe impact-related phenomena, ranging in scale from 10 −9 to 10 4 meters, demonstrating the central role played by impact processes in the long-term evolution of planetary bodies. Impact appears to be an important process shaping the exteriors of not only large planetary bodies, such as the moon, but also low-gravity bodies such as asteroids.impacts | sample-return mission | interplanetary dust | space weathering | comprehensive analysis S olar bodies have evolved from dust to planets with interactions between dust and debris, and asteroids are considered intermediate products of this evolution. Asteroids were not melted and retain their primitive morphology and geochemistry, thus allowing us to investigate interactions between solids and the solar nebula. Meteorites are regarded as fragments of asteroids that fall to Earth's surface. However, information regarding the outer surface of asteroids is presumably destroyed during atmospheric entry, preventing examination of solar space-exposed exteriors of planetary bodies other than that of the moon sampled by the Apollo missions. Nearly all the materials now residing in the planets were processed through high-velocity impacts; however, previous investigation of collisional processes on low-gravity solar bodies has been limited to remote observations by satellites, with no direct sampling of such bodies.The Japan Aerospace Exploration Agency (JAXA) conducted the Hayabusa mission with the goal of better understanding solar system evolution through direct sampling of an asteroid and return of the samples to Earth for detailed analytical work. A target was set to the near-Earth asteroid 25143 Itokawa, an example of a spectral type-S asteroid common in the inner part of the asteroid belt. On-site observations ...

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Platinum-group element (PGE) geochemistry may be used to constrain the timing of sulfide saturation in magmas, which influences Cu and Au fertility of evolving magmatic systems. We report new geochronological and geochemical analyses, with emphasis on PGE geochemistry, for a suite of regional hornblende-porphyritic diorite intrusions and ore-bearing porphyries from the super-giant Escondida and smaller Zaldivar Cu deposits of Northern Chile. The regional dioritic intrusions have zircon U-Pb ages between 39.6 to 37.1 Ma, which overlap with ages of ore-bearing Escondida and Zaldivar porphyries (38.1 to 35.0 Ma). Whole rock major and trace element, Sr-Nd-Pb and zircon O-Hf isotope geochemistry indicates that the regional diorites and ore-bearing porphyries are co-magmatic and originated from the same mantle-derived magma by fractional crystallization, with minor contamination by Paleozoic crust (~10%). The low concentrations of PGE in the regional diorites show that they reached sulfide saturation before the MgO content of the melt fell to 4.7 wt.%, the MgO state of the melt, and the magma volume are critical factors in determining the potential to form a porphyry Cu deposit. Plots of Pd/MgO against Y can be used as empirical indicators of magma fertility for porphyry mineralization, and to discriminate between Cu-Au and Cudominated systems, but cannot predict the size of the deposit. The super-giant status of the Escondida deposit is attributed to it being underlain by a large batholith with a calculated minimum mass of 10 12 tonnes (~400 km 3).