¹S. A. Prevec,¹S. H. Büttner
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13076]
¹Department of Geology, Rhodes University, Grahamstown, South Africa
Published by arrangement with John Wiley & Sons

The offset dykes of the Sudbury Igneous Complex comprise two distinct main magmatic facies, a high‐temperature inclusion‐free quartz diorite (QD), and a subsequently intruded lower temperature, mineralized, and inclusion‐rich quartz diorite (MIQD). The MIQD facies was emplaced after QD dykes had solidified. Key controlling factors of the two injection phases were (1) the development of a coherent roof, which confined the melt sheet; and (2) the periodic increase of melt and fluid pressure within the melt sheet. For the injection of QD melt, the melt pressure exceeded the normal stress acting on fracture surfaces. For the later refracturing of QD dykes and the injection of MIQD melt, the melt pressure increased further, exceeding the tensile strength of, and the normal stress acting on, QD dykes. We associate the melt pressure increase required for both injection episodes with degassing and devolatilization of cooling melt close to the roof. Within the hydraulically connected melt column, the related pressure increase was transmitted to the base of the melt sheet where QD and MIQD melt was extracted into dykes. Residual core to rim thermal gradients in the QD dykes produced tensile strength gradients, accounting for the typically central location of MIQD dykes within QD dykes.

¹Ronald T. Daly, ¹Peter H. Schultz
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13081]
¹Department of Earth, Environmental and Planetary Sciences, Brown University, , Providence, Rhode Island, USA
Published by arrangement with John Wiley & Sons

Impact angle plays a significant role in determining the fate of the projectile. In this study, we use a suite of hypervelocity impact experiments to reveal how impact angle affects the preservation, distribution, and physical state of projectile residues in impact craters. Diverse types of projectiles, including amorphous silicates, crystalline silicates, and aluminum, in two sizes (6.35 and 12.7 mm), were launched into blocks of copper or 6061 aluminum at speeds between 1.9 and 5.7 km s−1. Crater interiors preserve projectile residues in all cases, including conditions relevant to the asteroid belt. These residues consist of projectile fragments or projectile‐rich glasses, depending on impact conditions. During oblique impacts at 30° and 45°, the uprange crater wall preserves crystalline fragments of the projectile. The fragments of water‐rich projectiles such as antigorite remain hydrated. Several factors contribute to enhanced preservation on the uprange wall, including a weaker shock uprange, uprange acceleration as the shock reflects off the back of the projectile, and rapid quenching of melts along the projectile–target interface. These findings have two broader implications. First, the results suggest a new collection strategy for flyby sample return missions. Second, these results predict that the M‐type asteroid Psyche should bear exogenic, impactor‐derived debris.

¹Yasuhito Sekine,²Kenya Kodama,³Takamichi Kobayashi,²Seiji Obata,¹Yu Chang,⁴Nanako O. Ogawa,⁴Yoshinori Takano,⁴Naohiko Ohkouchi,²Koichiro Saiki,⁵Toshimori Sekine
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13075]
¹Department of Earth and Planetary Science, The University of Tokyo, , Bunkyo, Tokyo, Japan
²Department of Complexity Science and Engineering, The University of Tokyo, Kashiwa, Chiba, Japan
³National Institute for Materials Science, Tsukuba, Ibaraki, Japan
⁴Department of Biogeochemistry, JAMSTEC, Yokosuka, Kanagawa, Japan
⁵Center for High Pressure Science and Technology Advanced Research, , Shanghai, China
Published by arrangement with John Wiley & Sons

The present study systematically investigates shock‐induced alteration of organic simulants of planetary bodies (OSPBs) as a function of peak shock pressure and temperature by impact experiments. Our results show that the composition and structure of OSPBs are unchanged upon impacts at peak pressures ≤~5 GPa and temperatures ≤~350 °C. On the other hand, these are dramatically changed upon impacts at >7–8 GPa and > ~400 °C, through loss of hydrogen‐related bonds and concurrent carbonization, regardless of the initial compositions of OSPBs. Compared with previous results on static heating of organic matter, we suggest that shock‐induced alteration cannot be distinguished from static heating only by Raman and infrared spectroscopy. Our experimental results would provide a proxy indicator for assessing degree of shock‐induced alteration of organic matter contained in carbonaceous chondrites. We suggest that a remote‐sensing signature of the 3.3–3.6 μm absorption due to hydrogen‐related bonds on the surface of small bodies would be a promising indicator for the presence of less‐thermally‐altered (i.e., <350 °C) organic matter there, which will be a target for landing to collect primordial samples in sample‐return spacecraft missions, such as Hayabusa2 and OSIRIS‐REx.