Feathery Basalt

Image

"feathery" groundmass texture in Apollo 17 Basalt 71157,8

~1mm wide cross-polarized image of a portion of the groundmass in Apollo 17 high-Ti basalt 71157 (thin section ,8). The "feathery" texture results from the intergrowth of pyroxene (brown), plagioclase (white/gray/black), ilmenite (black), and some glass (black). The other major phase is olivine, which is present on the image borders and forms the plus-shaped cluster at right middle. There are several early literature (pre-1980s) references to feathery intergrowths, but the associated images have degraded in quality (many articles appear to be scans of photocopies).

AW#45: Geological Pilgrimage

The 45th Accretionary Wedge is hosted by the life as a geologist blog, which asks us to share “the sacred geological place that you must visit at least once in your lifetime…a single place, which is ‘geologically’ unique, relatively remote, and requires some difficulty to get to”. Now, pardon me while I take some liberties with the English language to write about the Moon.

That’s right, the Moon. Geologically Unique? Check. Remote? Check. Difficult to get to? Indeed. So much so that a mere eighteen have made the journey to lunar orbit, and only twelve of those have made the descent to the surface. It remains amazing crazy insane to see images and video of the Apollo missions. Human beings! On the Moon! Walking, driving, discovering, singing, and golfing on the Moon! Which brings me to the “once in your lifetime” part of this pilgrimage. The last footsteps on the Moon were made 40 years ago (this December). Back when Nixon was president. Back when there were almost half as many humans on the planet as there are today. Back before I was born. Taking the liberty to use the royal “you” in the call for posts, I would say that yes, the Moon is a place you/I/we must visit at least once in a lifetime.

Every mission was just a few small steps (or drives), but the science grew by leaps and bounds. The final mission, Apollo 17, had the longest surface stay, the first geologist, and the most returned samples, including the highest-Ti basalts in the solar system. Nowadays we’re making progress by taking a step back, with satellites characterizing the Moon from orbit (surface, gravimetrics, ionosphere, etc). Still awesome, but we need a human presence up there to continue exploring and inspiring.

Is the Moon not specific enough? Perhaps…OK, let’s focus on the Aristarchus Plateau. Why? Because it’s there.

The Moon. Aristarchus Crater is an easy-to-spot lunar feature, made even easier by a giant arrow. (Photo by me; 250mm, f/5.6 @ 1/2500s, ISO400; Dec 1, 2009)

Above, Aristarchus Crater is a beacon of light in the low-albedo mare of Oceanus Procellarum. Viewed in another ‘light’, the below RGB image highlights the diversity of features accessible in the region.

Aristarchus Plateau

Clementine RGB false-color ratio of Aristarchus Plateau, including Aristarchus Crater (bright blue-green, 40km diameter). Image is ~500x500km. Colors are based on UVVIS reflectance spectra ratios (in nanometers) where Red = 750/415; Green = 750/950; Blue = 415/750. See Pieters et al. (1994) for more details on spectra.

False-color ratios are used to demonstrate soil and mineralogical differences, and there are subtle variations that I’m not familiar with to explain concisely. At any rate, the Aristarchus Plateau contains a variety of colors features that we geologists should get a chance to see in our lifetime. To name a few: Pyroclastic deposits, sinuous rilles (collapsed lava tubes?), exposures of cryptomare, highlands, unique volcanism, and possibly the youngest surface basalts1. For more information on the A.P., start with one of the many LROC featured images of the Aristarchus Plateau.

Resources:

LPI Clementine Mapping Project: Source for the RGB false-color ratio image. Request your own map of Clementine satellite spectra! Make a custom spectra map, or request standard RGB false-color ratios, FeO, TiO2, or topography maps.

1Hiesinger, H., et al. (2003) Ages and stratigraphy of mare basalts in Oceanus Procellarum, Mare Nubium, Mare Cognitum, and Mare Insularum. Journal of Geophysical Research 108, E7, 5065, 27pp.