FIELD GUIDE to HUSBAND HILL, GUSEV CRATER. Shoshanna B
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Eighth International Conference on Mars (2014) 1031.pdf FIELD GUIDE TO HUSBAND HILL, GUSEV CRATER. Shoshanna B. Cole1,2 and Steve W. Squyres1, 1Department of Astronomy, Cornell University, Ithaca, NY 14853, 2 [email protected] Introduction: The Mars Exploration Rover Spir- Cumberland Ridge. In a rare occurrence in the Co- it’s trek across Husband Hill [1, 2] is the best- lumbia Hills, this site encompasses three outcrops side- documented hiking trail on Mars today. Many studies by-side. The elemental abundances of these layered have been conducted on the rich dataset covering this Watchtower Class exposures are nearly identical de- region [3, 4], including one which produced a field spite their varied mineralogies and textures [6]. They reconnaissance geologic map [5], yet new analyses and are particularly high in Ti and P, and their Cr is below observations have not been synthesized into a concise the detection threshold of Spirit’s Alpha Particle X-ray summary of the Husband Hill assemblage since 2006 Spectrometer (APXS) [8]. The iron oxidation state 3+ [6] – before Spirit had reached the summit. In this (Fe /Fetotal) increases systematically from 0.43 on Me- presentation, we will take a virtual field trip through thuselah, the westernmost outcrop, to 0.94 on the east- this late Noachian/early Hesperian terrain, following in ern side of the easternmost outcrop, Larry’s Lookout Spirit’s footsteps. On our way, we will “conduct” ac- [10]. As you walk the outcrops in this direction, ob- tivities that test hypotheses related to the emplacement serve the decreasing size of the fine-scale nodules and alteration of the features we observe. [11]. We’ll take some samples to calibrate the miner- The West Spur: After driving across 2km of ba- alogical variation detected by Spirit’s Mini-TES in- saltic plains, Spirit finally encountered evidence of strument [12]. In addition to the outcrops and the Gusev’s watery past at the base of the West Spur of beautiful view of Tennessee Valley to the west, there Husband Hill. Beyond the Gusev Plains/West Spur are some interesting float rocks at this location. Don’t unconformity lie beautifully layered outcrops [7] that miss Backstay, a basaltic exotic, and the rounded rocks are enriched in Br, Cl and S compared to the Adiron- to the south and west. dack Class basalts of the Gusev plains [6, 8]. We will Road to the Summit: Our next leg takes us first to gently excavate around the smaller Tetl and Coba out- the southwest, and then to the east as we follow the crops and the extensive Tikal exposure to test the hy- trail around Tennessee Valley to the Husband Hill pothesis that these are indeed bedrock. While we’re summit [2]. We’ll make three more stops before we here, be sure to note the included clasts that make these reach the summit. Clovis Class rocks morphologically distinct from other Independence. Take care not to miss Independ- Husband Hill rocks in hand sample. Keep a look out ence! This low-relief, rough-textured, layered outcrop for occasional Clovis Class float on the rest of the has the lowest iron content, and one of the highest Ni hike! enrichments, of the Husband Hill assemblage [13, 14]. Northwest Husband Hill: After Spirit investigat- It may contain the phyllosilicate montmorillonite [13]; ed several outcrops on the West Spur, she headed we will collect a sample to test this hypothesis back in WNW up onto Husband Hill proper, and then to Cum- lab. Like Watchtower, Independence is enriched in Ti berland Ridge, which overlooks Tennessee Valley [1]. and P and depleted in Cr [13, 14]. Take out your hand We’ll visit each of the outcrops she encountered. lens to examine its range of micro-textures [11]. Peace and Alligator. We’ll stop to appreciate the Voltaire. This complex set of outcrops displays a distinctive layering of the Peace Class ultramafic sand- variety of textures and morphologies. The current hy- stones. These strange exposures are composed of oli- pothesis is that they were deposited as impact melt vine-, pyroxene- and magnetite-rich clasts cemented by which incorporated local float [2]. Note the difference sulfate [6]. They have some of the lowest iron oxida- in size and roundedness of the incorporated clasts on tion states of the Husband Hill assemblage, yet have the northeastern and western regions. To the northeast, the highest sulfate of all Gusev rocks. The ultramafic the tabular Descartes Class outcrops include subround- material may be genetically related to the Algonquin ed to rounded clasts up to a few centimeters in size, sequence we’ll encounter later on [9], so we’ll obtain a while to the southwest, the Assemblee Subclass out- sample at this site for comparison back in lab. crop texture is nodular, and the included clasts are con- Paso Robles. We’ll briefly pause to examine this siderably smaller and well-rounded [2]. At least one of fascinating soil as we head towards Cumberland the larger clasts was determined to be Wishstone Class Ridge. Paso Robles was the first sulfate-rich soil that [2], the ubiquitous float of Husband Hill [15]. Despite Spirit encountered. Curiously, it’s also rich in phos- its location in the Voltaire region, Assemblee’s Fe and phorus, as are the nearby Cumberland Ridge outcrops Ni are similar to Independence, which led to its catego- [8]. rization as a subclass of Independence [14]. Unique Eighth International Conference on Mars (2014) 1031.pdf among the Husband Hill assemblage, Assemblee is with respect to the rest of the Algonquin Class out- significantly enriched in Cr [14]. We will excavate crops [14]. We will collect samples of each outcrop to around the Voltaire area to distinguish between two compare to the Peace Class sample we collected earli- emplacement hypotheses: are we examining bedrock, er, and to test the hypothesis that Larry’s Bench repre- or a discrete mélange block [2]? sents a mixture of Watchtower and Algonquin Class Irvine. Irvine was one of the most enigmatic fea- materials [14]. tures that Sprit observed. These angular, mildly alka- Comanche and Comanche Spur. We’ll end our line basaltic float rocks are arranged in a curvilinear hike at the first carbonate rock on Mars to be investi- formation suggestive of a dike [15, 16]. Once again, gated in-situ [20]. The Comanche and Comanche Spur there is a Cr depletion and Ti and P enrichment, though outcrops are lobed mounds at the base of Husband not so dramatic as for Watchtower and Independence Hill. While part of the Algonquin Series, their textures [14]. The non-volatile components of Barnhill Class are distinct from Algonquin subclass on the outcrop, of Home Plate are remarkably similar to Irvine, con- hand sample, and microscopic scales. They are mor- sistent with a genetic relationship [17]. We will exca- phologically complex, displaying multiple orientations vate around this area to see if we can find evidence of of planar features, fine-scale pitting, and fins represent- a dike, and collect samples to eventually compare to ing relatively erosion-resistant fracture fill [21]. We Barnhill (Home Plate is beyond the geographic extent will examine these outcrops closely to determine their of this field trip). bedding plane orientations, and obtain a relatively deep View from the Top: A magnificent vista awaits us sample to test the hypothesis that Comanche material at the Husband Hill Summit, the highest elevation for drapes Algonquin outcrop [20]. tens of kilometers in every direction. Spirit captured References: [1] Arvidson, R. E. et al. (2006), JGR, the “Everest Panorama” from this location. Gaze 111, E02S01, doi:10.1029/2005JE002499. [2] Arvid- down upon Tennessee Valley to the north, and Home son, R. E. et al. (2008), JGR, 113, E12S33, doi:10.1029/2008JE003183. [3] Special Section Plate to the south. If the sun is just right, we may catch (2006), JGR, 111, Issue E02. [4] Special Section a glint of light reflecting off of Spirit’s solar panels (2008), JGR, 113, Issue E12. [5] Crumpler, L. S. et al. from her resting place on the rim of Scamander Crater (2011), JGR, 116, E00F24, doi:10.1029/ by Home Plate. 2010JE003749. [6] Squyres S. W. et al. (2006) JGR, You may notice that the outcrop textures here are 111, E02S11, doi: 10.1029/2005JE002562. [7] Cole S. reminiscent of Larry’s Lookout on eastern Cumberland B. et al. (2014) in prep. [8] Ming D. W. et al. (2006) Ridge. They are indeed Watchtower Class [14], and JGR, 111, E02S12, doi: 10.1029/2005JE002560. [9] we will collect additional samples to compare to the Ming D. W. personal communication. [10] Morris R. earlier outcrops. V. et al. (2006) JGR, 111, E02S13, doi:10.1029/ Across Haskin Ridge and down to the Inner Ba- 2005JE002584. [11] Herkenhoff K. E. (2014) in prep. sin: For the last leg, we descend across Haskin Ridge [12] Ruff. S. W. et al. (2014) in prep. [13] Clark B. C. before turning south towards the Inner Basin of the III, et al. (2007) JGR, 112, E06S01, doi: Columbia Hills [2]. We’ll stop at six more outcrops, 10.1029/2006JE002756. [14] Ming D. W. et al. (2008) and end our trip just to the east of the El Dorado ripple JGR, 113, E12S39, doi: doi:10.1029/2008JE003195. field, a few hundred meters north of Home Plate. [15] Ruff, S. W. et al (2006), JGR, 111, E12S18, Kansas. Yet more Watchtower [14], though this doi:10.1029/2006JE002747. [16] McSween, H. Y. et time you wouldn’t know it from the texture, which al. (2006), JGR, 111, E09S91, doi:10.1029/ lacks the distinctive fine-scale layering we’ve observed 2006JE002698.