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Reexamining the relationship between Apollinaris Pateraand the basalts of the Gusev crater plains, Mars

Nicholas P. Lang,1 Harry Y. McSween Jr.,2 Livio L. Tornabene,3 Craig J. Hardgrove,2

and Philip R. Christensen4

Received 10 April 2009; revised 26 October 2009; accepted 10 November 2009; published 16 April 2010.

[1] A possible source of the Gusev crater basalts analyzed by the Spirit rover isApollinaris Patera. We test this hypothesis by identifying and analyzing potential lava flowpaths using Thermal Emission Imaging System, Mars Orbiter Camera, High ResolutionImaging Science Experiment, and Mars Orbiter Laser Altimeter data sets together withpublished geologic mapping. Image interpretation reveals three possible flow paths fromApollinaris onto Gusev crater floor via a breach in Gusev’s northwest rim; an unnamedcrater that must have postdated any potential flow along the paths currently blocks thebreach. After correcting for the unnamed crater, topographic profiles constructed alongpossible flow paths demonstrate that elevation along each path increases from ∼80 to430 m. For two of the pathways, this elevation change indicates that lavas could not havetraversed through them. The third profile, though, is less conclusive as the topography mayreflect a broad flexural arch. However, on the basis of two of the topographic profilestogether with the lack of obvious lava flow structures that indicate flow south through thebreach, we propose that Apollinaris was not the direct source of the Gusev basalts. Instead,we argue that it seems more likely that the Gusev basalts were sourced from belowthe crater itself. The similar ages (as derived from crater counts) of Apollinaris’s southflank and the Gusev plains lavas, however, suggest that the two volcanic regions may bepart of a common magmatic feature.

Citation: Lang, N. P., H. Y. McSween Jr., L. L. Tornabene, C. J. Hardgrove, and P. R. Christensen (2010), Reexamining therelationship between Apollinaris Patera and the basalts of the Gusev crater plains, Mars, J. Geophys. Res., 115, E04006,doi:10.1029/2009JE003397.

1. Introduction

[2] Basaltic rocks analyzed on the plains of Gusev craterby the Spirit rover represent the most completely charac-terized suite of erupted materials on the Martian surface[McSween et al., 2004, 2006a]. These basalts are olivine‐rich (picritic) with mildly alkaline properties and appear tohave formed from primitive magma produced by melting ofan undepleted mantle at depth and then erupted withoutsignificant fractionation [Monders et al., 2007]. Their esti-mated viscosities range from 2.3 to 50 Pa s, comparable tolunar mare lavas and Archean high‐Mg basalts on Earth[Greeley et al., 2005]. Crater counting by Greeley et al.[2005] near the Spirit rover landing site yields a modeledage of ∼3.65 Ga for the Gusev plains. However, despite our

range of knowledge regarding the Gusev basalts, their erup-tive source remains ambiguous. Identifying the source ofthese basalts is important for further understanding theirpetrogenesis and for constraining the geologic and magmatichistory of this region.[3] Some workers have proposed that the source of the

Gusev basalts was the large (∼200 km diameter) volcano,Apollinaris Patera, located ∼200 km north of Gusev. Spe-cifically, Martinez‐Alonso et al. [2005] suggest that lavason the floor of Gusev may have flowed directly fromApollinaris Patera via a breach in Gusev’s northwest corner.Such a scenario seems plausible given the low calculatedviscosities of the Gusev basalts [Greeley et al., 2005] andthe observation that some lavas on Mars have traveled fordistances of >1000 km (e.g., in the Daedalia Planum region)[Keszthelyi et al., 2008; Lang et al., 2009]. Such a scenariois also bolstered by the Greeley et al. [2005] crater‐modeledages of ∼3.76 Ga for Apollinaris’s south flank deposits,which is similar to the ∼3.65 Ga modeled age for the Gusevplains. Despite the fact that no volcanic constructs or fis-sures inside Gusev have been identified to date, an alter-native explanation is that the basalts were sourced fromdirectly below the crater [Greeley et al., 2005; see alsoMilam et al., 2003; McSween et al., 2006a, 2006b]. In thisscenario, the low calculated viscosities of the basalts might

1Department of Geology, Mercyhurst College, Erie, Pennsylvania,USA.

2Department of Earth and Planetary Sciences and Planetary GeoscienceInstitute, University of Tennessee, Knoxville, Tennessee, USA.

3Lunar and Planetary Laboratory, University of Arizona, Tucson,Arizona, USA.

4Mars Space Flight Facility, School of Earth and Space Exploration,Arizona State University, Tempe, Arizona, USA.

Copyright 2010 by the American Geophysical Union.0148‐0227/10/2009JE003397

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 115, E04006, doi:10.1029/2009JE003397, 2010

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explain the absence of obvious volcanic constructs withinthe crater [Greeley et al., 2005]. Here we test the hypothesisthat the basaltic lavas on the plains of Gusev crater origi-nated from Apollinaris Patera. Specifically, we integrateThermal Emission Imaging System (THEMIS), MarsOrbiter Camera (MOC), High Resolution Imaging ScienceExperiment (HiRISE), and Mars Orbiter Laser Altimeter(MOLA) gridded data with a published geologic map ofKuzmin et al. [2000] to identify and assess plausible flowpaths from Apollinaris Patera into Gusev crater. If basalticlavas did flow from Apollinaris onto the floor of Gusevcrater, then not only should the ages of the materials besimilar, but there should have existed an unimpeded flowpath connecting them.

2. Approach

2.1. Data Sets

[4] Data sets used in this study were from the Mars GlobalSurveyor (MGS) (1997–2006), Mars Odyssey (MO) (2001to present), and Mars Reconnaissance Orbiter (MRO) (2005to present) missions. MGS data included MOLA griddeddigital elevation model (DEM) (1/128th degree gridded dataset, which translates to ∼500 m/pixel) [Smith et al., 2001]and MOC imagery (∼3 m/pixel) (http://www.msss.com/moc_gallery/) [Malin and Edgett, 2001]; our motivation forusing the gridded DEM rather than Precision ExperimentData Record (PEDR) tracks was that the gridded DEMprovided more control in determining topography alongpossible lava flow paths (though some uncertainty is intro-duced; see sections 2.2 and 3.2.3) than individual PEDRtracks would. MO data included THEMIS visible (Vis,∼18 m/pixel) as well as daytime infrared (IR) (∼100 m/pixel)imagery [Christensen et al., 2004]; THEMIS Vis imageswere obtained from the THEMIS instrument public Web site(http://themis.asu.edu/), whereas THEMIS IR data wereobtained from the Java‐based applet jmars (http://jmars.asu.edu/) [Gorelick et al., 2003; Weiss‐Malik et al., 2005].MRO’s HiRISE camera [McEwen et al., 2007] provided thehighest‐resolution images (∼30 cm/pixel) that offered fur-ther morphologic context for MOC and THEMIS imagery.

2.2. Methodology

[5] To test the hypothesis that the basalts on the plains ofGusev were directly sourced from Apollinaris Patera, weemployed a multistep approach. First, we geologically andmorphologically characterized the region from the southflank of Apollinaris Patera to the northern edge of Gusevcrater, including the breach in Gusev’s northwest corner,using THEMIS Vis and daytime IR data with MOC andHiRISE imagery combined with the published geologic mapof Kuzmin et al. [2000]. This represents the region thatwould have been traversed by lava traveling from Apolli-naris into Gusev. Hence, characterizing this region allowedus to identify potential Apollinaris‐Gusev flow paths. Nor-malized THEMIS daytime IR imagery obtained from jmarsprovided a seamless mosaic for use as a base map. We alsoattempted to use THEMIS IR data to help distinguish dis-tinct spectral units in the study area. Unfortunately, DustCover Index (DCI) [Ruff and Christensen, 2002] valuesfrom 0.92 to 0.94 over this region indicate intermediatequantities of dust, which are sufficient to preclude spectral

determinations. Therefore, our work builds mainly uponresults and inferences from the Spirit rover mission inGusev, as well as morphologic (i.e., THEMIS Vis, MOC,and HiRISE) and morphometric (i.e., MOLA) arguments.[6] We constructed topographic profiles along potential

Apollinaris‐Gusev flow paths using the MOLA griddedDEM, taking into account an unnamed crater that impactedinto the breach (Figure 1). In order to account for theexcavation and deposition from this crater, we determinedthe transient (original) cavity diameter, depth of excavation,and the amount of rim uplift. We also determined the thick-ness of its ejecta blanket. We then subtracted the amountof uplift along the crater rim as well as the ejecta along eachflow path profile in an attempt to reconstruct the preimpacttopography along each path. This approach of accountingfor the unnamed impact crater is outlined in more detail insection 3. Once the profiles were constructed and “corrected”for the effects of the unnamed impact crater, we were ableto evaluate the potential for lava to have traveled fromApollinaris into Gusev.

3. Study

3.1. Geologic Framework and Flow Path Identification

[7] Apollinaris Patera is a ∼200 km diameter volcano[Robinson et al., 1993; Scott et al., 1993] possibly con-structed from both pyroclastic and effusive eruptions[Robinson et al., 1993] (Figure 1); crater‐modeled agesplace Apollinaris Patera between ∼3.5 Ga [Robinson et al.,1993] and ∼3.75 Ga [Greeley et al., 2005], ages that placeApollinaris at around the Noachian‐Hesperian boundary[Hartmann, 2005]. Gusev is a ∼160 km diameter impactcrater [Kuzmin et al., 2000] interpreted to have been the siteof fluviolacustrine activity from the late Noachian to themid‐Amazonian to late Amazonian [Cabrol et al., 1994;Cabrol and Brack, 1995; Cabrol and Grin, 1997; Kuzminet al., 2000] but that appears to have also experiencedvolcanic activity [Milam et al., 2003; Martinez‐Alonsoet al., 2005; McSween et al., 2004, 2006a, 2006b; Greeleyet al., 2005]. From north to south, the terrain betweenApollinaris and Gusev marks the transition from the north-ern lowlands to the southern highlands [Scott et al., 1993;Kuzmin et al., 2000] and is morphologically characterizedby Apollinaris’s south flank, an east‐west trending canyonsystem, and two distinct plateaus (P1 and P2 on Figure 1).[8] The south flank of Apollinaris Patera consists of a

channeled, fan‐shaped deposit of layered materials (Figures 2aand 2b) that extend from a breach in the southern part of theconstruct’s caldera [Robinson et al., 1993; Scott et al., 1993].On the basis of the proximity of these layered deposits to thevolcano, we interpret the south flank materials to be volcanic;Greeley et al. [2005]model the flank deposits at ∼3.76Ga. Thedistal edge of Apollinaris’s south flank marks the northernboundary of Plateau 1 (P1; Figures 2a and 2c). Althoughmuchof the contact between these two features has been dissectedand removed by the formation of the canyon system, it appearsthat at least some of the volcanic flankmaterialsmay have beenemplaced on top of P1 (Figure 2c), suggesting that the southflank postdated P1’s formation. It also seems likely thatbecause the canyon system cuts both the south flank and P1,canyon formation must also postdate P1 and volcanism atsouthern Apollinaris.

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[9] P1 forms an apparently planar surface at the 500 mcontour interval (Figure 2a) that, on the basis of the apparentonlapping relationship of Apollinaris south flank materialsonto P1, appears to be older than Apollinaris. Kuzmin et al.[2000] mapped P1 as a smooth surface composed of flu-

violacustrine deposits associated with aqueous activity inGusev crater. THEMIS Vis imagery illustrates P1’s smoothsurface, which appears to be geologically homogeneous (atTHEMIS Vis resolution), meaning that, with the exceptionof some impact craters and associated ejecta, P1’s surface

Figure 1. THEMIS daytime IR context map for the Apollinaris Patera–Gusev crater region. Dashedwhite boxes labeled 3.76 Ga and 3.65 Ga represent the areas crater counted by Greeley et al. [2005].Dashed black boxes show the locations of Figures 2a and 3a. P1 is Plateau 1; P2 is Plateau 2. Black starshows the landing location of the Spirit rover. THEMIS image obtained from jmars.

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Figure 2

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does not appear to be composed of multiple geologic units.Furthermore, except for a few north trending tectonic ridges(Figures 2a and 2d), P1 is devoid of tectonic structures. Alsoworth noting is that the available visible imagery of P1 doesnot reveal any surface textures consistent with primaryvolcanic morphologies, an observation consistent with theKuzmin et al. [2000] interpretation for P1.[10] To its south, P1 has an abrupt transition to a second,

topographically higher plateau (P2) that parallels the outsideof Gusev’s northern rim (Figures 2a, 2e, and 2f); P2 mate-rials appear to be sitting on top of P1 materials, and wetherefore interpret P2 materials to be younger than P1. Stepsmark local transitions from P1 to P2. However, the overalltransition is sharp, and at the resolution of available imag-ery, debris slopes separating the two morphologic featuresare absent (Figure 2f). Kuzmin et al. [2000] mapped P2 as

volcanic deposits, an interpretation consistent with layersexposed in the walls of P2 (Figures 2g and 2h), although thepossibility of P2 as Gusev‐related ejecta deposits cannot beexcluded. The base of P2 is denoted mostly by the −1500 mcontour, whereas the top locally reaches elevations above−1000 m (Figure 2a). Because P2 sits within this topo-graphic interval, it is most likely older than Apollinaris’ssouth flank materials. To elaborate, if P2 was emplaced afterthe materials on Apollinaris’s south flank, it seems likelythat the P2 materials would have extended across all of P1and up Apollinaris’s south flank to the −1500 m contour;this should especially be so if P2 materials accumulatedand ponded along the outside of Gusev’s northern rim(Figure 2a). However, this does not appear to have occurred.Although one could argue that P2 materials may have on-lapped onto Apollinaris and were then eroded away (in fact,

Figure 2. Imagery characterizing the terrain between Apollinaris Patera and Gusev crater. (a) Contoured (500 m spacing)THEMIS daytime IR context image of the terrain between Apollinaris Patera and Gusev crater. Dashed white boxes showthe locations of Figures 2b–2h. P1 is Plateau 1, and P2 is Plateau 2. White arrows indicate the locations of some tectonicridges that exist on P1. THEMIS image obtained from jmars; topography sourced from MOLA gridded DEM. (b) Portion ofMOC image S0602038 of layers exposed in an impact crater on Apollinaris’s south flank. On the basis of the proximity ofthese layers to Apollinaris, we interpret them to be volcanic in origin. (c) Portion of THEMIS Vis image V12951001 show-ing the contact between Apollinaris’s south flank and P1 (highlighted by white arrows). Apollinaris’s south flank appears tostand topographically higher than P1, suggesting that the flank materials were deposited on top of P1. (d) Portion ofTHEMIS Vis image V05712002 showing the smooth nature of the plateau’s surface. With the exception of a few impactcraters, this surface appears to be geologically homogeneous, meaning that it appears to consist of one geologic unit.Locally present are north trending tectonic ridges (highlighted by white arrows). (e) Portion of THEMIS Vis imageV01967003 showing the characteristics of P2. P2 stands topographically higher than P1 and forms a bench that parallelsthe outside of Gusev’s northern crater rim. (f) Portion of HiRISE image PSP_007737_1670 showing the nature of theboundary between P1 and P2 (highlighted by white arrows), which appears to be relatively sharp and locally marked bysteps. (g) Portion of THEMIS Vis image V13887003 showing more characteristics of P2 and the impact crater that impactsP2. The walls of the impact crater reveal that P2 consists of apparently horizontal layers. The dashed white box shows thelocation of Figure 2h, and the dashed black box shows the location of Figure 3b. (h) Portion of MOC image R2200307showing a higher‐resolution view of the P2 layers (highlighted by white arrows) exposed in walls of the unnamed crater.

Figure 2. (continued)

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P2 does appear to have experienced significant erosion),there is no evidence that Apollinaris’s south flank has un-dergone extensive erosion similar to that of P2. In order forP2 to have been emplaced on Apollinaris and then erodedaway, one would have to argue that extensive erosion onApollinaris stopped once P2 was stripped away, a situationthat does not seem geologically reasonable. Apollinaris’ssouth flank appears too pristine (i.e., the flank channelsseem to be too well preserved (Figure 2a)) to have beencovered over and then subsequently reexposed by erosion.Therefore, we interpret that P2must be older thanApollinaris’ssouth flank.[11] Bounding P2 immediately to its south is Gusev’s

northern crater rim, which, together with P2, is breached

near 12.9°S, 174.6°E. This has resulted in an apparentpathway connecting P1 to the northern floor of Gusev crater;it is through this breach that Martinez‐Alonso et al. [2005]predicted that Apollinaris lavas flowed into Gusev crater.The floor of northern Gusev shows qualitatively fewer im-pact craters than P1; however, Kuzmin et al. [2000] mappedthe floor as smooth material deposited by fluviolacustrineactivity, similar to P1. Milam et al. [2003] noted thatmaterials composing the floor of northern Gusev are layeredand interpreted them to be consistent with fluviolacustrine,aeolian, or volcaniclastic in origin. Martinez‐Alonso et al.[2005] noted surface textures consistent with volcanicflows in various parts of northern Gusev. However, wehave identified no morphologic features resembling volcanic

Figure 2. (continued)

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Figure 2. (continued)

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Figure 2. (continued)

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flows that suggest lava flows have entered into the craterthrough the breach.[12] If lava did flow into Gusev crater from the Apollinaris

construct, then it must have flowed south, likely extendingfrom Apollinaris’s south flank, across P1 and through thebreach of P2 and Gusev’s northwest crater rim, a distance of∼200 km. As mentioned in section 1, lavas traveling for suchlengths on Mars are not unprecedented. Specifically, lavaflows in the Daedalia Planum region have traveled south fromArsia Mons for distances of >1500 km [Keszthelyi et al.,2008; Lang et al., 2009]; such lengths are not unique toMars, as lava flows in Mare Imbrium on the Moon havetraveled up to ∼1200 km, and in Sternia Fluctus on Venus,they have traveled up to ∼1000 km [Zimbelman, 1998].Therefore, predicting that lava flows on Mars have traveledfor ∼200 km is completely reasonable. Further, a closer ex-amination of the breach (Figure 3a) reveals that it is charac-terized by three parallel, north trending valleys that are hereinreferred to as the western valley, middle valley, and easternvalley, respectively; thus, there are at least three paths thatlava could have traveled. All three valleys appear to havebeen affected by a ∼22 km diameter unnamed crater located inP2; Figure 3a shows the crater and the extent of its ejecta asmapped by Kuzmin et al. [2000] with outlines of the threevalleys. North of the unnamed impact crater, the westernvalley (Figure 3b) is an ∼18 km long, slightly sinuous troughthat is ∼2–3 km wide; this valley (if preexisting) likely servedas a conduit that funneled ejecta from the unnamed crater ontoP1 [e.g.,Kuzmin et al., 2000]. The western valley is truncatedat ∼18 km by the unnamed crater, causing the valley tobecome obscured; we have extrapolated the valley’s likelytrend south of the crater and into Gusev. The middle valley(Figure 3c) is a ∼75 km long trough that varies from ∼1 to7 km wide. The valley appears to follow along the rim of theunnamed crater and may have been disrupted by subsequentmodification of the rim. Much of the floor of the middlevalley hosts abundant blocks, and it is difficult to determinefrom Figure 3c whether they represent in‐place mesas orejecta deposits. The eastern valley (Figure 3d) is ∼20 kmwideand over 100 km long, making it the most prominent valley.On the basis of the mapping of Kuzmin et al. [2000], theeastern valley is partially blocked and infilled by ejecta fromthe unnamed crater; the eastern wall of the valley marks theboundary of the ejecta. Figure 3e is a HiRISE image of thesouthern end of the eastern valley and shows at least part ofthe ejecta consists of a thin (approximately meters to tens ofmeters thick) layer that may include blocks of what appears tobe P2. These blocks may be similar to what is observed inFigure 3c in that they may represent in‐place outcrops of P2and/or ejecta. On the basis of the trends of the western,middle, and eastern valleys, it seems plausible that the valleysmerge into one at the northern edge of the Gusev crater floor.Because the unnamed crater truncates the western valley andejecta partially fills the eastern valley, the unnamed craterlikely postdates all three valleys.

3.2. Topographic Analysis

[13] For lava to travel south along any of the flow paths, theroute must have maintained a constant or decreasing eleva-tion to the south. Therefore, a further test of the hypothesisthat Apollinaris lavas flowed into Gusev is the construction oftopographic profiles along the three possible flow paths. Any

increase in elevation along any of the paths toward the southwould have to be attributable to postvolcanic tectonism (in-cluding volcanic loading) or to the emplacement of a geologicunit subsequent to the flow of the lavas.3.2.1. Topographic Profiles[14] Figure 4 presents the topographic profiles constructed

using gridded MOLA data; the profiles extend from theeast‐west trending canyon system, across P1, and throughthe breach in Gusev crater’s northern rim. We constructedthree topographic profiles labeled A‐A′, B‐B′, and C‐C′,with each profile transecting one of the three identifiedvalleys. For each profile, we pay particular attention to thetopography and to the location of the cavity, rim, and ejectaof the unnamed crater. This is because the crater and ejectainterfere with all three pathways, making it unlikely that lavacould have traveled any of the pathways subsequent to theemplacement of the unnamed crater. Therefore, lava travelingthrough the breach must predate the crater [Martinez‐Alonsoet al., 2005]. In fact, on the basis of examination of availableTHEMIS, MOC, and HiRISE imagery, the ejecta representsthe only recognizable geologic unit that postdates the lava.Subsequently, analysis of the potential for lava to travel alongany of the three flow paths needs to account for the location ofejecta along each path with respect to elevation change.[15] The A‐A′ profile shows a slight increase in elevation

(∼100 m) toward the south along P1 prior to intersection withthe ejecta blanket (as mapped by Kuzmin et al. [2000]).Within the ejecta blanket, there is a ∼100 m topographicdepression before the profile crosses P2. Along P2, topog-raphy increases to elevations above −1500 m, and examina-tion of visible imagery here shows that some of this elevationincrease is attributable to the uplifted rim of the unnamedcrater. Elevation then decreases to below −2800 m where theprofile crosses the unnamed crater. Once out of the cavity andbeyond the rim, the profile exhibits a gradual decrease inelevation to the south toward the floor of Gusev crater.[16] The first ∼30 km of the B‐B′ profile show a slight

decrease in elevation of ∼40 m along P1 before a sudden∼80m increase in elevation before intersecting with the ejectablanket. As the profile, and hence flow path, nears the craterrim, the topography dramatically undulates; the cause ofthe undulation is most likely due to interaction of the profilewith the abundant blocks present in the valley. However, asmentioned in section 3.1, it is unclear how many of theseblocks are the result of subsequent landscape modificationdue to the unnamed crater. Moving away from the crater andonto the floor of Gusev crater, the topography becomes moregentle and the elevation levels out.[17] Similar to B‐B′, the C‐C′ profile shows a slight de-

crease in elevation of ∼50 m along P1. However, at ∼25 km,there is a sudden 100 m increase in elevation that is followedby a broadly planar surface. At ∼70 km, there is an abruptincrease in elevation of ∼200 m followed by undulatingtopography that shows a gradual decrease to the south thatbecomes smoother on the northern floor of Gusev crater.3.2.2. Topographic Profiles and the Unnamed Crater[18] Overall, the three topographic profiles in Figure 4

show elevation increases from Apollinaris toward Gusev.At first order, for lava to have traveled from Apollinaris toGusev, such elevation changes require the lava to have flo-wed uphill. However, because the formation of the unnamedcrater must postdate flow along the three pathways, could the

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Figure 3a

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unnamed crater potentially account for all of the increases inelevation along each pathway? Specifically, could the ejectabe more extensive than mapped by Kuzmin et al. [2000]?Further, are all the high elevations surrounding the cratercavity (e.g., A‐A′) related to rim uplift associated with thecratering process? Answering these questions requires esti-mating the amount of uplift, excavation, and deposition thathas occurred at the unnamed impact with respect to thetopographic profiles so as to reconstruct and model the ap-proximate topography prior to the emplacement of the un-named impact. Estimating such factors is not straightforward

and is difficult to quantify accurately [e.g., Stewart andValiant, 2006]. However, because we are only attemptingto approximate (to an order of magnitude) the extent to whichthe unnamed impact has contributed to the topography alongeach profile, we take a “back of the envelope” approach toconstraining the unnamed crater’s properties while notingpossible caveats to our approach.3.2.2.1. Volume Balance[19] We begin by quantifying the extent of the ejecta as

mapped by Kuzmin et al. [2000] with the goal of making arough volume estimate that can be compared to the volume

Figure 3a. Imagery characterizing the breach in Gusev’s northwest corner. (top) Contoured (500 m spacing) THEMISdaytime IR image of the breach and the unnamed crater that has subsequently blocked it. Dashed boxes show the locationsof Figures 3b–3e. THEMIS daytime IR image obtained from jmars; topography sourced from MOLA gridded DEM.(bottom) Same region as the top image but with the impact ejecta as mapped by Kuzmin et al. [2000] shown. The labeleddashed black arrows highlight the three potential pathways that lava may have traveled from P1 onto the floor of Gusev.

Figure 3b. THEMIS Vis and MOLA data of the western valley. (right) Portion of THEMIS Vis imageV13887003 showing the western valley. (top left) Gridded MOLA DEM showing the western valleylocation. (bottom left) Same as Figure 3b (top left), but without the location box. The white dashedhachured lines highlight the valley boundaries with the hachures pointing downslope.

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of the unnamed crater’s transient cavity. If the extent of theejecta mapped by Kuzmin et al. [2000] is correct, then thevolume of the ejecta should theoretically be on the sameorder of magnitude as the volume of the transient cratercavity. Calculating the volume of the crater cavity requiresdetermining the original, or transient, diameter (Dt) of thecrater as well as the depth of excavation (de). To calculatethe transient diameter of the crater, we follow Grieve et al.[1981] and Melosh [1989] and use a conservative estimate:

Dt � 0:5 to 0:7Da; ð1Þ

where Da is the apparent, or current, diameter of the crater,which we measured from Kuzmin et al. [2000] to be ∼22 km(see Table 1). Because we are looking for an estimate of the

transient diameter, we use an average of the 0.5–0.7 range(0.6), which results in a transient diameter of ∼13 km.[20] On the basis of Maxwell’s Z model of excavation

flow fields [Maxwell, 1977; Pike, 1980; Grieve et al., 1981;Melosh, 1989], the depth of excavation (de) is defined as

de � 0:1Dt; ð2Þ

which, using the value obtained from (1), results in a de of∼1.3 km, the approximate depth of the crater cavity as con-firmed by MOLA and as seen in A‐A′ (Figure 4). However,the final depth of a transient cavity is a combination of bothexcavation and displacement of the target during the impactprocess, where only ∼1/3 of the crater cavity is attributed to

Figure 3c. THEMIS Vis and MOLA data of the middle valley. (right) Portion of THEMIS Vis imagesV13887003 and V1818003 showing the middle valley. (top left) Gridded MOLA DEM showing the mid-dle valley location. (bottom left) Same as Figure 3c (top left), but without the location box. The whitedashed hachured lines highlight the valley boundaries with the hachures pointing downslope.

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excavation and ∼2/3 are attributed to downward and outwarddisplacement of the expanding transient cavity [e.g.,Melosh,1989]. Therefore, de should not equal the final depth of thecrater cavity even when accounting for postimpact modifi-cation including infilling and wall collapse. Subsequently, wetake our calculated de value as a gross overestimate of theexcavation depth.[21] The volume of the transient unnamed crater (vc) can

be roughly estimated by approximating the crater as aspherical cap [Harris and Stocker, 1998]:

vc ¼ �=6ð Þ 3 0:5D2t

� �þ d2e� �

de; ð3Þ

which results in a crater volume of ∼90 km3. Because thevalue of de used in (3) is likely an overestimate, the valueobtained from (3) is also likely an overestimate.

[22] The ejecta volume (vb) can be estimated following themethodology of McGetchin et al. [1973]:

vb ¼ 2� t0 0:5Dtð Þ2; ð4Þ

where t0, the thickness of the ejecta blanket at the transientcrater rim, can be determined from [McGetchin et al., 1973]

t0 ¼ 0:14 0:5Dtð Þ0:74 r= 0:5Dtð Þð Þ�3:0; ð5Þ

where r is the distance from the center of the transient craterto the point where the thickness is being calculated, which inthis case is the crater rim. This means that in calculating thethickness of the ejecta at the crater rim, r represents thetransient crater radius, which results in the second part of the

Figure 3d. THEMIS Vis and MOLA data of the eastern valley. (right) Portion of THEMIS Vis imagesV1818003 and V01967003 showing the eastern valley. (top left) Gridded MOLA DEM showing the east-ern valley location. (bottom left) Same as Figure 3d (top left), but without the location box. The whitedashed hachured lines highlight the valley boundaries with the hachures pointing downslope.

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equation ((r/(0.5Dt))−3.0) reducing to 1. As such, (5) gives an

ejecta thickness value of ∼93 m at the transient crater rim.[23] Using (4) and (5) results in an ejecta blanket volume

of ∼25 km3, which is approximately a factor of 4 less thanthe calculated crater volume. At first order, this seems tosuggest that the ejecta may be more extensive than mappedby Kuzmin et al. [2000]. However, both volumes arethe same order of magnitude, which, when paired withthe possible gross overestimates that stemmed from ourcalculated de value, makes us confident that the extent ofthe impact ejecta as mapped by Kuzmin et al. [2000] isreasonable.3.2.2.2. Ejecta Thickness and Crater Cavity[24] Building upon the calculation of the crater cavity and

ejecta volumes, each profile can be corrected for the cratercavity and ejecta blanket. To correct for the crater cavityrequires (1) knowing the original, or transient (Dt), diameterof the impact crater, (2) knowing the thickness of the ejectaat the apparent diameter (Da) of the crater rim, and (3)calculating the amount of uplift that has occurred along thecrater rim; correcting for the crater cavity depth is critical forreconstructing the A‐A′ profile. Correcting for the ejectarequires calculating the thickness of the ejecta along each flow

path; correcting for the ejecta is critical for reconstructing allthree profiles.[25] We begin correcting for the crater cavity by estimating

the amount of uplift and ejecta deposition that has occurred atthe crater rim. On the basis of the unnamed crater’s diameterand depth to diameter ratio of ∼0.045, we view this as acomplex crater, leading us to use the empirical relationshipfor rim height for complex craters as a conservative estimate[Garvin et al., 2003]:

hr ¼ 0:02D0:84a ; ð6Þ

which results in an hr value of ∼270 m at the original craterrim. This final rim height estimate is not entirely a conse-quence of uplift but is also influenced by [Melosh, 1989](1) an overturned flap, (2) the augmentation of the rim frommultiple breccia and impact melt dike injections into thetransient crater wall, and (3) subsequent erosion of the craterrims with time. This uplift does not occur at just one singlepoint at the rim crest but drops off to zero over a distance of∼1.3 to 1.7 crater radii as measured from the transient craterrim [Melosh, 1989]. This amounts to a distance of ∼10 km forthis situation of the unnamed crater.

Figure 3e. Portion of HiRISE image PSP_007737_1670 showing a portion of the impact ejecta towardthe southern end of the eastern valley (highlighted by white arrows). At least part of the ejecta blanketconsists of a relatively thin (on the order of meters to tens of meters thick?) layer here. P2 locally outcropshere, but it is unclear if the blocks are in place and/or represent ejecta blocks.

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[26] We use (5) to calculate the thickness of the ejectablanket (tb) at any point along the pathway as a function ofdistance from the crater center where tb substitutes for t0 andr is the distance from the center of the transient cavity to thepoint where the thickness is being calculated. Table 2 liststhe thickness of the ejecta blanket along each of the threepathways at 5 km increments as calculated using (3) andshows that the thicknesses vary from <1 to ∼20 m.[27] Assuming that the amount of uplift was the same

around the crater rim, we can use our calculated value of hrplus the ejecta thickness at the rim of Da (Table 2) to esti-mate the preimpact surface elevation at the crater cavity forprofile A‐A′. Subtracting both hr and the ejecta thicknessfrom the current rim of the crater should result in the pre-impact elevations. However, to do so, we need to accountfor the effect of widening of the crater on the erasing of rimuplift; the widening of the crater is ultimately occurringbecause of blocks of the uplifted rim sliding down towardthe crater floor, meaning that rim uplift is being erased bycrater modification [Melosh, 1989]. To account for thiswidening and, thus, to determine the current lateral extent

of rim uplift, we can take the difference between the tran-sient crater radius (∼6.5 km) and the current crater radius(∼11 km) and then subtract that from ∼1.5Dt (∼10 km); thisamounts to uplift extending for ∼5.5 km from the currentrim. Further, because the amount of uplift decreases as afunction of distance from the transient crater rim, theamount of uplift present in the remaining 5.5 km should beless than the 270 m of uplift initially calculated as existing atthe edge of the transient crater’s rim (i.e., equation (6)).From Melosh [1989], it can be taken that this uplift maydecrease as an exponential function. However, for simplicityin our calculations, we assume that uplift decreases linearlyfrom the crater rim. Subsequently, if the amount of upliftthat occurred at the transient crater’s rim was 270 m and theuplift is 0 m at 10 km away, then, assuming a linear de-crease, we can simply determine the amount of uplift inbetween. To illustrate, if uplift extends for ∼5.5 km from thecurrent crater rim, then 4.5 km of uplifted rim have beenremoved, which would mean that there is a current uplift of∼150 m at the crater’s current rim. However, if uplift de-creases exponentially from the crater rim as indicated by

Figure 4. Topographic profiles along each of the three flow paths. THEMIS daytime IR images showingthe distribution of the ejecta [Kuzmin et al., 2000] from the unnamed crater and the locations of each ofthe three profiles. THEMIS daytime IR from jmars; topography data sourced from MOLA gridded data.

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Melosh [1989], then this value is likely an overcalculation.Further, the elevations of the crater rim represented in pro-file A‐A′ (Figure 4) are approximately −1400 m and ap-proximately −1600 m. Subtracting 170 m (150 m of rimuplift plus 20 m of ejecta) from both crater rim elevationsand extending it out one crater radii (∼5.5 km) results inelevations of −1570 m and −1770 m, respectively. Thepreimpact surface elevation should therefore reside betweenthese two elevations such that the topography sloped southfrom approximately −1570 m to approximately −1770 m.Performing such a correction on the A‐A′ profile is criticalbecause it passes directly through the impact crater; thepathway goes across the crater rim. In addition, although theB‐B′ profile does not pass through the crater, it does crossalong the crater rim, meaning that it too needs to be cor-rected for rim uplift. However, the B‐B′ profile is at a dis-tance of 5 km from the current crater rim, which translates to∼14 m of uplift along B‐B′. The C‐C′ profile is at a distancewell beyond that affected by rim uplift, meaning that rimuplift does not need to be corrected for in that profile.[28] This approach to determining the preimpact surface

elevation is similar to that described by Stewart and Valiant[2006]. Stewart and Valiant [2006] estimated the topogra-phy of the preimpact surface for Martian impacts by con-necting a fraction of the crater rim with the surface beyondthe ejecta blanket [see Stewart and Valiant 2006, Figure 2];the preimpact surface should theoretically reside at the ele-vation that is beyond the ejecta blanket. However, becausethe surfaces along each of the three topographic profileshave some slopes to them (and are not flat as is assumed inthe Stewart and Valiant [2006] approach), we cannot easilydraw a line from the crater rim to beyond the ejecta blanket.Instead, we simply subtracted the estimated rim height andejecta thickness and used the subsequent elevation as thepreimpact surface elevation.3.2.2.3. “Corrected” Profiles[29] Subsequently, each profile can be reconstructed, or

“corrected,” on the basis of the values obtained from themethods described in sections 3.2.2.1 and 3.2.2.2 (Figure 5).[30] The corrected A‐A′ profile has the uplifted crater rim,

the crater cavity, and the ejecta blanket removed. Removingthe ∼170 m of rim uplift and ejecta on P2 results in surfaceelevations of approximately −1570 m and approximately−1770 m, which, as described in sections 3.2.2.1 and3.2.2.2, reveals the approximate preimpact surface. On thetopographic profile, this results in P2 having a gradual slopeto the south toward the floor of Gusev crater. Removal ofthe ejecta blanket shows minimal elevation change resultingin negligible change to the profile. Despite P2’s overall

Table 1. Values Used in Calculating Crater and Ejecta Parameters

Symbol Meaning Value Source

Da Apparent (final) crater diameter 22 km Measured from Kuzmin et al. [2000]Dt Transient (initial) crater diameter 11 km Equation (1)de Initial depth of crater excavation 1.3 km Equation (2)vc Impact crater volume 90 km3 Equation (3)vb Ejecta blanket volume 25 km3 Equation (4)p Pi 3.14 ‐t0 Ejecta thickness at the transient crater rim 93 m Equation (5)tb Ejecta thickness along a flow path See Table 2 Equation (5)r Distance from the center of the crater to a specific point in the ejecta blanket ‐ Measured from Kuzmin et al. [2000]hr Crater rim uplift 0.1 km Equation (6)

Table 2. Calculated Ejecta Thicknesses at 5 km Increments AlongEach Topographic Profile

IncrementDistance From

Crater Center (km)Calculated EjectaThickness (m)

Western Valley1 35 0.592 29 1.053 24 1.844 19 3.725 15 7.556 (north rim of Da) 11 19.157 (south rim of Da) 11 19.158 15 7.559 20 3.1210 25 1.6311 29 1.0512 35 0.5913 40 0.40

Middle Valley1 28 1.162 23 2.093 18 4.374 14 9.295 13 11.606 12 14.757 12 14.758 13 11.609 15 7.5510 19 3.7211 22 2.3912 29 1.0413 32 0.7814 37 0.50

Eastern Valley1 31 0.862 27 1.293 28 1.164 26 1.455 28 1.166 24 1.847 25 1.638 23 2.099 22 2.3910 20 3.1911 18 4.3712 17 5.1913 19 3.7214 22 2.3915 29 1.0516 32 0.7817 37 0.50

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southerly slope, however, the profile still shows inclines of∼100 and 430 m at ∼45 and 70 km, respectively. In addition,because we assumed a linear decrease in our accounting forrim uplift, we should note that this profile is likely anovercorrection of the real topography. This means that to-pography along A‐A′ may be higher than what is indicatedin the profile.[31] The corrected B‐B′ profile shows corrections only for

the impact ejecta. Similar to the corrected A‐A′ profile, thereis negligible change to the profile with removal of the ejectaand rim uplift. Because it is unclear how much the blocks inthe middle valley can be attributed to modification after theimpact event, we have left the signal of that topographywithin the profile. Regardless, on P1 at ∼40 km, there is an∼80 m increase in elevation.[32] The corrected C‐C′ profile has also only been cor-

rected for the ejecta blanket, and similar to the B‐B′ profile,removal of the ejecta has had a negligible effect on theprofile. There is still a notable two‐step increase in elevationat ∼25 and 70 km of ∼100 and 180 m, respectively.3.2.3. Summary and Discussion[33] Even when correcting for the impact crater, uplifted

rim, and ejecta, the topographic profiles along each possible

flow path reveal that the surface across P1, and prior toreaching the breach of P2 and Gusev’s northern rim, in-creases in elevation between ∼80 and 430 m. We shouldnote, though, that because we are using gridded MOLA toconstruct our topographic profiles instead of individualPEDR tracks, there is most likely uncertainty within each ofour constructed profiles. To elaborate, although the along‐track shot spacing for MOLA is fairly constant at ∼300 m,the across‐track spacing is larger and irregular and can be aslarge as 4 km in the vicinity of the equator [Smith et al.,2001]. Because of this large and irregular grid spacing,not every grid cell will have a MOLA data point within it,meaning that there are interpolated values within the griddeddata set. This suggests that we may be reaching the limits ofresolution in the MOLA data presented here. In fact, someof the very short wavelength jaggedness observed in thetopography presented in this paper (i.e., Figures 2a, 4, and 5)may reflect the resolution limit. That said, we believe thatthe overall trends in the topography presented here areaccurate. For example, topographic undulations such as at∼60 km in the A‐A′ profile (Figures 4 and 5), at ∼40 km inthe B‐B′ profiles, and at ∼30 and 70 km in the C‐C′ pro-files are all relatively gradual, occurring at length scales of

Figure 5. Topographic profiles shown in Figure 4, but corrected for the unnamed crater and its ejectablanket.

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≥15 km. Such length scale changes in topography seem tosuggest that we are resolving the overall topographic trendswithin each of the analyzed valleys.

4. Discussion

[34] Comparison of the corrected topographic profileswith the geology described between Apollinaris and Gusevindicates that the increases in elevation cannot be attributedto obvious short‐wavelength faulting and/or folding [e.g.,Kuzmin et al., 2000]. Although north trending tectonic ridgesare present locally, no obvious tectonic structures are presentthat can be directly associated with topographic changesalong each of the three flow paths (Figure 2a). It is pos-sible that long‐wavelength topographic warping (lithosphericflexure) due to the loading of Apollinaris Patera could affectthe topography along each profile [e.g., McGovern andSolomon, 1993]. In fact, the corrected A‐A′ profile(Figure 5) does seem to generally resemble a broad and gentleflexural arch profile, though a central divot does exist at∼60 km. However, slight decreases in elevation toward thesouth in profiles B‐B′ and C‐C′ together with the multitieredelevation increases in the C‐C′ profile suggest that con-tributions to topography from lithospheric flexure are smallcompared to other sources of topography in both of thoseprofiles; both B‐B′ and C‐C′ seem to show short‐wavelengthsources of topography in the corrected profiles (Figure 5)(i.e., at ∼30 km in B‐B′ and ∼30 km and ∼70 km in C‐C′).Because the B‐B′ and C‐C′ profiles seem to show shorter‐wavelength topography sources, it is possible that the cor-rected A‐A′ profile (because of its close location to the B‐B′and C‐C′ profiles) may have more complex shorter‐wave-length topography than what we have shown in Figure 5. Inaddition, on the basis of the analysis here using availableimagery, the majority of the elevation increases cannot beattributed to any obvious geologic units emplaced subsequentto any lava flow into the northern part of Gusev. Together,these observations suggest that this rise in topography (atleast in the B‐B′ and C‐C′ profiles) is mostly primary andindicate that if lavas did flow from Apollinaris into Gusev,they would have had to traverse ∼80–100 m uphill. Specifi-cally, for the case of the C‐C′ profile, lava would have had totraverse up two distinct rises. Climbing such inclines wouldrequire pressure‐driven flow for distances of 20 to 60 km upslopes of ∼0.001° to 0.003°. Such a scenario seems unlikelyfor lava flows. In addition, for the A‐A′ profile, assuming thatthe divot at ∼60 km predates any hypothetical Apollinarislava flow, the lava would had to have filled (and therebyerased) the central divot before continuing into Gusev crater.Therefore, on the basis of the assumption that the divot in theA‐A′ profile occurred before any hypothetical Apollinarislava flowed across P1, we conclude that it is unlikely thatApollinaris‐sourced lavas could have flowed into Gusevcrater. However, if the divot occurred after Apollinaris ac-tivity and we assume that the A‐A′ profile does reflect aflexural arch profile with no complex short‐wavelengthtopography (which may not be the case if the closely locatedB‐B′ and C‐C′ profiles show such effects) where southflowing Apollinaris lavas predated flexural arch formation,then there may have existed a more or less level pathway from

Apollinaris into Gusev through the westernmost valley. Iftrue, then we cannot robustly conclude that lavas fromApollinaris did not flow into Gusev crater [see Martinez‐Alonso et al., 2005]. That said, if south flowing Apollinarislavas postdated, instead of predated, occurrence of the flex-ural arch, then lava flow into Gusev via the western valleywould be unlikely as the flows would have to have traversed a∼400 m hill. In addition, the lack of any obvious lava flowstructures across the surface of P1 that indicate a flow di-rection to the south through the breach seems to suggest thatlavas did not travel from the Apollinaris construct and intoGusev crater. Although P1 qualitatively exhibits fewer im-pact craters than the northern floor of Gusev crater, meaningthat P1 could have been resurfaced subsequent to lava flowemplacement, the absence of obvious volcanic morphologiesnear the breach on Gusev’s floor strongly suggests that lavadid not flow into the crater via the breach. Therefore, wefollow Greeley et al. [2005] and favor the alternative expla-nation that the Gusev basalts were locally erupted within thecrater through fractures or from volcanic constructs that havebeen subsequently modified, destroyed, or buried. However,we do not discount the possibility of Apollinaris pyroclasticdeposits existing within Gusev. Explosive eruptions mostlikely contributed to the construction of Apollinaris Patera[Robinson et al., 1993], and it seems likely that ash from thoseeruptions could have been deposited onto the floor of Gusev[e.g., Kerber et al., 2008; see also Milam et al., 2003].[35] Even if the Gusev basalts are not sourced from the

Apollinaris construct, the similar ages of Apollinaris’ssouthern flank deposits and Gusev materials [Greeley et al.,2005] raise the possibility that the two are magmaticallyrelated [Greeley et al., 2005]. Perhaps Apollinaris magma-tism and Gusev magmatism reflect different regions across alarge plume. The mildly alkaline nature of the Gusev basalts[McSween et al., 2006b] might be consistent with a plumeinterpretation in which Gusev represents tapping of a plumemargin where lower degrees of partial melting occur. In sucha scenario, magma generated by the plumewould rise throughthe crust with some magma possibly stalling and accumu-lating in magma chambers and eventually rising to the Gusevfloor via preexisting fractures and zones of weakness thatlikely exist beneath (and were likely generated by) Gusevcrater. This situation may be analogous to lunar mare lavaemplacement where low‐viscosity basaltic lavas sourcedfrom >100 km depth filled large impact basins over possibletime scales of millions of years [Head, 1976; see alsoGreeleyet al., 2005].[36] A plume hypothesis may be testable through continued

geologic mapping and spectroscopic studies across theregion. Specifically, the identification of (likely buried?)regional fracture systems connecting Apollinaris and Gusevmay be attributable to the interaction of a plume head on thebase of the lithosphere [e.g., Ernst and Buchan, 2001]. Fur-ther, although the DCI [Ruff and Christensen, 2002] showsthe Apollinaris region to be moderately dust covered andhence not suitable for spectroscopic analysis at THEMISor Thermal Emission Spectrometer resolutions, the obser-vation of layered deposits on the volcano’s southern flank(Figure 2b) raises the possibility that future spectroscopicinstruments may be able to analyze Apollinaris volcanic

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materials. Compositional analysis of these deposits wouldyield more insight into their petrogenesis and allow for con-tinued comparison with the Gusev basalts.

5. Summary and Conclusions

[37] We have used THEMIS, MOC, HiRISE, and MOLAdata together with published geologic mapping to test thehypothesis that basalt on the plains of Gusev crater wassourced from the Apollinaris Patera construct. Characteriza-tion of the region between Apollinaris and Gusev suggeststhat if lava did travel from Apollinaris into Gusev, it musthave traversed south across a plateau (P1) and along one ormore pathways in a breach in Gusev’s northwest rim. To-pographic profiles along two possible flow paths require thelavas to have traveled ∼80–200 m uphill (the B‐B′ and C‐C′corrected profiles), an unlikely scenario. However, for thethird profile (the A‐A′ corrected profile), it is less conclusivethat the lava had to have traveled through it, as it may be areflection of a simple flexural arch. On the basis of two of thetopographic profiles and the lack of obvious flow structuresindicating flow south through the breach, though, it seemsmore feasible that the basalts on the Gusev crater plains werederived from below the crater itself; this does not exclude,however, the possibility that ash deposits from Apollinarisexist within Gusev. Although we postulate that it is unlikelythat the Gusev basaltic lavas are from Apollinaris, the similarages of the Gusev basalts and Apollinaris flank depositssuggest that these materials are parts of a common magmaticprovince, perhaps fed by a large plume.

[38] Acknowledgments. We thank the MO, MGS, and MRO teamsfor data used in this study. Many thanks to P.McGovern and two anonymousreviewers for thoughtful and thorough reviews which greatly enhancedand improved this manuscript. Discussions with C. Fedo, D. Finkelstein,and T. Usui helped improve the quality of this work.We also thank K. Thaisenfor help generating the topographic contours on Figures 2a and 3a. This workwas partly supported by THEMIS Co‐Investigator subcontract ASU 01‐082to H.Y.M.

ReferencesCabrol, N. A., and A. Brack (1995), Episodic oasis for water‐dependent lifeon Mars, Proc. Lunar Planet. Sci. Conf., 26th, 201–202.

Cabrol, N. A., and E. A. Grin (1997), Hydrogeology and exobiology sig-nificance of Martian large crater lakes, in Conference on Early Mars:Geologic and Hydrologic Evolution, Physical and Chemical Environ-ments, and the Implications for Life, edited by S. M. Clifford et al.,pp. 14–15, Lunar and Planet. Inst., Houston, Tex.

Cabrol, N. A., R. Landheim, R. Greeley, and J. D. Farmer (1994), Fluvialprocesses in Ma’adim Vallis and the potential of Gusev as a high prioritysite, Proc. Lunar Planet. Sci. Conf., 25th, 213–214.

Christensen, P. R., et al. (2004), The Thermal Emission Imaging System(THEMIS) for the Mars 2001 Odyssey Mission, Space Sci. Rev., 110,85–130, doi:10.1023/B:SPAC.0000021008.16305.94.

Ernst, R. E., and K. L. Buchan (2001), The use of mafic dike swarms inidentifying and locating mantle plumes, Spec. Pap. Geol. Soc. Am.,352, 103–140.

Garvin, J. B., et al. (2003), Craters on Mars: Global geometric propertiesfrom gridded MOLA topography, in Sixth International Conference onMars, Jet Propul. Lab., NASA, Pasadena, Calif.

Gorelick, N. S., M. Weiss‐Malik, B. Steinberg, and S. Anwar (2003),JMARS: A multimission data fusion application, Lunar Planet. Sci.[CD‐ROM], XXXIV, Abstract 2057.

Greeley, R., F. H. Bernard, H. Y. McSween, G. Neukum, P. Pinet, M. vanKan, S. C. Werner, D. A. Williams, and T. E. Zegers (2005), Fluid lavaflows in Gusev crater, Mars, J. Geophys. Res., 110, E05008, doi:10.1029/2005JE002401.

Grieve, R. A. F., et al. (1981), Multi‐ring basins: Formation and evolution,Proc. Lunar Planet. Sci. Conf., 12th, 791–814.

Harris, J. W., and H. Stocker (1998), Handbook of Mathematics and Com-putational Science, 107 pp., Springer, New York.

Hartmann, W. K. (2005), Martian cratering 8: Isochron refinement and thechronology of Mars, Icarus, 174, 294–320, doi:10.1016/j.icarus.2004.11.023.

Head, J. W. (1976), Lunar volcanism in space and time, Rev. Geophys., 14,265–300, doi:10.1029/RG014i002p00265.

Kerber, L., J. W. Head, J. B. Madeleine, L. Wilson, and F. Forget (2008),Modeling ash dispersal from Apollinaris Patera: Implications for theMedusae Fossae Formation, Proc. Lunar Planet. Sci. Conf., 39th,1881–1882.

Keszthelyi, L., W. Jaeger, A. McEwen, L. Tornabene, R. Beye, C. Dundas,and M. Milazzo (2008), High Resolution Imaging Science Experiment(HiRISE) images of volcanic terrains from the first 6 months of the MarsReconnaissance Orbiter Primary Science Phase, J. Geophys. Res., 113,E04005, doi:10.1029/2007JE002968.

Kuzmin, R. O., R. Greeley, R. Landheim, N. A. Cabrol, and J. D. Farmer(2000), Geologic map of the MTM‐15182 andMTM‐15187 Quadrangles,Gusev Crater–Ma’adim Vallis region, Mars,U.S. Geol. Surv. Misc. Invest.Ser., Map I‐2666, scale 1:500,000.

Lang, N. P., L. L. Tornabene, H. Y. McSween, and P. R. Christensen(2009), Tharsis sourced relatively dust‐free lavas and their possiblerelationship to Martian meteorites, J. Volcanol. Geotherm. Res., 185,103–115, doi:10.1016/j.jvolgeores.2008.12.014.

Malin, M. C., and K. S. Edgett (2001), Mars Global Surveyor Mars OrbiterCamera: Interplanetary cruise through primary mission, J. Geophys. Res.,106, 23,429–23,570, doi:10.1029/2000JE001455.

Martinez‐Alonso, S., B. M. Jakosky, M. T. Mellon, and N. E. Putzig(2005), A volcanic interpretation of Gusev crater surface materials fromthermophysical, spectral, and morphologic evidence, J. Geophys. Res.,110, E01003, doi:10.1029/2004JE002327.

Maxwell, D. E. (1977), Simple Z model of cratering, ejection, and over-turned flap, in Impact and Explosion Cratering, edited by D. J. Roddyet al., pp. 1003–1008, Pergamon, New York.

McEwen, A. S., et al. (2007), Mars Reconnaissance Orbiter’s High Reso-lution Imaging Science Experiment (HiRISE), J. Geophys. Res., 112,E05S02, doi:10.1029/2005JE002605.

McGetchin, T. R., M. Settle, and J. W. Head (1973), Radial thickness var-iation in impact crater ejecta: Implications for lunar basin deposits, EarthPlanet. Sci. Lett., 20, 226–236, doi:10.1016/0012-821X(73)90162-3.

McGovern, P. J., and S. C. Solomon (1993), State of stress, faulting, anderuption characteristics of large volcanoes on Mars, J. Geophys. Res.,98, 23,553–23,579, doi:10.1029/93JE03093.

McSween, H. Y., et al. (2004), Basaltic rocks analyzed by the Spirit roverin Gusev crater, Science, 305, 842–845, doi:10.1126/science.3050842.

McSween, H. Y., et al. (2006a), Characterization and petrologic interpreta-tion of olivine‐rich basalts at Gusev crater, Mars, J. Geophys. Res., 111,E02S10, doi:10.1029/2005JE002477.

McSween, H. Y., et al. (2006b), Alkaline volcanic rocks from the ColumbiaHills, Gusev crater, Mars, J. Geophys. Res., 111, E09S91, doi:10.1029/2006JE002698.

Melosh, H. J. (1989), Impact Cratering: A Geologic Process, 245 pp.,Oxford Univ. Press, New York.

Milam, K. A., K. R. Stockstill, J. E. Moersch, H. Y. McSween, L. L.Tornabene, A. Ghosh, M. B. Wyatt, and P. R. Christensen (2003),THEMIS characterization of theMERGusev crater landing site, J. Geophys.Res., 108(E12), 8078, doi:10.1029/2002JE002023.

Monders, A. G., E. Medard, and T. L. Grove (2007), Phase equilibriuminvestigations of the Adirondack class basalts from the Gusev plains,Gusev crater, Mars, Meteorit. Planet. Sci., 42, 131–148.

Pike, R. J. (1980), Control of crater morphology by gravity and target type:Mars, Earth, Moon, Proc. Lunar Planet. Sci. Conf., 11th, 2159–2189.

Robinson, M. S., P. J. Mouginis‐Mark, J. R. Zimbelman, S. S. C. Wu, K. K.Ablin, and A. E. Howington‐Kraus (1993), Chronology, eruption dura-tion, and atmospheric contribution of the Martian volcano ApollinarisPatera, Icarus, 104, 301–323, doi:10.1006/icar.1993.1103.

Ruff, S. W., and P. R. Christensen (2002), Bright and dark regions onMars: Particle size and mineralogical characteristics based on ThermalEmission Spectrometer data, J. Geophys. Res., 107(E12), 5127, doi:10.1029/2001JE001580.

Scott, D. H., J. M. Dohm, and D. J. Applebee (1993), Geologic map ofscience study area 8, Apollinaris Patera region of Mars, U.S. Geol. Surv.Misc. Invest. Ser., Map I‐2351, scale 1:500,000.

Smith, D. E., et al. (2001), Mars Orbiter Laser Altimeter: Experiment andsummary after the first year of global mapping of Mars, J. Geophys. Res.,106, 23,689–23,722, doi:10.1029/2000JE001364.

Stewart, S. T., and G. J. Valiant (2006), Martian subsurface properties andcrater formation processes inferred from fresh impact crater geometries,Meteorit. Planet. Sci., 41, 1509–1537.

LANG ET AL.: APOLLINARIS PATERA–GUSEV BASALT CONNECTION E04006E04006

19 of 20

Weiss‐Malik, M., N. S. Gorelick, and P. R. Christensen (2005), JMARS: AGIS system for Mars and other planets, Eos Trans. AGU, 86(52), FallMeet. Suppl., Abstract P21C‐0169.

Zimbelman, J. R. (1998), Emplacement of long lava flows on planetary sur-faces, J. Geophys. Res., 103, 27,503–27,516, doi:10.1029/98JB01123.

P. R. Christensen, Mars Space Flight Facility, School of Earth and SpaceExploration, Arizona State University, PO Box 876305, Tempe, AZ 85287,USA. (phil.christensen@asu.edu)

C. J. Hardgrove and H. Y. McSween Jr., Department of Earth andPlanetary Sciences, University of Tennessee, 306 Earth and PlanetaryScience Bldg., Knoxville, TN 37996, USA. (chardgro@utk.edu; mcsween@utk.edu)N. P. Lang, Department of Geology, Mercyhurst College, 501 E. 38th St.,

Erie, PA 16546, USA. (nlang@mercyhurst.edu)L. L. Tornabene, Lunar and Planetary Laboratory, University of Arizona,

Tucson, AZ 85721, USA. (livio@lpl.arizona.edu)

LANG ET AL.: APOLLINARIS PATERA–GUSEV BASALT CONNECTION E04006E04006

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