Drawing from our results, we have found that

three of the four proposed hypotheses are not

consistent with our data.

There was no visual evidence of volcanic

features or structures in the majority of the

impact structures studied. Two craters

demonstrate fracturing within the crater floor but

there is no visible sign of volcanic material being

extruded from them. All identified PSA deposits

[6] have less than 5% mafic materials [10] – a feat

that would be exceedingly difficult to accomplish

by volcanism through a crust replete with mafic

material.

According to Pieters et al. [6], no known spinel

deposits are located in ejecta materials nor along

the crater floor. Mg-spinel deposits are locally

distributed and in small percentages in central

peaks and specific locales along the wall within

the crater structure.

33 of the 36 impact structures studied, did not

excavate material from depths of 10 kilometers or

greater (Figures 8-9). 10 km is the depth

necessary to attain the temperatures and

pressures that would form Mg-spinels by igneous

or metamorphic activity.

Based upon our results and those of Treiman

[12], we propose that the Mg-spinel deposits are

a result of an impact event into an anorthositic

crust with a near-surface mafic intrusion (i.e dike

swarm) (Fig. 9). The impact energy provides the

necessary pressure (>0.5kbar), temperature

(1300ºC) needed to melt the anorthositic crust

and the mafic intrusion, and thereby for spinel.

This spinel is then brought up to the lunar

surface through the central peak during the uplift

stage of crater formation.

36 of the analyzed spinel-bearing impact structures showed no evidence of volcanic structures

or features such as pyroclastic deposits, volcanoes, rilles, or domes within the crater walls,

crater floor, or central peak . Two structures (Dalton and Pitatus) demonstrate evidence

of fracturing in the crater floor but no evidence of volcanic materials being extruded from them.

No Mg-spinel deposits were found in impact ejecta [14] or nearby regions of any of the 36

structures analyzed.

26 of the studied impact structures with a central peak (30), excavated to depths ranging

between 3.5-9.0 kilometers. Four impact structures excavated at depths ranging from 9.7 -12.5

kilometers (Figure 8).

Excavation Depths as Indications of Magnesium

Spinel Formation via Impact MeltingGARNIER, Mikala, ESCHENFELDER, Jonas, FINTEL, Alysa,

Kickapoo High School, 3710 S. Jefferson Ave, Springfield, MO 65807

Introduction Research and Data Conclusions

References

AcknowledgementsRegion of StudyDr. Georgiana Kramer for her student mentoring on scientific analysis and critique of the methods of

science.

Dagmar Eschenfelder for her contributions on the understanding of the fundamentals and applications

of chemistry to the formation of magnesium spinels in the laboratory.

Dr. Oliver Stratmann and Dr. Stephan Will for their contributions on the physics and chemistry of

magnesium spinel formation and their review of scientific concepts and theories proposed in this

research.

Since the launch of Chandrayaan-1 on October

22, 2008, data from the Moon Mineralogy Mapper

(M3) has provided extensive insight into the

composition of the lunar surface. The latest

discovery was that of the pink-spinel anorthosite

(PSA). This new rock has a very unique

composition which consists of anorthosite, 20-

30% Mg-spinel (MgAl2O4), and less than 5% of

mafic materials [10]. The Mg-spinel in this

anorthosite requires certain conditions to form,

such as high pressures and high temperatures.

The spinel’s composition can only be achieved

by an interaction of a basaltic mix with the

anorthositic crust. Such interactions have been

hypothesized in four theories; volcanism,

impactor remnants, excavation, and impact

melting [6,7.9,12]. The purpose of this research

was to determine a plausible explanation for the

origin of these Mg-spinels by testing these four

hypotheses. Understanding the origin of Mg-

spinels can provide a more accurate explanation

of the origins and formation of this newly

identified rock type and a better understanding

of the construction of the lunar crust.

[1] Cintala, Mark, Richard A.F. Grieve. (1998). Scaling Impact melting and crater dimensions: Implications for the

lunar cratering record. Meteoritics & Planetary Science Volume 33, Issue 4, pages 889–912.

[2] Dhingra, Deepak, Carle M. Pieters, and James W. Head. (2014). Nature and distribution of olivine at

Copernicus Crater: new insights about origin from integrated high resolution mineralogy and imaging. Lunar

and Planetary Science Conference, 45, n. pag.

[3] Lal, D., et al. (2011). Identification of spinel group of minerals on central peak of crater Theophilus. Lunar and

Planetary Science Conference, 42, n. pag.

[4] Martel, Linda M. V. and G. Jeffrey Taylor. (2014). Moon’s Pink Mineral. Planetary Science Research

Discoveries, n. pag.

[5] Pieters, C. M. et al. (2011). Mg-spinel lithology: A new rock type on the lunar farside. Journal of Geophysical

Research, 116, 1-14.

[6] Pieters, Carle M, et al. (2014). The distribution of Mg-spinel across the Moon and constraints on crustal

origin. American Mineralogist. 99, 1893-1910.

[7] Prissel, T.C., et. al. (2014). Pink Moon: The petrogenesis of pink spinel anorthosites and implications

concerning mg-suite magmatism. Earth and Planetary Science Letters, 144-156.

[8] Prissel, T.C., et al. (2013). An uncollected member of the mg-suite: Mg-Al Pink spinel anorthosites and their

place on the Moon. Lunar and Planetary Science Conference, 44, n. pag.

[9] Prissel, T. C. et al. (2012). Melt-wallrock reactions on the Moon: Experimental constraints on the formation of

newly discovered Mg-spinel anorthosites. Lunar and Planetary Science Conference, 43, n. pag.

[10] Taylor, L.A. and C. M. Pieters. (2013) Pink-spinel anorthosite formation: considerations for a feasible

petrogenesis. Lunar and Planetary Science Conference, 44, n. pag.

[11] Sun, Y. et al. (2013). Detection of Mg-spinel bearing central peaks using M3 images. Lunar and Planetary

Science Conference, 44, n. pag.

[12] Treiman, A. H., et al. (2015). Lunar rocks rich in Mg-Al spinel: Enthalpy constraints suggest origins by

impact melting. Lunar and Planetary Science Conference, 46, n. pag.

[13] Wieczorek, Mark A. and Maria T. Zuber. (2001). The composition and origin of the lunar crust: constraints

from central peaks and crustal thinkness modeling. Geophysical Research Letters, 28(21), 4023-4026.

(14) Yue, Z. et al. (2013). Projectile remnants in central peaks of lunar impact craters. Nature Geoscience pg. 1-3.

(15) Croft, S.K. (1980), Cratering Flow Fields; Implications for the excavation and transient expansion stages of

crater formation. Lunar and Planetary Science Conf. 11th p. 2347-2378

Methodology

We analyzed 36 spinel-bearing craters [cf, 6] using

high-resolution images from the Lunar

Reconnaissance Orbiter Camera Narrow Angle

Camera. All 36 craters were analyzed to determine if

the spinel deposits were in close proximity to any

volcanic structures or features. We then analyzed

the ejecta material and nearby regions to determine

if any spinel deposits were located in the ejecta

blanket. The diameters of all 36 impact structures

analyzed in this study were obtained from the

Lunar Impact Crater Database

( http://www.lpi.usra.edu/resources/). We then

calculated the transient crater diameters (Dtc) using

the formula Dtc≈[DrDsc0.18]1/1.18 [, where Dr is the

final (measured) crater diameter and Dsc is the

diameter of the simple-to-complex transition (=

1.87x106 cm) [15]. We calculated the excavation

depths (de) using the formula de=Dtc*0.1 [1]. We

then compared our excavation depths to the depths

needed for the formation of Mg-spinel by deep-

seated plutons [8,9].

Figure 2: Joliot crater

Location: 25.9 93.4

Excavation Depth: 12.3 km

Crustal thickness: 25-35 km

Although this crater exceeds the 10 km boundary and could have

possibly been excavated, the crater is closely associated with

impact melt. This indicates that there is a direct relationship

between the impact and the extreme pressures and heat that is

needed for spinel formation.

Figure 3: Eudoxus crater

Location: 44.1 16.6

Excavation Depth: 5.7km

Crustal thickness: 30-40 km

This crater represents a crater with a shallow excavation depth.

The excavation depth is less than the required 10 km, proving that

spinels can form higher in the crust from the impactor providing

the necessary enthalpy rather than excavation.

Figure 4: Tycho Crater

Location: -43.3 -11.1

Excavation Depth: 6.7km

Crustal thickness: 25-35 km

Tycho is also closely associated with impact melt, which

indicates great heat and pressure from the impactor thus

reheating the basaltic dike and creating the specific chemistry

necessary for spinel formation. There is a single exposure of

spinel in the central peak of this crater.

Figure 9: This image depicts the intrusion of basaltic dike swarms in the subsurface of the lunar crust. It depicts the

10 km boundary necessary for spinel formation due to adequate temperatures and pressures. As the basaltic magma

reacts with the crustal chemistry, the extensive process of creating the magnesium spinels begin. [8]

Figure 5: Copernicus Crater

Location: 8.9 -19.5

Excavation Depth: 7.5km

Crustal thickness: 25-35

Copernicus has one single spinel located on a knob off the

central peak. This crater is a large impact with a final

diameter of 96.07 kilometers.

Figure 8: This graph depicts the 30 craters in which the spinels can be found in the central peaks. Prissel and his

colleagues concluded that 10 km is the boundary for magnesium spinels to be able to form by intruding plutons. The

reasoning behind this is that the conditions below this 10 km is a suitable forming environment due to the correct

temperatures (1300º C)and pressures (>.5kb). All but two of the craters we analyzed excavated materials closer to the

surface meaning that the magnesium spinels could not have been uplifted from that depth. [8,9].

Results

Figure 1: Distribution of craters studied in this research on the lunar nearside (left) and farside (right)

We’re gonna have to science the ‘poo out of this We’re gonna have to science the ‘poo out of this

Figure 6: Dalton Crater

Location: 17.1 -84.5

Excavation Depth: 5 km

Crustal thickness: 30-40 km

The

Figure 7: Ball Crater

Location: -39.9 -8.4

Excavation Depth: 3.6 km

Crustal thickness: 25-35 km

Ball crater is a small spinel-bearing craters located in the

southern hemisphere. The spinel is only located in the central

peak in this crater.