Apollo 17 regolith, 71501,262: A record of impact events and mare volcanism in lunar glasses

Abstract

Twelve impact glasses that span a wide compositional range have been found to record ages ranging from 102 ± 20 Ma to 3740 ± 50 Ma. The compositions of these impact glasses show that some have been produced by impact events within the Apollo 17 region, whereas others appear to be exotic to the landing site. As the data sets that include compositions and ages of lunar impact glasses increase, the impact history in the Earth-Moon system will become better constrained.

Moon's volcanic history revealed in glassy spherules from Apollo 17 soil 76501

“…When corrected for terrestrial Pb, these three VLT analyses define a concordia age of 3671 AE 53 Ma (MSWD = 0.017, probability = 0.9). That would agree with the 40 Ar/ 39 Ar age of 3630 AE 40 Ma reported for an Apollo 17 VLT glass by Zellner et al (2009). This date was interpreted as the crystallization age of an evolved magma to account for its very low MgO/Al 2 O 3 (0.59) and compositional proximity to a magmatic line of descent.…”

Moon's volcanic history revealed in glassy spherules from Apollo 17 soil 76501

“…When corrected for terrestrial Pb, these three VLT analyses define a concordia age of 3671 AE 53 Ma (MSWD = 0.017, probability = 0.9). That would agree with the 40 Ar/ 39 Ar age of 3630 AE 40 Ma reported for an Apollo 17 VLT glass by Zellner et al (2009). This date was interpreted as the crystallization age of an evolved magma to account for its very low MgO/Al 2 O 3 (0.59) and compositional proximity to a magmatic line of descent.…”

Lunar Impact Glasses: Probing the Moon's Surface and Constraining its Impact History

“…Results of 40 Ar/ 39 Ar studies indicate that impact spherules are more likely to be young and thus reflect recent impact events, in agreement with reported 40 Ar/ 39 Ar ages (e.g., Culler et al, 2000;Hui, 2011;Levine et al, 2005) and the U-Th-Pb "chemical ages" (e.g., Nemchin et al, 2013;Norman et al, 2012Norman et al, , 2013Zellner et al, 2013). The impact glass shards, on the other hand, represent impact events with ages than span the history of the Moon (Figure 4).…”

“…Several impact glasses collected at each of the Apollo 14, 16, and 17 landing sites have formation ages of ~800 My (Zellner et al, ), and similar ages are seen in samples from the Apollo 12 landing site (e.g., Barra et al, ; Levine et al, ). Though these impact samples may be attributed to the Copernicus event (e.g., Bogard et al, ), the samples were collected at four widely separated landing sites (i.e., several hundred kilometers distant from each other), and geochemical signatures of the Apollo 14 and 16 impact glasses show that at least a few of them originated in different terrains.…”

“…In general, studies of lunar impact glasses should include major‐ and trace‐element compositions, 40 Ar/ 39 Ar ages (including an assessment of the quality of the age data; e.g., “good,” “fair,” “poor”; see supporting information S1), sizes, and shapes (e.g., Nguyen & Zellner, ; Zellner et al, , ; Zellner & Delano, ). Quantitative constraints for choosing appropriate samples for 40 Ar/ 39 Ar analyses based on composition and size have been suggested (e.g., minimum size of 200 μm; Nguyen & Zellner, ; Zellner & Delano, ) because of the dependence of Ar retention on these parameters and the diffusive effect of diurnal heating (e.g., Gombosi et al, ; Lee, ; Mysen & Richet, ; Zellner & Delano, ).…”

“…Compared to the 40 Ar/ 39 Ar ages of impact glass spherules (Culler et al, 2000;Levine et al, 2005), the derived U-Th-Pb chemical ages of impact glass spherules also show a preponderance of ages <500 My old. However, Zellner et al (2013) found no such trend in the recent impact flux (see Section 2.2.3) when including 40 Ar/ 39 Ar ages of both spherules and shards (Section 3).…”

Moon's volcanic history revealed in glassy spherules from Apollo 17 soil 76501

“…When corrected for terrestrial Pb, these three VLT analyses define a concordia age of 3671 AE 53 Ma (MSWD = 0.017, probability = 0.9). That would agree with the 40 Ar/ 39 Ar age of 3630 AE 40 Ma reported for an Apollo 17 VLT glass by Zellner et al (2009). This date was interpreted as the crystallization age of an evolved magma to account for its very low MgO/Al 2 O 3 (0.59) and compositional proximity to a magmatic line of descent.…”

Lunar Impact Glasses: Probing the Moon's Surface and Constraining its Impact History

“…Results of 40 Ar/ 39 Ar studies indicate that impact spherules are more likely to be young and thus reflect recent impact events, in agreement with reported 40 Ar/ 39 Ar ages (e.g., Culler et al, 2000;Hui, 2011;Levine et al, 2005) and the U-Th-Pb "chemical ages" (e.g., Nemchin et al, 2013;Norman et al, 2012Norman et al, , 2013Zellner et al, 2013). The impact glass shards, on the other hand, represent impact events with ages than span the history of the Moon (Figure 4).…”

“…Several impact glasses collected at each of the Apollo 14, 16, and 17 landing sites have formation ages of ~800 My (Zellner et al, ), and similar ages are seen in samples from the Apollo 12 landing site (e.g., Barra et al, ; Levine et al, ). Though these impact samples may be attributed to the Copernicus event (e.g., Bogard et al, ), the samples were collected at four widely separated landing sites (i.e., several hundred kilometers distant from each other), and geochemical signatures of the Apollo 14 and 16 impact glasses show that at least a few of them originated in different terrains.…”

“…In general, studies of lunar impact glasses should include major‐ and trace‐element compositions, 40 Ar/ 39 Ar ages (including an assessment of the quality of the age data; e.g., “good,” “fair,” “poor”; see supporting information S1), sizes, and shapes (e.g., Nguyen & Zellner, ; Zellner et al, , ; Zellner & Delano, ). Quantitative constraints for choosing appropriate samples for 40 Ar/ 39 Ar analyses based on composition and size have been suggested (e.g., minimum size of 200 μm; Nguyen & Zellner, ; Zellner & Delano, ) because of the dependence of Ar retention on these parameters and the diffusive effect of diurnal heating (e.g., Gombosi et al, ; Lee, ; Mysen & Richet, ; Zellner & Delano, ).…”

“…Compared to the 40 Ar/ 39 Ar ages of impact glass spherules (Culler et al, 2000;Levine et al, 2005), the derived U-Th-Pb chemical ages of impact glass spherules also show a preponderance of ages <500 My old. However, Zellner et al (2013) found no such trend in the recent impact flux (see Section 2.2.3) when including 40 Ar/ 39 Ar ages of both spherules and shards (Section 3).…”

Moon's volcanic history revealed in glassy spherules from Apollo 17 soil 76501

“…When corrected for terrestrial Pb, these three VLT analyses define a concordia age of 3671 AE 53 Ma (MSWD = 0.017, probability = 0.9). That would agree with the 40 Ar/ 39 Ar age of 3630 AE 40 Ma reported for an Apollo 17 VLT glass by Zellner et al (2009). This date was interpreted as the crystallization age of an evolved magma to account for its very low MgO/Al 2 O 3 (0.59) and compositional proximity to a magmatic line of descent.…”

Lunar Impact Glasses: Probing the Moon's Surface and Constraining its Impact History

“…Results of 40 Ar/ 39 Ar studies indicate that impact spherules are more likely to be young and thus reflect recent impact events, in agreement with reported 40 Ar/ 39 Ar ages (e.g., Culler et al, 2000;Hui, 2011;Levine et al, 2005) and the U-Th-Pb "chemical ages" (e.g., Nemchin et al, 2013;Norman et al, 2012Norman et al, , 2013Zellner et al, 2013). The impact glass shards, on the other hand, represent impact events with ages than span the history of the Moon (Figure 4).…”

“…Several impact glasses collected at each of the Apollo 14, 16, and 17 landing sites have formation ages of ~800 My (Zellner et al, ), and similar ages are seen in samples from the Apollo 12 landing site (e.g., Barra et al, ; Levine et al, ). Though these impact samples may be attributed to the Copernicus event (e.g., Bogard et al, ), the samples were collected at four widely separated landing sites (i.e., several hundred kilometers distant from each other), and geochemical signatures of the Apollo 14 and 16 impact glasses show that at least a few of them originated in different terrains.…”

“…In general, studies of lunar impact glasses should include major‐ and trace‐element compositions, 40 Ar/ 39 Ar ages (including an assessment of the quality of the age data; e.g., “good,” “fair,” “poor”; see supporting information S1), sizes, and shapes (e.g., Nguyen & Zellner, ; Zellner et al, , ; Zellner & Delano, ). Quantitative constraints for choosing appropriate samples for 40 Ar/ 39 Ar analyses based on composition and size have been suggested (e.g., minimum size of 200 μm; Nguyen & Zellner, ; Zellner & Delano, ) because of the dependence of Ar retention on these parameters and the diffusive effect of diurnal heating (e.g., Gombosi et al, ; Lee, ; Mysen & Richet, ; Zellner & Delano, ).…”

“…Compared to the 40 Ar/ 39 Ar ages of impact glass spherules (Culler et al, 2000;Levine et al, 2005), the derived U-Th-Pb chemical ages of impact glass spherules also show a preponderance of ages <500 My old. However, Zellner et al (2013) found no such trend in the recent impact flux (see Section 2.2.3) when including 40 Ar/ 39 Ar ages of both spherules and shards (Section 3).…”