Major lunar crustal terranes: Surface expressions and crust‐mantle origins

In light of global remotely sensed data, the igneous crust of the Moon can no longer be viewed as a simple, globally stratified cumulus structure, composed of a flotation upper crust of anorthosite underlain by progressively more mafic rocks and a residual-melt (KREEP) sandwich horizon near the base of the lower crust. Instead, global geochemical information derived from Clementine multispectral data and Lunar Prospector gamma-ray data reveals at least three distinct provinces whose geochemistry and petrologic history make them geologically unique: (1) the Procellarum KREEP Terrane (PKT), (2) the Feldspathic High-lands Terrane (FHT), and (3) the South Pole-Aitken Terrane (SPAT). The PKT is a mafic province, coincident with the largely resurfaced area in the Procellarum-Imbrium region whose petrogenesis relates to the early differentiation of the Moon. Here, some 40% of the Th in the Moon's crust is concentrated into a region that constitutes only about 10% of the crustal volume. This concentration of Th (average ∼5 ppm), and by implication the other heat producing elements, U and K, led to a fundamentally different thermal and igneous evolution within this region compared to other parts of the lunar crust. Lower-crustal materials within the PKT likely interacted with underlying mantle materials to produce hybrid magmatism, leading to the magnesian suite of lunar rocks and possibly KREEP basalt. Although rare in the Apollo sample collection, widespread mare volcanic rocks having substantial Th enrichment are indicated by the remote data and may reflect further interaction between enriched crustal residues and mantle sources. The FHT is characterized by a central anorthositic region that constitutes the remnant of an anorthositic craton resulting from early lunar differentiation. Basin impacts into this region do not excavate significantly more mafic material, suggesting a thickness of tens of kilometers of anorthositic crust. The feldspathic lunar meteorites may represent samples from the anorthositic central region of the FHT. Ejecta from deep-penetrating basin impacts outside of the central anorthositic region, however, indicate an increasingly mafic composition with depth. The SPAT, a mafic anomaly of great magnitude, may include material of the upper mantle as well as lower crust; thus it is designated a separate terrane. Whether the SPA basin impact simply uncovered lower crust such as we infer for the FHT remains to be determined.

[1]  L. Haskin.  The Imbrium impact event and the thorium distribution at the lunar highlands surface , 1998 .

[2]  A. E. Ringwood,et al.  A dynamic model for mare basalt petrogenesis , 1976 .

[3]  G. Ryder.  Lunar ferroan anorthosites and mare basalt sources: The mixed connection , 1991 .

[4]  W. Boynton,et al.  A lunar meteorite found outside the Antarctic , 1991, Nature.

[5]  G. Layne,et al.  Ion microprobe investigation of plagioclase and orthopyroxene from lunar Mg-suite norites: Implications for calculating parental melt REE concentrations and for assessing postcrystallization REE redistribution , 1996 .

[6]  G. Ryder,et al.  Serenitatis and Imbrium impact melts - Implications for large-scale layering in the lunar crust , 1977 .

[7]  J. Wood.  Bombardment as a cause of the lunar asymmetry , 1973 .

[8]  R. Korotev.  Some things we can infer about the Moon from the composition of the Apollo 16 regolith , 1997 .

[9]  Richard E. Lingenfelter,et al.  Analysis and interpretation of lunar laser altimetry. , 1972 .

[10]  R. Korotev,et al.  Lunar meteorite Queen Alexandra Range 93069 and the iron concentration of the lunar highlands surface , 1996 .

[11]  David W. Hughes,et al.  Books-Received - the Geology of Multi-Ring Impact Basins - the Moon and Other Planets , 1993 .

[12]  R. Korotev.  Concentrations of radioactive elements in lunar materials , 1998 .

[13]  G. J. Taylor,et al.  Abundance and Distribution of Iron on the Moon , 1995, Science.

[14]  S. Keihm,et al.  The Revised Lunar Heat Flow Values , 1976 .

[15]  David A. Morrison,et al.  Did a Thick South Pole-Aitken Basin Melt Sheet Differentiate to Form Cumulates? , 1998 .

[16]  Carle M. Pieters,et al.  Mineralogy of the lunar crust: Results from Clementine , 1999 .

[17]  J. Laul.  Chemistry of the Apollo 12 highland component , 1986 .

[18]  P. Spudis,et al.  Beginning and end of lunar mare volcanism , 1983, Nature.

[19]  R. Reedy,et al.  Lunar Surface Radioactivity: Preliminary Results of the Apollo 15 and Apollo 16 Gamma-Ray Spectrometer Experiments , 1973, Science.

[20]  David E. Smith,et al.  Topography of the Moon from the Clementine lidar , 1997 .

[21]  A. Binder,et al.  Lunar Prospector: overview. , 1998, Science.

[22]  K. Rasmussen,et al.  Megaregolith insulation, internal temperatures, and bulk uranium content of the moon , 1987 .

[23]  J. McCauley,et al.  Geologic Map of the Near Side of the Moon , 1971 .

[24]  I. S. Mccallum,et al.  Stratigraphy of the lunar highland crust: Depths of burial of lunar samples from cooling-rate studies , 1996 .

[25]  David E. Smith,et al.  The Shape and Internal Structure of the Moon from the Clementine Mission , 1994, Science.

[26]  David E. Smith,et al.  The lunar crust: Global structure and signature of major basins , 1996 .

[27]  R. Radocinski,et al.  Thorium concentrations in the lunar surface. I - Regional values and crustal content , 1977 .

[28]  D. Lindstrom,et al.  Apollo 12 ropy glasses revisited , 1994 .

[29]  G. Kallemeyn,et al.  Compositional implications regarding the lunar origin of the ALHA81005 Meteorite , 1983 .

[30]  Roger J. Phillips,et al.  Potential anomalies on a sphere: Applications to the thickness of the lunar crust , 1998 .

[31]  J. McCauley,et al.  Geological provinces of the near side of the moon , 1971 .

[32]  R. Korotev.  The great lunar hot spot and the composition and origin of the Apollo mafic (“LKFM”) impact‐melt breccias , 2000 .

[33]  De Hon.  Thickness of the western mare basalts. , 1979 .

[34]  R. Korotev,et al.  A ferroan region of the lunar highlands as recorded in meteorites MAC88104 and MAC88105 , 1991 .

[35]  N. Grevesse,et al.  Abundances of the elements: Meteoritic and solar , 1989 .

[36]  G. J. Taylor,et al.  The complex stratigraphy of the highland crust in the Serenitatis region of the Moon inferred from mineral fragment chemistry , 1997 .

[37]  Stephen J. Keihm,et al.  Lunar Thermal Regime to 500 KM , 1977 .

[38]  P. Spudis,et al.  A chemical and petrological model of the lunar crust , 1986 .

[39]  P. C. Hess,et al.  A model for the thermal and chemical evolution of the Moon's interior: implications for the onset of mare volcanism , 1995 .

[40]  H. Haack,et al.  Megaregolith insulation and the duration of cooling to isotopic closure within differentiated asteroids and the Moon , 1990 .

[41]  L. Taylor,et al.  Petrologic constraints on the origin of the Moon , 1984 .

[42]  M. Lindstrom.  Alkali gabbronorite, ultra‐KREEPy melt rock and the diverse suite of clasts in North Ray Crater feldspathic fragmental breccia 67975 , 1984 .

[43]  J. J. Gillis,et al.  Geology of the Smythii and Marginis region of the Moon: Using integrated remotely sensed data , 2000 .

[44]  D. Vaniman,et al.  Lunar highland melt rocks - Chemistry, petrology and silicate mineralogy , 1980 .

[45]  L. Taylor,et al.  Chronology and petrogenesis of the lunar highlands alkali suite: Cumulates from KREEP basalt crystallization , 1995 .

[46]  Paul H. Warren,et al.  Geochemical investigation of two lunar mare meteorites: Yamato-793169: and Asuka-881757 , 1993 .

[47]  Carle M. Pieters,et al.  Tsiolkovsky crater: A window into crustal processes on the lunar farside , 1999 .

[48]  Carle M. Pieters,et al.  Mineralogy of the Mafic Anomaly in the South Pole‐Aitken Basin: Implications for excavation of the lunar mantle , 1997 .

[49]  Roger J. Phillips,et al.  The “Procellarum KREEP Terrane”: Implications for mare volcanism and lunar evolution , 2000 .

[50]  J. Wasson,et al.  Contribution of the mantle to the lunar asymmetry , 1980 .

[51]  D. Lindstrom,et al.  Lunar meteorite Yamato-791197: A polymict anorthositic norite breccia , 1986 .

[52]  R. Korotev,et al.  Geochemistry of 2-4-mm particles from Apollo 14 soil (14161) and implications regarding igneous components and soil-forming processes , 1991 .

[53]  Thomas H. Prettyman,et al.  High resolution measurements of absolute thorium abundances on the lunar surface , 1999 .

[54]  B. Jolliff.  Large-Scale Separation of K-frac and REEP-frac in the Source Regions of Apollo Impact-Melt Breccias, and a Revised Estimate of the KREEP Composition , 1998 .

[55]  L. Taylor,et al.  Processes involved in the formation of magnesian‐suite plutonic rocks from the highlands of the Earth's Moon , 1995 .

[56]  D. Lindsley,et al.  The Apollo 15 yellow impact glasses: Chemistry, petrology, and exotic origin , 1982 .

[57]  David E. Smith,et al.  The Clementine Mission to the Moon: Scientific Overview , 1994, Science.

[58]  J. Longhi,et al.  Two-stage models for lunar and terrestrial anorthosites Petrogenesis without a magma ocean , 1985 .

[59]  Paul G. Lucey,et al.  FeO and TiO2 concentrations in the South Pole‐Aitken basin: Implications for mantle composition and basin formation , 1998 .

[60]  R. Phillips,et al.  Lunar Multiring Basins and the Cratering Process , 1999 .

[61]  A. Metzger,et al.  Lunar highland crustal models based on iron concentrations - Isostasy and center-of-mass displacement , 1980 .

[62]  M. Lindstrom,et al.  Apennine Front revisited - Diversity of Apollo 15 highland rock types , 1988 .

[63]  P. Spudis,et al.  Chemical composition and origin of Apollo 15 impact melts , 1987 .

[64]  J. Wasson,et al.  Further foraging for pristine nonmare rocks - Correlations between geochemistry and longitude , 1980 .

[65]  J. J. Gillis,et al.  Lateral and Vertical Heterogeneity of Thorium in the Procellarum KREEP Terrane: As Reflected in the Ejecta Deposits of Post-Imbrium Craters , 1999 .

[66]  S. Maurice,et al.  Global elemental maps of the moon: the Lunar Prospector gamma-Ray spectrometer. , 1998, Science.

[67]  Paul H. Warren,et al.  Megaregolith thickness, heat flow, and the bulk composition of the Moon , 1985, Nature.

[68]  Paul D. Spudis,et al.  Ancient Multiring Basins on the Moon Revealed by Clementine Laser Altimetry , 1994, Science.

[69]  P. Schultz.  Forming the South-Pole Aitken Basin: The Extreme Games , 1997 .

[70]  Paul G. Lucey,et al.  Mapping the FeO and TiO2 content of the lunar surface with multispectral imagery , 1998 .