Pristine Highland Rocks Rock Names Ferroan anorthosite suite

Pristine Highland Rocks • Rock Names • Ferroan anorthosite suite • Mg-rich suite – – Troctolites Norites Gabbro-norites Others • Evolved Lithologies (Alkali suite) – – KREEP basalts Alkali anorthosites and other rocks “Granites” (felsites) Ferrobasaltic “rocks” Jeff Taylor Pristine Highland Rocks 1

Rock Names Le Maitre et al. (2002) Jeff Taylor Pristine Highland Rocks 2

Rock Names Le Maitre et al. (2002) Jeff Taylor Pristine Highland Rocks 3

Rock Names Le Maitre et al. (2002) Jeff Taylor Pristine Highland Rocks 4

Three Suites of Highland Igneous Rocks • Distinctive groups on plots involving Mg# [molar Mg/(Mg+Fe)] vs An in plagioclase (or other variants of that) • Ferro-anorthosites: Mg# < 75 (most < 65) • Plagioclase is very rich in Ca (high anorthite content) FAN suite Chap 2, New Views of the Moon Jeff Taylor Pristine Highland Rocks 5

Three Suites of Highland Igneous Rocks Jeff Taylor Pristine Highland Rocks 6

Three Suites of Highland Igneous Rocks Jeff Taylor Pristine Highland Rocks 7

Three Suites of Highland Igneous Rocks Jeff Taylor Pristine Highland Rocks 8

Three Suites of Highland Igneous Rocks Jeff Taylor Pristine Highland Rocks 9

Three Suites of Highland Igneous Rocks Jeff Taylor Pristine Highland Rocks 10

Three Suites of Highland Igneous Rocks Jeff Taylor Pristine Highland Rocks 11

Ferroan Anorthosite Suite • Most > 85 vol% plagioclase – Many 99 vol% – Some only 70 -80 vol% Warren (1993) Jeff Taylor Pristine Highland Rocks 12

Ferroan Anorthosite Suite 0. 5 mm 15415 • Some anorthosites (like 15415) have remnant cumulate texture, but have been granulated (sheared), and then metamorphosed. • Shows complex history of highlands crust. • Complex history makes it difficult to date the rocks. Jeff Taylor Pristine Highland Rocks 13

Anorthosite 62236: Remnant texture preserved in places 0. 5 mm Jeff Taylor Pristine Highland Rocks 14

Anorthosite clast 67915, 137: Cumulate texture still visible, though rock is shocked. Jeffmm Taylor 0. 25 Pristine Highland Rocks 15

Anorthosite clast 67915, 137: Cumulate texture still visible, though rock is shocked. Jeffmm Taylor 0. 25 Pristine Highland Rocks 16

Anorthosite 60025: Rock crushed, but there are mafic-rich regions, exsolution in pyroxene, big crystals. 0. 5 cm Jeff Taylor Pristine Highland Rocks 17

Ferroan Anorthosite Suite • Anorthosite suite can be subdivided another way: – Mafic magnesian • > 11 vol% mafic silicates • Mg# > 65 – Anorthositic, ferroan • Mg# < 65 • These most abundant – Anorthsitic, sodic • Plag has An 94 -95 vs An>95 for the others – Mafic ferroan • > 8 vol% mafic silicates • Mg# < 55 James et al. (1989) Jeff Taylor Pristine Highland Rocks 18

Ferroan Anorthosite Suite Orthopyroxene • Trends of minor and trace element concentrations in orthopyroxene, augite, and plagioclase in FAS rocks more complicated than a simple case of crystallization in a single fractionating magma. – No magma ocean? – Or a complicated magma ocean? • Concentrations in ppm (except for mg#) Jeff Taylor Floss et al. (1998) Pristine Highland Rocks 19

Plotting Rare Earth Elements Abundances in CI chondrites Anders E. and Grevesse N. (1989) Abundances of the elements: Meteoritic and solar. Geochim. et Cosmochim. Acta 53, 197 -214. http: //epsc. wustl. edu/admin/resources/chondritic_abundances. html Jeff Taylor Pristine Highland Rocks 20

Plotting Rare Earth Elements • • • REE plotted in order of increasing atomic number and decreasing ionic radius Smoothed out by dividing conc by conc in CI chondrites Can be normalized to something else (e. g. , suspected parent magma) Jeff Taylor Pristine Highland Rocks 21

Ferroan Anorthosite Suite • Large positive Eu anomalies on REE plots • Normalized concentrations fairly low (1 -2 x chondrites) Jeff Taylor Pristine Highland Rocks 22

REE in Plagioclase Jeff Taylor Pristine Highland Rocks 23

Trace Element Behavior • For dilute solutions, like trace elements, we can use D, the distribution coefficient: CS is the concentration of an element in the solid (mineral). CL is the concentration of an element in the liquid (magma). • Incompatible elements have D << 1 • Compatible elements have D >> 1 Jeff Taylor Pristine Highland Rocks 24

REE Partition Coefficients La Ce Nd Olivine. 0001 Sm Eu Gd Dy Er Yb Lu . 0006. 0007. 003. 008. 019. 03 Jeff Taylor Plagioclase Orthopyroxene. 042. 007. 0302. 009. 0236. 014. 017 1. 2. 0105. 0089. 0077. 0065. 0068 Pristine Highland Rocks . 022. 015. 037. 06. 10. 17. 22 25

REE in Parent Magmas Jeff Taylor Pristine Highland Rocks 26

Mg Suite (a. k. a. Magnesian Suite) • Diverse in – Mineral abundances – Mineral compositions – Bulk compositions • More mafic than ferroan anorthosite suite • Rock types: – – Dunite: >90% olivine Troctolites: half olivine, half plagioclase Norites: half low-Ca pyroxene, half plagioclase Gabbro-norites: half (about) plagioclase, low-Ca pyroxene about equal to augite (richer in alkali elements cf norites, troctolites) Jeff Taylor Pristine Highland Rocks 27

Mg-rich Suite Bulk compositions Mineral compositions Higher mg#, Mg. O, and Fe. O than rocks in the ferroan anorthosite suite. Jeff Taylor Pristine Highland Rocks 28

Highland Igneous Rocks Courtesy of Josh Cahill Jeff Taylor Pristine Highland Rocks 29

Mg-rich Suite 0. 5 mm Dunite 72415 Jeff Taylor Pristine Highland Rocks 30

0. 5 mm Norite 76266 Jeff Taylor Pristine Highland Rocks 31

Mg-rich Suite • Gabbro-norites – High-Ca pyroxene about equal in abundance as low. Ca pyroxene – Higher in Ti and Ti/Sm than other Mg-suite rocks – Richer in alkali elements— many are classified as members of the alkalic suite – REE similar to norites and abundance seems to be correlated with Mg# Jeff Taylor Pristine Highland Rocks 67915, 193 ~2 mm across 32

Mg-rich Suite Mg-suite rocks have higher REE than ferroan anorthosites. Gabbro-norites have similar REE contents as norites Troctolites Norites Troctolites Jeff Taylor Norites Pristine Highland Rocks 33

Mg-Suite Parent Magmas Jeff Taylor Pristine Highland Rocks 34

Mg-Suite Parent Magmas Jeff Taylor Pristine Highland Rocks 35

Alkali Suite • KREEP basalts – Definition of “KREEP” – Nature of the rocks • Alkali suite (anorthosites, norites, gabbro-norites) • Granites (felsites) • Ferrobasaltic “rocks” Jeff Taylor Pristine Highland Rocks 36

Alkali Suite Jeff Taylor Pristine Highland Rocks 37

Alkali Suite Jeff Taylor Pristine Highland Rocks 38

Alkali Suite Jeff Taylor Pristine Highland Rocks 39

KREEP • KREEP is a distinctive chemical component in some lunar rocks (both highlands and mare basalts)—it is not a rock type • Gets its name from enrichments in incompatible elements, such as K, REE, P, Zr, U, Th • Its REE pattern is surprisingly uniform in rocks containing the KREEP signature • May be late-stage fractional crystallization product of the magma ocean Jeff Taylor Chondrite-normalized La/Lu = 2. 2 Pristine Highland Rocks Data from Warren, 1989 40

KREEP basalts • High contents of trace elements • Typical KREEP rare earth pattern Jeff Taylor Pristine Highland Rocks 41

KREEP basalts • Classic volcanic texture: rock 15386 0. 5 mm Jeff Taylor 15386 Pristine Highland Rocks 42

KREEP basalts Texture similar to terrestrial basalts (specifically similar to pahoehoe). 0. 5 mm 15386 Jeff Taylor Hawaiian pahoehoe Pristine Highland Rocks 43

KREEP basalts • Composed mostly of plagioclase and pigeonite • Pyroxenes typical of basaltic compositions, trending from pigeonite to subcalcic augite to augite Jeff Taylor Pristine Highland Rocks 44

KREEP basalts • A-15 KREEP basalts appear to be an igneous system—they plot along a cotectic • A-15 KREEP basalts show an extensive low-P fractional crystallization sequence, ending with a rock called the quartz monzodiorite • A-17 KREEP basalts not related to A-15, but only limited sampling Jeff Taylor Pristine Highland Rocks 45

KREEP basalts: Quartz Monzodiorite • Found at Apollo 14 and 15 • Evolved composition: – High REE – High Fe/Mg • Fractional crystallization product of KREEP basalt • Suggests alkalic rocks can be formed by fractionation of a KREEP basalt magma Jeff Taylor 1 mm Pristine Highland Rocks 46

Alkali Suite • • Alkali Anorthosites > 90% plagioclase (more or less) Plagioclase is very sodic, by lunar standards High REE and have typical KREEP patterns Rich in phosphate minerals (which is where REE reside) Jeff Taylor Mafic Alkalic Rocks • Gabbro-norites and norites • Really are plagioclaserich mafic cumulates • Anorthosites and granites only from Apollo 12, 14, and 15, but mafic ones from A-16 and 17, too (western and eastern near side) Pristine Highland Rocks 47

Jeff Taylor Pristine Highland Rocks 48

“Granites” Kspar Qtz Kspar 0. 5 mm Jeff Taylor Pristine Highland Rocks 49

Granites • Not really coarse-grained rocks like terrestrial granites, and they do not compose huge intrusions —should be called “felsites. ” – Biggest is a 1. 9 -gram fragment in a breccia! – But they do have some coarse, graphic intergrowths consisting of quartz and albite • REE pattern not exactly KREEP-like 1 mm Jeff Taylor Pristine Highland Rocks 50

Ferrobasaltic Rocks • Found as fine-grained melts or even glasses • Rich in Fe. O (> 25 wt%) • Very rich in REE • Formation likely to have involved silicate liquid immiscibility, which may have produced felsites at the same time Jeff Taylor Pristine Highland Rocks 51

Ferrobasalts – Felsite Pair Jeff Taylor Pristine Highland Rocks 52

Parent Magmas (from Plagioclase) Jeff Taylor Pristine Highland Rocks 53

Terrestrial Continents Continental crust/primitive mantle = 30 Upper crust/primitive mantle = 55 Granite/primitive mantle = 100 Moon evolved rocks/lunar primitive mantle = 1000 Jeff Taylor Pristine Highland Rocks 54