Physics
Scientific paper
Nov 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983lpsc...14..165m&link_type=abstract
(American Geophysical Union and NASA, Lunar and Planetary Science Conference, 14th, Houston, TX, Mar. 14-18, 1983) Journal of Ge
Physics
8
Anorthosite, Breccia, Chemical Composition, Chronology, Lunar Crust, Lunar Rocks, Abundance, Argon Isotopes, Calcium, Feldspars, Gabbro, Potassium, Xenon Isotopes, Moon, Crust, Age, Composition, Clasts, Breccias, Samples, Lunar, 67915, Procedure, Chronology, Lithology, Anorthosites, Mineralogy, Abundance, Isotopic Ratios, Argon, Metamorphism, Photomicrographs, Isotopes, Xenon, Formation, Origin
Scientific paper
The composition and chronology of clasts representing three minor lithologies in consortium breccia 67915 are discussed. The lithologies studied are: sodic ferrogabbro, pristine troctolitic anorthosite (67915,26), and granulitic troctolitic anorthosite (67915,67). These lithologies were presumed to represent samples of the ancient lunar crust. The pristine troctolitic anorthosite, a typical member of the pristine anorthosite suite, contains little or no trapped liquid consistent with its two-phase mineralogy. The plagioclase separates have Ar-39-Ar-40 plateau ages of 4.10 + or - 0.06 b.y., and a final rise in the age pattern may represent a 'memory' of the earlier evolution. The granulitic troctolitic anorthosite, which has 13 times larger REE abundances, displays a continuous rise of the Ar-40/Ar-39 ratio. The last 25 percent of the Ar-39 release data establish a minimum age of over 3.5 b.y., but the Pu-244/Nd chronology suggests an age of about 4.3 b.y. The sodic ferrogabbro samples, which appear to be members of the Mg-gabbronorite group of pristine rocks, show large Ar losses but indicate plateaus in the low-temperature data, suggesting a metamorphic event more recently than 260 m.y. ago, a time that is consistent with the North Ray impact event 50 m.y. ago.
Aeschlimann U.
Eberhardt Peter
Geiss Johannes
Grägler N.
Jeffrey Taylor G.
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