[ { "id": "authors:808m1-61y13", "collection": "authors", "collection_id": "808m1-61y13", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131023-140546018", "type": "article", "title": "Initial Pb of the Am\u00eetsoq gneiss, West Greenland, and implications for the age of the Earth", "author": [ { "family_name": "Gancarz", "given_name": "A. J.", "clpid": "Gancarz-A-J" }, { "family_name": "Wasserburg", "given_name": "G. J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" } ], "abstract": "Pb isotopic abundances and U-Th-Pb concentrations are reported for feldspar megacrysts from the 3.59 AE old Am\u00eetsoq gneisses, Godthaab District, West Greenland. The distinctive Pb in the feldspars is the most primitive terrestrial Pb so far observed. It is observed in feldspars which are from different geographic localities and which exhibit varying degrees of deformation and recrystallization. This appear to be either the initial Pb in the Am\u00eetsoq gneiss or the initial Pb only slightly modified by subsequent metamorphism in a low ^(238)U/^(204)Pb environment. ^(238)U/^(204)Pb in the feldspars is low and the corrections for in situ produced Pb are only 0.4% for ^(207)Pb/^(206)Pb and 0.6% for ^(204)Pb/^(206)Pb. The mean corrected isotopic abundances are ^(204)Pb/^(206)Pb = 0.08720, ^(207)Pb/^(206)Pb = 1.1513, and ^(208)Pb/^(206)Pb = 2.7350. The feldspars contain a very small amount of easily leachable radiogenic Pb which is correlated with U and which indicates the formation of U-rich phases at about 2.7 AE. The matrix surrounding the feldspar megacrysts contains Pb which is much evolved relative to the megacrysts and this matrix does not appear to have behaved as a simple closed system. Element redistribution and open system behavior at about 2.7 AE is also suggested by Pb in feldspar from a dike cutting across the gneiss. Assuming that the Am\u00eetsoq gneiss feldspar Pb corrected for in situ U decay was the initial Pb in the gneiss at 3.59 AE (Baadsgaard, 1973), a single-stage \"age of the earth\" is determined as 4.47 \u00b1 0.05 AE and \u03bc is 8.5. This is indistinguishable from the single-stage age for modern rocks and is distinctly younger than the 4.55 AE age of some meteorites. If the feldspar Pb was modified by metamorphism at 2.7 AE the model age of the earth is calculated as 4.53 AE which is similar to the 4.55 AE age of some meteorites. Two-stage models using the nominal 3.59 AE initial Pb indicate that if the earth is ~4.55 AE old then \u03bc values were low in the early Earth's history and differentiation occurred within a few hundred million years after the planet formed.", "doi": "10.1016/0016-7037(77)90073-4", "issn": "0016-7037", "publisher": "Elsevier", "publication": "Geochimica et Cosmochimica Acta", "publication_date": "1977-09", "series_number": "9", "volume": "41", "issue": "9", "pages": "1283-1301" }, { "id": "authors:w9mz9-ga798", "collection": "authors", "collection_id": "w9mz9-ga798", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180315-083426044", "type": "article", "title": "The age and petrography of two Luna 20 fragments and inferences for widespread lunar metamorphism", "author": [ { "family_name": "Podosek", "given_name": "F. A.", "clpid": "Podosek-F-A" }, { "family_name": "Huneke", "given_name": "J. C.", "clpid": "Huneke-J-C" }, { "family_name": "Gancarz", "given_name": "A. J.", "clpid": "Gancarz-A-J" }, { "family_name": "Wasserburg", "given_name": "G. J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" } ], "abstract": "Ages were determined by the ^(40)Ar-^(39)Ar method on two metaclastic rocks returned from the lunar highlands north of Mare Fecunditatis by the Luna 20 probe. Both samples gave very well-defined argon retention ages of 3.90 \u00b1 0.04 AE which are indistinguishable from each other within a resolution of 0.02 AE. Both fragments, 22006 and 22007, are highly recrystallized polymict breccias; there is no evidence for loss of radiogenic ^(40)Ar, and the age almost surely dates the time of recrystallization. The cosmic ray exposure ages of these fragments are similar and high: 900 million years for 22006, 1300 million years for 22007. 22007 also contains substantial trapped argon with a high ^(40)Ar^(36)Ar ratio.\nThe Luna 20 results greatly extend the area of the Moon's surface exhibiting a well-defined record of metamorphism at 3.9 AE. So far, lunar history in the interval 4.6\u22123.9 AE is not preserved in the ages of surface rocks. This obliteration suggests lunar-wide metamorphic conditions occurring or terminating at this time as a result of major impacts.", "doi": "10.1016/0016-7037(73)90186-5", "issn": "0016-7037", "publisher": "Elsevier", "publication": "Geochimica et Cosmochimica Acta", "publication_date": "1973-04", "series_number": "4", "volume": "37", "issue": "4", "pages": "887-904" }, { "id": "authors:bfc0a-dx324", "collection": "authors", "collection_id": "bfc0a-dx324", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180313-073633736", "type": "article", "title": "Constrained least-squares analysis of petrologic problems with an application to lunar sample 12040", "author": [ { "family_name": "Reid", "given_name": "M. J.", "orcid": "0000-0001-7223-754X", "clpid": "Reid-M-J" }, { "family_name": "Gancarz", "given_name": "A. J.", "clpid": "Gancarz-A-J" }, { "family_name": "Albee", "given_name": "A. L.", "clpid": "Albee-A-L" } ], "abstract": "Many petrologic problems, which may be expressed as a set of linear equations, have been solved by least-squares analysis. In many cases insufficient attention has been paid to the physical conditions of the model resulting in incorrect application of the method. This paper presents a systematic treatment of the application of least-squares analysis to petrologic problems including the direct utilization of physical constraints and weighting factors in the problem, and the assessment of uncertainties in the solution. As an example, least-squares analysis is used to examine, in detail, the mass balance equations for lunar rock 12040 and to determine the consistency of the available analytical data.", "doi": "10.1016/0012-821X(73)90212-4", "issn": "0012-821X", "publisher": "Elsevier", "publication": "Earth and Planetary Science Letters", "publication_date": "1973-01", "series_number": "2", "volume": "17", "issue": "2", "pages": "433-445" }, { "id": "authors:pajwe-h2643", "collection": "authors", "collection_id": "pajwe-h2643", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180307-083914238", "type": "article", "title": "Comparative petrology of Apollo 16 sample 68415 and Apollo 14 samples 14276 and 14310", "author": [ { "family_name": "Gancarz", "given_name": "A. J.", "clpid": "Gancarz-A-J" }, { "family_name": "Albee", "given_name": "A. L.", "clpid": "Albee-A-L" }, { "family_name": "Chodos", "given_name": "A. A.", "clpid": "Chodos-A-A" } ], "abstract": "Petrographic and electron microprobe studies of Apollo 16 igneous rock 68415 and Apollo 14 rocks 14276 and 14310 show that all three samples differ from the mare basalts and are characterized by plagioclase as the first liquidus phase and by the abundance of plagioclase which is in part cumulate in origin. Major and minor element abundances and isotopic data prohibit the derivation of rocks like any of these samples from one another by magmatic fractionation during their crystallization. They could have originated by partial melting of an old, more Al-rich source material without isotopic equilibration with the residuum, by complete melting of three independent sources, or by contamination with old radiogenic material. The existence of such feldspathic basalts indicates that the generation of Al-rich magmas may have been an important and widespread lunar process.", "doi": "10.1016/0012-821X(72)90150-1", "issn": "0012-821X", "publisher": "Elsevier", "publication": "Earth and Planetary Science Letters", "publication_date": "1972-11", "series_number": "3", "volume": "16", "issue": "3", "pages": "307-330" }, { "id": "authors:pwa0y-hwm50", "collection": "authors", "collection_id": "pwa0y-hwm50", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180228-105651836", "type": "article", "title": "Mineralogy, petrology, and chemistry of a Luna 16 basaltic fragment, sample B-1", "author": [ { "family_name": "Albee", "given_name": "A. L.", "clpid": "Albee-A-L" }, { "family_name": "Chodos", "given_name": "A. A.", "clpid": "Chodos-A-A" }, { "family_name": "Gancarz", "given_name": "A. J.", "clpid": "Gancarz-A-J" }, { "family_name": "Haines", "given_name": "E. L.", "clpid": "Haines-E-L" }, { "family_name": "Papanastassiou", "given_name": "D. A.", "clpid": "Papanastassiou-D-A" }, { "family_name": "Ray", "given_name": "L.", "clpid": "Ray-L" }, { "family_name": "Tera", "given_name": "F.", "clpid": "Tera-F" }, { "family_name": "Wasserburg", "given_name": "G. J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" }, { "family_name": "Wen", "given_name": "T.", "clpid": "Wen-T" } ], "abstract": "Luna 16 sample B-1 was the largest fragment (62 mg) obtained in the sample exchange with the USSR. Petrologic, mineralogic, and chemical investigations have been made on this fragment in conjunction with Rb-Sr and ^(40)Ar/^(39)Ar investigations by our colleagues. Sample B-1 is a fine-grained ophitic basalt but is distinguished from the Apollo samples by containing a single pyroxene, predominantly pigeonitic, an ilmenite content (7%) intermediate to that of the Apollo 11 and 12 samples, and subequal amounts of pyroxene (50%) and plagioclase (40%). Chemically it is distinguished by a high Sr content (437 ppm) and a high K/U value (4700). The K-content (1396 ppm) is higher than that of Luna 16 soil sample A-2.", "doi": "10.1016/0012-821X(72)90110-0", "issn": "0012-821X", "publisher": "Elsevier", "publication": "Earth and Planetary Science Letters", "publication_date": "1972-01", "series_number": "2", "volume": "13", "issue": "2", "pages": "353-367" }, { "id": "authors:wrwhf-x2e12", "collection": "authors", "collection_id": "wrwhf-x2e12", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180228-104559203", "type": "article", "title": "Petrologic and mineralogic investigation of some crystalline rocks returned by the Apollo 14 mission", "author": [ { "family_name": "Gancarz", "given_name": "A. J.", "clpid": "Gancarz-A-J" }, { "family_name": "Albee", "given_name": "A. L.", "clpid": "Albee-A-L" }, { "family_name": "Chodos", "given_name": "A. A.", "clpid": "Chodos-A-A" } ], "abstract": "Apollo 14 crystalline rocks (14053 and 14310) and crystalline rock fragments (14001,7,1; 14001,7,3; 14073; 14167,8,1 and 14321,191,X-1) on which Rb/Sr, ^(40)Ar-^(39)Ar, or cosmic ray exposure ages have been determined by our colleagues were studied with the electron microprobe and the petrographic microscope. Rock samples 14053 and 14310 are mineralogically and petrologically distinct from each other. On the basis of mineralogic and petrologic characteristics all of the fragments, except 14001,7,1, are correlative with rock 14310. Sample 14073 is an orthopyroxene basalt with chemical and mineralogic affinities to 'KREEP', the 'magic' and 'cryptic' components. Fragment 14001,7,1 is very similar to Luny Rock I.", "doi": "10.1016/0012-821X(71)90050-1", "issn": "0012-821X", "publisher": "Elsevier", "publication": "Earth and Planetary Science Letters", "publication_date": "1971-09", "series_number": "1", "volume": "12", "issue": "1", "pages": "1-18" } ]