Beryllium in Antarctic Ultrahigh-Temperature Granulite-Facies Rocks and its Role in Partial Melting of the Lower Continental Crust

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Title: Beryllium in Antarctic Ultrahigh-Temperature Granulite-Facies Rocks and its Role in Partial Melting of the Lower Continental Crust

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Text: Geologic evolution of the Napier Complex began in the Early Archean (3800 Ma) prior to a regional ultrahigh temperature metamorphic event (up to 7-11 kbar, 1050-1120 degrees C) sometime between 2550 and 2480 Ma, after which metamorphic and igneous activity was largely confined to mafic dike emplacement and amphibolite to granulite-facies events at 1600 Ma, ~1000-900 Ma and 540-520 Ma along the periphery and in highly localized shear zones. U-Pb isotopic data reported in the literature for zircon from a pegmatite (sample #2233) and for monazite from a paragneiss at "Zircon Point", Khmara Bay, gave upper and lower intercept ages of 2400-2500 Ma and ~1100 Ma, respectively. Electron microprobe age determinations from monazite-(Ce) in pegmatites and quartz granulites show considerable micrometer-scale age heterogeneity. Monazite-(Ce) grains in the pegmatites are coarse (1 to 5 cm) and exhibit considerable chemical variation (up to 28 wt% ThO2). Th, U, and Pb compositional maps of these coarse monazites show sector and growth zoning, but apparent age maps exhibit no consistent age domains. Apparent age variations are continuous with a few scattered, slightly older domains. Chemical ages from 5 micrometers spots vary from 2352 +/-85 Ma to 800 +/-40 Ma and are observed to vary as much as 400 Ma in apparent age over a 30 micrometer distance. Alkali feldspars in contact with monazite-(Ce) grains are strongly enriched in Pb. An aureole 2 to 4 mm thick surrounding the monazite-(Ce) contains 0.2 to 2.0 wt% PbO, and K-feldspar included in monazite-(Ce) contains up to 9.9 wt% PbO. Monazite-(Ce) grains from quartz granulites range from 20 to 100 micrometers and tend to be more uniform in composition (6 - 8 wt% ThO2 and 0.6 to 1 wt% PbO). They have higher Y and have measurable HREE contents. Apparent age maps exhibit scattered, uniformly old apparent age domains (~2400 +/-100Ma). They also have both linear and irregular, variable apparent age domains, varying from 1650 to 2010 Ma. We attribute the chronological heterogeneity to partial lead loss during a late-Proterozoic event at ~1100 Ma that resulted in partial lead loss. Lead from the pegmatitic monazite-(Ce) diffused into contiguous alkali feldspar. Where there are linear zones of low apparent age, lead loss may have been controlled by fractures, whereas irregular micron-scale heterogeneity suggests recrystallization. TEM investigations of monazite-(Ce) at the sub-micron scale are underway to evaluate these two alternatives. --- Makarochkinite, a new beryllosilicate mineral of the aenigmatite group. Together with J. Barbier, E.P. Shcherbakova and others I have succeeded in obtaining approval of makarochkinite, Ca2Fe2+4Fe3+TiSi4BeAlO20, as new mineral species from the Commission on New Minerals and Mineral Names, International Mineralogical Association (number 2002-009). Validation of makarochkinite as a mineral distinct from i is part of a larger crystallographic study of beryllosilicate members of the aenigmatite group and related minerals, including beryllian sapphirine, khmaralite, surinamite and welshite. A manuscript is currently presently being written up; a portion of this study has been accepted for oral presentation at the 32nd International Geological Congress in Florence, Italy, August, 2004. In both makarochkinite and hogtuvaite, the one Be per formula unit is evenly divided between the T1 and T4 (Q3) sites so that Be-O-Be bridges are minimized. Ca and Na occupy the 7-coordinated M8 and M9 sites, and Mg together with Fe occupy the M1-6 octahedral sites without evidence of strong ordering in either case. The shorter average M7-O distances (2.03 angstroms) and the associated Ueq displacement parameters led to assign all Ti to the M7 octahedral sites in both structures, together with Fe3+ and other minor high-valent elements. As a result, the M7 site occupancy in makarochkinite (59% Ti + 37% Fe) establishes it as a distinct mineral and also distinguishes it from hogtuvaite (70% Fe + 24% Ti). In contrast to makarochkinite and hogtuvaite, surinamite has only one T site joined to three others (so-called Q3 site), and this T site is fully occupied by Be, with negligible Be on other T sites. Welshite contains more Be than either makarochkinite or hogtuvaite, and we are currently trying to refine Be occupancy of this complex mineral. --- Beryllium and boron minerals in Indian granulite-facies rocks. The Eastern Ghats belt of southeastern India is an ultrahigh-temperature granulite-facies terrain having many similarities to the Napier Complex; moreover, these two terrains are believed to have been juxtaposed in Gondwana reassemblies. For these reasons, a report of surinamite, a beryllosilicate found in Napier Complex anatectic pegmatites, attracted my interest. A study of the Eastern Ghats surinamite paragenesis would be highly relevant to my project on beryllium and its minerals in the Napier Complex. However, no surinamite was found either by me or by one co-author of the original report. My conclusion that the reported surinamite was misidentified hypersthene was published in Current Science. In the course of studying rocks from the locality where surinamite was reported to occur, I discovered prismatine, a new locality for India, and this find was published in Mineralogical Magazine.

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REFERENCE: Journal Publications: Asami, A., Suzuki, K. and Grew, E.S. (2002) Chemical Th-U-total Pb dating by electron microprobe analysis of monazite, xenotime and zircon from the Archean Napier Complex, East Antarctica: Evidence for ultra-high-temperature metamorphism at 2400Ma. Precambrian Research, 114, 249-275 Barbier, J., Grew, E.S., Halenius, E.,Halenius, U. and Yates, M.G. (2002) The role of Fe and cation order in the crystal chemistry of surinamite, (Mg,Fe2+)3(Al,Fe3+)3O[AlBeSi3O15]: A crystal structure, Moessbauer spectroscopic, and optical spectroscopic study. Am. Mineral., 87, 501-513 Christy, A.G., Tabira, Y., Holscher, A., Grew, E. S., and Schreyer, W. (2002) Synthesis of beryllian sapphirine in the system MgO-BeO-Al2O3-SiO2-H2O and comparison with naturally occurring beryllian sapphirine and khmaralite. Part 1: Experiments, TEM and XRD. American Mineralogist, v. 87, p. 1104-1112 Christy, A.G. and Grew. E.S. (2004) Synthesis of beryllian sapphirine in the system MgO-BeO-Al2O3-SiO2-H2O and comparison with naturally occurring beryllian sapphirine and khmaralite. Part 2: a chemographic study of Be content as a function of P, T, assemblage and FeMg-1 exchange. American Mineralogist 89, 327-338. Ren, L., Grew, E.S., Xiong, M., and Ma, Z. (2003) Wagnerite-Ma5bc, a new polytype of Mg2(PO4)(F,OH) from granulite-facies paragneiss, Larsemann Hills, Prydz Bay, East Antarctica.  Canadian Mineralogist, 41, 393-411. Grew, E.S., Rao, A.T., Raju, K.K.V.S., Hejny, C., Moore, J.M., Waters, D.J., Yates, M.G., Shearer, C.K. (2003) Prismatine and ferrohogbomite-2N2S in granulite-facies Fe- oxide lenses in the Eastern Ghats Belt at Venugopalapuram, Vizianagaram district, Andhra Pradesh, India: do such lenses have a tourmaline-enriched lateritic precursor? Mineralogical Magazine, 67, 1081-1098. Asami, A., Suzuki, K. and Grew, E.S. (in press) Th-U-total Pb monazite and zircon ages from Alasheyev Bight to the Sør Rondane Mountains, East Antarctica: Constraints on the position of the Mozambique suture in eastern Queen Maud Land. Journal of Geology. Book(s) of other one-time publications(s): Grew, E. S. (2002) Mineralogy, petrology and geochemistry of beryllium: An introduction and list of beryllium minerals. In Grew, E. S., ed. Beryllium: Mineralogy, Petrology, and Geochemistry. Reviews in Mineralogy and Geochemistry, Mineralogical Society of America, no. 50, p. 1-76 Grew, E. S. (2002) Beryllium in metamorphic environments (emphasis on aluminous compositions). In Grew, E. S., ed. Beryllium: Mineralogy, Petrology, and Geochemistry. Reviews in Mineralogy and Geochemistry, Mineralogical Society of America, no. 50, p. 487-549

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Theme_Keyword: EARTH SCIENCE > SOLID EARTH > ROCKS/MINERALS/CRYSTALS > ELEMENTS > MAJOR ELEMENTS

Theme_Keyword: EARTH SCIENCE > SOLID EARTH > ROCKS/MINERALS/CRYSTALS > ELEMENTS > TRACE ELEMENTS

Theme_Keyword: EARTH SCIENCE > SOLID EARTH > ROCKS/MINERALS/CRYSTALS > IGNEOUS ROCKS

Theme_Keyword: EARTH SCIENCE > SOLID EARTH > ROCKS/MINERALS/CRYSTALS > METAMORPHIC ROCKS

Theme_Keyword: EARTH SCIENCE > SOLID EARTH > ROCKS/MINERALS/CRYSTALS > MINERALS

Theme_Keyword: ELECTRON MICROPROBES

Theme_Keyword: ION MICROPROBES

Theme_Keyword: Boron

Theme_Keyword: Beryllium

Theme_Keyword: Lithium

Theme_Keyword: B

Theme_Keyword: Be

Theme_Keyword: Li

Theme_Keyword: Partial Melting

Theme_Keyword: Continental Crust

Theme_Keyword: Granulites

Theme_Keyword: Pegmatitic Leucosomes

Theme_Keyword: Mineralogy

Theme_Keyword: Metamorphism

Theme_Keyword: Napier Complex

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Place_Keyword: CONTINENT > ANTARCTICA > ENDERBY LAND

Place_Keyword: GEOGRAPHIC REGION > POLAR

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Contact_Organization: UMAINE/DES > Department of Earth Sciences, University of Maine

Contact_Person: EDWARD GREW

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Metadata_Review_Date: 20100707

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Contact_Person: EDWARD GREW

Contact_Position: DIF AUTHOR

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Address_Type: Mailing and Physical Address

Address: Department of Geological Sciences

Address: University of Maine

Address: 5790 Bryand Research Center

City: Orono

State_or_Province: ME

Postal_Code: 04469-5790

Country: US

Contact_Voice_Telephone: +1 207 581 2169

Contact_Facsimile_Telephone: +1 207 581 2202

Contact_Electronic_Mail_Address: esgrew@maine.edu

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