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We applied SHRIMP zircon U-Pb age dating to ultrahigh-temperature (UHT) sapphirine-bearing orthopyroxene garnet (SOG) granulite and biotite-hornblende (Bt-Hbl) gneiss in the Schirmacher Hills, East Antarctica. In the Bt-Hbl gneiss, concordant ages of 657 ± 7.1 and 807 ± 9.1 Ma were obtained from zircon overgrowth rims and zircon cores, with oscillatory and irregular zoning, respectively. The zircon overgrowth rims (657 ± 7.1 Ma) with low Th/U ratios from the Bt-Hbl gneiss are interpreted as having a metamorphic origin. Oscillatory-zoned and/or irregularly zoned zircon cores may have crystallized during an igneous event at 807 ± 9.1 Ma; 800-Ma igneous events have not previously been recognized in central Dronning Maud Land (DML) inland nunatak. Zircons in the SOG granulite yielded a concordant age of 643 ± 6.5 Ma, using analyses of sector-zoned and simple-zoned grains. These zircons have relatively high Th/U ratios with a narrow range, and they occur in association with garnet breaking down to form cordierite. The 643 ± 6.5-Ma age obtained from these zircons is interpreted as the timing of crystallization from a high-Th/U partial melt soon after peak metamorphism. The combination of a ca. 800-Ma igneous age and 660-640-Ma metamorphic ages obtained from Schirmacher Hills is different from that of other neighboring parts of central DML. In addition, a metamorphic PT path involving ultrahigh temperatures at early and subsequent isobaric cooling (IBC) stages at around 650 Ma has not previously been known in the central DML nunatak region. The Ca. 650-Ma UHT metamorphic event probably occurred in a back-arc tectonic setting and predates the main collisional event of central DML (ca. 550-500 Ma). [ABSTRACT FROM AUTHOR]

U-Pb zircon dating indicates that the Balugaon Anorthosite Massif of the Chilka Lake Domain, Eastern Ghats Belt, India, crystallized at 983.0 ± 2.5 Ma, ∼200 m.yr. earlier than previously inferred from ferrodiorite that intruded the massif. An integration of the new date with published structural data indicates that the anorthosite intruded a crust that was deformed twice before the intrusion. Furthermore, U-Th-Pb chemical dating of monazite cores (714 ± 11 Ma) and rims (655 ± 12 Ma) yields results consistent with progressive high-grade metamorphism of the anorthosite, and monazite + allanite rims (463 ± 22 Ma) around apatite indicate low-grade pan-African thermal activity. The 714- 655-Ma dates possibly correspond to convergence and oblique collision between the Eastern Ghats-Rayner Block and western Australia in the mid-Neoproterozoic. [ABSTRACT FROM AUTHOR]

Ages based on electron microprobe analysis using the chemical Th-U-total Pb isochron method (CHIME) were determined for monazite and zircon in 12 granulite-facies paragneiss samples from four exposures on or near the coast of East Antarctica: Mt. Vechernyaya (Alasheyev Bight; 46° E, Rayner Complex), East Ongul Island (39°35' E, Lützow- Holm Complex), the southernmost Yamato Mountains (36° E, Yamato-Belgica Complex), and the Sør Rondane Mountains (23°-28° E). Monazite occurs in textural equilibrium with silicate minerals in all samples and as inclusions in garnet in three of these and is presumed to have crystallized under granulite-facies conditions. Most of the analyzed monazite grains appear to be chronologically homogeneous, but many others are markedly zoned. The CHIME ages on rims of the latter range from 514 ± 27 to 553 ± 11 Ma, consistent with ages on the apparently homogeneous grains, 517 ± 14 to 544 ± 5 Ma. Apparent ages on cores of the zoned grains range from 620 to 760 Ma, and in a few cases, CHIME ages can be extracted, the youngest of which are 628 ± 32 and 622 ± 11 Ma. Ages obtained on the rims of zircons texturally coexisting with monazite range from 485 ± 58 to 530 ± 17 Ma, whereas ages of the cores show bimodal distribution with peaks at about 730 and 1100 Ma. The CHIME ages clustering around ∼530 Ma are interpreted to date the granulite-facies events in the four study areas, an interpretation supported by SHRIMP data on zircon from these areas. The Neoproterozoic ages on monazite cores suggest the intriguing possibility that the area between 45° E (west of Alasheyev Bight) and 25° E (within the Sør Rondane Mountains) constitutes a Cambrian monometamorphic belt in which sediments were deposited during the Neoproterozoic or early Cambrian with much less involvement of older rocks; i.e., the Mozambique suture could pass between 45° E and 25° E. [ABSTRACT FROM AUTHOR]

Analyzes the dating of single zircon grains from granite cuttings from southeastern Georgia. Age of the granite; Composition; Implications of the new data to the Suwannee terrane subcrop age province boundaries.

Presents an uranium-lead isotope study of zircon and titanite from rocks in and around the Ramagiri Schist Belt of the eastern Dharwar Craton, India, to determine the geological history of the terranes that constitute the belt. Inference of the minimum age of the crust's magmatic precursors; Evidence for accretionary origin of the eastern Dharwar Craton.

Studies the zircons in metasediments and metaigneious rocks from six widely separated localities throughout the Lutzow-Holm Complex (HLC) and two locations from the Yamato-Belgica Complex (YBC). Ion microprobe dating of zircons; Cambrian organic belt in East Antarctica; Correlation with Sri Lankan complexes; Significance of Sri Lanka in Godwana reconstruction.