Edward S. Grew

Carbonaceous Material in Some Metamorphic Rocks of New England and Other Areas

Carbonaceous material in regionally metamorphosed coal, black slate, graphite schist, and mica schist shows the following continuous changes with increasing metamorphic grade: increase in particle size; loss of hydrogen, nitrogen, and oxygen ; increase in the carbon content; a decrease in the peak width of the (002) reflection; and a shift of the (002) reflection to a higher

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 2400 Ma

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Needs and opportunities in mineral evolution research

position. These changes are greatest in the chlorite zone, where distinct (111) lines replace an unmodulated (111) band. In this study, only carbonaceous material from the staurolite and sillimanite zones is pure carbon. A large extent of layer ordering is acquired in the chlorite and biotite zones, but well-ordered graphite, comparable with Ceylon graphite, is limited to the sillimanite zone. There is little growth in the carbonaceous particles until the staurolite zone; in lower-grade zones, they rarely exceed 0.02 mm. The temperature at which layer ordering first appears in regionally metamorphosed rock is roughly 300°-500° (P = 3 kbar or more) ; in the laboratory it is 1,500°-2,000° (P ~ 1 bar). Well-ordered graphite probably formed at 660°-690° and 4.5-5.0 kbar in the Narragansett basin, Rhode Island. Complete graphitization of heat-treated carbons in the laboratory usually requires temperatures of 2,500°-3,600° (P ~ 1 bar). The relatively low temperatures of graphitization in metamorphic rocks, compared with the temperatures required for the process in the laboratory, might be due to the greater hydrostatic pressure, to deformation, to duration of heat treatment, to silicate minerals acting as catalysts, and to an ambient fluid phase under pressure.

Monazite and Zircon Dating by the Chemical Th‐U‐Total Pb Isochron Method (CHIME) from Alasheyev Bight to the Sør Rondane Mountains, East Antarctica: A Reconnaissance Study of the Mozambique Suture in Eastern Queen Maud Land

Abstract Uranium-lead and thorium-lead ages were obtained from perrierite and zircons in two samples from the Eastern Ghats Province of South India, a sapphirine-bearing granulite from Anakapalle and a charnockite from Visakhapatnam. The isotopic data are concordant or close to concordant at 1 Ga, which is interpreted to be the age of granulite-facies metamorphism and charnockite plutonism in the vicinity of Anakapalle and Visakhapatnam, and provides the first report of a late Proterozoic granulite-facies event in the Eastern Ghats Province. In reassemblies of Gondwanaland based on DuToits original proposal, the Eastern Ghats Province is juxtaposed against a high-grade terrain in East Antarctica affected by a granulite-facies event and charnockitic plutonic activity 800–1100 Ma ago. The ages reported here suggest that a portion of the Eastern Ghats Province represents an extension of the late Proterozoic terrain from Antarctica into India. The radiometric results on the Anakapalle rocks are the first evidence in South India for sapphirine formation during the late Proterozoic; other South Indian sapphirine localities appear to be Archaean in age. A review of sapphirine localities in the Indo-Antarctic metamorphic terrain indicates that sapphirine developed under a range of pressure-temperature conditions during the Archaean and Proterozoic. Evidence for a systematic change in peak metamorphic conditions with time is obscured by these regional variations. Characterization of the entire pressure-temperature path, in addition to estimates for the peak conditions, is needed to distinguish the Archaean and Proterozoic metamorphic regimes.

U-Pb data on granulite facies rocks from fold island, Kemp Coast, East Antarctica

Abstract The chemical Th–U–total Pb isochron method (CHIME) of dating was carried out on monazite, xenotime, zircon, and polycrase in six samples of ultra-high-temperature (UHT) granulites and one of pegmatite from five localities in the Napier Complex, Enderby Land, East Antarctica. Despite the chronological heterogeneity in many grains, the CHIME ages overall show strong evidence for a major event near 2420 Ma. Analyzed monazite and xenotime grains, except monazite from Mt. Riiser-Larsen, have a narrow range of CHIME ages: 2412±42 Ma from Beaver Island and 2429±36, 2421±18 and 2431±22 Ma from Reference Peak. These ages are indistinguishable from CHIME ages on zircon (2436±17 and 2420±20 Ma) and on central older domains of monazite (2404±54 Ma) from Mt. Riiser-Larsen, and on a zircon rim (2430±15 Ma) from Mt. Cronus. We conclude that the ca. 2420 Ma ages relate to the UHT metamorphism, but we do not exclude the possibility that lead loss has lowered the ages by some 50 Ma. This interpretation is consistent with a preponderance of ages obtained by other methods on the Napier Complex particularly the ca. 2475±25 Ma age for a generation of pegmatites coeval with the UHT event and containing the UHT mineral assemblage beryllian sapphirine–khmaralite+quartz. Events prior to 2500 Ma and after 2420 Ma have also left their imprint on the CHIME ages, for example, a 3646 Ma CHIME age suggests that a zircon core is inherited, whereas ca. 2200 and 2000 Ma CHIME ages in zoned monazite could be due to further lead loss during post-UHT activity. The much younger CHIME age of 1094±67 Ma for monazite from a pegmatite at ‘Zircon Point’, Casey Bay, confirms 1000–1100 Ma lead loss ages reported for this region, and could result from fluid activity in an outlier of Rayner activity near the boundary between the Rayner and Napier Complexes. Approximately 2500 Ma ages have been reported from granulite-facies (but not UHT) rocks in the Madras and Nilgiri blocks in South India; these blocks and the Napier Complex could have constituted a single structural unit by late Archean time.

Mercury (Hg) mineral evolution: A mineralogical record of supercontinent assembly, changing ocean geochemistry, and the emerging terrestrial biosphere

Abstract Tourmaline has recently been shown to incorporate large amounts of substituent B at the tetrahedral site. To characterize the response of the tourmaline atomic arrangement to differing amounts of substitution of B for Si, five samples were separated from a core-to-rim (∼3 mm) section of an Fe-bearing olenite with a dark green core and a nearly colorless rim from Koralpe, Austria. Crystal structures of the five samples were refined to R values <0.018 using three-dimensional X-ray methods, and the compositions of the crystals were determined by electron microprobe, secondary ion mass spectrometric, and Mössbauer analyses. From core to rim, [4]B increases monotonically from 0.35 to 0.65 apfu, whereas the mean T-O distance decreases from 1.621 to 1.610 Å. Optimized formulae using chemical and structural data range from X(Na0.632Ca0.145⃞0.223) Y(Al1.320Fe2+1.202Li0.190Mg0.086Ti0.028Mn2+0.024⃞0.150) ZAl6.00 B3.00T(Si5.525B0.333Al0.130Be0.012) O27 [(OH)3.19O0.81] (core composition) to X(Na0.408Ca0.290K0.002⃞0.300) Y(Al2.338Li0.365Fe2+0.084Mn2+0.009Mg0.005Ti0.005⃞0.194) ZAl6.00 B3.00T(Si4.989B0.615Al0.362Be0.034) O27 [(OH)3.41O0.59] (rim composition). The variation of chemistry and structure, coupled with short-range order constraints, demonstrates that (1) the average tetrahedral bond length () reflects the substitution of [4]B, (2) tourmaline samples with relatively high Fe2+ contents (ca. 1 apfu Fe2+) and distances up to 1.621 Å can contain significant amounts of [4]B (up to ca. 0.3 apfu), (3) the presence of substantial [4]B is limited to, or more common in Al-rich tourmalines, (4) the presence of [4]B substituents favors OH at the O3 site, (5) the presence of Ca or Na at the X site is not simply correlated with occupancy of [4]B in the adjacent tetrahedral ring, and (6) no two B-substituted tetrahedra will link through bridging O atoms.

Boralsilite, Al16B6Si2O37, and “boron-mullite:” Compositional variations and associated phases in experiment and nature

Abstract Progress in understanding mineral evolution, Earth’s changing near-surface mineralogy through time, depends on the availability of detailed information on mineral localities of known ages and geologic settings. A comprehensive database including this information, employing the mindat.org web site as a platform, is now being implemented. This resource will incorporate software to correlate a range of mineral occurrences and properties vs. time, and it will thus facilitate studies of the changing diversity, distribution, associations, and characteristics of individual minerals as well as mineral groups. The Mineral Evolution Database thus holds the prospect of revealing mineralogical records of important geophysical, geochemical, and biological events in Earth history.

Boralsilite (Al 16 B 6 Si 2 O 37 ); a new mineral related to sillimanite from pegmatites in granulite-facies rocks

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 \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape