Oriented multiphase needles in garnet from ultrahigh-temperature granulites, Connecticut, U.S.A.
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Jennifer A. Axler
und
Jay J. Ague
Abstract
This study investigates distinctive oriented, needle-shaped multiphase inclusions found within cores of garnets from felsic granulites of the Upper Member of the Bigelow Brook Formation and the Brimfield Schist (northeastern Connecticut, U.S.A.). The rocks crop out in the southern end of the Central Maine Terrane and thus are a part of the Acadian/Neoacadian Orogen. The typical mineral assemblage is garnet + sillimanite + K-feldspar + plagioclase + quartz + cordierite + biotite ± spinel. The sillimanite is commonly pseudomorphous after kyanite.
The multiphase needle inclusions and associated exsolved needles of rutile and ilmenite are mostly oriented parallel to <111> of garnet. The multiphase needles contain various combinations of quartz, micas, chlorite, rutile, graphite, a siliceous compositionally variable phase (“Phase-CV”), Zn-spinel, apatite, zircon, and rare ilmenite. We hypothesize that they represent inclusions of fluid that adhered to exsolving Ti±Fe oxide needles (mostly rutile) or extended along zones of weakness in garnet. This requires that multiphase needle formation occurred in response to cooling and/or decompression. The needles ultimately decrepitated during retrogression. We note that micaceous needle-shaped multiphase inclusions are rarely described; the closest analogs of which we are aware are found in UHP garnets of the Erzgebirge (Perchuk 2008).
The Brimfield Schist in this area underwent ultrahigh-temperature metamorphism (UHTM) of ~1000 °C at a minimum pressure of ~1 GPa (Ague et al. 2013). Here we provide new temperature estimates for the adjacent Upper Member of the Bigelow Brook Formation. Ternary feldspar reintegration using the activity model of Benisek et al. (2004) and Zr-in-rutile thermometry (Tomkins et al. 2007) give average temperatures of ~990 and ~1010 °C, respectively, at 1 GPa for this unit. Therefore, the recently discovered UHT zone in the Brimfield Schist of northeastern Connecticut extends to the east to include the Upper Member of the Bigelow Brook Formation. Consequently, the first confirmed regional UHT locality in the United States is larger than initially recognized, and is at least 25 km long and 5-10 km wide. The oriented, elongate multiphase inclusions and petrographically obvious oriented Ti±Fe oxide needles may be useful indicators of extreme temperature and/or pressure rocks in other field areas.
© 2015 by Walter de Gruyter Berlin/Boston
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Artikel in diesem Heft
- Reaching new boundaries for in-situ U-Th geochronology
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- Phosphoran olivine overgrowths: Implications for multiple impacts to the Main Group pallasite parent body
- Diffusion of phosphorus in olivine and molten basalt
- Oceanic lavas sampling the high-3He/4He mantle reservoir: Primitive, depleted, or re-enriched?
- U-Th baddeleyite geochronology and its significance to date the emplacement of silica undersaturated magmas
- Polycrystallinity of green rust minerals and their synthetic analogs: Implications for particle formation and reactivity in complex systems
- Fe pre-enrichment: A new method to counteract iron loss in experiments on basaltic melts
- Fe-Mg diffusion in spinel: New experimental data and a point defect model
- Age, petrochemistry, and origin of a REE-rich mineralization in the Longs Peak-St. Vrain batholith, near Jamestown, Colorado (U.S.A.)
- Laser-induced breakdown spectroscopy (LIBS) as a tool for in situ mapping and textural interpretation of lithium in pegmatite minerals
- Evidence for Nb2+ and Ta3+ in silicate melts under highly reducing conditions: A XANES study
- Elastic softening of leucite and the lack of polar domain boundaries
- New thermobarometers for martian igneous rocks, and some implications for secular cooling on Mars
- An updated calibration of the plagioclase-liquid hygrometer-thermometer applicable to basalts through rhyolites
- Water effects on the anharmonic properties of forsterite
- Synthesis and structure of a stuffed derivative of α-quartz, Mg0.5AlSiO4
- Equation of state and elasticity of the 3.65 Å phase: Implications for the X-discontinuity
- Ca-Zn solid solutions in C2/c pyroxenes: Synthesis, crystal structure, and implications for Zn geochemistry
- Aluminum environments in synthetic Ca-Tschermak clinopyroxene (CaAlAlSiO6) from Rietveld refinement, 27Al NMR, and first-principles calculations
- Trioctahedral Fe-rich micas: Relationships between magnetic behavior and crystal chemistry
- High-pressure compressibility and phase stability of Mn-dolomite (kutnohorite)
- Composition dependence of spin transition in (Mg,Fe)SiO3 bridgmanite
- Oriented multiphase needles in garnet from ultrahigh-temperature granulites, Connecticut, U.S.A.
- Solubility and solution mechanisms of chlorine and fluorine in aluminosilicate melts at high pressure and high temperature
- Volatiles in magmas related to the Campanian Ignimbrite eruption: Experiments vs. natural findings
- Aluminosilicate melts and glasses at 1 to 3 GPa: Temperature and pressure effects on recovered structural and density changes
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- P-V-T equation of state and high-pressure behavior of CaCO3 aragonite
- A possible new Al-bearing hydrous Mg-silicate (23 Å phase) in the deep upper mantle
- Synthesis of large wadsleyite single crystals by solid-state recrystallization
- Decagonite, Al71Ni24Fe5, a quasicrystal with decagonal symmetry from the Khatyrka CV3 carbonaceous chondrite
- Earth’s “missing” minerals
- Magnetite-rutile symplectite derived from ilmenite-hematite solid solution in the Xinjie Fe-Ti oxide-bearing, mafic-ultramafic layered intrusion (SW China)
- New Mineral Names
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