Precambrian(?) Crystallization and Permian(?) Metamorphism of Hypersolvus Granite in the Avalonian Terrane of Rhode Island

Day, Howard W.; Brown, Vernon; Abraham, K.

doi:10.1130/gsab-p2-91-1669

Cited by 6 publications

(4 citation statements)

References 0 publications

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“…5b,d). The monophase aggregates presumably represent former coarse (>1 cm) igneous grains of feldspar and quartz, which are common throughout the less deformed interior of the Scituate granite pluton (Quinn, 1971; Day et al ., 1980).…”

Section: Mylonitic Gneisssupporting

confidence: 58%

Diffusion creep and partial melting in high temperature mylonitic gneisses, Hope Valley shear zone, New England Appalachians, USA

Garlick¹,

Gromet²

2004

Journal Metamorphic Geology

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Field, petrographic, microstructural and isotopic studies of mylonitic gneisses and associated pegmatites along the Hope Valley shear zone in southern Rhode Island indicate that late Palaeozoic deformation (c. 275 Ma) in this zone occurred at very high temperatures (>650°C). High-energy cuspate ⁄ lobate phase boundary microstructures, a predominance of equant to sub-equant grains with low internal lattice strain, and mixed phase distributions indicate that diffusion creep was an important and possibly predominant deformation mechanism. Field and petrographic evidence are consistent with the presence of an intergranular melt phase during deformation, some of which collected into syntectonic pegmatites. Rb ⁄ Sr isotopic analyses of tightly sampled pegmatites and wall rocks confirm that the pegmatites were derived as partial melts of the immediately adjacent, isotopically heterogeneous mylonitic gneisses. The presence of syntectonic interstitial melts is inferred to have permitted a switch from dislocation creep to melt-enhanced diffusion creep as the dominant mechanism in these relatively coarse-grained mylonitic gneisses (200-500 lm syn-deformational grain size). A switch to diffusion creep would lead to significant weakening, and may explain why the Hope Valley shear zone evolved into a major regional tectonic boundary. This work identifies conditions under which diffusion creep operates in naturally deformed granitic rocks and illuminates the deformation processes involved in the development of a tectonic boundary between two distinct Late Proterozoic (Avalonian) basement terranes.

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Section: Mylonitic Gneisssupporting

confidence: 58%

Diffusion creep and partial melting in high temperature mylonitic gneisses, Hope Valley shear zone, New England Appalachians, USA

Garlick¹,

Gromet²

2004

Journal Metamorphic Geology

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“…with low Mg biotites from alkaline environments reported by Day et al (1980). The biotites show low sodium content in the alkali site varying from 0'036 to 0,246.…”

Section: Ai3+ Fe3~ti 4 + Fe2+znz+ Mn2+mentioning

confidence: 70%

Geochemistry of coexisting hornblende and biotite from the Ambalavayal granite, Kerala

Santosh

1986

J Earth Syst Sci

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Major and trace element geochemistry of coexisting hornblendes and biotites from the Ambalavayal granite, northern Kerala, are presented. The hornblendes correspond to edenitic composition, whereas the biotites co~'respond to annite. The hornblendes typically show high A1203 contents (9'69-11.89 %) comparable with those from anorogenic granites. The biotites are characteristically low Mg-type, similar to those reported from alkaline rocks. The distribution coetticients calculated for all the major and trace elements are presented and an evaluation of the nature of variation indicate near-chemical equilibrium conditions during the crystallization of the two minerals. The hornblende-biotite tie lines in the Fe 3 +-Fe2÷-Mg compositional triangle, lie parallel to those of buffered biotites, indicating crystallization in an environment closed to oxygen and well above the Ni-NiO buffer. It is inferred that thefH20 increased towards the residual stage and fO2 values were high, in the range of 10-15 bars.

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“…Within the Scituate granite gneiss of central Rhode Island (Fig. 1) the grade of metamorphism increases from northeast to southwest (Day et al, 1980). In northwest Rhode Island, where kyanite is present, the Hope Valley Shear zone is characterized by amphibolite-grade ductile deformation.…”

Section: Alleghanian Metamorphismmentioning

confidence: 99%

“…1). In western Rhode Island, two-feldspar geothermometry yields minimum temperatures of about 450" C (Day et al, 1980;Simpson & Wintsch, 1989).…”

Section: Alleghanian Metamorphismmentioning

confidence: 99%

Fluid inclusion evidence for basement decompression during Permo‐Triassic extension, SE New England, USA

O’Hara

1991

Journal Metamorphic Geology

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C0,-bearing fluid inclusions in strongly lineated but weakly foliated late Precambrian gneisses within the Hope Valley Shear zone of Connecticut and Rhode Island are of mixed composition (Xco2=0.1; 7 wt% NaCl equivalent) and variable density (0.59-0.86 g/ml) and occur mainly as isolated inclusions. Also present are dilute (3 wt% NaCl equivalent) aqueous inclusions which occur on healed fractures related to greenschist facies retrograde metamorphism. Isochores for dense isolated C0,-bearing inclusions indicate pressures of 7.5-9 kbar at 500-600" C, the estimated temperature conditions of peak metamorphism. Published 4oAr/39Ar hornblende plateau age spectra indicate cooling through about 500" C at 265 f 5 Ma. Isochores for low-density C0,-bearing inclusions and aqueous inclusions intersect at the conditions of retrograde metamorphism (325-400" C) and indicate pressures of 3-4 kbar. Published 40Ar/39Ar biotite plateau ages indicate cooling through about 300" C at 250 f 5 Ma. These data define a P -T uplift curve for the region which is convex towards the temperature axis and indicate uplift rates between 0.4 and 3.3 mm/year in Permian time. Exhumation of basement gneisses was coeval with normal (west-down) motion along the regional basement-cover contact (Honey Hill-Lake Char-Willimantic fault system), and is interpreted as due to post-orogenic extensional collapse of the Alleghanian orogeny.

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Precambrian(?) Crystallization and Permian(?) Metamorphism of Hypersolvus Granite in the Avalonian Terrane of Rhode Island

Cited by 6 publications

References 0 publications

Diffusion creep and partial melting in high temperature mylonitic gneisses, Hope Valley shear zone, New England Appalachians, USA

Diffusion creep and partial melting in high temperature mylonitic gneisses, Hope Valley shear zone, New England Appalachians, USA

Geochemistry of coexisting hornblende and biotite from the Ambalavayal granite, Kerala

Fluid inclusion evidence for basement decompression during Permo‐Triassic extension, SE New England, USA

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