Experimental investigation of the formation of cordierite-orthopyroxene parageneses in pelitic rocks

Hoffer, E.; Grant, J. A.

doi:10.1007/bf00376257

Cited by 46 publications

(19 citation statements)

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“…These cordierites have no subsolidus metamorphic history, and thus could possibly be euhedral and free of inclusions. Other reactions, most of which are dehydration melting reactions (Hensen and Green, 1973;Green 1976;Abbott and Clarke, 1979;Hoffer and Grant, 1980;Grant 1985 et al, 1985). (d) Garnet with reaction rim of Type 2b cordierite in Violet Town volcanics (after Wall, 1984).…”

Section: Magmatic --Formation As the Results Of Solid-melt Reactions Tmentioning

confidence: 99%

Cordierite in felsic igneous rocks: a synthesis

Clarke

1995

Mineral. mag.

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Cordierite is a characteristic mineral of many peraluminous felsic igneous rocks. A combination of T-P-X parameters, which overlap the stability conditions for felsic magmas, control its formation. Critical among these parameters are relatively low T, low P, and typically high (Mg+Fe2 § Mg/Fe 2+, A/CNK, aAl20~, and fo2.Spatial and textural information indicate that cordierite may originate in one of three principal ways in felsic igneous rocks: Type 1 Metamorphic: (a) xenocrystic (generally anhedral, many inclusions, spatial proximity to country rocks and pelitic xenoliths); (b) restitic (generally anhedral, high-grade metamorphic inclusions); Type 2 Magmatic: (a,b) peritectic (subhedral to euhedral, associated with leucosomes in migmatites or as reaction rims on garnet); (c) cotectic (euhedral, grain size compatibility with host rock, few inclusions); (d) pegmatitic (large subhedral to euhedral grains, associated with aplite-pegmatite contacts or pegmatitic portion alone); and Type 3 Metasomatic (spatially related to structural discontinuities in host, replacement of feldspar and/or biotite, intergrowths with quartz). Of these, Type 2a (peritectic) and Type 2c (cotectic) predominate in granitic and rhyolitic rocks derived from fluid-undersaturated peraluminous magmas, and Type 2d (pegmatitic) may be the most common type in fluid-saturated systems.

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Section: Magmatic --Formation As the Results Of Solid-melt Reactions Tmentioning

confidence: 99%

Cordierite in felsic igneous rocks: a synthesis

Clarke

1995

Mineral. mag.

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“…Likewise, the lack of biotite breakdown to orthopyroxene provides a constraint. Biotite stability increases with increased Mg/Mg+Fe and Altola1 (Hewitt & Wones, 1984) Hoffer & Grant, 1980). Rare metasediments in the Central Gneiss Complex contain apparently retrograded garnets; garnet-biotite geothermometry on these gives temperatures (Ferry & Spear, 1978) between 600°C and 650°C.…”

Section: Metamorphic Conditions In the Cgc Boca De Quadramentioning

confidence: 99%

Migmatite structures in the Central Gneiss Complex, Boca de Quadra, Alaska

Mclellan

1988

Journal Metamorphic Geology

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Abstract. Migmatite structures in the Coast Plutonic-Metamorphic Complex are well exposed in the inlet of Boca de Quadra, southeast Alaska. Two types of anatectic migmatites are present. Patch migmatites formed by in situ melting and subsequent crystallization of melt. Diktyonitic migmatites comprise a discontinuous veined network of leucocratic material, in which leucosomes enclose boudins of host rock. The margins of these boudins show the development of both melanosomes and shear band fabrics.Strain analysis of diktyonitic melanosomes indicates that these regions have undergone volume decreases of 2&27%. This volume decrease is attributed to melt extraction into the adjacent fracture-filling leucosomes. Thus, diktyonitic migmatites formed by shear-induced segregation of partial melt, whereas in patch migmatites the lack of shear stresses inhibited melt segregation. The variable structural style of anatectic migmatites in Boca de Quadra is not related to host-rock composition, but may be due to differences in the amount of differential stress during migmatization. These in turn may be controlled by host-rock strength andlor diachroneity of migmatization and deformation.Determination of volume changes during migmatization using strain analysis is potentially capable of discriminating intrusive and anatectic migmatites and consequently of documenting melt segregation and subsequent migration across crustal levels.

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“…Orthopyroxene compositions and calculated partial melt compositions are similar to those produced in the experimental melting of pelites (Hoffer and Grant, 1980). All of the xenoliths analyzed in this study have undergone partial melting based on their chemical compositions and mineral assemblages.…”

Section: Geologic Settingmentioning

confidence: 87%