Isotope Geochemistry and Chemical Evolution of the Mantle and Crust

Patchett, P. Jonathan

doi:10.1002/rog.1991.29.s2.457

Cited by 3 publications

(1 citation statement)

References 529 publications

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“…If a pluton is 1000 km 3 in volume and was derived by 30% melting, then there must have been =3000 km 3 of source rock. The deep crust, the likely source region for most I-type granites, is probably heterogeneous on various scales (Patchett 1991;Miller et al 1987) and it is conceivable that most source regions are heterogeneous on this scale. Some of the consequences of melting in a heterogeneous source region are considered below.…”

Section: Characteristics Of Melts In Heterogeneous Source Regionsmentioning

confidence: 99%

Spatial, compositional and rheological constraints on the origin of zoning in the Criffell pluton, Scotland

Stephens¹

1992

Earth and Environmental Science Transactions of the Royal Socie

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The Criffell pluton in southwestern Scotland (397 Ma, a Newer Granite of late Caledonian age) is concentrically zoned with outer granodiorites of typically I-type aspect passing into inner granite with more evolved characteristics. The zonation is examined in terms of the compositional surfaces of bulk parameters such as SiO2 and Rb/Sr and compositional variation is best modelled as multi-pulse, there being greater variation in bulk composition between pulses than within pulse. Published variations in Sr, Nd and O isotopes reflect the derivation of the pulses from separate and isotopically distinct sources. Other evidence for open-system behaviour includes mingling with mafic magmas to form enclaves, whereas closed-system behaviour is indicated by restite separation in the early granodiorites, and fractional crystallisation in the late granites. A dominant infracrustal I-type magma formed the first pulse followed by magma derived from more evolved crustal rocks (mainly metasediments of varying ages and maturities). Experimental fluid-absent melting of amphibolite and metapelite at about 900°C has shown that significant quantities of melt can be generated, respectively with I-type and S-type characteristics. Despite having similar bulk compositions, these melts have very different viscosities and densities for the same H2O contents (ηS-type>ηI-type and ρS-type≤ρI-type). It is argued that the rheological controls on magma escape from the source region along complex and tortuous pathways favour the more fluid I-type melts over the more viscous (and only slightly less dense) S-type melts. This constraint could have the effect of reversing the expected buoyancy-driven emplacement sequence, and may represent an alternative rheological differentiation mechanism for the formation of some zoned plutons.

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Section: Characteristics Of Melts In Heterogeneous Source Regionsmentioning

confidence: 99%

Spatial, compositional and rheological constraints on the origin of zoning in the Criffell pluton, Scotland

Stephens¹

1992

Earth and Environmental Science Transactions of the Royal Socie

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Nd isotopic evidence for the position of southernmost Indian terranes within East Gondwana

Brandon

Meen

1995

Precambrian Research

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Spatial, compositional and rheological constraints on the origin of zoning in the Criffell pluton, Scotland

Stephens¹

1992

Geological Society of America Special Papers

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The Criffell pluton in southwestern Scotland (397 Ma, a Newer Granite of late Caledonian age) is concentrically zoned with outer granodiorites of typically I-type aspect passing into inner granite with more evolved characteristics. The zonation is examined in terms of the compositional surfaces of bulk parameters such as Si0 2 and Rb/Sr and compositional variation is best modelled as multi-pulse, there being greater variation in bulk composition between pulses than within pulse. Published variations in Sr, Nd and O isotopes reflect the derivation of the pulses from separate and isotopically distinct sources. Other evidence for open-system behaviour includes mingling with mafic magmas to form enclaves, whereas closed-system behaviour is indicated by restite separation in the early granodiorites, and fractional crystallisation in the late granites. A dominant infracrustai I-type magma formed the first pulse followed by magma derived from more evolved crustal rocks (mainly metasediments of varying ages and maturities). Experimental fluid-absent melting of amphibolite and metapelite at about 900°C has shown that significant quantities of melt can be generated, respectively with I-type and S-type characteristics. Despite having similar bulk compositions, these melts have very different viscosities and densities for the same H,0 contents (rj s ., ypc > rj,_ type and /O s . lype < Pi-type)-It is argued that the rheological controls on magma escape from the source region along complex and tortuous pathways favour the more fluid I-type melts over the more viscous (and only slightly less dense) S-type melts. This constraint could have the effect of reversing the expected buoyancy-driven emplacement sequence, and may represent an alternative rheological differentiation mechanism for the formation of some zoned plutons.

show abstract

Isotope Geochemistry and Chemical Evolution of the Mantle and Crust

Cited by 3 publications

References 529 publications

Spatial, compositional and rheological constraints on the origin of zoning in the Criffell pluton, Scotland

Spatial, compositional and rheological constraints on the origin of zoning in the Criffell pluton, Scotland

Nd isotopic evidence for the position of southernmost Indian terranes within East Gondwana

Spatial, compositional and rheological constraints on the origin of zoning in the Criffell pluton, Scotland

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