HR: 1340h
AN: V13E-0595    [Abstracts]
TI: Disaggregation of Quartzite Enclaves in the S-type Vega Pluton, North-Central Norway
AU: * Vietti, L A
EM: lvietti@uwyo.edu
AF: University of Wyoming, Department of Geology and Geophysics, Dept. 3006, Laramie, WY 82071 United States
AU: McCulloch, L
EM: lindym@umail.ucsb.edu
AF: Texas Tech University, Department of Geosciences, Lubbock, TX 79409 United States
AU: Marko, W T
EM: wayne.t.marko@ttu.edu
AF: Texas Tech University, Department of Geosciences, Lubbock, TX 79409 United States
AU: Barnes, M A
EM: Melanie.Barnes@ttu.edu
AF: Texas Tech University, Department of Geosciences, Lubbock, TX 79409 United States
AU: Frost, C D
EM: frost@uwyo.edu
AF: University of Wyoming, Department of Geology and Geophysics, Dept. 3006, Laramie, WY 82071 United States
AU: Nordgulen, O
EM: oystein.nordgulen@ngu.no
AF: Norwegian Geological Survey, Leiv Eirikssons 39, Trondheim, N-7491 Norway
AB: The Vega pluton is a ca. 470 Ma S-type granodiorite that underlies much of the island of Vega and nearby islands off the north-central coast of Norway. The pluton contains abundant enclaves of migmatite, siliceous gneiss, calc-silicate, quartzite, marble, and mafic igneous rocks plus sparse ultramafic ones. The largest of these is a 1500 m x 500 m enclave of impure quartzite located in the southeastern part of the pluton. Field relations suggest that this quartzite enclave was partially disaggregated by granitic magma. Our geologic mapping, petrologic, geochemical and isotopic results are used to evaluate the sources of the granitic magma and the processes by which large screens of wall rock are reduced to smaller enclaves in S-type intrusions. The large quartzite enclave is elongate N35°E, parallel to its internal compositional banding, which is marked primarily by variations in biotite content. The enclave is best described as a series of planar quartzite screens separated by sheets of Vega granodiorite. These sheets are characteristically enclave-rich, as is typical of the Vega granodiorite throughout the pluton. However, in a number of places enclaves are found within the quartzite but host Vega granodiorite is lacking. Leucogranitic dikes cut the quartzite screens and Vega-type sheets; these dikes vary from anastamosing to planar. Some of the leucogranite is sparsely garnetiferous. Some of these dikes can be traced into a larger, pod-like body of tourmaline-bearing leucogranite located between a quartzite screen and Vega granodiorite sheet near the northernmost limits of the quartzite. Geochemical and Nd and Sr isotopic data indicate that the Vega pluton is compositionally heterogeneous, as is typical of S-type granitic intrusions. The compositions of the leucogranitic dikes and pods suggest that they represent in part the felsic melt expelled from the crystal- and enclave-rich Vega granodiorite, but also contain components derived by partial melting of the impure (biotite- and feldspar-rich) parts of the quartzite. We hypothesize that the quartzite enclave was disaggregated by hydraulic fracturing and intrusion of Vega granodiorite. In some locations, some or all of the granodioritic magma was removed from these fractures, stranding enclaves within the quartzite. Leucogranitic melts expelled from the Vega granodiorite locally mixed with partial melts of (arkosic portions?) of the quartzite in a series of events late in the history of the pluton. Our observations suggest that disaggregation of enclaves in S-type intrusions is a function of physical disruption and in situ partial melting.
DE: 3618 Magma chamber processes (1036)
DE: 3619 Magma genesis and partial melting (1037)
DE: 3640 Igneous petrology
DE: 3642 Intrusive structures and rocks
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005