Abstract
| Originalsprog | Engelsk |
|---|---|
| Tidsskrift | Lithos |
| Vol/bind | 93 |
| Udgave nummer | 3-4 |
| Sider (fra-til) | 234-247 |
| ISSN | 0024-4937 |
| DOI | |
| Status | Udgivet - 2007 |
Emneord
- Det Natur- og Biovidenskabelige Fakultet
- isotoper
- granit
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Isotopic evidence for multiple contributions to felsic magma chambers : Gouldsboro granite, coastal Maine. / Waight, Tod Earle; Wiebe, R.A.; Krogstad, E.J.
I: Lithos, Bind 93, Nr. 3-4, 2007, s. 234-247.Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › peer review
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TY - JOUR
T1 - Isotopic evidence for multiple contributions to felsic magma chambers
T2 - Gouldsboro granite, coastal Maine
AU - Waight, Tod Earle
AU - Wiebe, R.A.
AU - Krogstad, E.J.
PY - 2007
Y1 - 2007
N2 - The Gouldsboro Granite forms part of the Coastal Maine Magmatic Province, a region characterized by granitic plutons that are intimately linked temporally and petrogenetically with abundant co-existing mafic magmas. The pluton is complex and preserves a felsic magma chamber underlain by contemporaneous mafic magmas; the transition between the two now preserved as a zone of chilled mafic sheets and pillows in granite. Mafic components have highly variably isotopic compositions as a result of contamination either at depth or following injection into the magma chamber. Intermediate dikes with identical isotopic compositions to more mafic dikes suggest that closed system fractionation may be occurring in deeper level chambers prior to injection to shallower levels. The granitic portion of the pluton has the highest Nd isotopic composition (eNd=+3.0) of plutons in the region whereas the mafic lithologies have Nd isotopic compositions (eNd=+3.5) that are the lowest in the region and similar to the granite and suggestive of prolonged interactions and homogenization of the two components. Sr and Nd isotopic data for felsic enclaves are inconsistent with previously suggested models of diffusional exchange between the contemporaneous mafic magmas and the host granite to explain highly variable alkali contents. The felsic enclaves have relatively low Nd isotopic compositions (eNd=+2 - +1) indicative of the involvement of a third, lower eNd melt during granite petrogenesis, perhaps represented by pristine granitic dikes contemporaneous with the nearby Pleasant Bay Layered Intrusion. The dikes at Pleasant Bay and the felsic enclaves at Gouldsboro likely represent remnants of the silicic magmas that originally fed and replenished the overlying granitic magma chambers. The large isotopic (and chemical) contrasts between the enclaves and granitic dikes and granitic magmas may be in part a consequence of extended interactions between the granitic magmas and co-existing mafic magmas by mixing, mingling and diffusion. Alternatively,the granitic magmas may represent an additional crustal source. Using granitic rocks such as these with abundant evidence for interactions with mafic magmas complicate their use in constraining crustal sources and tectonic settings. Fine-grained dike rocks may provide more meaningful information, but must be used with caution as these may also have experienced compositional changes during mafic-felsic interactions.
AB - The Gouldsboro Granite forms part of the Coastal Maine Magmatic Province, a region characterized by granitic plutons that are intimately linked temporally and petrogenetically with abundant co-existing mafic magmas. The pluton is complex and preserves a felsic magma chamber underlain by contemporaneous mafic magmas; the transition between the two now preserved as a zone of chilled mafic sheets and pillows in granite. Mafic components have highly variably isotopic compositions as a result of contamination either at depth or following injection into the magma chamber. Intermediate dikes with identical isotopic compositions to more mafic dikes suggest that closed system fractionation may be occurring in deeper level chambers prior to injection to shallower levels. The granitic portion of the pluton has the highest Nd isotopic composition (eNd=+3.0) of plutons in the region whereas the mafic lithologies have Nd isotopic compositions (eNd=+3.5) that are the lowest in the region and similar to the granite and suggestive of prolonged interactions and homogenization of the two components. Sr and Nd isotopic data for felsic enclaves are inconsistent with previously suggested models of diffusional exchange between the contemporaneous mafic magmas and the host granite to explain highly variable alkali contents. The felsic enclaves have relatively low Nd isotopic compositions (eNd=+2 - +1) indicative of the involvement of a third, lower eNd melt during granite petrogenesis, perhaps represented by pristine granitic dikes contemporaneous with the nearby Pleasant Bay Layered Intrusion. The dikes at Pleasant Bay and the felsic enclaves at Gouldsboro likely represent remnants of the silicic magmas that originally fed and replenished the overlying granitic magma chambers. The large isotopic (and chemical) contrasts between the enclaves and granitic dikes and granitic magmas may be in part a consequence of extended interactions between the granitic magmas and co-existing mafic magmas by mixing, mingling and diffusion. Alternatively,the granitic magmas may represent an additional crustal source. Using granitic rocks such as these with abundant evidence for interactions with mafic magmas complicate their use in constraining crustal sources and tectonic settings. Fine-grained dike rocks may provide more meaningful information, but must be used with caution as these may also have experienced compositional changes during mafic-felsic interactions.
KW - Faculty of Science
KW - isotoper
KW - granit
KW - Enclaves
KW - Maine
KW - isotopes
KW - Magma-mingling
KW - Granite
U2 - 10.1016/j.lithos.2006.03.066
DO - 10.1016/j.lithos.2006.03.066
M3 - Journal article
VL - 93
SP - 234
EP - 247
JO - Lithos
JF - Lithos
SN - 0024-4937
IS - 3-4
ER -