The Seiland Igneous Province, Northern Norway : age, provenance, and tectonic significance

Show simple item record Roberts, Richard James 2008-06-27T11:44:17Z 2008-06-27T11:44:17Z 2008-06-27T11:44:17Z
dc.description.abstract The Seiland Igneous Province, of which 5400 km2 is exposed, is hosted within a discrete terrane within the northernmost part of the Caledonian orogenic belt. The Province consists of numerous mafic and ultramafic plutons emplaced into a sedimentary succession indicative of a continental setting. Accompanying this mafic magmatism is a significant volume of intermediate monzonitic and dioritic rock (10% of the total exposed igneous rock), as well as numerous nepheline syenite and carbonatitic intrusions. This study reports ID-TIMS U-Pb analyses on magmatic zircons from a range of intrusions, which indicate that the bulk of the Seiland magmatism took place between 560 Ma and 570 Ma, whereas previous studies had produced a range of ages between 420 Ma and 830 Ma. The data indicate that only one magmatic episode is represented in the rocks of the Seiland Igneous Province, invalidating previous models involving multiple rifting events over a period of 300 m.y. Detailed geochemical investigation of several plutons from an evolved high alkali suite of gabbroic intrusions in the Seiland Igneous Province has shown that these plutons are generally enriched in trace elements compared to layered intrusions from other areas across the globe, but that geochemically the gabbros are relatively homogenous. The rocks yield εHf and εNd values for the gabbroic rocks ranging from +8 to -6 and from +4 to -4, respectively, indicative of the contamination of mantlederived material with crustal material. The most primitive isotopic values are similar to those obtained from the carbonatites and nepheline syenites, indicating the same mantle source gave rise to the magmas that were subsequently emplaced as the Seiland Igneous Province. The homogeneous trace element content of the different mafic rocks most likely indicates a relatively homogeneous mantle source for the original magmas of the province, which has subsequently been affected by processes of assimilation and crustal contamination. The monzonitic and dioritic bodies in the Seiland Igneous Province are not derived from melted silicic crustal material and may have been formed by the melting of pre-existing mafic material. The new geochronology invalidates the metamorphic framework previously proposed for the Seiland Igneous Province, which postulated several orogenic events between the emplacement of the magmas and the Caledonian Orogeny. There is no evidence for metamorphic activity in the period between 570 Ma and 420 Ma, and there are monazites in gneissic rocks hosted within mafic rocks of Seiland age that preserve an age of 640 Ma. This leads to the conclusion that only one metamorphic event, the 420 Ma Caledonian Orogeny caused by the collision of Baltica and Laurentia, affected the Seiland terrane after the emplacement of the Seiland magmas. The new data obtained lead to a model for the evolution of the Seiland Province in which a number of heavily modified and contaminated mantle-derived mafic magmas derived from the mantle were emplaced into the continental crust of the Seiland nappe between 560 and 570 Ma. This magmatism was accompanied by the injection of alkaline magmas into the same area of the crust, and the melting of mafic rock emplaced earlier. This magmatic event is considered to have occurred in an extensional stress regime, possibly during intracontinental rifting or back-arc spreading. This event took place well before the 420 Ma Caledonian Orogeny, and thus the Seiland Igneous Province can be considered a remnant of an older geological terrane that was emplaced onto the margin of Baltica during the Caledonian Orogeny. en
dc.format.extent 61815062 bytes
dc.format.mimetype application/pdf
dc.language.iso en en
dc.subject Seiland en
dc.subject Finnmark en
dc.subject Pluton en
dc.subject U-PB Zircon en
dc.title The Seiland Igneous Province, Northern Norway : age, provenance, and tectonic significance en
dc.type Thesis en

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