The Tectonothermal evolution and provenance of the Tyrone Central Inlier, Ireland: Grampian imbrication of an outboard Laurentian microcontinent?

first_imgThe Tyrone Central Inlier is a metamorphic terrane of uncertain affinity situated outboard of themain Dalradian outcrop (south of the Fair Head–Clew Bay Line) and could represent sub-arc basement topart of the enigmatic Midland Valley Terrane. Using a combination of isotopic, structural and petrographicevidence, the tectonothermal evolution of the Tyrone Central Inlier was investigated. Sillimanite-bearingmetamorphic assemblages (c. 670 degreesC, 6.8 kbar) and leucosomes in paragneisses are cut by granite pegmatites,which post-date two deformation fabrics. The leucosomes yield a weighted average 207Pb/206Pb zircon ageof 467 +/- 12 Ma whereas the main fabric yields a 40Ar–39Ar biotite cooling age of 468 +/- 1.4 Ma. Thepegmatites yield 457 +/- 7 Ma and 458 +/- 7 Ma Rb–Sr muscovite–feldspar ages and 40Ar–39Ar step-heatingplateaux of 466 +/- 1 Ma and 468 +/- 1 Ma, respectively. The metasedimentary rocks yield PalaeoproterozoicSm–Nd model ages and laser ablation inductively coupled plasma mass spectrometry detrital zircon U–Pbanalyses from a psammitic gneiss yield age populations at 1.05–1.2, 1.5, 1.8, 2.7 and 3.1 Ga. Combined,these data permit correlation of the Tyrone Central Inlier with either the Argyll or the Southern HighlandGroup of the Dalradian Supergroup. The inlier was thus part of Laurentia onto which the Tyrone ophiolitewas obducted.last_img read more

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