The construction of the Donegal composite batholith, Irish Caledonides: Temporal constraints from U-Pb dating of zircon and titanite

Magmatic and tectonic processes can transport large volumes of magma generated in the deep crust as discrete pulses to shallower crustal depths, resulting incremental construction large, composite batholiths over thousands tens millions years. The Silurian Early Devonian Donegal batholith Ireland is a classic example which regional geological syntheses lithogeochemical data show that emplacement was syn- post-kinematic with respect terminal phases (ca. 437−415 Ma) Caledonian orogeny. We used U-Pb dating zircon titanite investigate time. Imaging these minerals reveals complex, zoned grains distinct autocrystic (growth during pluton emplacement) antecrystic lower incubation) domains well xenocrysts (incorporated from wall rocks). To determine ages inherited domains, growth zones were targeted for using laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS). Taken together, isotopic indicate magmatism occurred at least 30 m.y., between ca. 430 Ma 400 Ma. Batholith bracketed by 427−423 Ardara latest Main Trawenagh Bay plutons Ma). Although apparently volumetrically minor, spatially associated mafic rocks (appinite suite, lamprophyre dikes, enclaves granitoid plutons) yield ranging 431−416 Ma, indicates ongoing much batholith.