No abstract

The Eurekan Orogeny records Paleogene convergence between Greenland and the Canadian Arctic. The complexity of the region, well represented by the disputed magnitude of Cenozoic sinistral displacement of Greenland relative to Ellesmere Island, stems from the simultaneous evolution of multiple tectonic regimes, as well as overprinting of later tectonic activity. Presented here is a plate model of regional crustal deformation constructed with the interactive GPlates software that enables an evaluation of previous reconstructions of the Eurekan Orogeny. This model is built upon a synthesis of published geological and geophysical data and their interpretations. It incorporates two phases of deformation from ~63 to 35 Ma. Phase 1, ~63 to ~55 Ma, involves ~85 km of Paleocene extension between Ellesmere and Devon Island, extension of ~20 km between Axel Heiberg and Ellesmere Island, and ~85 km of sinistral strike slip along the Nares Strait/Judge Daly Fault System, matching a range of 50–100 km indicated by the offset of marker beds, facies contacts, and platform margins between the conjugate Greenland and Ellesmere Island margins. Phase 2, ~55 to 35 Ma, results in total east‐west compression of ~30 km and ~200 km of north‐south compression across Ellesmere Island. This model confirms, for the first time, that key observations from subregions deformed by the Eurekan Orogeny are compatible on a broad scale. We have also identified potential problem areas in southwestern Ellesmere Island that are less compatible with a best fit model, given current constraints. This deforming plate model offers a platform and base model for future research.

We present a novel method for the measurement of lithium isotopes in garnet utilising glass reference materials and secondary ion mass spectrometry (SIMS). Measured lithium isotopic compositions of natural garnets are heterogeneous, making them unreliable reference materials for in situ determination. However, SIMS lithium isotope measurements of glasses derived from these natural garnets are isotopically identical to their parent garnets and more homogeneous, demonstrating that they can be used as reliable reference materials. To characterise the composition dependence of instrumental mass fractionation (IMF), oxide and silicate powders were used to synthesise custom-made glass reference materials (CGRMs) with garnet-equivalent compositions. Results for six CGRMs measured by SIMS show a significant linear relationship between IMF and FeO and MnO contents. Corrections for this compositional IMF result in changes of up to 12‰ within the compositional range explored. Uncertainty in IMF-corrected SIMS analyses with a 20 μm spot is in the range of 2.5 to 4.5‰, depending on the garnet composition and reference materials used. The method for in situ lithium isotope measurement in garnet by SIMS presented here is highly adaptable, valid across a range of Al-rich garnet compositions, and yields spatial resolution and precision necessary to address a range of geological applications.