Paper No. 279-1
Presentation Time: 9:00 AM-6:30 PM
COMPARING PALEOPROTEROZOIC ORTHOGNEISSES IN NORTHERN IDAHO WITH GLACIAL IGNEOUS CLASTS OF EAST ANTARCTICA; EVIDENCE FOR LINKAGE BETWEEN NORTHWEST LAURENTIA AND EAST ANTARCTICA DURING COLUMBIA SUPERCONTINENT ASSEMBLY
A comparison of whole-rock chemistries, U-Pb ages, and Hf-isotope compositions of granitic orthogneisses from the Priest River complex (PRC) of northern Idaho with a suite of granitic glacial clasts from East Antarctica (EA) help to test a potential link between NW Laurentia and EA during the Paleoproterozoic assembly of supercontinent Columbia. Metaigneous rocks from the Priest River and Clearwater complexes of northern Idaho occur near the Neoproterozoic rifted margin of western Laurentia and define a basement block with bimodal Neoarchean and Paleoproterozoic ages (2.76-2.65 Ga and 1.88 -1.84 Ga, respectively). The Paleoproterozoic PRC orthogneisses have granitic, granodioritic to tonalitic compositions, and the 1.88 to 1.85 Ga EA clasts are granitic to granodioritic. Both groups show coherent petrogenetic trends; both are dominantly alkali-calcic to calcic, metaluminous to weakly peraluminus, and have magnesian to weakly ferroan Fe-index values. The groups also have overlapping major-element oxide and trace-element values and patterns. Both exhibit decoupled LIL/HFS patterns and negative Nb-Ta spikes. Chondrite-normalized REE patterns are fractionated with enriched LREE (Lan = 25-634) to weakly enriched HREE (Lun = 1-37). Zircon Hf-isotope compositions are likewise similar; the PRC orthogneisses have initial εHf values ranging from -6.5 to -0.5, and the EA clasts range from -6.5 to -1.1 (with one outlier at +4.8). Two PRC amphibolite inclusions (dissected dikes) within the 2.65 Ga Pend Oreille Gneiss are basaltic to basaltic andesite in composition. They have zircon U-Pb ages of 1.87 Ga and 1.84 Ga, calc-alkaline compositions, and exhibit moderate trace-element and REE enrichments with distinct Nb-Ta negative spikes like the orthogneisses. The PRC orthogneisses and EA granitoids exhibit chemical signatures similar to modern subduction-related, continental-margin arc systems. On tectonic discrimination diagrams, both groups plot within arc-related granitoid fields. The calc-alkaline mafic inclusions also support an arc setting. Based on the considerable overlap of ages, geochemical trends, and Hf-isotope compositions, the PRC and EA rocks suggest a potential linkage associated with a common continental magmatic-arc setting during Paleoproterozoic time.