T77 Provenance Analysis in Modern and Ancient Sedimentary Systems

Monday, 10 October 2011
8:00 AM - 12:00 PM
Room 211CD

DETRITAL ZIRCONS DEFINE NORTH AMERICAN PROVENANCE OF MISSISSIPPIAN ANTLER BASIN AND BALTIC-CALEDONIAN PROVENANCE OF MILLIGEN FORMATION AND YOUNGER STRATA OF THE PIONEER THRUST PLATE, CENTRAL IDAHO

Paper number: T77-7
Program: Technical Sessions
Time: 9:20 AM – 9:35 AM

Authors

Abstract

Detrital zircons in Ordovician through Permian sedimentary rocks across the central Idaho thrust belt contain two provenance barcodes controlled by different source rocks involved in the Devonian and Mississippian Antler orogeny.

Above Proterozoic and Cambrian sandstones within the eastern “carbonate assemblage” of the North American passive margin (Copper Basin and Hawley Creek thrust plates) the Middle Ordovician Kinnikinic Quartzite has a surprisingly constant Paleoproterozoic and older (> 1800 Ma) detrital-zircon assemblage. Mesoproterozoic and Grenvillian-age grains are sparse. Exposures of the Kinnikinic are the most probable source for detrital zircons in the Early Mississippian Antler transtensional basin (Salmon River Assemblage and Copper Basin Group). The southwestern boundary of the central Idaho Antler basin was Kinnikinic Quartzite on an uplifted block of North American continental basement, and the boundary fault is now concealed below the Pioneer thrust plate.

In the western, siliceous assemblage (Pioneer thrust plate) the lower Milligen Formation (Cait Quartzite) contains tongues of the east-derived Kinnikinic-recycled zircons, but sandstones in the upper Milligen and overlying Wood River formations contain a wide range of Paleo-, Meso-, and Neo- Proterozoic (<1800 Ma) grains plus an important 440 to 420 Ma Late Ordovician and Silurian age-peak. It seems reasonable that this Silurian grain- population links the Milligen with either the Yreka terrane of the northern Klamath Mountains or the Okanagan subterrane of Quesnellia in southern British Columbia. Further, the diverse Proterozoic recycled grain populations resemble those of terranes in Arctic Alaska with Caledonian-Baltic grain populations (via the Northwest Passage), and including 1.49 to 1.61 Ga grains of the North American magmatic gap.

The sinistral transtensional Milligen Formation continental-slope rift-basin was thus marginal to the North American passive margin in Early Devonian time and connected to a northern or western exotic terrane in Late Devonian time. The Mesozoic Pioneer thrust fault structurally conceals the block-faulted Antler highland and juxtaposes Paleozoic strata with fundamentally different provenance.