Evaluation of 0.706 87Sr/86Sr Line as Marker for North American Continental Edge

Palinspastic restoration analysis challenges the suitability of the 0.706 87Sr/86Sr line as a definitive indicator for the edge of North America. Findings suggest a suture zone west of the line and question its role in delineating the continental margin based on rock compositions and distribution in regions like California, Nevada, Idaho, and Canada. The study concludes that the boundary delineation is more complex than previously thought, with North American rocks extending beyond traditional definitions.

• Palinspastic restoration
• 87Sr/86Sr line
• North America
• Continental margin
• Rock compositions

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1. 1 Palinspastic restoration of the thrust belt places classically defined North American rocks west of the edge of North America as defined by 0.706 87Sr/86Sr line Havranek and Mize (unpublished manuscript) Presented by Alex Holmwood

2. 2 Initial 87Sr/86Sr ratio of igneous rocks in California and Great Basin varies systematically 0.706 contour near California: consistent with trend and near boundary between Paleozoic miogeosynclinal and eugeosynclinal rocks 0.706 line marks boundary between shelf deposition and eugeosynclinal deposition Is 0.706 line a good indicator of the North American continental margin?

3. 3 0.706 line ~100 W of Precambrian basement in Nevada Runs northward to Idaho roughly along Idaho suture zone

4. 4 Idaho: klippes of material with 87Sr/86Sr ratio >0.706 However, are lower than surrounding ratios

5. 5 0.706 line not defined well in Washington or Canada High density of a different 87Sr/86Sr values Canada: isotopic ratios occur as part of transition zone rather than a defined border

6. 6 Conclusions 0.706 87Sr/86Sr line not appropriate marker for edge of North America Restoration places many North American rocks beyond shelf edge Suture between North America and accreted terranes is >100 km west of 87Sr/86Sr contour (Evans and others, 2002)