Travels of the Cache Creek Terrane: a paleomagnetic, geobarometric and Ar/Ar study of the Jurassic Fourth of July Batholith, Canadian Cordillera |
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| Authors: | Michael J Harris David T A Symons William H Blackburn Craig J R Hart Mike Villeneuve |
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| Institution: | a Earth Sciences, University of Windsor, Windsor, ON, Canada N9B 3P4;b Royal Roads University, Victoria, BC, Canada V9B 5Y2;c Yukon Geology Program, Box 2703 [F-3], Whitehorse, YT, Canada Y1A 2C6;d Geochronology Section, Geological Survey of Canada, 601 Booth St., Ottawa, ON, Canada K1A 0E8 |
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| Abstract: | The Middle Jurassic Fourth of July Batholith and cross-cutting mafic dikes have been studied geochronologically, geobarometrically and paleomagnetically to estimate subsequent tectonic motion of the Cache Creek Terrane (CCT) in the northern Canadian Cordillera. 40Ar/39Ar hornblende ages from a granodiorite phase are similar to U–Pb zircon ages and indicate rapid cooling of the batholith upon intrusion, suggesting that the magnetization age is coincident with the 173-Ma crystallization age. Argon ages of biotite from the granodiorite and two mafic dikes have similar ages of 165 Ma, which dates cooling through 280 °C.Aluminum-in-hornblende geobarometry indicates differential uplift of the batholith across a north–south fault zone along Atlin Lake with >6 km more uplift on its eastern side. Also, the eastern side has been tilted downward to the south–southwest by 9°.Combined paleomagnetic data from 20 granitoid and 11 mafic dike sites yield an in situ paleopole at 55°W, 63°N (dp=5°, dm=5°) and a tilt-corrected paleopole at 81°W, 55°N (dp=5°, dm=6°). Compared to the 173-Ma reference pole for the North American craton, the tilt-corrected pole suggests a significant southward translation of 16.1±3.7° and a significant clockwise rotation of 107±7°. The translation estimate is similar to the Jurassic Teslin Crossing pluton in the Stikine Terrane, however, the rotation estimate is very different. This could indicate that the Cache Creek Terrane was at a similar latitude of the Stikine Terrane, but the two were not yet amalgamated. |
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| Keywords: | Paleomagnetism Tectonic motions Canadian Cordillera Ar-age dating Jurassic |
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