Dating the Tertiary evolution of the Albion-Raft River- Grouse Creek Metamorphic Core Complex
The Albion-Raft River-Grouse Creek metamorphic core complex (ARGMCC) is located in southern Idaho and northern Utah. The rocks exposed there preserve Late Eocene to Oligocene plutonism, extension, and high-grade metamorphism at mid-crustal levels. Exhumation of these rocks along low-angle mylonite zones and high-angle normal faults occurred in the Miocene. The ARGMCC is bordered to the north by Miocene volcanics of the Snake River Plain, and lies on the northern edge of the Basin and Range province.
In the Albion Mountains, the scenic spires and monoliths of the 30 Ma Almo pluton were an important landmark for California-bound emigrants in the mid-1800's. Today it is an international rock-climbing mecca as the City of Rocks National Preserve.
Zircons from the Almo pluton show evidence of inheritance both from a long-lived magmatic system (antecrysts) and from a Late Archean crustal source. Crystallization age for the Almo pluton is given by the outer rims at 30.4 ± 0.2 Ma. Low temperatures given by measured Ti in zircon from Oligocene rims of 618-701 degrees C plus the abundant zircon inheritance suggest low-temperature, likely hydrous crustal melting.
In the Albion and Grouse Creek Mountains, the country rocks to the Oligocene plutons reach peak metamorphic grade during intrusion and preserve extensional-sense deformation along the Middle Mountain shear zone. Garnet-staurolite-sillimanite-biotite assemblages are common in pelitic rocks, and sillimanite helps to define the lineation (upper left). Late stage pegmatites (upper right, in quartzite) are often boudinaged.
Using the SHRIMP-RG at Stanford University, monazites from the country rocks to the 28 Ma Vipoint pluton were analyzed. Monazites grains from a psammitc schist contain patchy zonation and grains with 140 Ma cores and Oligocene overgrowths. Detrital zircons from the same unit have narrow metamorphic rims that are ca. 140-110 Ma. This suggests that Oligocene metamorphism locally overprinted a late Cretaceous event.
Konstantinou, Alexandros, John Valley, Ariel Strickland, Elizabeth L. Miller, Chris Fisher, et al. 2013. “Geochemistry and Geochronology of the Jim Sage Volcanic Suite, Southern Idaho: Implications for Snake River Plain Magmatism and Its Role in the History of Basin and Range Extension.” GEOSPHERE 9 (6). GEOLOGICAL SOC AMER, INC: 1681–1703. DOI: 10.1130/GES00948.1
Konstantinou, Alexandros, Ariel Strickland, Elizabeth L. Miller, and Joseph P. Wooden. 2012. “Multistage Cenozoic Extension of the Albion-Raft River-Grouse Creek Metamorphic Core Complex: Geochronologic and Stratigraphic Constraints.” GEOSPHERE 8 (6). GEOLOGICAL SOC AMER, INC: 1429–66. DOI: 10.1130/GES00778.1
Strickland, A., E. L. Miller, and J. Wooden. 2011. “Syn-Extensional Crustal Melting and Plutonism in the Albion-Raft River-Grouse Creek Metamorphic Core Complex.” Journal of Geology 119, Konstantinou, Alexandros, Ariel Strickland, Elizabeth Miller, Jeffrey Vervoort, Christopher M. Fisher, et al. 2013. “Synextensional Magmatism Leading to Crustal Flow in the Albion-Raft River-Grouse Creek Metamorphic Core Complex, Northeastern Basin and Range.” TECTONICS 32 (5). AMER GEOPHYSICAL UNION: 1384–1403. DOI: 10.1002/tect.20085
Strickland, Ariel, Elizabeth L. Miller, and Joseph L. Wooden. 2011. “The Timing of Tertiary Metamorphism and Deformation in the Albion-Raft River-Grouse Creek Metamorphic Core Complex, Utah and Idaho.” JOURNAL OF GEOLOGY 119 (2). UNIV CHICAGO PRESS: 185–206. DOI: 10.1086/658294