HR: 0800h
AN: T11B-0574    [Abstracts]
TI: Zircon U-Pb ages for the McKinley Sequence and Associated Plutons, Central Alaska Range
AU: * Hung, C
EM: chieqchan@yahoo.com.tw
AF: Department of Geosciences, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 10617 Taiwan(R.O.C.), Taipei, 106, Taiwan
AU: Chung, S
EM: sunlin@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 10617 Taiwan(R.O.C.), Taipei, 106, Taiwan
AU: Cole, R
EM: ron.cole@allegheny.edu
AF: Department of Geology, Allegheny College, 520 N. Main St. Meadville, PA 16335, Meadville, 16335, Armenia
AU: Iizuka, Y
EM: yiizuka@earth.sinica.edu.tw
AF: Institute of Earth Sciences, Academia Sinica, 128 Academia Road Sec. 2, Nankang Taipei 115 Taiwan, ROC, Taipei, 115, Taiwan
AU: Chiu, H
EM: r91224204@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 10617 Taiwan(R.O.C.), Taipei, 106, Taiwan
AU: Chu, C
EM: julie0104@yam.com
AF: Department of Geosciences, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 10617 Taiwan(R.O.C.), Taipei, 106, Taiwan
AU: Gallet, S
EM: gallet@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 10617 Taiwan(R.O.C.), Taipei, 106, Taiwan
AB: Plutonic rocks in the Central Alaska Range were emplaced during important tectonic events including the end of Late Cretaceous-Paleocene arc magmatism, the terminal phase of terrane accretion, ridge subduction, strike- slip faulting, oroclinal rotation of western Alaska, and resumption of arc magmatism during Eocene time along the proto-Aleutian arc system. This study builds on previous studies of these rocks by providing comprehensive age and geochemical data for plutons in the context of these tectonic events. Here we report the first set of LA- ICPMS zircon U-Pb ages for (1) the McKinley Sequence granites, (2) a set of composite plutons and (3) the Foraker pluton. Four samples dated from the McKinley Sequence include two peraluminous granites that yielded ²⁰⁶Pb/²³⁸U ages of 62±1 and 60±1 Ma and two A-type granites of 57±1 and 51±1 Ma. Two granodiorites from the composite plutons and a granite from the Foraker pluton gave ages of 69±1, 67±1 and 37±1 Ma, respectively. Our results indicate that the composite plutons and the McKinley granites have an older age range than previously known and that the McKinley granites can be divided into two magma suites marked with peraluminous and A-type compositions that took place in ca. 62-60 and 57-51 Ma, respectively. These plutonic rocks, excluding the A-type granites, are products of the ending phase of Late Cretaceous-Paleocene arc magmatism. Subsequent generation of the A-type granites may be attributed to ridge subduction, a mechanism that may have also accounted for broadly coeval volcanism in the nearby Cantwell basin and northern Talkeetna Mountains. The Foraker plutons are products of renewed magmatism along the proto-Aleutian arc. Our preliminary Nd and Sr isotope data suggest a temporal change in the magma”¦s isotopic compositions, with the Foraker granites showing high eNd(T) values of about +6 and the composite and McKinley Sequence rocks showing lower and heterogeneous eNd(T) values from +3 to -3. More analyses will further constrain mantle reservoirs beneath central Alaska and the influence of terrane accretion on continental margin magmatism.
DE: 1020 Composition of the continental crust
DE: 3640 Igneous petrology
DE: 3660 Metamorphic petrology
DE: 8104 Continental margins: convergent
SC: Tectonophysics [T]
MN: 2007 Fall Meeting