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The Tlikakila complex in southern Alaska: A suprasubduction-zone ophiolite between the Wrangellia Composite terrane and North America

By
Jeffrey M. Amato
Jeffrey M. Amato
1
Department of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA
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Matthew J. Bogar
Matthew J. Bogar
1
Department of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA
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George E. Gehrels
George E. Gehrels
2
Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA
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G. Lang Farmer
G. Lang Farmer
3
Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309, USA
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William C. McIntosh
William C. McIntosh
4
Bureau of Mines and Geology, Socorro, New Mexico 87801, USA
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Published:
January 01, 2007

The Tlikakila complex is a northeast-striking ∼5-km-wide and ∼75-km-long belt of lower greenschist-facies sedimentary and igneous rocks in the Lake Clark region of south-central Alaska. It forms the only exposures of pre-Cretaceous rocks between the Peninsular terrane and the Farewell terrane. Protoliths include basalt, gabbro, ultramafic rocks, limestone, chert, mudstone, chertpebble conglomerate, and minor quartz sandstone. Geochemical analyses of igneous rocks indicate primitive island arc compositions. Rare earth element (REE) patterns of the volcanic rocks and gabbro are flat with most elements between 5 and 15 times chondrite values. Initial 87Sr/86Sr isotope ratios range from 0.7042 to 0.7065. εNd ranges from + 9.3 to +2.6. The complex is older than 192 Ma based on a 40Ar/39Ar date of white mica from a pegmatite vein in a metasedimentary rock and younger than ca. 293 Ma based on the youngest zircon in a chertpebble conglomerate. Detrital zircon ages suggest source rocks included the Yukon-Tanana and Wrangellia-Alexander terranes. Previously reported Norian conodonts in nearby correlative limestone indicate at least some of the complex is Late Triassic. Metamorphism reached peak temperatures of 350–450 °C based on mineral assemblages in metapelite and metabasite. Three 40Ar/39Ar dates of biotite from metapelite indicate metamorphism at 177 ± 1 Ma. We interpret the Tlikakila complex as a dismembered suprasubduction-zone ophiolite that originated near a trench above a north-dipping subduction zone in Late Triassic time. This subduction eventually created the Talkeetna arc. A second north-dipping subduction zone closed the intervening basin between the Talkeetna arc and the southern Alaska continental margin. Metamorphism and deformation of the Tlikakila complex was coeval with either collision of the arc or shallowing of this slab at ca. 177 Ma.

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GSA Special Papers

Tectonic Growth of a Collisional Continental Margin: Crustal Evolution of Southern Alaska

Kenneth D. Ridgway
Kenneth D. Ridgway
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Jeffrey M. Trop
Jeffrey M. Trop
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Jonathan M.G. Glen
Jonathan M.G. Glen
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J. Michael O'Neill
J. Michael O'Neill
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Geological Society of America
Volume
431
ISBN print:
9780813724317
Publication date:
January 01, 2007

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