| Reference Type | Journal (article/letter/editorial) |
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| Title | Paleogene geology and chronology of southwestern Umnak Island, Aleutian Islands, Alaska |
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| Journal | Canadian Journal of Earth Sciences |
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| Authors | McLean, Hugh | Author |
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| Hein, J. R. | Author |
| Year | 1984 (February 1) | Volume | 21 |
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| Issue | 2 |
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| Publisher | Canadian Science Publishing |
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| DOI | doi:10.1139/e84-018Search in ResearchGate |
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| Generate Citation Formats |
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| Mindat Ref. ID | 478174 | Long-form Identifier | mindat:1:5:478174:9 |
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| GUID | 0 |
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| Full Reference | McLean, Hugh, Hein, J. R. (1984) Paleogene geology and chronology of southwestern Umnak Island, Aleutian Islands, Alaska. Canadian Journal of Earth Sciences, 21 (2) 171-180 doi:10.1139/e84-018 |
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| Plain Text | McLean, Hugh, Hein, J. R. (1984) Paleogene geology and chronology of southwestern Umnak Island, Aleutian Islands, Alaska. Canadian Journal of Earth Sciences, 21 (2) 171-180 doi:10.1139/e84-018 |
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| In | (1984, February) Canadian Journal of Earth Sciences Vol. 21 (2) Canadian Science Publishing |
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| Abstract/Notes | The rocks of southwestern Umnak Island (Nikolski area) consist mainly of a slightly deformed marine sedimentary sequence intruded by hypabyssal quartz diorite sills and small plutons. Laminated and thin-bedded argillaceous and tuffaceous mudstone and siltstone reflect volcanic arc sedimentation from late Eocene to early Oligocene time. Zeolite facies minerals formed during diagenesis include heulandite, analcime, quartz, chlorite, and smectite. Radiometric dates from sill rock and plutons yield apparent ages of about 30 Ma, i.e, middle Oligocene. Chemical data from igneous rocks exhibit calc-alkaline and tholeiitic volcanic arc differentiation trends. Dikes of pyroxene basalt yield K/Ar apparent ages as old at 17 Ma, and a columnar-jointed plug of pyroxene basalt is as young as 1 Ma. The fossil ages and radiometric dates from southwestern Umnak Island are similar to those reported from other central and eastern Aleutian islands, and indicate uniformity in the chronology and tectonic development of the archipelago during the Paleogene. Paleomagnetic data suggest possible northward movement but remain equivocal and more work is indicated. |
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