The Gravina Sequence: Remnants of a Mid-Mesozoic oceanic arc in southern southeast Alaska
Fragments of Upper Jurassic to Lower Cretaceous volcanic and basinal strata constitute the Gravina belt in southeast Alaska. In the Ketchikan area the Gravina belt is made up of two lithotectonic units. The lower unit consists of coarse marine pyroclastic and volcaniclastic strata, mafic flows, brec...
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American Geophysical Union
1991
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ftcaltechauth:oai:authors.library.caltech.edu:at91t-qm438 2024-09-15T18:16:31+00:00 The Gravina Sequence: Remnants of a Mid-Mesozoic oceanic arc in southern southeast Alaska Rubin, Charles M. Saleeby, Jason B. 1991-08-10 https://doi.org/10.1029/91JB00591 unknown American Geophysical Union https://doi.org/10.1029/91JB00591 oai:authors.library.caltech.edu:at91t-qm438 eprintid:49295 resolverid:CaltechAUTHORS:20140905-133126729 info:eu-repo/semantics/openAccess Other Journal of Geophysical Research B, 96(B9), 14551-14568, (1991-08-10) info:eu-repo/semantics/article 1991 ftcaltechauth https://doi.org/10.1029/91JB00591 2024-08-06T15:35:04Z Fragments of Upper Jurassic to Lower Cretaceous volcanic and basinal strata constitute the Gravina belt in southeast Alaska. In the Ketchikan area the Gravina belt is made up of two lithotectonic units. The lower unit consists of coarse marine pyroclastic and volcaniclastic strata, mafic flows, breccia, and fine-grained tuff which are locally intruded by hypabyssal bodies of diorite and quartz diorite. The volcanic rocks are characterized by tholeiitic arc basalts, lack felsic volcanic strata, and overlie Upper Triassic and older strata of the Alexander terrane. Augite and/or hornblende-bearing porphyritic rocks are common and locally intrude the Alexander terrane basement, where they are thought to represent the intrusive equivalents of lavas within the section. Age constraints for the volcanic unit, based on structural and stratigraphic relations with adjacent units, are late Middle to Late Jurassic. The Gravina belt upper unit consists of fine- to coarse-grained turbidites and related conglomeratic channel-fill deposits. The basinal rocks unconformably overlie Permian and Triassic rocks of the Taku terrane and remnants of the lower volcanic part of the Gravina sequence which overlie the Alexander terrane. The conglomerate units contain mostly volcanic and plutonic lithic clasts, some of which yield Pb-U zircon ages of 154–158 Ma. The predominance of pyroclastic deposits interbedded with massive flows, tuff, breccia, and argillaceous turbidites, and the lithologic and chemical composition of the volcanic rocks indicate a submarine volcanic arc setting for the Gravina sequence. The basinal pyroclastic rocks are inferred to have been shed from submarine stratovolcanos during the Late Jurassic. Epiclastic rocks were deposited as submarine fans, derived in part from erosion of a magmatic arc. The presence of fine-grained tuffaceous turbidites implies ongoing, but distant, volcanism. The pyroclastic and volcaniclastic rocks represent remnants of a Late Jurassic oceanic arc constructed on a composite basement ... Article in Journal/Newspaper Ketchikan Alaska Caltech Authors (California Institute of Technology) Journal of Geophysical Research: Solid Earth 96 B9 14551 14568 |
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Caltech Authors (California Institute of Technology) |
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description |
Fragments of Upper Jurassic to Lower Cretaceous volcanic and basinal strata constitute the Gravina belt in southeast Alaska. In the Ketchikan area the Gravina belt is made up of two lithotectonic units. The lower unit consists of coarse marine pyroclastic and volcaniclastic strata, mafic flows, breccia, and fine-grained tuff which are locally intruded by hypabyssal bodies of diorite and quartz diorite. The volcanic rocks are characterized by tholeiitic arc basalts, lack felsic volcanic strata, and overlie Upper Triassic and older strata of the Alexander terrane. Augite and/or hornblende-bearing porphyritic rocks are common and locally intrude the Alexander terrane basement, where they are thought to represent the intrusive equivalents of lavas within the section. Age constraints for the volcanic unit, based on structural and stratigraphic relations with adjacent units, are late Middle to Late Jurassic. The Gravina belt upper unit consists of fine- to coarse-grained turbidites and related conglomeratic channel-fill deposits. The basinal rocks unconformably overlie Permian and Triassic rocks of the Taku terrane and remnants of the lower volcanic part of the Gravina sequence which overlie the Alexander terrane. The conglomerate units contain mostly volcanic and plutonic lithic clasts, some of which yield Pb-U zircon ages of 154–158 Ma. The predominance of pyroclastic deposits interbedded with massive flows, tuff, breccia, and argillaceous turbidites, and the lithologic and chemical composition of the volcanic rocks indicate a submarine volcanic arc setting for the Gravina sequence. The basinal pyroclastic rocks are inferred to have been shed from submarine stratovolcanos during the Late Jurassic. Epiclastic rocks were deposited as submarine fans, derived in part from erosion of a magmatic arc. The presence of fine-grained tuffaceous turbidites implies ongoing, but distant, volcanism. The pyroclastic and volcaniclastic rocks represent remnants of a Late Jurassic oceanic arc constructed on a composite basement ... |
format |
Article in Journal/Newspaper |
author |
Rubin, Charles M. Saleeby, Jason B. |
spellingShingle |
Rubin, Charles M. Saleeby, Jason B. The Gravina Sequence: Remnants of a Mid-Mesozoic oceanic arc in southern southeast Alaska |
author_facet |
Rubin, Charles M. Saleeby, Jason B. |
author_sort |
Rubin, Charles M. |
title |
The Gravina Sequence: Remnants of a Mid-Mesozoic oceanic arc in southern southeast Alaska |
title_short |
The Gravina Sequence: Remnants of a Mid-Mesozoic oceanic arc in southern southeast Alaska |
title_full |
The Gravina Sequence: Remnants of a Mid-Mesozoic oceanic arc in southern southeast Alaska |
title_fullStr |
The Gravina Sequence: Remnants of a Mid-Mesozoic oceanic arc in southern southeast Alaska |
title_full_unstemmed |
The Gravina Sequence: Remnants of a Mid-Mesozoic oceanic arc in southern southeast Alaska |
title_sort |
gravina sequence: remnants of a mid-mesozoic oceanic arc in southern southeast alaska |
publisher |
American Geophysical Union |
publishDate |
1991 |
url |
https://doi.org/10.1029/91JB00591 |
genre |
Ketchikan Alaska |
genre_facet |
Ketchikan Alaska |
op_source |
Journal of Geophysical Research B, 96(B9), 14551-14568, (1991-08-10) |
op_relation |
https://doi.org/10.1029/91JB00591 oai:authors.library.caltech.edu:at91t-qm438 eprintid:49295 resolverid:CaltechAUTHORS:20140905-133126729 |
op_rights |
info:eu-repo/semantics/openAccess Other |
op_doi |
https://doi.org/10.1029/91JB00591 |
container_title |
Journal of Geophysical Research: Solid Earth |
container_volume |
96 |
container_issue |
B9 |
container_start_page |
14551 |
op_container_end_page |
14568 |
_version_ |
1810454539112808448 |