Regional progressive high‐pressure metamorphism, Seward Peninsula, Alaska
Abstract Blueschist‐facies rocks on the Seward Peninsula constitute a structurally coherent terrane measuring at least 100 × 150 km. Radiometric age data indicate that high‐pressure metamorphism probably occurred in Jurassic rather than in Palaeozoic or Precambrian time, as previously suggested. Pro...
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crwiley:10.1111/j.1525-1314.1984.tb00284.x 2024-06-02T08:10:48+00:00 Regional progressive high‐pressure metamorphism, Seward Peninsula, Alaska FORBES, R. B. EVANS, B. W. THURSTON, S. P. 1984 http://dx.doi.org/10.1111/j.1525-1314.1984.tb00284.x https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1525-1314.1984.tb00284.x https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1525-1314.1984.tb00284.x en eng Wiley http://onlinelibrary.wiley.com/termsAndConditions#vor Journal of Metamorphic Geology volume 2, issue 1, page 43-54 ISSN 0263-4929 1525-1314 journal-article 1984 crwiley https://doi.org/10.1111/j.1525-1314.1984.tb00284.x 2024-05-03T11:48:05Z Abstract Blueschist‐facies rocks on the Seward Peninsula constitute a structurally coherent terrane measuring at least 100 × 150 km. Radiometric age data indicate that high‐pressure metamorphism probably occurred in Jurassic rather than in Palaeozoic or Precambrian time, as previously suggested. Protolith sediments (Nome Group) are of intracontinental basin or continental margin type, and of lower Palaeozoic and possibly late Precambrian age, thus predating the high pressure metamorphism by more than 200 m.y. Blueschist‐facies mineral assemblages were developed in almost all lithologies of the Nome Group, and are best preserved in FeTi‐rich metabasites (glaucophane + almandine + epidote) and pelites (glaucophane + chloritoid + phengite). A lawsonite–crossite subfacies was developed in possible Nome Group rocks on the east flank of the Darby Mountains. Albite–epidote–amphibolite facies assemblages characterize Nome Group rocks in the southwestern part of the Peninsula. Metamorphism in the central zone of the terrane passed from early lawsonitic to subsequent epidote–almandine–glaucophane schist subfacies with the local development (east of the Nome River) of eclogitic assemblages. The high pressure metamorphic minerals were synkinematic with the development of mesoscopic‐scale intrafolial isoclinal folds and a flattening foliation of consistent orientation. Initiation of uplift probably corresponded to the growth of barroisite rims on earlier sodic and actinolitic amphiboles, and partial post‐kinematic greenschist facies replacements record later stages of decompression. Ophiolites and melange are not associated with the Seward Peninsula blueschists. The high‐pressure metamorphism was caused by tectonic loading of a continental plate by an allochthon of indeterminate origin. The PT conditions of high pressure metamorphism were approximately 9–11 kbar, 400–450°C, thus falling between the PT paths of the Shuksan and Franciscan terranes. Article in Journal/Newspaper Nome Seward Peninsula Alaska Wiley Online Library Darby ENVELOPE(162.217,162.217,-77.667,-77.667) Journal of Metamorphic Geology 2 1 43 54 |
institution |
Open Polar |
collection |
Wiley Online Library |
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crwiley |
language |
English |
description |
Abstract Blueschist‐facies rocks on the Seward Peninsula constitute a structurally coherent terrane measuring at least 100 × 150 km. Radiometric age data indicate that high‐pressure metamorphism probably occurred in Jurassic rather than in Palaeozoic or Precambrian time, as previously suggested. Protolith sediments (Nome Group) are of intracontinental basin or continental margin type, and of lower Palaeozoic and possibly late Precambrian age, thus predating the high pressure metamorphism by more than 200 m.y. Blueschist‐facies mineral assemblages were developed in almost all lithologies of the Nome Group, and are best preserved in FeTi‐rich metabasites (glaucophane + almandine + epidote) and pelites (glaucophane + chloritoid + phengite). A lawsonite–crossite subfacies was developed in possible Nome Group rocks on the east flank of the Darby Mountains. Albite–epidote–amphibolite facies assemblages characterize Nome Group rocks in the southwestern part of the Peninsula. Metamorphism in the central zone of the terrane passed from early lawsonitic to subsequent epidote–almandine–glaucophane schist subfacies with the local development (east of the Nome River) of eclogitic assemblages. The high pressure metamorphic minerals were synkinematic with the development of mesoscopic‐scale intrafolial isoclinal folds and a flattening foliation of consistent orientation. Initiation of uplift probably corresponded to the growth of barroisite rims on earlier sodic and actinolitic amphiboles, and partial post‐kinematic greenschist facies replacements record later stages of decompression. Ophiolites and melange are not associated with the Seward Peninsula blueschists. The high‐pressure metamorphism was caused by tectonic loading of a continental plate by an allochthon of indeterminate origin. The PT conditions of high pressure metamorphism were approximately 9–11 kbar, 400–450°C, thus falling between the PT paths of the Shuksan and Franciscan terranes. |
format |
Article in Journal/Newspaper |
author |
FORBES, R. B. EVANS, B. W. THURSTON, S. P. |
spellingShingle |
FORBES, R. B. EVANS, B. W. THURSTON, S. P. Regional progressive high‐pressure metamorphism, Seward Peninsula, Alaska |
author_facet |
FORBES, R. B. EVANS, B. W. THURSTON, S. P. |
author_sort |
FORBES, R. B. |
title |
Regional progressive high‐pressure metamorphism, Seward Peninsula, Alaska |
title_short |
Regional progressive high‐pressure metamorphism, Seward Peninsula, Alaska |
title_full |
Regional progressive high‐pressure metamorphism, Seward Peninsula, Alaska |
title_fullStr |
Regional progressive high‐pressure metamorphism, Seward Peninsula, Alaska |
title_full_unstemmed |
Regional progressive high‐pressure metamorphism, Seward Peninsula, Alaska |
title_sort |
regional progressive high‐pressure metamorphism, seward peninsula, alaska |
publisher |
Wiley |
publishDate |
1984 |
url |
http://dx.doi.org/10.1111/j.1525-1314.1984.tb00284.x https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1525-1314.1984.tb00284.x https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1525-1314.1984.tb00284.x |
long_lat |
ENVELOPE(162.217,162.217,-77.667,-77.667) |
geographic |
Darby |
geographic_facet |
Darby |
genre |
Nome Seward Peninsula Alaska |
genre_facet |
Nome Seward Peninsula Alaska |
op_source |
Journal of Metamorphic Geology volume 2, issue 1, page 43-54 ISSN 0263-4929 1525-1314 |
op_rights |
http://onlinelibrary.wiley.com/termsAndConditions#vor |
op_doi |
https://doi.org/10.1111/j.1525-1314.1984.tb00284.x |
container_title |
Journal of Metamorphic Geology |
container_volume |
2 |
container_issue |
1 |
container_start_page |
43 |
op_container_end_page |
54 |
_version_ |
1800756727962927104 |