Structural history of the Chugach metamorphic complex in the Tana River region, eastern Alaska: A record of Eocene ridge subduction

Abstract

Research Article| November 01, 1995 Structural history of the Chugach metamorphic complex in the Tana River region, eastern Alaska: A record of Eocene ridge subduction Terry L. Pavlis; Terry L. Pavlis 1Department of Geology and Geophysics, University of New Orleans, New Orleans, Louisiana 70148 Search for other works by this author on: GSW Google Scholar Virginia B. Sisson Virginia B. Sisson 2Department of Geology and Geophysics, MS-126, Rice University, Houston, Texas 77005-1892 Search for other works by this author on: GSW Google Scholar Author and Article Information Terry L. Pavlis 1Department of Geology and Geophysics, University of New Orleans, New Orleans, Louisiana 70148 Virginia B. Sisson 2Department of Geology and Geophysics, MS-126, Rice University, Houston, Texas 77005-1892 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1995) 107 (11): 1333–1355. https://doi.org/10.1130/0016-7606(1995)107<1333:SHOTCM>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Terry L. Pavlis, Virginia B. Sisson; Structural history of the Chugach metamorphic complex in the Tana River region, eastern Alaska: A record of Eocene ridge subduction. GSA Bulletin 1995;; 107 (11): 1333–1355. doi: https://doi.org/10.1130/0016-7606(1995)107<1333:SHOTCM>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Chugach metamorphic complex of southern Alaska is an Eocene high-temperature (T), low-pressure (P) fore-arc metamorphic belt related to subduction of the Kula-Farallon spreading center beneath western North America. The Chugach metamorphic complex has a three-phase ductile deformational history that records major changes in kinematic axes during a short interval of geologic time (∼8 m.y.). The earliest deformation (D1) is a regional event recognized throughout the flysch subterrane of the Chugach terrane. D1 is a regional layer-parallel slaty/phyllitic cleavage developed during accretion and subsequent shortening. In the Chugach metamorphic complex, D1 predates high-temperature metamorphism. During prograde metamorphism, there were two major structural events. D2 records orogen-parallel extensional accompanied by vertical shortening with components of pure shear and top-to-the-east simple shear. D2 is synchronous with melt injections (Ti2) in the gneissic core of the complex and large plutons throughout the complex. D3 records a return to subhorizontal contraction perpendicular to the margin and is interpreted as a dextral transpressional event. D3 contraction produced a dramatic thickening of the complex in a regional-scale D3 anticlinorium. In the gneissic core, the presence of melt (Ti3) strongly influenced D3. Finite strain data and field observations indicate that both F2 and F3 have axes that are parallel to the stretching direction, yet these are not sheath folds because strains are too low. Instead the structures are examples of folds that developed with their axes parallel to the elongation axis.Together these observations provide further evidence for our previous interpretations that the Chugach metamorphic complex is a manifestation of an Eocene plate reorganization at ca. 56–52 Ma. Plate models predict that before 56 Ma the Kula–Farallon–North American triple junction migrated southward and is associated with a time-transgressive fore-arc plutonic belt. After plate reorganization, the triple junction either backtracked northward (Kula Plate model) or continued southward with intermittent northward motion (Pacific-Farallon model). We interpret the D2-to-D3 progression as either a result of highly oblique subduction of the Kula plate followed by more orthogonal—but still dextral-oblique—convergence of the Farallon plate (Kula Plate model), or a special case of Pacific–Farallon–North American interaction. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.