scholarly journals Oligocene-Neogene lithospheric-scale reactivation of Mesozoic terrane accretionary structures in the Alaska Range suture zone, southern Alaska, USA: Reply

2021 ◽  
Author(s):  
Trevor S. Waldien ◽  
Sarah M. Roeske ◽  
Jeffrey A. Benowitz ◽  
Evan Twelker ◽  
Meghan S. Miller
Keyword(s):  
Suture Zone ◽  
Alaska Range ◽  
Denali Fault

Topics of discussion raised by Lowey (2021) include the correlation of ultramafic-intermediate intrusions hosted within the Clearwater metasediments/Dezadeash Formation and their displacement by the Denali fault. These topics were not main points of Waldien et al. (2021), but instead logical extrapolations of the information presented and synthesized therein. Here we re-emphasize the key findings of Waldien et al. (2021) and discuss only the relevant aspects of the ultramafic-intermediate intrusions and their displacement.

scholarly journals Alternating asymmetric topography of the Alaska range along the strike-slip Denali fault: Strain partitioning and lithospheric control across a terrane suture zone

Tectonics ◽  
2014 ◽  
Vol 33 (8) ◽  
pp. 1519-1533 ◽  
Author(s):  
Paul G. Fitzgerald ◽  
Sarah M. Roeske ◽  
Jeffery A. Benowitz ◽  
Steven J. Riccio ◽  
Stephanie E. Perry ◽  
...  
Keyword(s):  
Strike Slip ◽  
Suture Zone ◽  
Strain Partitioning ◽  
Alaska Range ◽  
Denali Fault

scholarly journals Cretaceous to Miocene magmatism, sedimentation, and exhumation within the Alaska Range suture zone: A polyphase reactivated terrane boundary

Geosphere ◽  
2019 ◽  
Vol 15 (4) ◽  
pp. 1066-1101 ◽  
Author(s):  
Jeffrey M. Trop ◽  
Jeff Benowitz ◽  
Ronald B. Cole ◽  
Paul O’Sullivan
Keyword(s):  
Late Cretaceous ◽  
Detrital Zircon ◽  
Volcanic Rocks ◽  
Strike Slip ◽  
Suture Zone ◽  
Fault System ◽  
Arc Magmatism ◽  
Alaska Range ◽  
Denali Fault ◽  
Dike Swarms

AbstractThe Alaska Range suture zone exposes Cretaceous to Quaternary marine and nonmarine sedimentary and volcanic rocks sandwiched between oceanic rocks of the accreted Wrangellia composite terrane to the south and older continental terranes to the north. New U-Pb zircon ages, 40Ar/39Ar, ZHe, and AFT cooling ages, geochemical compositions, and geological field observations from these rocks provide improved constraints on the timing of Cretaceous to Miocene magmatism, sedimentation, and deformation within the collisional suture zone. Our results bear on the unclear displacement history of the seismically active Denali fault, which bisects the suture zone. Newly identified tuffs north of the Denali fault in sedimentary strata of the Cantwell Formation yield ca. 72 to ca. 68 Ma U-Pb zircon ages. Lavas sampled south of the Denali fault yield ca. 69 Ma 40Ar/39Ar ages and geochemical compositions typical of arc assemblages, ranging from basalt-andesite-trachyte, relatively high-K, and high concentrations of incompatible elements attributed to slab contribution (e.g., high Cs, Ba, and Th). The Late Cretaceous lavas and bentonites, together with regionally extensive coeval calc-alkaline plutons, record arc magmatism during contractional deformation and metamorphism within the suture zone. Latest Cretaceous volcanic and sedimentary strata are locally overlain by Eocene Teklanika Formation volcanic rocks with geochemical compositions transitional between arc and intraplate affinity. New detrital-zircon data from the modern Teklanika River indicate peak Teklanika volcanism at ca. 57 Ma, which is also reflected in zircon Pb loss in Cantwell Formation bentonites. Teklanika Formation volcanism may reflect hypothesized slab break-off and a Paleocene–Eocene period of a transform margin configuration. Mafic dike swarms were emplaced along the Denali fault from ca. 38 to ca. 25 Ma based on new 40Ar/39Ar ages. Diking along the Denali fault may have been localized by strike-slip extension following a change in direction of the subducting oceanic plate beneath southern Alaska from N-NE to NW at ca. 46–40 Ma. Diking represents the last recorded episode of significant magmatism in the central and eastern Alaska Range, including along the Denali fault. Two tectonic models may explain emplacement of more primitive and less extensive Eocene–Oligocene magmas: delamination of the Late Cretaceous–Paleocene arc root and/or thickened suture zone lithosphere, or a slab window created during possible Paleocene slab break-off. Fluvial strata exposed just south of the Denali fault in the central Alaska Range record synorogenic sedimentation coeval with diking and inferred strike-slip displacement. Deposition occurred ca. 29 Ma based on palynomorphs and the youngest detrital zircons. U-Pb detrital-zircon geochronology and clast compositional data indicate the fluvial strata were derived from sedimentary and igneous bedrock presently exposed within the Alaska Range, including Cretaceous sources presently exposed on the opposite (north) side of the fault. The provenance data may indicate ∼150 km or more of dextral offset of the ca. 29 Ma strata from inferred sediment sources, but different amounts of slip are feasible.Together, the dike swarms and fluvial strata are interpreted to record Oligocene strike-slip movement along the Denali fault system, coeval with strike-slip basin development along other segments of the fault. Diking and sedimentation occurred just prior to the onset of rapid and persistent exhumation ca. 25 Ma across the Alaska Range. This phase of reactivation of the suture zone is interpreted to reflect the translation along and convergence of southern Alaska across the Denali fault driven by highly coupled flat-slab subduction of the Yakutat microplate, which continues to accrete to the southern margin of Alaska. Furthermore, a change in Pacific plate direction and velocity at ca. 25 Ma created a more convergent regime along the apex of the Denali fault curve, likely contributing to the shutting off of near-fault extension-facilitated arc magmatism along this section of the fault system and increased exhumation rates.

scholarly journals Oligocene-Neogene lithospheric-scale reactivation of Mesozoic terrane accretionary structures in the Alaska Range suture zone, southern Alaska, USA: Comment

2021 ◽  
Author(s):  
Grant Lowey
Keyword(s):  
Suture Zone ◽  
Ultramafic Rocks ◽  
Metamorphic Rocks ◽  
Geologic Mapping ◽  
Alaska Range ◽  
Denali Fault ◽  
South Central ◽  
Ultramafic Complex ◽  
History Of ◽  
Ultramafic Intrusion

Waldien et al. (2021) present new bedrock geologic mapping, U-Pb geochronology, and 40Ar/39Ar thermochronology from the eastern Alaska Range in south-central Alaska to determine the burial and exhumation history of metamorphic rocks associated with the Alaska Range suture zone, interpret the history of faults responsible for the burial and exhumation of the metamorphic rocks, and speculate on the relative importance of the Alaska Range suture zone and related structures during Cenozoic reactivation. They also propose that ultramafic rocks in their Ann Creek map area in south-central Alaska (herein referred to as the “Ann Creek ultramafic complex”) correlate with the Pyroxenite Creek ultramafic complex in southwestern Yukon, and that this correlation is “consistent with other estimates of >400 km” of offset on the Denali fault. However, despite Waldien et al.’s (2021) claim that the purportedly offset ultramafic rocks are “similar” and that characteristics of the Ann Creek ultramafic complex “make a strong case” for a faulted portion of an Alaska-type ultramafic intrusion, their paper gives short shrift in describing the Pyroxenite Creek ultramafic complex and in discussing previous estimates of displacement on the Denali fault. In Addition, Waldien et al. (2021) are either unaware of or ignore several key references of the Pyroxenite Creek ultramafic complex and estimates of displacement on the Denali fault. As a result, Waldien et al.’s (2021) claim of a “correlation” between allegedly offset ultramafic rocks is suspect, and their reference to “other estimates of >400 km” of offset on the Denali fault is incorrect, or at the very least misleading.

Structural geology of the Nenana River segment of the Denali fault system, central Alaska Range

1977 ◽  
Vol 88 (9) ◽  
pp. 1217 ◽  
Author(s):  
ROBERT G. HICKMAN ◽  
CAMPBELL CRADDOCK ◽  
KIRK W. SHERWOOD
Keyword(s):  
Structural Geology ◽  
Fault System ◽  
Alaska Range ◽  
Denali Fault

SEDIMENTARY AND VOLCANIC RECORD OF NEOGENE TRANSPRESSIONAL FORELAND BASIN DEVELOPMENT ALONG THE CENTRAL DENALI FAULT SYSTEM, EASTERN ALASKA RANGE

2016 ◽  
Author(s):  
Wai K. Allen ◽  
◽  
Kenneth D. Ridgway ◽  
Jeff Benowitz ◽  
Trevor S. Waldien ◽  
...  
Keyword(s):  
Foreland Basin ◽  
Fault System ◽  
Alaska Range ◽  
Denali Fault ◽  
Basin Development

Mesozoic and Cenozoic tectonics of the eastern and central Alaska Range: Progressive basin development and deformation in a suture zone

2002 ◽  
Vol 114 (12) ◽  
pp. 1480-1504 ◽  
Author(s):  
Kenneth D. Ridgway ◽  
Jeffrey M. Trop ◽  
Warren J. Nokleberg ◽  
Cameron M. Davidson ◽  
Kevin R. Eastham
Keyword(s):  
Suture Zone ◽  
Alaska Range ◽  
Basin Development ◽  
Cenozoic Tectonics
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