Cenozoic tectono-thermal history of the southern Talkeetna Mountains, Alaska: Insights into a potentially alternating convergent and transform plate margin

Abstract The Mesozoic–Cenozoic convergent margin history of southern Alaska has been dominated by arc magmatism, terrane accretion, strike-slip fault systems, and possible spreading-ridge subduction. We apply 40Ar/39Ar, apatite fission-track (AFT), and apatite (U-Th)/He (AHe) geochronology and thermochronology to plutonic and volcanic rocks in the southern Talkeetna Mountains of Alaska to document regional magmatism, rock cooling, and inferred exhumation patterns as proxies for the region’s deformation history and to better delineate the overall tectonic history of southern Alaska. High-temperature 40Ar/39Ar thermochronology on muscovite, biotite, and K-feldspar from Jurassic granitoids indicates postemplacement (ca. 158–125 Ma) cooling and Paleocene (ca. 61 Ma) thermal resetting. 40Ar/39Ar whole-rock volcanic ages and 45 AFT cooling ages in the southern Talkeetna Mountains are predominantly Paleocene–Eocene, suggesting that the mountain range has a component of paleotopography that formed during an earlier tectonic setting. Miocene AHe cooling ages within ∼10 km of the Castle Mountain fault suggest ∼2–3 km of vertical displacement and that the Castle Mountain fault also contributed to topographic development in the Talkeetna Mountains, likely in response to the flat-slab subduction of the Yakutat microplate. Paleocene–Eocene volcanic and exhumation-related cooling ages across southern Alaska north of the Border Ranges fault system are similar and show no S-N or W-E progressions, suggesting a broadly synchronous and widespread volcanic and exhumation event that conflicts with the proposed diachronous subduction of an active west-east–sweeping spreading ridge beneath south-central Alaska. To reconcile this, we propose a new model for the Cenozoic tectonic evolution of southern Alaska. We infer that subparallel to the trench slab breakoff initiated at ca. 60 Ma and led to exhumation, and rock cooling synchronously across south-central Alaska, played a primary role in the development of the southern Talkeetna Mountains, and was potentially followed by a period of southern Alaska transform margin tectonics.

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Rock and age relationships within the Talkeetna forearc accretionary complex in the Nelchina area, southern Alaska

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2018-0268 ◽

2020 ◽

Vol 57 (6) ◽

pp. 709-724

Author(s):

John Barefoot ◽

Elisabeth S. Nadin ◽

Rainer J. Newberry ◽

Alfredo Camacho

Keyword(s):

Subduction Zone ◽

Elevated Temperatures ◽

Accretionary Prism ◽

Fault System ◽

Petrographic Analysis ◽

Spreading Ridge ◽

Current Configuration ◽

Ridge Subduction ◽

South Central ◽

Subduction Zone Processes

Subduction zone processes are challenging to study because of the rarity of good exposures and the complexity of rock relationships within accretionary prisms. We report the results of field mapping and petrographic, geochemical, and geochronological analyses of the McHugh Complex accretionary prism mélange in south-central Alaska that was recently exposed due to retreat of the Nelchina Glacier. Our new mapping and analyses of the mélange, as well as adjacent Talkeetna arc intrusives, suggests that the previously mapped trace of the Border Ranges fault should shift northward in this location. Detailed petrographic analysis places this mélange exposure with the Potter Creek assemblage of the McHugh Complex. Blocks of pillow lavas within the mélange have both mid-ocean ridge basalt and intra-plate geochemical affinities, attesting to the complex relations of subduction-zone inputs in an alternating erosive–accretionary margin. A new zircon U–Pb age and geochemical analyses of a set of felsic dikes that cross-cut the accretionary sequence provide constraints on the regional tectonic evolution, including near-trench plutonism associated with the migration of a subducting spreading ridge along the southern Alaska margin during the Paleocene–Eocene. The McHugh section and cross-cutting dikes in this location are pervasively hydrothermally altered, which we attribute to elevated temperatures related to ridge subduction. Late-stage motion along the Border Ranges fault system, which is also recorded in the area, may also have contributed to the widespread alteration. Our data indicate that the Talkeetna volcanic arc and associated accretionary prism sediments were in their current configuration by 55 Ma.

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The role of Central American barriers in shaping the evolutionary history of the northernmost glassfrog,Hyalinobatrachium fleischmanni(Anura: Centrolenidae)

PeerJ ◽

10.7717/peerj.6115 ◽

2019 ◽

Vol 7 ◽

pp. e6115 ◽

Cited By ~ 4

Author(s):

Angela M. Mendoza ◽

Wilmar Bolívar-García ◽

Ella Vázquez-Domínguez ◽

Roberto Ibáñez ◽

Gabriela Parra Olea

Keyword(s):

Genetic Structure ◽

Central America ◽

Population Expansion ◽

Central American ◽

Fault System ◽

Mountain Range ◽

Amphibian Species ◽

Biogeographic History ◽

History Of ◽

The Impact

The complex geological history of Central America has been useful for understanding the processes influencing the distribution and diversity of multiple groups of organisms. Anurans are an excellent choice for such studies because they typically exhibit site fidelity and reduced movement. The objective of this work was to identify the impact of recognized geographic barriers on the genetic structure, phylogeographic patterns and divergence times of a wide-ranging amphibian species,Hyalinobatrachium fleischmanni. We amplified three mitochondrial regions, two coding (COI and ND1) and one ribosomal (16S), in samples collected from the coasts of Veracruz and Guerrero in Mexico to the humid forests of Chocó in Ecuador. We examined the biogeographic history of the species through spatial clustering analyses (Geneland and sPCA), Bayesian and maximum likelihood reconstructions, and spatiotemporal diffusion analysis. Our data suggest a Central American origin ofH. fleischmanniand two posterior independent dispersals towards North and South American regions. The first clade comprises individuals from Colombia, Ecuador, Panama and the sister speciesHyalinobatrachium tatayoi; this clade shows little structure, despite the presence of the Andes mountain range and the long distances between sampling sites. The second clade consists of individuals from Costa Rica, Nicaragua, and eastern Honduras with no apparent structure. The third clade includes individuals from western Honduras, Guatemala, and Mexico and displays deep population structure. Herein, we synthesize the impact of known geographic areas that act as barriers to glassfrog dispersal and demonstrated their effect of differentiatingH. fleischmanniinto three markedly isolated clades. The observed genetic structure is associated with an initial dispersal event from Central America followed by vicariance that likely occurred during the Pliocene. The southern samples are characterized by a very recent population expansion, likely related to sea-level and climatic oscillations during the Pleistocene, whereas the structure of the northern clade has probably been driven by dispersal through the Isthmus of Tehuantepec and isolation by the Motagua–Polochic–Jocotán fault system and the Mexican highlands.

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River profile response to normal fault growth and linkage: An example from the Hellenic forearc of south-central Crete, Greece

10.5194/esurf-2016-52 ◽

2016 ◽

Cited By ~ 1

Author(s):

Sean F. Gallen ◽

Karl W. Wegmann

Keyword(s):

Drainage Basin ◽

Profile Analysis ◽

Normal Fault ◽

Drainage Area ◽

Fault System ◽

Stream Power ◽

River Incision ◽

South Central ◽

History Of ◽

Fault Growth

Abstract. Topography is a reflection of the tectonic and geodynamic processes that act to uplift the Earth's surface and the erosional processes that work to return it to base level. Numerous studies have shown that topography is a sensitive recorder or tectonic signals. A quasi-physical understanding of the relationship between river incision and rock uplift has made the analysis of fluvial topography a popular technique for deciphering relative, and some argue absolute, histories of rock uplift. Here we present results from a study of the fluvial topography from south-central Crete demonstrating that river longitudinal profiles indeed record the relative history of uplift, but several other processes make it difficult to recover quantitative uplift histories. Prior research demonstrates that the south-central coastline of Crete is bound by a large (~100 km long) E-W striking composite normal fault system. Marine terraces reveal that it is uplifting between 0.1–1.0 mm yr−1. These studies suggest that two normal fault systems, the offshore Ptolemy and onshore South-Central Crete faults linked together in the recent geologic past (Ca. 0.4–1 Myrs bp). Fault mechanics predicts that when adjacent faults link into a single fault the uplift rate in the linkage zone will increase rapidly. Using river profile analysis we show that rivers in south-central Crete record the relative uplift history of fault growth and linkage, as theory predicts that they should. Calibration of the commonly used stream power incision model shows that the slope exponent, n, is ~ 0.5, contrary to most studies that find n ≥ 1. Analysis of fluvial knickpoints shows that migration distances are not proportional to upstream contributing drainage area, as predicted by the stream power incision model. Maps of the transformed stream distance variable, χ, indicate that drainage basin instability, drainage divide migration and river capture events complicate river profile analysis in south-central Crete. Waterfalls are observed in southern Crete and appear to operate under less efficient and different incision mechanics than assumed by the stream power incision model. Drainage area exchange and waterfall formation are argued to obscure linkages between empirically derived metrics and quasi-physical descriptions of river incision, making is difficult to quantitatively interpret rock uplift histories from river profiles in this setting. Karst hydrology, break down of assumed drainage area-discharge scaling and chemical weathering might also contribute to the failure of the stream power incision model to adequately predict the behavior of the fluvial system in south-central Crete.

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Assessing the role of orogen-parallel faulting in post-orogenic exhumation: low-temperature thermochronology across the Norumbega Fault System, Maine

Canadian Journal of Earth Sciences ◽

10.1139/e07-073 ◽

2008 ◽

Vol 45 (3) ◽

pp. 287-301 ◽

Cited By ~ 11

Author(s):

David P. West ◽

Mary K. Roden-Tice ◽

Jaime K. Potter ◽

Nellie Q. Barnard

Keyword(s):

Low Temperature ◽

New England ◽

Vertical Displacement ◽

Fault System ◽

Late Mesozoic ◽

South Central ◽

History Of ◽

Northern New England ◽

Restraining Bend

As a part of a regional effort to determine the extent of low-temperature thermochronological discontinuities across major orogen-parallel faults in northern New England, 41 apatite fission track (AFT) ages and 11 (U–Th)/He ages are used to constrain the ∼65 to 100 °C cooling history of rocks flanking a 160 km long segment of the Norumbega fault system in southern and south-central Maine. These data are used to evaluate the role of this structure in the late Mesozoic and younger exhumation history of the northern Appalachians. AFT ages flanking the fault system range from 159 to 95 Ma and record cooling below ∼100 °C in the late Mesozoic. (U–Th)/He ages from the same region range from 126 to 100 Ma and record cooling below ∼65 °C. Previously published AFT ages from an ∼40 km long segment of the fault system just north of Casco Bay reveal a dramatic time–temperature discontinuity across the structure and suggest kilometre-scale late Mesozoic displacement in this region. However, new AFT and (U–Th)/He ages along the strike of the Norumbega fault system to the northeast and southwest of this discontinuity show no significant differences in late Mesozoic cooling and suggest no significant displacements occurred along these portions of the fault system during this time. Collectively the data suggest differential late Mesozoic reactivation of the Norumbega fault system with the reactivation localized in areas that had previously experienced episodes of vertical displacement in the late Paleozoic (i.e., the “Casco Bay restraining bend”).

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