Stratigraphy, age, and provenance of the Eocene Chumstick basin, Washington Cascades; implications for paleogeography, regional tectonics, and development of strike-slip basins

2021 ◽  
Author(s):  
Erin E. Donaghy ◽  
Paul J. Umhoefer ◽  
Michael P. Eddy ◽  
Robert B. Miller ◽  
Taylor LaCasse
Keyword(s):  
Sediment Accumulation ◽  
Sedimentary Basins ◽  
River System ◽  
Strike Slip ◽  
Depositional Environments ◽  
Sediment Supply ◽  
Sediment Provenance ◽  
High Temporal Resolution ◽  
Sediment Routing ◽  
Depositional Architecture

Strike-slip faults form in a wide variety of tectonic settings and are a first-order control on the geometry and sediment accumulation patterns in adjacent sedimentary basins. Although the structural and depositional architecture of strike-slip basins is well documented, few studies of strike-slip basins have integrated depositional age, lithofacies, and provenance control within this context. The Chumstick basin formed in central Washington during a regional phase of dextral, strike-slip faulting and episodic magmatism associated with Paleogene ridge-trench interaction along the North America margin. The basin is bounded and subdivided by major strike-slip faults that were active during deposition of the intra-basinal, non-marine Chumstick Formation. We build on the existing stratigraphy and present new, detailed lithofacies mapping, conglomerate clast counts (N = 16; n = 1429), and sandstone detrital zircon analyses (N = 16; n = 1360) from the Chumstick Formation to document changes in sediment provenance, routing, and deposition. These data allow us to reconstruct regional Eocene paleo-drainage systems of Washington and Oregon and suggest that drainage within the Chumstick basin fed a regional river system that flowed to a forearc or marginal basin on the newly accreted Siletzia terrane. More generally, excellent age control from five interbedded tuffs and high sediment accumulation rates allow us to track the evolving sedimentary system over the Formation’s ca. 4−5 m.y. depositional history. This is the first time lithofacies and provenance variations can be constrained at high temporal resolution (0.5−1.5 m.y. scale) for an ancient strike-slip basin and permits a detailed reconstruction of sediment routing pathways and depositional environments. As a result, we can assess how varying sediment supply and accommodation space affects the depositional architecture during strike-slip basin evolution.

From surface processes modelling to high-resolution drilling record: resolving key controls on sediment production and stratigraphic development in the Corinth Rift, Greece

2021 ◽  
Author(s):  
Sofia Pechlivanidou
Keyword(s):  
Process Model ◽  
Sediment Accumulation ◽  
Drainage System ◽  
Sediment Supply ◽  
Surface Processes ◽  
High Temporal Resolution ◽  
Seismic Reflection Data ◽  
Sediment Production ◽  
Drilling Data ◽  
The Impact

<p>The Corinth Rift, Greece, is a young (~5 Ma) sea-level controlled rift and one of the most rapidly extending areas on Earth. The unique combination of high strain and sedimentation rate with a closed drainage system and the well preserved syn-rift sedimentary record makes the Corinth Rift an ideal laboratory for understanding interactions between surface processes and tectonics and their implications for syn-rift stratigraphy.</p><p>The Corinth Rift has exceptional onshore and offshore field data coverage and as such it represents one of the best natural examples for model calibration. To this end, offshore sediment packages mapped from seismic reflection data were used to validate the surface process model pyBadlands, by comparing the total real and modeled sediment volumes and deposition patterns over the past 130 kyr.  Our results shed light on the impact of tectonic forcing on sediment fluxes by showing that sediment supply to the rift is not primarily controlled by relief development, but instead by tectonically-driven tilting of the landscape. This is the first time that this has been demonstrated for a natural system and challenges the view that relief is a key control on catchment averaged erosion rates.</p><p>Moreover, recent drilling data from IODP Expedition 381 in the Corinth Rift generated a complete record of the syn-rift sequence offshore and provided the first age constraints to enable us to resolve sediment accumulation rates with high temporal resolution. The new cores record climate-driven cyclic variations in the basin paleoenvironment, alternating between glacial/isolated and interglacial/marine periods. A key finding is that sedimentation rates are <span>markedly </span><span>increased during glacial/isolated periods. Furthermore, bed frequency and bed thicknesses show significant stratigraphic variability and highlight the dominance of gravity flow sedimentation which represents > 60% of the total sedimentation during the last glacial-interglacial cycle.</span></p><p>This extraordinary offshore drilling data when combined with surface processes modelling will provide an unprecedented opportunity to address the challenge of resolving tectonic versus climatic controls on sediment production and stratigraphic development within rift basins.</p>

Transient landscape response to abrupt precipitation increase at the Pleistocene-Holocene transition, offshore Sumatra

2021 ◽  
Author(s):  
Sarah Mosser ◽  
Anne Bernhardt ◽  
Mahyar Mohtadi ◽  
Tilmann Schwenk
Keyword(s):  
High Resolution ◽  
Time Scale ◽  
Landscape Evolution ◽  
Sediment Cores ◽  
Sediment Accumulation ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Sediment Routing ◽  
Precipitation Increase ◽  
Compositional Changes

<p>Active continental margins play a major role in exporting terrestrial sediment to the oceans. Yet, the response of a sediment-routing system to a specific climate change is poorly quantified. The terrestrial-to-marine sediment-routing systems on West Sumatra can be used as a natural laboratory to quantify these changes. Rivers efficiently deliver sediment from the high-relief Barisan mountains to the enclosed marine forearc Mentawai Basin along this active subduction margin. The Holocene climatic history of the region is well known and shows an abrupt precipitation increase at the Pleistocene-Holocene transition (~12 ka BP) as recorded previously in δ<sup>18</sup>O time-series measured on planktonic foraminifera.</p><p>Here we analyze multiple late Quaternary sediment records spanning the last 14 ka from the Mentawai Basin, offshore Sumatra. We use volumetric sediment budgets and multivariate statistics on high-resolution elemental compositions to assess changes in sediment flux and composition based on ~150 km of high-resolution sub-bottom sediment profiles (covering 435 km²) and six sediment cores. Radiocarbon ages were taken at every ~35 cm within the sediment cores.</p><p>Our results, from sediment budget calculation and sedimentation rates within the cores, show that absolute rates of sediment supply to the marine forearc basin remained constant throughout the Holocene (542-566 g/m²/yr, 68% quantile, 0.1 and 0.2 cm/yr, respectively). However, the sediment composition varies drastically with comparable patterns all over the basin. The compositional changes are characterized by an 8000-year damped oscillation between terrestrial clastic (Al, Si, Ti, Zr, Fe, K, Rb) and marine authigenic (Ca, Sr) sediment supply. From ~12 to 8 ka BP, the relative amount of clastic rock-forming elements is increasing, then decreasing from ~8 to 4 ka BP, and finally increasing again from 4 ka BP to the present. Using a dynamical system modeling approach, we link the beginning of this oscillation to the abrupt precipitation increase at the interglacial transition at ~ 12 ka BP. We interpret the oscillation to reflect a persistent erosional feedback between physical and chemical weathering caused by ongoing landscape adaptation to the abrupt Pleistocene-Holocene transition. The total amount of sediment accumulation, however, does not follow this trend. Thus, the sedimentary composition shows ongoing landscape transience, whereas the uniform sediment accumulation rates imply a landscape in steady state.</p><p>These results have two major implications for future landscape evolution: a) the time scale of landscape transience far exceeds the time scale of abrupt climate transition, b) in this study, the sediment flux to the ocean floor does not mirror landscape transience because the excess terrestrial clastic sediment is compensated by decreased deposition of marine carbonates. These implications call for the implementation of compositional changes of exported sediments into landscape evolution models since so far most landscape models focus on the amount of exported sediment.</p>

Seismic Energy Release from Intra-Basin Sources along the Dead Sea Transform and Its Influence on Regional Ground Motions

2020 ◽  
Author(s):  
Roey Shimony ◽  
Zohar Gvirtzman ◽  
Michael Tsesarsky
Keyword(s):  
Ground Motions ◽  
Seismic Energy ◽  
Sedimentary Basins ◽  
Seismic Wave Propagation ◽  
Dead Sea ◽  
Strike Slip ◽  
Dead Sea Transform ◽  
Bay Area ◽  
The Dead ◽  
Surrounding Areas

ABSTRACT The Dead Sea Transform (DST) dominates the seismicity of Israel and neighboring countries. Whereas the instrumental catalog of Israel (1986–2017) contains mainly M<5 events, the preinstrumental catalog lists 14 M 7 or stronger events on the DST, during the past two millennia. Global Positioning System measurements show that the slip deficit in northern Israel today is equivalent to M>7 earthquake. This situation highlights the possibility that a strong earthquake may strike north Israel in the near future, raising the importance of ground-motion prediction. Deep and narrow strike-slip basins accompany the DST. Here, we study ground motions produced by intrabasin seismic sources, to understand the basin effect on regional ground motions. We model seismic-wave propagation in 3D, focusing on scenarios of Mw 6 earthquakes, rupturing different active branches of the DST. The geological model includes the major structures in northern Israel: the strike-slip basins along the DST, the sedimentary basins accompanying the Carmel fault zone, and the densely populated and industrialized Zevulun Valley (Haifa Bay area). We show that regional ground motions are determined by source–path coupling effects in the strike-slip basins, before waves propagate into the surrounding areas. In particular, ground motions are determined by the location of the rupture nucleation within the basin, the near-rupture lithology, and the basin’s local structure. When the rupture is located in the crystalline basement or along material bridges connecting opposite sides of the fault, ground motions behave predictably, decaying due to geometrical spreading and locally amplified atop sedimentary basins. By contrast, if rupture nucleates or propagates into shallow sedimentary units of the DST strike-slip basins, ground motions are amplified within, before propagating outside. Repeated reflections from the basin walls result in a “resonant chamber” effect, leading to stronger regional ground motions with prolonged durations.

scholarly journals Holocene sea level and climate interactions on wet dune slack evolution in SW Portugal: A model for future scenarios?

The Holocene ◽  
2018 ◽  
Vol 29 (1) ◽  
pp. 26-44 ◽  
Author(s):  
Manel Leira ◽  
Maria C Freitas ◽  
Tania Ferreira ◽  
Anabela Cruces ◽  
Simon Connor ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Environmental Changes ◽  
Sediment Accumulation ◽  
High Energy ◽  
Sediment Supply ◽  
Dune Slack ◽  
Ecological Stability ◽  
The Holocene ◽  
Climate Interactions

We examine the Holocene environmental changes in a wet dune slack of the Portuguese coast, Poço do Barbarroxa de Baixo. Lithology, organic matter, biological proxies and high-resolution chronology provide estimations of sediment accumulation rates and changes in environmental conditions in relation to sea-level change and climate variability during the Holocene. Results show that the wet dune slack was formed 7.5 cal. ka BP, contemporaneous with the last stages of the rapid sea-level rise. This depositional environment formed under frequent freshwater flooding and water ponding that allowed the development and post-mortem accumulation of abundant plant remains. The wetland evolved into mostly palustrine conditions over the next 2000 years, until a phase of stabilization in relative sea-level rise, when sedimentation rates slowed down to 0.04 mm yr−1, between 5.3 and 2.5 cal. ka BP. Later, about 0.8 cal. ka BP, high-energy events, likely due to enhanced storminess and more frequent onshore winds, caused the collapse of the foredune above the wetlands’ seaward margin. The delicate balance between hydrology (controlled by sea-level rise and climate change), sediment supply and storminess modulates the habitat’s resilience and ecological stability. This underpins the relevance of integrating past records in coastal wet dune slacks management in a scenario of constant adaptation processes.

The Toba Volcanic Event and Interstadial/Stadial Climates at the Marine Isotopic Stage 5 to 4 Transition in the Northern Indian Ocean

2002 ◽  
Vol 57 (1) ◽  
pp. 22-31 ◽  
Author(s):  
Hartmut Schulz ◽  
Kay-Christian Emeis ◽  
Helmut Erlenkeuser ◽  
Ulrich von Rad ◽  
Christian Rolf
Keyword(s):  
Arabian Sea ◽  
Water Productivity ◽  
Ice Core ◽  
Sediment Cores ◽  
Sediment Accumulation ◽  
Sediment Supply ◽  
Volcanic Event ◽  
Additional Support ◽  
Marine Isotope Stage 5 ◽  
A Minor

AbstractThe Toba volcanic event, one of the largest eruptions during the Quaternary, is documented in marine sediment cores from the northeastern Arabian Sea. On the crest of the Murray Ridge and along the western Indian continental margin, we detected distinct concentration spikes and ash layers of rhyolithic volcanic shards near the marine isotope stage 5–4 boundary with the chemical composition of the “Youngest Toba Tuff.” Time series of the Uk′37-alkenone index, planktic foraminiferal species, magnetic susceptibility, and sediment accumulation rates from this interval show that the Toba event occurred between two warm periods lasting a few millennia. Using Toba as an instantaneous stratigraphic marker for correlation between the marine- and ice-core chronostratigraphies, these two Arabian Sea climatic events correspond to Greenland interstadials 20 and 19, respectively. Our data sets thus depict substantial interstadial/stadial fluctuations in sea-surface temperature and surface-water productivity. We show that variable terrigenous (eolian) sediment supply played a crucial role in transferring and preserving the productivity signal in the sediment record. Within the provided stratigraphic resolution of several decades to centennials, none of these proxies shows a particular impact of the Toba eruption. However, our results are additional support that Toba, despite its exceptional magnitude, had only a minor impact on the evolution of low-latitude monsoonal climate on centennial to millennial time scales.

Sediment slugs: large-scale fluctuations in fluvial sediment transport rates and storage volumes

1995 ◽  
Vol 19 (4) ◽  
pp. 500-519 ◽  
Author(s):  
A.P. Nicholas ◽  
P.J. Ashworth ◽  
M.J. Kirkby ◽  
M.G. Macklin ◽  
T. Murray
Keyword(s):  
Sediment Transport ◽  
Sediment Supply ◽  
Fluvial Systems ◽  
Event Scale ◽  
Fluvial Sediment ◽  
Sediment Routing ◽  
Basin Scale ◽  
Wide Range ◽  
And Storage ◽  
Fluvial Sediment Transport

Variations in fluvial sediment transport rates and storage volumes have been described previously as sediment waves or pulses. These features have been identified over a wide range of temporal and spatial scales and have been categorized using existing bedform classifications. Here we describe the factors controlling the generation and propagation of what we term sediment slugs. These can be defined as bodies of clastic material associated with disequilibrium conditions in fluvial systems over time periods above the event scale. Slugs range in magnitude from unit bars (Smith, 1974) up to sedimentary features generated by basin-scale sediment supply disturbances (Trimble, 1981). At lower slug magnitudes, perturbations in sediment transport are generated by local riverbank and/or bed erosion. Larger-scale features result from the occurrence of rare high- magnitude geomorphic events, and the impacts on water and sediment production of tectonics, glaciation, climate change and anthropogenic influences. Simple sediment routing functions are presented which may be used to describe the propagation of sediment slugs in fluvial systems. Attention is drawn to components of the fluvial system where future research is urgently required to improve our quantitative understanding of drainage-basin sediment dynamics.

scholarly journals Three-dimensional approach to understanding the relationship between the Plio-Quaternary stress field and tectonic inversion in the Triassic Cuyo Basin, Argentina

2015 ◽  
Vol 7 (1) ◽  
pp. 459-494
Author(s):  
L. Giambiagi ◽  
S. Spagnotto ◽  
S. M. Moreiras ◽  
G. Gómez ◽  
E. Stahlschmidt ◽  
...  
Keyword(s):  
Stress Field ◽  
Three Dimensional ◽  
Sedimentary Basins ◽  
Strike Slip ◽  
Stress Regime ◽  
Basin Inversion ◽  
Structural Style ◽  
Tectonic Inversion ◽  
The Impact ◽  
The Relationship

Abstract. The Cacheuta sub-basin of the Triassic Cuyo Basin is an example of rift basin inversion contemporaneous to the advance of the Andean thrust front, during the Plio-Quaternary. This basin is one of the most important sedimentary basins in a much larger Triassic NNW-trending depositional system along the southwestern margin of the Pangea supercontinent. The amount and structural style of inversion is provided in this paper by three-dimensional insights into the relationship between inversion of rift-related structures and spatial variations in late Cenozoic stress fields. The Plio-Quaternary stress field exhibits important N–S variations in the foreland area of the Southern Central Andes, between 33 and 34° S, with a southward gradually change from pure compression with σ1 and σ2 being horizontal, to a strike-slip type stress field with σ2 being vertical. We present a 3-D approach for studying the tectonic inversion of the sub-basin master fault associated with strike-slip/reverse to strike-slip faulting stress regimes. We suggest that the inversion of Triassic extensional structures, striking NNW to WNW, occurred during the Plio–Pleistocene in those areas with strike-slip/reverse to strike-slip faulting stress regime, while in the reverse faulting stress regime domain, they remain fossilized. Our example demonstrates the impact of the stress regime on the reactivation pattern along the faults.

Sedimentology and Evolution of the Fluvial-Deltaic System: A Modern Depositional Model Analog from the Red Sea Coastal Region, Saudi Arabia

2021 ◽  
Author(s):  
Osman Abdullatif ◽  
Mutasim Osman ◽  
Mazin Bashri ◽  
Ammar Abdlmutalib ◽  
Mohamed Yassin
Keyword(s):  
Red Sea ◽  
Coastal Plain ◽  
Depositional Environments ◽  
Hydrocarbon Reservoirs ◽  
Sediment Supply ◽  
Arabian Shield ◽  
Space And Time ◽  
Groundwater Aquifers ◽  
Coastal Sabkha ◽  
Lithofacies Association

Abstract Siliciclastic sediments represent important lithological unit of the Red Sea coastal plain. Their subsurface equivalents are important targets of groundwater aquifer and hydrocarbon reservoirs in the region. The lithofacies of the modern fluvial deltaic system has several distinct geomorphic units and sub-environments such as alluvial, fluvial, delta plain, aeolian, intertidal, coastal sabkha and eustuarine sediments. This study intends to characterize the lithofacies and the depositional environments and to produce an integrated facies model for this modern fluvial-deltaic system. The study might provide a valuable modern analog to several important subsurface Neogene formations that act as important hydrocarbon reservoirs and groundwater aquifers. The study integrates information and data obtained from landsats, maps and detailed field observation and measurements of facies analysis of the fluvial and deltaic along traveses from the Arabian Shield to the Red Sea coast. The lithofacies sediment analysis revealed four main lithofacies associations namely lithofacies A,B,C ad D. Lithoacies Associations A, which represents the oldest unit is dominated by coarse gravel with minor sands facies. While the lithofacies B is dominated byfine gravel and sand lithofacies, occasionally pebbly, vary from horizontal, planar to massive sands with minor laminated to massive silts and mud facies. The lithofacies in A and B show lateral proximal to distal variation as well as characteristic vertical stacking patterns. The Facies Association A and B indicates a change in fluvial depositional styles from gravelly alluvial fans to gravelly sandy fluvial systems. The lithofacies association C represents the recent fluvial system which consists of minor gravel lag deposits associated maily with various sand lithofacies of planner, horizontal and massive sand associated with massive and limainted sand and mud lithofacies. The lithofacies Association D is dominated with Barchan sand dunes local interfigger with muddy iinterdunes and sand sheets. Lithofacies D occupies rather more distal geomporphic position of the fluvial deltaic system that is adjace to coastal sabkha. The lithofacies associations described here document the evolution and development of the coastal plain sediments through space and time under various autocyclic and allocyclic controls. This included the tectonics and structural development associated with the Red Sea rifting and opening since the Oligocene – Miocene time. Others controls include the evolution of the Arabian shield (provenance) and the coastal plain through space and time as controlled by tectonics, sediment supply, climate and locally by autocyclic environmental This study might be beneficial for understanding the controls and stratigraphic evolution of the Red Sea region and will be of great value for reservoir and aquifer characterization, development and management. This modern analog model can also help in providing geological baseline information that would be beneficial for understanding similar ancient fluvial deltaic sediments. The study might provide guides and leads to understand the subsurface facies, stratigraphic architecture and heterogeneity of any potential groundwater aquifers and hydrocarbon reservoirs.

Competing sediment sources during Paleozoic closure of the Marathon-Ouachita remnant ocean basin

2019 ◽  
Vol 132 (1-2) ◽  
pp. 3-16 ◽  
Author(s):  
Zihui Gao ◽  
Nicholas D. Perez ◽  
Brent Miller ◽  
Michael C. Pope
Keyword(s):  
Ocean Basin ◽  
Sediment Provenance ◽  
Thrust Belt ◽  
Sediment Sources ◽  
Volcanic Arc ◽  
Delaware Basin ◽  
Continental Scale ◽  
Sediment Routing ◽  
West Texas ◽  
Fold And Thrust Belt

Abstract The Paleozoic construction of Pangea advanced southwestward from the Appalachian system to the Marathon fold-and-thrust belt in west Texas and progressively closed a remnant ocean basin between Laurentia and Gondwana. The resulting collisional orogen was a potential driver of Ancestral Rocky Mountain tectonism and impacted continental-scale sediment routing. New detrital zircon U-Pb geochronologic and heavy mineral provenance data from Ordovician–Pennsylvanian strata in the Marathon fold-and-thrust belt, and Permian strata in the Guadalupe Mountains of west Texas record changes in sediment provenance during the tectonic development of southwestern Laurentia and the Delaware Basin. In the Marathon fold-and-thrust belt, Ordovician rocks (Woods Hollow and Marathon Formations) record peri-Gondwanan sediment sources prior to continent collision. Syncollisional Mississippian and Pennsylvanian rocks (Tesnus, Haymond, Gaptank Formations) record contributions from distal Appalachian sources, recycled material from the active continental suture, and volcanic arc material from Gondwana. Near the Guadalupe Mountains, postcollisional Permian strata (Delaware Mountain Group) from the northern Delaware Basin margin suggest a dominantly southern catchment that was sourced from the deforming suture and Gondwanan arc. The results demonstrate that both plates and the active suture zone were sources for the siliciclastic wedge, but their proportions differed through time. These results also suggest that the delay between initial late Mississippian suturing in the Marathon region and increased mid-Permian siliciclastic deposition into the northern Delaware Basin may have been linked to a southward catchment expansion that integrated the collisional belt and southern volcanic arc into a broadly north-directed sediment dispersal system.

Accelerating exhumation in the Eocene North American Cordilleran hinterland: Implications from detrital zircon (U-Th)/(He-Pb) double dating

2019 ◽  
Vol 132 (1-2) ◽  
pp. 198-214 ◽  
Author(s):  
Andrew S. Canada ◽  
Elizabeth J. Cassel ◽  
Daniel F. Stockli ◽  
M. Elliot Smith ◽  
Brian R. Jicha ◽  
...  
Keyword(s):  
North American ◽  
Detrital Zircon ◽  
Sedimentary Basins ◽  
Metamorphic Core Complex ◽  
Crustal Thickening ◽  
Sediment Provenance ◽  
Core Complex ◽  
Extensional Faulting ◽  
Lag Times ◽  
Metamorphic Core

AbstractBasins in orogenic hinterlands are directly coupled to crustal thickening and extension through landscape processes and preserve records of deformation that are unavailable in footwall rocks. Following prolonged late Mesozoic–early Cenozoic crustal thickening and plateau construction, the hinterland of the Sevier orogen of western North America underwent late Cenozoic extension and formation of metamorphic core complexes. While the North American Cordillera is one of Earth’s best-studied orogens, estimates for the spatial and temporal patterns of initial extensional faulting differ greatly and thus limit understanding of potential drivers for deformation. We employed (U-Th)/(He-Pb) double dating of detrital zircon and (U-Th)/He thermochronology of detrital apatite from precisely dated Paleogene terrestrial strata to quantify the timing and magnitude of exhumation and explore the linkages between tectonic unroofing and basin evolution in northeastern Nevada. We determined sediment provenance and lag time evolution (i.e., the time between cooling and deposition, which is a measure of upper-crustal exhumation) during an 8 m.y. time span of deposition within the Eocene Elko Basin. Fluvial strata deposited between 49 and 45 Ma yielded Precambrian (U-Th)/He zircon cooling ages (ZHe) with 105–740 m.y. lag times dominated by unreset detrital ages, suggesting limited exhumation and Proterozoic through early Eocene sediment burial (<4–6 km) across the region. Minimum nonvolcanic detrital ZHe lag times decreased to <100 m.y. in 45–43 Ma strata and to <10 m.y. in 43–41 Ma strata, illustrating progressive and rapid hinterland unroofing in Eocene time. Detrital apatite (U-Th)/He ages present in ca. 44 and 39 Ma strata record Eocene cooling ages with 1–20 m.y. lag times. These data reflect acceleration of basement exhumation rates by >1 km/m.y., indicative of rapid, large-magnitude extensional faulting and metamorphic core complex formation. Contemporaneous with this acceleration of hinterland exhumation, syntectonic freshwater lakes developed in the hanging wall of the Ruby Mountains–East Humboldt Range metamorphic core complex at ca. 43 Ma. Volcanism driven by Farallon slab removal migrated southward across northeastern Nevada, resulting in voluminous rhyolitic eruptions at 41.5 and 40.1 Ma, and marking the abrupt end of fluvial and lacustrine deposition across much of the Elko Basin. Thermal and rheologic weakening of the lithosphere and/or partial slab removal likely initiated extensional deformation, rapidly unroofing deeper crustal levels. We attribute the observed acceleration in exhumation, expansion of sedimentary basins, and migrating volcanism across the middle Eocene to record the thermal and isostatic effects of Farallon slab rollback and subsequent removal of the lowermost mantle lithosphere.

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