scholarly journals The Permian Monos Formation: Stratigraphic and detrital zircon evidence for Permian Cordilleran arc development along the southwestern margin of Laurentia (northwestern Sonora, Mexico)

Geosphere ◽  
2021 ◽  
Author(s):  
Stephen C. Dobbs ◽  
Nancy R. Riggs ◽  
Kathleen M. Marsaglia ◽  
Carlos M. González-León ◽  
M. Robinson Cecil ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Detrital Zircon ◽  
Coastal Upwelling ◽  
Cold Water ◽  
Primary Source ◽  
Leading Edge ◽  
Middle Permian ◽  
Magmatic Arc ◽  
Southwestern Margin ◽  
Laurentian Margin

The southwestern margin of Laurentia transitioned from a left-lateral transform margin to a convergent margin by middle Permian time, which initiated the development of a subduction zone and subsequent Cordilleran arc along western Laurentia. The displaced Caborca block was translated several hundred kilometers from southern California, USA, to modern Sonora, Mexico, beginning in Pennsylvanian time (ca. 305 Ma). The Monos Formation, a ~600-m-thick assemblage of mixed bioclastic and volcaniclastic units exposed in northwestern Sonora, provides lithostratigraphic, petrographic, and geochronologic evidence for magmatic arc development associated with subduction by middle Permian time (ca. 275 Ma). The Monos Formation was deposited in a forearc basin adjacent to a magmatic arc forming along the southwestern Laurentian margin. Detrital zircon U-Pb geochronology suggests that Permian volcanic centers were the primary source for the Monos Formation. These grains mixed with far-traveled zircons from both Laurentia and Gondwana. Zircon age spectra in the Monos Formation are dominated by a ca. 274 Ma population that makes up 65% of all analyzed grains. The remaining 35% of grains range from 3.3 Ga to 0.3 Ma, similar to age spectra from Permian strata deposited in the Paleozoic sequences in the western continental interior. An abundance of Paleozoic through early Neoproterozoic ages suggests that marginal Gondwanan sources from Mexico and Central America also supplied material to the basin. The Monos Formation was deposited within tropical to subtropical latitudes, yet faunal assemblages are biosiliceous and heterotrophic. The lack of photozoan assemblages suggests that cold-water coastal upwelling combined with sedimentation from the Cordilleran arc and Laurentian continent promoted conditions more suitable for fauna resilient to biogeochemically stressed environments. We propose that transform faulting and displacement of the Caborca block ceased by middle Permian time and a subduction zone developed along the southwestern margin of Laurentia as early as early Permian time. The Monos basin developed along the leading edge of the continent as a magmatic arc developed, and facies indicate a consistent shoaling trend over the span of deposition.

A U–Pb geochronological review of the Proterozoic history of the eastern Grenville Province

2002 ◽  
Vol 39 (5) ◽  
pp. 795-829 ◽  
Author(s):  
Charles F Gower ◽  
Thomas E Krogh
Keyword(s):  
Continental Margin ◽  
Leading Edge ◽  
Passive Margin ◽  
Grenville Province ◽  
Mafic Magmatism ◽  
Magmatic Arc ◽  
The North ◽  
Geological Evolution ◽  
Thrust Zone ◽  
Laurentian Margin

The geological evolution of the eastern Grenville Province can be subdivided into three stages. During the first stage, namely pre-Labradorian (> 1710 Ma) and Labradorian (1710–1600 Ma) events, a continental-marginal basin was created and subsequently destroyed during accretion of a magmatic arc formed over a south-dipping subduction zone. Subduction was short-lived and arrested, leading to a passive continental margin. The second stage addresses events between 1600 and 1230 Ma. The passive margin lasted until 1520 Ma, following which a continental-margin arc was constructed during Pinwarian (1520–1460 Ma) orogenesis. Elsonian (1460–1230 Ma) distal-inboard, mafic and anorthositic magmatism, decreasing in age northward, is explained by funnelled flat subduction, possibly associated with an overridden spreading centre. As the leading edge of the lower plate advanced, it was forced beneath the Paleoproterozoic Torngat orogen root between the Archean Superior and North Atlantic cratons, achieving its limit of penetration by 1290 Ma. Static north-northeast-trending rifting then ensued, with mafic magmatism flanked by felsic products to the north and south. Far-field orogenic effects heralded the third stage, lasting from 1230 to 955 Ma. Until 1180 Ma, the eastern Grenville Province was under the distal, mild influence of Elzevirian orogenesis. From 1180 to 1120 Ma, mafic and anorthositic magmatism occurred, attributed to back-arc tectonism inboard of a post-Elzevirian Laurentian margin. Quiescence then prevailed until Grenvillian (1080–980 Ma) continent–continent collision. Grenvillian orogenesis peaked in different places at different times as thrusting released stress, thereby precipitating its shift elsewhere (pressure-point orogenesis). High-grade metamorphism, thrusting and minor magmatism characterized the Exterior Thrust Zone, in contrast to voluminous magmatism in the Interior Magmatic Belt. Following final deformation, early posttectonic anorthositic–alkalic–mafic magmatism (985–975 Ma) and late posttectonic monzonitic–syenite–granite magmatism (975–955 Ma) brought the active geological evolution of this region to a close.

scholarly journals Tectonic influence on axial-transverse sediment routing in the Denver Basin

2022 ◽  
Author(s):  
Glenn R. Sharman ◽  
Daniel F. Stockli ◽  
Peter Flaig ◽  
Robert G. Raynolds ◽  
Marieke Dechesne ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
Detrital Zircon ◽  
Foreland Basin ◽  
The Other ◽  
Front Range ◽  
Denver Basin ◽  
Dispersal Patterns ◽  
Magmatic Arc ◽  
Sedimentary Sequences ◽  
Basin Fill

ABSTRACT Detrital zircon U-Pb and (U-Th)/He ages from latest Cretaceous–Eocene strata of the Denver Basin provide novel insights into evolving sediment sourcing, recycling, and dispersal patterns during deposition in an intracontinental foreland basin. In total, 2464 U-Pb and 78 (U-Th)/He analyses of detrital zircons from 21 sandstone samples are presented from outcrop and drill core in the proximal and distal portions of the Denver Basin. Upper Cretaceous samples that predate uplift of the southern Front Range during the Laramide orogeny (Pierre Shale, Fox Hills Sandstone, and Laramie Formation) contain prominent Late Cretaceous (84–77 Ma), Jurassic (169–163 Ma), and Proterozoic (1.69–1.68 Ga) U-Pb ages, along with less abundant Paleozoic through Archean zircon grain ages. These grain ages are consistent with sources in the western U.S. Cordillera, including the Mesozoic Cordilleran magmatic arc and Yavapai-Mazatzal basement, with lesser contributions of Grenville and Appalachian zircon recycled from older sedimentary sequences. Mesozoic zircon (U-Th)/He ages confirm Cordilleran sources and/or recycling from the Sevier orogenic hinterland. Five of the 11 samples from syn-Laramide basin fill (latest Cretaceous–Paleocene D1 Sequence) and all five samples from the overlying Eocene D2 Sequence are dominated by 1.1–1.05 Ga zircon ages that are interpreted to reflect local derivation from the ca. 1.1 Ga Pikes Peak batholith. Corresponding late Mesoproterozoic to early Neoproterozoic zircon (U-Th)/He ages are consistent with local sourcing from the southern Front Range that underwent limited Mesozoic–Cenozoic unroofing. The other six samples from the D1 Sequence yielded detrital zircon U-Pb ages similar to pre-Laramide units, with major U-Pb age peaks at ca. 1.7 and 1.4 Ga but lacking the 1.1 Ga age peak found in the other syn-Laramide samples. One of these samples yielded abundant Mesozoic and Paleozoic (U-Th)/He ages, including prominent Early and Late Cretaceous peaks. We propose that fill of the Denver Basin represents the interplay between locally derived sediment delivered by transverse drainages that emanated from the southern Front Range and a previously unrecognized, possibly extraregional, axial-fluvial system. Transverse alluvial-fluvial fans, preserved in proximal basin fill, record progressive unroofing of southern Front Range basement during D1 and D2 Sequence deposition. Deposits of the upper and lower D1 Sequence across the basin were derived from these fans that emanated from the southern Front Range. However, the finer-grained, middle portion of the D1 Sequence that spans the Cretaceous-Paleogene boundary was deposited by both transverse (proximal basin fill) and axial (distal basin fill) fluvial systems that exhibit contrasting provenance signatures. Although both tectonic and climatic controls likely influenced the stratigraphic development of the Denver Basin, the migration of locally derived fans toward and then away from the thrust front suggests that uplift of the southern Front Range may have peaked at approximately the Cretaceous-Paleogene boundary.

Mid-Ordovician subduction, obduction, and eduction in western Newfoundland; an eclogite problem

2021 ◽  
Author(s):  
J.F. Dewey ◽  
J.F. Casey
Keyword(s):  
Subduction Zone ◽  
Shear Zone ◽  
Continental Margin ◽  
Amphibolite Facies ◽  
Island Arcs ◽  
Early Ordovician ◽  
The North ◽  
Shelf Slope ◽  
Major Strike ◽  
Laurentian Margin

Abstract. The narrow, short-lived Taconic-Grampian Orogen occurs along the north-western margin of the Appalachian-Caledonian Belt from, at least, Alabama to Scotland, a result of the collision of a series of early Ordovician oceanic island arcs with the rifted margin of Laurentia. The present distribution of Taconian-Grampian ophiolites is unlikely to represent a single fore-arc from Alabama to Scotland colliding at the same time with the continental margin along its whole length; more likely is that there were several Ordovician arcs with separate ophiolites. The collision suture is at the thrust base of obducted fore-arc ophiolite complexes, and obduction distance was about two hundred kilometres. Footwalls to the ophiolites are, sequentially towards the continent, continental margin rift sediments and volcanics and overlying rise sediments, continental shelf slope carbonates, and sediments of foreland flexural basins. The regionally-flat obduction thrust complex between the ophiolite and the rifted Laurentian margin is the collision suture between arc and continent. A particular problem in drawing tectonic profiles across the Taconic-Grampian Zone is several orogen-parallel major strike-slip faults, both sinistral and dextral, of unknown displacements, which may juxtapose portions of different segments. In western Newfoundland, most of the Grenville basement beneath the Fleur-de-Lys metamorphic complex (Neoproterozoic to early Ordovician meta-sediments) was eclogitised during the Taconic Orogeny and separated by a massive shear zone from the overlying Fleur-de-Lys, which was metamorphosed at the same time but in the amphibolite facies. The shear zone continued either to a distal intracontinental “subduction zone” or to the main, sub-fore-arc, subduction zone beneath which the basement slipped down to depths of up to seventy kilometres at the same time as the ophiolite sheet and its previously-subcreted metamorphic sole were being obducted above. Subsequently, the eclogitised basement was returned to contact with the amphibolite-facies cover by extensional detachment eduction, possibly enhanced by subduction channel flow, which may have been caused by slab break-off and extension during subduction polarity flip. Although the basal ophiolite obduction thrust complex and the Fleur-de-Lys-basement subduction-eduction surfaces must have been initially gently-dipping to sub-horizontal, they were folded and broken by thrusts during late Taconian, late Ordovician Salinic-Mayoian, and Acadian shortening.

Jurassic Arc: Reconstructing the Lost World of eastern Gondwana

Geology ◽  
2021 ◽  
Author(s):  
Elliot K. Foley ◽  
R.A. Henderson ◽  
E.M. Roberts ◽  
A.I.S. Kemp ◽  
C.N. Todd ◽  
...  
Keyword(s):  
Detrital Zircon ◽  
Tectonic Setting ◽  
Magmatic Arc ◽  
Continental Arc ◽  
Key Factor ◽  
Igneous Activity ◽  
Competing Models ◽  
Juvenile Crust ◽  
Sedimentary Fill ◽  
Continental Magmatic Arc

The tectonic setting of the Australian sector of the eastern Gondwanan margin during the Jurassic and Cretaceous is enigmatic. Whether this involved convergent tectonism and a long-lived continental magmatic arc or rift-related extension unrelated to subduction is debated. The paucity of Australian Jurassic–Cretaceous igneous outcrops makes resolving these competing models difficult. We used the detrital zircon record of the Jurassic–Cretaceous Great Australian Superbasin (GAS) as a proxy for igneous activity. We attribute the persistent magmatism recorded in GAS sedimentary fill throughout the Mesozoic to ca. 95 Ma to continuation of the established Paleozoic continental arc system. The detrital zircon record signals short (~10 m.y.) pulses of elevated Jurassic and Cretaceous magmatic activity and strongly positive εHf values, indicating juvenile crust or mantle-derived magmatism. Margin reconstruction indicates sustained continental growth at rates of at least ~55 km3 km–1 m.y.–1, mainly to the tract now represented by submerged northern Zealandia, due to the retreat of this arc system. We posit that arc retreat was a key factor in rapid crust generation and preservation, and that continental sedimentary systems globally may host cryptic records of juvenile crustal addition that must be considered in estimating crustal growth rates along convergent plate margins.

A close look at the middle Adriatic upwelling: schematized ROMS model simulations

2021 ◽  
Author(s):  
Gordana Beg Paklar ◽  
Zoran Pasaric ◽  
Mirko Orlic ◽  
Antonio Stanesic
Keyword(s):  
Wind Stress ◽  
Coastal Upwelling ◽  
Cold Water ◽  
Model Simulation ◽  
Initial Density ◽  
Wind Component ◽  
Ekman Pumping ◽  
Flat Bottom ◽  
Roms Model ◽  
Adcp Measurements

<p>Strong upwelling driven by the NNW winds was detected off the eastern middle Adriatic coast in May 2017. High resolution CTD data revealed thermocline doming by about 20 m at approximately 20 km from the coast. Main characteristics of the upwelling event are reproduced in the realistic ROMS model simulation. Adriatic scale ROMS model having 2.5 km horizontal resolution, forced by the air-sea fluxes calculated using surface fields from operational weather forecast model ALADIN-HR (Tudor et al., 2013; Termonia et al., 2018), river discharges, tides and water mass exchange through the Strait of Otranto, reproduces cold water dome and two-layer offshore flow in accordance with CTD and shipborne ADCP measurements. Significant improvement in the upwelling simulations is obtained using increased drag coefficient. The location of upwelling is correctly modelled, although with somewhat lower upper layer temperatures if compared with measurements. Moreover, the surface cyclonic circulation indicated by ADCP measurements along the cross-Adriatic transect is also evident in the model results. In order to improve understanding of the upwelling mechanism, several schematized numerical experiments are conducted. Wind fields from dynamical adaptation (Zagar and Rakovec, 1999; Ivatek-Sahdan and Tudor, 2004) of ALADIN-HR8 (8 km horizontal grid spacing) wind forecast to 2 km grid, are decomposed by the Natural Helmholtz-Hodge Decomposition (HHD) into divergence-free (incompressible), rotation-free (irrotational), and harmonic (translational) component (Bhatia et al., 2014). The components thus obtained and their combinations are used for calculation of the wind stress instead of the total wind field. Simulations with decomposed wind stress are conducted in the Adriatic domains with both flat bottom and realistic topography. Schematized simulations reveal that the positive rotational wind component is responsible for the rising of thermocline through Ekman pumping and it is more pronounced in the flat bottom basin. In the simulations with divergent wind component, the thermocline doming disappears and only coastal upwelling is reproduced. Additional idealised simulations with homogeneous NW wind stress are performed assuming both two-layer and uniform initial density field.</p>

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