Far‐field tilting of Laurentia during the Ordovician and constraints on the evolution of a slab under an ancient continent

Abstract

Abstract. During a brief period of 10 to 15 million years in the Middle-Ordovician, the Michigan Basin departed from its bull's-eye subsidence pattern and tilted toward the east. opening to the Appalachian basin. This tilting is observed in maps of tectonic subsidence estimated for the Black River and Trenton Formations and extends over 300 km across the Michigan Basin and into eastern Wisconsin. Contours of constant tectonic subsidence rate are approximately parallel to the inferred position of the Laurentian-Iapetus convergent margin. The distance between the inferred position of the subduction zone to the limit of tilting is approximately 1000 km. Three alternative models for the tilting are tested, two relying on the rigidity of the continental lithosphere and a third on the viscous flow generated by a subducted slab. In the fllSt elastic model we assume the edge of the elastic plate is simply loaded from above (by a fold and thrust sheet, volcanic pile, etc.). This model, however, cannot simultaneously satisfy the space of tectonic subsidence and subsidence rate, even for lithospheres which have a rigidity of 1 ()28 Nm. In the second elastic model, the Laurentian continental margin descends into a trench of an eastward dipping slab, that is, a slab descending under the Iapetus ocean. This process cannot generate any significant far field displacements, even for extremely rigid plates, and must be rejected. For the third model we use fmite element solutions of a negatively buoyant slab in a viscous medium with a faulted lithosphere. Such slabs can easily generate not only realistic trenches on the under thrusting plate but also significantly tilt the lithosphere as much as 1000 km from the plate margin. The magnitude and distribution of far-field displacements depend on the age, length, and dip angle of the slab. In contrast to the elastic models, penetration of a westdipping slab beneath the continent can reproduce both the extent. magnitude, and rate of tectonic subsidence observed in the Trenton and Black River Formations. The observed data are best fit by an old slab (140 Ma), which initially descended at a moderate dip (20"-30") for 10-15 m.y., which then steepened as the slab penetrated deeper into the mantle. At the position of the previous Ordovician plate margin, there are narrow, block faulted basins which underwent rapid subsidence -10 m. y. before the Michigan Basin tilted toward the east. We propose that these earlier subsidence events were caused by the initial descent of the slab under the preexisting CambroOrdovician passive margin. The time lag of -10 m.y. may be due to the time it takes the slab to penetrate the upper mantle. This result is important for understanding the time evolution of mantle convection and mechanisms for the initiation of subduction.

Cratonic Basins

“…30.6b). Westward subduction of an Iapetus slab is supported by eastward tilting in Middle Ordovician time of sedimentary rocks in the Michigan Basin (Coakley and Gurnis 1995) and was used in the numerical simulation of cratonic sequences by Burgess et al (1997). The Paleozoic history of the Cordilleran margin of Laurentia is well known but complex (Dickinson 2009), starting as a passive continental margin following rifting of Rodinia, but was strongly modified by Mediterranean-style subduction zone roll-back and extensional back-arc formation during the Antler and Sonoma orogenies.…”

“…By the Late Silurian, continent-continent suturing took place between the Baltica and Laurentian plates. At this stage, the Michigan Basin was individualized as a circular shaped depocenter and its history was yoked to that of the Appalachian orogen and its foreland basin system (Coakley and Gurnis, 1995 (Bally, 1989), which caused the Williston Basin to be disconnected from the Alberta foreland basin system. Subsequently, by latest Mississippian, major continent-continent collision between Gondwana and the North American plate led to widespread uplift and erosion of the sub-Absaroka unconformity and the reactivation of old lineaments.…”

Mantle temperature as a control on the time scale of thermal evolution of extensional basins

“…Subduction during the Late Ordovician to Early Silurian may have altered the subsidence history (Burgess et al, 1997). Shortening, in the form of the Taconic Orogeny along the eastern margin of North American plate may have caused flexural subsidence across the Illinois and Michigan Basins (Coakley and Gurnis, 1995). Accelerated subsidence and extended periods of erosion across the North American basins during the Late Devonian to Early Mississippian and the Mississippian to Permian may likewise be related to continental collision events such as the formation of the Marathon-Ouachita Orogens and possibly a mantle plume associated with the Great Meteor hotspot track (Armitage and Allen, 2010;Hanne et al, 2004;Kominz et al, 2008).…”

Achievements and Challenges in Sedimentary Basin Dynamics: A Review

“…Heine et al (2008) find that the movement of lithospheric plates relative to the underlying mantle, as well as variations in the large-scale mantle convection patterns can interfere with mantle-driven dynamic subsidence and can contribute to the creation and destruction of accommodation space in intracratonic basins. Other models for mantle-flow induced dynamic topography affecting continental domains, particularly adjacent to foreland basins, were advanced by e.g., Harper (1984), Coackley and Gurnis (1995), Burgess and Moresi (1999) and Pysklywec and Mitrovioca (2000), mainly invoking corner flow above deep reaching subducted slabs dipping beneath continental lithosphere.…”