Aseismic ridge subduction as a driver for the Ordovician Taconic orogeny and Utica foreland basin in New England and New York State

Abstract

Aseismic ridge subduction is common along modern convergent margins. We enumerate six criteria that can be used to recognize aseismic ridge subduction in orogens, including a magmatic gap with uplift followed by bimodal volcanism, which commonly includes explosive, voluminous rhyodacitic volcanism that erupts far from the trench. Features temporally linked with the explosive volcanism include retroarc thrusts and consequent thrust-loaded retroarc foreland basin development. Using these criteria to examine features of the Taconic orogen, together with new stratigraphic and structural data from the Utica basin that constrain the basin subsidence architecture and thrust timing, we propose that at least the older units of the 456-435 Ma Oliverian Plutonic Suite in New England were generated during steepening of the downgoing slab after passage of a subducting aseismic ridge. Weakened crust from delamination and decompression melting promoted westerly directed thrusts (present-day coordinates) that loaded the Taconic retroarc foreland. The resulting Utica basin subsided rapidly and nearly synchronously over an ~150-kmwide region and contains interbedded 453-451 Ma ash layers from the Oliverian Plutonic Suite or coeval plutons to the south. This history of basin subsidence indicates that the major thrust loads that drove development of the Utica basin were emplaced over a similarly brief interval beginning ca. 455 Ma. Thus, the Taconic thrusts, the Utica basin, the volcanic ashes, and the early Oliverian felsic magmatic units could all be related to an aseismic ridge subduction event. Because of the ubiquity of seamount chains, we expect that aseismic ridge subduction affected other segments of the Taconic orogen.

Exhumation of the high‐pressure Richarddalen Complex in NW Svalbard: Insights from 40Ar/39Ar geochronology

“…Most of the older accretionary events recorded in the Uppermost Allochthon occurred during the arc collision at 470–450 Ma (Figure 6; e.g. Jacobi & Mitchell, 2018, references therein), which is consistent with our results. However, the locus of an arc collision zone remains uncertain.…”

“…It may have been proximal to the Laurentian margin (e.g. Jacobi & Mitchell, 2018) or formed due to westward subduction of the Iapetus plate or the outermost Baltica‐Iapetus transition zone beneath an intra‐Iapetus island arc (Figure 6). Evidence for an island arc (e.g.…”

A restudy of the Sandbian to Katian (Upper Ordovician) graptolites from the East Qilianshan (Chilianshan), Northwest China

“…Even dicellograptids are less diverse and exhibit lower richness in the East Qilianshan faunas than those of the Yangtze region. A similar contrast is evident in faunas recorded from North America between oceanic settings along the ancient Laurentian margin versus those from the Taconic retroarc foreland basin (Goldman and Bergström, 1997; Jacobi and Mitchell, 2018) as well as in the contrasts between the oceanic rocks deposited along the margin of Laurentia in what is now southern Scotland and the contemporaneous and relatively closely juxtaposed Avalonian clastic shelf setting of Wales (Zalasiewicz et al, 1995). Thus, the faunal differentiation of the present faunas might have been related to ecological characteristics associated with the different environments of the rapidly filling, clastic sediment-dominated, back-arc basin of East Qilianshan and the more openly oceanic setting represented in platform basin of the Yangtze region characterized by anoxic bottom-water conditions and a large pelagic sediment contribution from dust and surface productivity (e.g., Zhao et al, 2016; Li et al, 2017).…”

Growth of continental crust in intra-oceanic and continental-margin arc systems: Analogs for Archean systems

“…Some of these, such as the Pelham dome in Massachusetts (Figure 8) have cores of Gondwanan-affinity circa 613 Ma gneisses (Tucker and Robinson, 1990), intruded by Late Ordovician (454-442 Ma) plutonic suites, and overlain by metasedimentary rocks as young as Devonian before they were deformed into the domal fold nappes (Robinson et al, 1992). Some of the domes are intruded by several generations of intermediate composition magmas of the TTG suite, with ages as young as 445 Ma (Hollocher et al, 2002) which is up to 10 Myr younger than the 455-451 Ma Taconic arc/continent collisional orogeny (Jacobi and Mitchell, 2018;Hildebrand and Whalen, 2021), and with geochemical signatures (no Eu anomalies, low Y, depleted in heavy REE) that are characteristic of magmas worldwide related to slab failure (Hildebrand and Whalen, 2014a, 2021. The mantling sequence (Ammonoosuc volcanics) include generally tholeiitic basalt, some andesite and dacite, metamorphosed sea-floor hydrothermal deposits now 2006) with modifications from Karabinos et al (2017).…”