Integrating zircon trace-element geochemistry and high-precision U-Pb zircon geochronology to resolve the timing and petrogenesis of the late Ediacaran–Cambrian Wichita igneous province, Southern Oklahoma Aulacogen, USA

Abstract

The bimodal Wichita igneous province (WIP) represents the only exposed Ediacaran to Cambrian anorogenic magmatic assemblage present along the buried southern margin of Laurentia and was emplaced during rifting in the Southern Oklahoma Aulacogen prior to Cambrian opening of the southern Iapetus Ocean. Here, we establish the first high-precision U-Pb zircon geochronological framework for the province. Weighted mean 206Pb/238U dates from mafic and felsic rocks in the Wichita Mountains indicate emplacement in a narrow time frame from 532.49 ± 0.12 Ma to 530.23 ± 0.14 Ma. Rhyolite lavas in the Arbuckle Mountains farther east yield weighted mean 206Pb/238U dates of 539.20 ± 0.15 Ma and 539.46 ± 0.13 Ma. These dates for the WIP indicate that magmatism in the Southern Oklahoma Aulacogen postdated the ca. 540 Ma rift-drift transition along the Appalachian margin to the east. Wholerock trace-element and isotopic geochemistry, supplemented by trace elements in zircon, tracks the evolution of magma sources during WIP petrogenesis. These data indicate that initial melting and assimilation of subcontinental mantle lithosphere by an uprising mantle plume were followed by increasing involvement of asthenospheric melts with time. We suggest that upwelling of this plume in the area of the Southern Oklahoma Aulacogen triggered an inboard jump of the spreading center active along the eastern margin of Laurentia, which led to separation of the Precordillera terrane (now located in Argentina) from the Ouachita embayment present in the southern Laurentian margin.

Early Cambrian renewal of the geodynamo and the origin of inner core structure

“…We conducted anisotropy tests (Methods) which yielded anisotropy factors 35 varying from 0.7 to 1.4. We also considered the effect of cooling rate, using a cooling time constrained by GMLC geochronology of ~500 kyr 13 . This cooling time indicates that the GMLC anorthosites record the time-averaged paleomagnetic field, but that our raw data may overestimate the intensity [36][37][38] by a factor of ~1.5.…”

“…In addition, pTRMs of corresponding positive/negative laboratory field direction pairs must be within 30% of each other. We use cooling rate correction formulations 36 that, in turn, employ an anorthosite cooling time constrained by the high precision U-Pb ages of the GMLC anorthosite and later Roosevelt Gabbro 13 of ~500 kyr.…”

“…1). U-Pb zircon geochronology yields an age of 532.49 ± 0.12 Ma for these anorthosites 13 . Fe-Ti oxide needles have been reported in plagioclase from GMLC anorthosites 14 similar to other occurrences yielding high fidelity paleomagnetic and paleointensity data 7,15 , suggesting that these rocks are ideal candidates for application of the single-crystal paleointensity (SCP) technique 7,11,[16][17][18][19][20][21][22].…”

Three Major Failed Rifts in Central North America: Similarities and Differences

“…Rifting is thought to have begun in latest Precambrian, but the oldest dates come from SOA igneous rocks dated at ca. 540 Ma (Wall et al, 2021).…”

“…The SOA's geologic and tectonic history has three major phases. The first involved emplacement of the Wichita Igneous Province during development of a rift beginning in the Ediacaran to mid-Cambrian (Brewer et al, 1983;Perry, 1989;Wall et al, 2021). Extensional and transtensional tectonism within the SOA developed during the latest Precambrian-Cambrian opening of the southern Iapetus Ocean as part of Rodinia's breakup (Robert et al, 2021).…”