Linking Hess Rise and the Mid-Pacific Mountains to the Marquesas and Pitcairn Hotspots Through Improved 40Ar/39Ar Geochronology and Plate Motion Models.

Abstract:

Large igneous provinces (LIPs) are often attributed to the initial impact of a plume head, while hotspot tracks represent the stable tail of the plume. The Hess Rise and Mid-Pacific Mountain LIPs remain centers of debate, as no long-lived tracks from the plume tails have been mapped. Here we present ⁴⁰Ar/³⁹Ar incremental heating age determinations for dredged samples from the Line Islands, some of which were previously dated using either K/Ar or total fusion ⁴⁰Ar/³⁹Ar methodologies. After filtering age determinations using modern quality control criteria, we present a model for Line Island formation that separates the lineament into three sections, each produced from different processes. The interpretations are aided by new 100-80 Ma Pacific plate motion constraints from the Rurutu and Samoa hotspot trails in the Western Pacific.

The Southern Line Islands (Boudeuse Ridge) has limited data but is currently best explained by Easter plume volcanism on the Pacific Plate in the late Cretaceous. The central Kingman Reef/Kiribati region is still poorly understood due to the diversity of lava flow ages and more depleted isotopic signatures. The widespread volcanism around 70 Ma, coupled with the volcanic ridge structures in this segment are best explained by lithospheric extension (Davis et al. 2002), which is still active in the Pukapuka Ridge region. The Northern Line Islands is best explained through 75-65 Ma Marquesas-sourced volcanism in the west (Johnson Seamounts) and 100-80 Ma Pitcairn-sourced volcanism in the east (Karin Ridge). The ages and improved APM model indicate that the Pitcairn hotspot likely sourced the Mid-Pacific Mountains. The Marquesas plume track is now modeled to pass through the Johnson Seamounts and include Hess Rise and potentially Shatsky Rise. Age determinations and isotopic chemical tracers from the Northampton Seamounts and Liliuokalani Ridge are required to test whether the Marquesas Hotspot represents a 140 Myr old plume that is intermittently expressed when the plume underlies major fracture zones/pre-existing volcanic conduits in the Pacific lithosphere.