Seventeen Million Years of Volcanism Recorded Within the South Hawaiian
Seamount Province: Implications for Tectonic Drivers of Intraplate
Volcanism
Abstract
Upwelling and decompression of mantle plumes is the primary mechanism
for large volumes of intraplate volcanism; however, many seamounts do
not correlate spatially, temporally, or geochemically with plumes. One
region of enigmatic volcanism in the ocean basins that is not clearly
attributable to plume-derived magmatism are the Geologist Seamounts and
the wider South Hawaiian Seamount Province (∼19°N, 157°W). Here we
present new bathymetric maps as well as 40Ar/39Ar age determinations and
major and trace element geochemistry for six remote-operated vehicle
recovered igneous rock samples (NOAA-OER EX1504L3) and two dredged
samples (KK840824-02) from the Geologist Seamounts. The new ages
indicate volcanism was active from 90–87 Ma and 74–73 Ma, inferring
that, in conjunction with previous ages of ~84 Ma,
seamount emplacement initiated near the paleo Pacific-Farallon spreading
ridge and volcanism continued for at least ~17 m.y.
Geochemical analyses indicate that Geologist Seamounts lava flows are
highly alkalic and represent low-degree partial mantle melts primarily
formed from a mixture of melting within the garnet and spinel stability
field. The ages and morphology infer the seamounts were likely not
related to an extinct plume. Instead, we build upon previous models that
local microblock formation corresponded with regional lithospheric
extension. We propose the microblock was bounded by the Molokai and
short-lived Kana Keoki fracture zones. Regional deformation and
corresponding volcanism among the Geologist Seamounts associated with
the microblock potentially occurred in pulses contemporaneous to
independently constrained changes in Pacific Plate motion —indicating
that major changes in plate vectors can generate intraplate volcanism.