2025 June LIP of the Month

Pacific hotspots reveal a Louisville-Ontong-Java Nui tectonic link

Konter, J. G., Finlayson, V. A. (vfinlays@umd.edu), Konrad, K., Jackson, M. G., Koppers, A. A. P., Wessel, P., Beethe, S., Bizimis, M., Alverson, A., Kelley, C.

Extracted and modified from:

1. Introduction

Volcanic hotspots are thought to form by melting in an upwelling mantle plume head followed by melting of the plume tail. Plate motion then generates an age-progressive volcanic track originating from a large igneous province (LIP) to a presently-active hotspot.

The most voluminous LIP on Earth is the ~120 Ma Ontong Java Plateau (OJP) in the mid-Pacific (Figure 1). However, the OJP lacks an obvious connection to a younger hotspot track. Although the Louisville hotspot track was originally proposed as a candidate, limited constraints for Pacific absolute plate and plume motion prior to 80 Ma suggest a mismatch (Chandler et al., 2013). Furthermore, the genetic relationships between the isotopic compositions of LIPs and hotspot tracks are often difficult to constrain due to temporal variations in mantle source contributions, even when a geographic relationship is clearly established between the two (Hoernle et al., 2015).

2. Formation of the OJP

The OJP is a fragment of a far larger “superplateau” emplaced largely around ~116 Ma (Davidson, Koppers, Sano, et al., 2023) that rapidly fragmented into the Ontong-Java, Manihiki, and Hikurangi plateaux (Chandler et al., 2012, 2013; Taylor, 2006), referred to herein as Ontong Java-Nui (OJP-Nui). Shortly after, or near-contemporaneously with the formation of the three plateaus, the short-lived (~120-95 Ma) Ellice Basin opened (Benyshek et al., 2019; Davidson, Koppers, & Konter, 2023; Konter et al., 2025; Taylor, 2006), splitting the OJP-Nui superplateau apart (Figure 1).

In addition to the kinematic evidence, some geochemical evidence supports the superplateau (and fragmentation) hypothesis. (Timm et al., 2011) found evidence of geochemically similar lavas erupted around the same time from both the Manihiki and Ontong Java plateaux, suggesting a genetic relationship exists between the two platforms (Figure 2). The Hikurangi Plateau also hosts lavas both co-eval with and isotopically similar to lavas produced at both OJP and the Manihiki Plateau (e.g., Figure 2; Hoernle et al., 2010).

Several origins have been proposed for the OJP. While the mantle plume origin hypothesis is most commonly accepted for the origin of the OJP and other LIPs (e.g., Campbell, 2005; Mahoney et al., 1993), the lack of any clear geochemical or tectonic links to a hotspot track invited alternative hypotheses. One such alternative suggested a bolide impact (Ingle & Coffin, 2004) as a possible origin for the OJP and several nearby, co-eval, geochemically similar basins argued to be potential crater remnants in the Western Pacific.

3. Challenges linking the OJP and Louisville

The ~79-0 Ma Louisville hotspot track is unusually isotopically homogeneous compared to most other hotspot tracks so far documented. The Louisville track samples an almost exclusively FOZO-like (FOcal or FOcus ZOne; Hart et al., 1992) mantle source (Beier et al., 2011; Vanderkluysen et al., 2014). By comparison, the OJP-Nui superplateau is far more heterogeneous, sampling a range of depleted (Depleted MORB Mantle or DMM-like) to enriched (Enriched Mantle 1 or EM1-like) and even some HIMU-like (high time-integrated μ, where μ=²³⁸U/²⁰⁴Pb) compositions at various stages of its emplacement (Figure 2; Hoernle et al., 2010; Mahoney et al., 1993; Mahoney & Spencer, 1991; Tejada et al., 1996, 2002, 2004, 2023; Timm et al., 2011).

The contrast in diversity of sampled components has precluded efforts to establish a genetic link between the OJP and Louisville, although Vanderkluysen et al. (2014) argued in favor of commonality between the two provinces (Figure 2). Additional sampling later revealed the presence of FOZO-like samples along the Eastern Salient of the OJP that closely resemble compositions found along the Louisville track, strengthening the case for a genetic link between hotspot and LIP (Tejada et al., 2023).

4. New constraints on old models

Absolute plate motion (APM) of a tectonic plate can be constrained using hotspot tracks, on the assumption that mantle plumes thought to underlie many hotspots remain mostly fixed in the mantle (Morgan, 1972). Existing Pacific models rely on age-distance data from the continuous Hawaiʻi-Emperor and Louisville tracks, but their tracks older than ~80 Ma are subducted. Elsewhere on the Pacific plate, only discontinuous seamount tracks formed prior to 80 Ma (Doubrovine et al., 2012; Duncan & Clague, 1985; Koppers et al., 2021; Koppers & Sager, 2014; Tarduno et al., 2009; Wessel & Kroenke, 2009) are documented. Currently, models require ~1,200 km of latitudinal motion to link the Louisville plume to the OJP-Nui (Chandler et al., 2013; Figure 3; see Panel G), yet paleolatitude estimates from ~70 Ma to today remain within error of its present location (Konrad et al., 2018; Koppers et al., 2007) suggesting that any significant Louisville plume motion occurred earlier.

5. An OJP-Louisville tectonic link

Konter et al. (2025) proposed a revision to the Cretaceous portion of Pacific APM models, where the fewest geochronological constraints are available from hotspot tracks, particularly hotspots known to have produced long-lived tracks (Figure 1). Through a combination of geochemistry and geochronology (Finlayson et al., 2018; Jackson et al., 2010, 2014; Konrad et al., 2018; Konter & Jackson, 2012; Koppers et al., 2012), we demonstrate that Samoa and Rurutu-Arago are the longest-lived Pacific hotspots, traceable to >120 Ma before subducting into the Mariana Trench. Konter et al. (2025) demonstrate that the EM2-to-EM1 Cretaceous Magellan Seamounts in the Western Pacific are age-progressive with present-day Samoan volcanism (Figure 4). New data from seamounts sampled during EX1606 (R/V Okeanos Explorer) from the Wake Island region are FOZO-like to weakly HIMU-like. Although these lavas proved difficult to obtain ⁴⁰Ar/³⁹Ar geochronology from, one lava yielded a robust 91.3 Ma age, linking it to the HIMU-to-FOZO Rurutu-Arago hotspot, currently active in the Cook-Austral region of the South Pacific (Figures 1, 4).

Using these suites of co-eval seamounts from the Magellan and Wake regions, (Konter et al., 2025) were able to recalculate the 100-80 Ma stage pole of the (Koppers et al., 2001) APM model, which notably suggests an increase in the angular velocity of the stage pole. Originally calculated by Koppers et al. (2001) to be 0.425 degrees/Myr, the modified 100-80 Ma stage pole by Konter et al. (2025) calculates an angular velocity of 0.975 degrees/Myr, which significantly increases the length of the Cretaceous portions of Pacific hotspot track reconstructions.

These newly-defined portions of the Rurutu-Arago and Samoan tracks better constrain plate rotation between 80-100 Ma, allowing us to update Pacific absolute plate motion models, and independently link the Louisville volcanic track to OJP-Nui without requiring major plume motion. The longer segment produced by the modified APM model accounts for the ~1200 km offset between OJP-Nui and the Louisville hotspot in APM modeling, placing the Louisville hotspot near the hypothesized triple junction of the OJP-Nui, near the present-day Eastern Salient of the OJP (Figure 3). Also critical is the identification of several seamounts in the Ellice Basin, east of the OJP Eastern Salient, that were volcanically active between ~115-90 Ma, much older than the dominant ~70-42 Ma volcanism in the region that has been linked to the Rurutu-Arago hotspot (Finlayson et al., 2018; Konter et al., 2008; Figure 4) and which formed shortly after the generation of the oceanic crust upon which they sit (Benyshek et al., 2019; Konter et al., 2025). These lavas are moderately isotopically depleted and heavily altered, with mantle sources originally resembling what was most likely a mixture of FOZO and DMM (Konter et al., 2025). When comparing the ages and locations of these unusually old Ellice Basin seamounts to revised APM model reconstructions, they are demonstrably age-progressive with the Louisville hotspot track and the OJP. Despite the strong alteration signature evident in the lavas, the depleted isotopic signature present in the lavas may be consistent with a geochemical transition from the more diverse (including DMM-like) mantle compositions of the OJP into the homogeneous Louisville mantle source. These seamounts may thus comprise a previously unrecognized early expression of the Louisville hotspot track emerging shortly after the breakup of OJP-Nui.

References