RESEARCH LETTER Observational Test of the Global Moving Hot Spot 10.1029/2019GL083663 Reference Frame Key Points: Chengzu Wang1 , Richard G. Gordon1 , Tuo Zhang1 , and Lin Zheng1 • The fit of the Global Moving Hotspot Reference Frame (GMHRF) to 1Department of Earth, Environmental, and Planetary Sciences, William Marsh Rice University, Houston, TX, USA observed geologically young trends of hot spot tracks is evaluated • The data are fit significantly worse (p = 0.005) by the GMHRF than by Abstract The Global Moving Hotspot Reference Frame (GMHRF) has been claimed to fit hot spot tracks fixed hot spots better than the fixed hot spot approximation mainly because the GMHRF predicts ≈1,000 km southward • Either plume conduits do not advect motion through the mantle of the Hawaiian mantle plume over the past 80 Ma. As the GMHRF is passively with mantle flow or the GMHRF mantle velocity field is determined by starting at present and calculating backward in time, it should be most accurate and incorrect reliable for the recent geologic past. Here we compare the fit of the GMHRF and of fixed hot spots to the observed trends of young tracks of hot spots. Surprisingly, we find that the GMHRF fits the data significantly Supporting Information: worse (p = 0.005) than does the fixed hot spot approximation. Thus, either plume conduits are not passively • Supporting Information S1 advected with the mantle flow calculated for the GMHRF or Earth's actual mantle velocity field differs substantially from that calculated for the GMHRF. Correspondence to: Hot spots are the surface manifestations of plumes of hot rock that R. G. Gordon, Plain Language Summary [email protected] rise from deep in the mantle. The tracks of hot spots, such as the Hawaiian island and seamount chain, have been used in two very different ways to estimate the motion of tectonic plates relative to the deep mantle. Originally, it was assumed that the hot spots are “fixed” and do not move relative to each other or Citation: Wang, C., Gordon, R. G., Zhang, T., & relative to the deep mantle. In a later approach, termed the “Global Moving Hotspot Reference Frame” Zheng, L. (2019). Observational test of (GMHRF), the motion of each hot spot relative to the deep mantle was predicted from a calculation of the the global moving hot spot reference global flow of mantle rocks. The latter approach assumes that hot spot motion can be reliably calculated over frame. Geophysical Research Letters, 46, 8031–8038. https://doi.org/10.1029/ the past 130 million years, but does not test its predictions using data from the trends of young hot spot 2019GL083663 chains. We compare the statistical fit of the GMHRF and fixed hot spots using data from the observed trends of young hot spot tracks. Surprisingly, we find that the GMHRF fits the data significantly worse than Received 14 MAY 2019 does the fixed hot spot approximation. Thus, simple fixed hot spots provide the more useful reference frame Accepted 20 JUN 2019 Accepted article online 3 JUL 2019 and some assumptions made to construct the GMHRF are incorrect. Published online 29 JUL 2019 1. Introduction Nearly 50 years ago, Morgan (1971, 1972) proposed that hot spots, sites of intraplate volcanism or excessive volcanism along a plate boundary, are approximately fixed in location and provide a reference frame for determining plate motion relative to the deep mantle. He further proposed that plumes of hot rock rise up from deep in the mantle and are the cause of hot spots at the surface, which had been proposed by Wilson (1963) to explain the origin of chains of seamounts and islands, such as the Hawaiian island chain. Since Morgan's (1971, 1972) work, hot spot tracks have been widely used to estimate plate motion relative to the deep mantle, especially for geologically current plate motions (e.g., Chase, 1978; Gripp & Gordon, 1990, 2002; Minster et al., 1974; Minster & Jordan, 1978; Morgan & Morgan, 2007; Wang et al., 2017, 2018, 2019). How fast individual hot spots move relative to each other and relative to the lower mantle has long been debated. If relative velocities of individual hot spots are low, it would provide support for the usefulness of the fixed hot spot approximation, while high individual hot spot velocities would indicate the need for alternative methods, possibly including a moving hot spot reference frame with its attendant complexity and additional adjustable parameters. Prior studies resulted in inconsistent opinions concerning hot spot velocities. For example, Morgan (1981, 1983) and Duncan (1981) found that individual hot spots move rela- tive to a mean hot spot reference frame at ≈3 to 5 mm/a. Recent work is consistent with these early results and find that nominal relative velocities between Pacific hot spots and Indo‐Atlantic hot spots over the past 50 Ma are only 2−6 mm/a over the past 48 Ma (Andrews et al., 2006; Koivisto et al., 2014). In contrast, to ≈ – fi ©2019. American Geophysical Union. explain the track of the Emperor chain ( 50 80 Ma) on the Paci c plate, several studies found that the velo- All Rights Reserved. city of the Hawaiian hot spot was as high as 40 to 80 mm/a in early Cenozoic and Late Cretaceous time WANG ET AL. 8031 Geophysical Research Letters 10.1029/2019GL083663 (Konrad et al., 2018; Norton, 1995; Raymond et al., 2000; Tarduno et al., 2003). Morgan (1981), Duncan (1981), and Koivisto et al. (2014) have argued, however, that the high apparent velocity of the Hawaiian hot spot during the formation of the Emperor chain is an artifact of missing motion in the global plate motion circuit, most likely due to unmodeled motion between East and West Antarctica, as seems required by paleomagnetic data (Gordon & Cox, 1980; Acton & Gordon, 1994; but see a differing opinion in Doubrovine & Tarduno, 2008). Acting in part on the belief that the Hawaiian hot spot moved southward relative to the mantle during the formation of the Emperor chain, a belief that we do not share (Petronotis et al., 1994; Petronotis & Gordon, 1989; Woodworth & Gordon, 2018b), Doubrovine et al. (2012) asserted that the fixed hot spot reference frame should be abandoned and replaced by a so‐called Global Moving Hotspot Reference Frame (GMHRF) for which hot spot velocities are predicted from a velocity field calculated for the mantle over the past ≈130 Ma. If indeed the motion of hot spots could be reliably calculated (or predicted) over the past ≈130 Ma from models of flow in the mantle, it would advance global geophysics. How far can one rely, however, on these predicted velocities between hot spots? After all, the mantle‐plume system is complex and any estimate of mantle flow must be based on many simplifying assumptions. Our understanding of many key variables in a mantle flow model, such as mantle viscosity structure, may not be sufficiently well constrained for reliable calculations. Given these potential sources of uncertainty, it would be useful to be able to test the predictions of any such model with observations not used in the construction of the model. Fortunately, Morgan and Morgan (2007) developed a data set of the trends of young hot spot chains. This rich data set was evidently not used by Doubrovine et al. (2012) in developing the GMHRF and thus could be used to test its predictions. Because errors accumulate with age and the calculations for the GMHRF proceed from the present Earth backward in time, the predictions from the GMHRF should be at their most reliable and accurate for the recent geologic past. Here we investigate the following question: is the improvement in fit to trends of young hot spot tracks realized by the GMHRF large enough to justify the considerable complexity and its additional adjustable parameters relative to the simple fixed hot spot approximation? Surprisingly, we find that the GMHRF fits the observed trends of young hot spot tracks much worse than the assumption of fixed hot spots. 2. Data: Hot Spot Trends and Uncertainties Morgan and Morgan (2007) estimated the trends of 57 young tracks of hot spots produced by 54 hot spots (their Table 1). Following Wang et al. (2017, 2019), we omit the Comores track, leaving 56 hot spot tracks. Doubrovine et al. (2012) estimate the locations as a function of time of 44 hot spots (their Table S6). Thirty eight of the hot spots modeled by Doubrovine et al. (2012) correspond to 41 of the 56 trends of hot spot tracks adopted by Wang et al. (2019). Thus, we use the observed trends of these 41 tracks (Figure 1 and Table S1 in the supporting information) to test the predictions of the GMHRF. We adopt the current hot spot locations and current trends from Morgan and Morgan (2007). The uncertainties in trends are calculated objectively using hot spot track length and width (Gripp & Gordon, 2002; Wang et al., 2019). 3. Methods 3.1. Predicted Velocities of Hot Spots Steinberger and O'Connell (1998) proposed a method to estimate plume and hot spot velocity through numerical modeling of mantle convection and advection of plume conduits in the mantle flow field. Following Steinberger and O'Connell (1998), Doubrovine et al. (2012) computed a large‐scale mantle flow field from global plate motions, a radial mantle viscosity structure, and a mantle density structure inferred from seismic tomography. A plume conduit is inserted into the flow field under the assumption that plume conduits do not influence larger‐scale mantle flow. Plume velocity is determined by a sum of the mantle flow velocity and plume vertical buoyant rising velocity. The hot spot velocities adopted herein are determined from the hot spot locations at present and at 5 Ma given by Doubrovine et al.