Periodic Reporting for period 1 - ISOSEA (ISOLATED SEAMOUNTS AS WINDOWS INTO UPPER MANTLE GEOCHEMICAL HETEROGENEITY)
Reporting period: 2023-03-01 to 2025-02-28
Summary of the context and overall objectives of the project
The goal of the ISOSEA project was to characterize upper mantle heterogeneities using the composition of non-hotspot isolated seamounts and seamount provinces as windows into the upper mantle. To achieve this, we compiled published data for non-hotspot related seamounts and studied additional samples obtained from International Ocean Discovery Program (IODP) and the GEOMAR archives to fully characterize the petrological, geochemical and melting processes associated with them. We used samples from seamounts near and around the Mid-Pacific Mountains as the main case study of the project and as a proxy to understand similar seamount provinces. Although studies have considered the Mid-Pacific Mountains a Large Igneous Province (generally believed to be formed by mantle plumes) there have been variable models proposed for their origin to date, including plume and non-plume models. A major goal of this study was to determine the origin of the Mid-Pacific Mountains and surrounding seamount structures, specifically to determine if they are hotspot related or not. We also look at the Emperor seamount chain and related seamounts to get an idea of how hotspot volcanoes and related seamounts look geochemically in order to compare with the seamounts around the Mid-Pacific Mountains.
Isolated seamounts and seamount provinces that are unrelated to deep mantle upwellings (mantle plumes), sample upper mantle heterogeneities and thus provide a window into compositional variations in the upper mantle. Our working hypothesis is that enriched reservoirs exist in the upper mantle, and they are a result of the shallow recycling of younger oceanic crust and continental lithospheric materials (upper and/or lower crust and subcontinental lithospheric mantle). The upper mantle is generally considered to be geochemically depleted due to the extraction of continental crust and the formation of oceanic crust at mid-ocean ridges. As a result, it typically exhibits unradiogenic (low) Sr and Pb isotopic compositions, along with radiogenic (high) Nd and Hf isotopic signatures (Hofmann, 1997). Nevertheless, enriched domains within the upper mantle may differ from this simplified model in one or more of these isotopic systems. Compared to deep mantle enriched reservoirs, such as HIMU and EM endmembers (Homrighausen et al., 2018; Jackson et al., 2018; Willbold and Stracke, 2010), these upper mantle heterogeneities are expected to develop over shorter timescales, reflecting the relatively faster recycling processes operating in the upper mantle compared to those in the lower mantle (Hoernle et al., 2006; Sobolev et al., 2007).
As mentioned, we focused on one of the most isolated structures found on the seafloor: the Mid-Pacific Mountains (MPM), a large structure that extends ~2200km in an E-W direction in the middle of the Pacific Ocean. This feature comprises seamounts, guyots, volcanic elongated ridges, and thicker plateaus that sit on top of seafloor with a varying range of ages according to the available magnetic lineations (Seton et al., 2020); from west to east seafloor ages decrease from ~155 Ma to ~110 Ma. A seamount province located to the SE of the MPM, lies between the structure and the continuation of the Line Island hotspot track (Davis et al., 2002; Pockalny et al., 2021), however, unlike the hotspot seamounts, this seamount province does not seem to have an age progressive track and their relationship with the MPM and the Line Islands remain unclear.
In the past, a series of seagoing expeditions occurring in the 70’s and 90’s targeted several locations within and around the MPM, including expeditions DSDP 17-164, -165A, -166, -167, -169 & -170, DSDP32-313, and ODP 143-865A & 866A, which drilled boreholes on top of guyots, seamounts, plateaus, ridges, and normal ocean seafloor (Fig. 1). Even though the goals of each of the cores were variable (sedimentology, paleontology, paleoclimate reconstructions, for example), in all cases the drilling continued until reaching the basaltic bedrock, penetrating a few cm to m into the rocks. In most cases, limited geochemical analyses were performed on the basalts and very few included radiogenic isotope measurements or 40Ar/39Ar dating, yielding incomplete datasets.
Thus, for the ISOSEA Project we requested samples from the IODP Gulf Coast Repository pertaining to the mentioned drilled cores (Fig. 1). In each case, we reviewed all the available report data, including photographs and descriptions of the cores to ensure that we were requesting the least altered material. From the ~60 samples received, 35 fulfill the criteria for fresh material (i.e. absence of secondary minerals, lack of filled vesicles or fractures, unaltered phenocrysts, dark grey to black groundmasses).
Prior to this study, these unique samples from the non-hotspot-related seamounts and ridges had not been comprehensively analyzed, lacking both high-resolution geochemical and geochronological data acquired using modern analytical techniques. Through the ISOSEA project, we conducted state-of-the-art analyses that resulted in critical new insights into the origin, composition, and tectonic evolution of this isolated region. These results provide an essential contribution to our understanding of Pacific plate history and offer a robust geochemical framework for interpreting intraplate volcanism in this part of the ocean basin.
References
Davis, A.S. Gray, L.B. Clague, D.A. Hein, J.R. 2002. The Line Islands revisited: New 40Ar/39Ar geochronologic evidence for episodes of volcanism due to lithospheric extension. Geochemistry, Geophysics, Geosystems 3, 1–28. https://doi.org/10.1029/2001GC000190(opens in new window)
Hoernle, K., White, J.D.L. van den Bogaard, P., Hauff, F., Coombs, D.S. Werner, R., Timm, C., Garbe-Schönberg, D., Reay, A., Cooper, A.F. 2006. Cenozoic intraplate volcanism on New Zealand: Upwelling induced by lithospheric removal. Earth and Planetary Science Letters 248, 350–367. https://doi.org/10.1016/j.epsl.2006.06.001(opens in new window)
Hofmann, A.W. 1997. Mantle geochemistry: the message from oceanic volcanism. Nature 385, 219–229.
Homrighausen, S., Hoernle, K., Hauff, F., Geldmacher, J., Wartho, J.-A. van den Bogaard, P., Garbe-Schönberg, D., 2018. Global distribution of the HIMU end member: Formation through Archean plume-lid tectonics. Earth-Science Reviews 182, 85–101. https://doi.org/10.1016/j.earscirev.2018.04.009(opens in new window)
Jackson, M.G. Becker, T.W. Konter, J.G. 2018. Evidence for a deep mantle source for EM and HIMU domains from integrated geochemical and geophysical constraints. Earth and Planetary Science Letters 484, 154–167.
Pockalny, R., Barth, G., Eakins, B., Kelley, K.A. Wertman, C., 2021. Multiple melt source origin of the Line Islands (Pacific Ocean). Geology 49, 1358–1362. https://doi.org/10.1130/G49306.1(opens in new window)
Seton, M., Müller, R.D. Zahirovic, S., Williams, S., Wright, N.M. Cannon, J., Whittaker, J.M. Matthews, K.J. McGirr, R., 2020. A Global Data Set of Present-Day Oceanic Crustal Age and Seafloor Spreading Parameters. Geochemistry, Geophysics, Geosystems 21, e2020GC009214. https://doi.org/10.1029/2020GC009214(opens in new window)
Sobolev, A.V. Hofmann, A.W. Kuzmin, D.V. Yaxley, G.M. Arndt, N.T. Chung, S.-L. Danyushevsky, L.V. Elliott, T., Frey, F.A. Garcia, M.O. Gurenko, A.A. Kamenetsky, V.S. Kerr, A.C. Krivolutskaya, N.A. Matvienkov, V.V. Nikogosian, I.K. Rocholl, A., Sigurdsson, I.A. Sushchevskaya, N.M. Teklay, M., 2007. The Amount of Recycled Crust in Sources of Mantle-Derived Melts. Science 316, 412–417. https://doi.org/10.1126/science(opens in new window)
Willbold, M., Stracke, A., 2010. Formation of enriched mantle components by recycling of upper and lower continental crust. Chemical Geology 276, 188–197. https://doi.org/10.1016/j.chemgeo.2010.06.005(opens in new window)
Isolated seamounts and seamount provinces that are unrelated to deep mantle upwellings (mantle plumes), sample upper mantle heterogeneities and thus provide a window into compositional variations in the upper mantle. Our working hypothesis is that enriched reservoirs exist in the upper mantle, and they are a result of the shallow recycling of younger oceanic crust and continental lithospheric materials (upper and/or lower crust and subcontinental lithospheric mantle). The upper mantle is generally considered to be geochemically depleted due to the extraction of continental crust and the formation of oceanic crust at mid-ocean ridges. As a result, it typically exhibits unradiogenic (low) Sr and Pb isotopic compositions, along with radiogenic (high) Nd and Hf isotopic signatures (Hofmann, 1997). Nevertheless, enriched domains within the upper mantle may differ from this simplified model in one or more of these isotopic systems. Compared to deep mantle enriched reservoirs, such as HIMU and EM endmembers (Homrighausen et al., 2018; Jackson et al., 2018; Willbold and Stracke, 2010), these upper mantle heterogeneities are expected to develop over shorter timescales, reflecting the relatively faster recycling processes operating in the upper mantle compared to those in the lower mantle (Hoernle et al., 2006; Sobolev et al., 2007).
As mentioned, we focused on one of the most isolated structures found on the seafloor: the Mid-Pacific Mountains (MPM), a large structure that extends ~2200km in an E-W direction in the middle of the Pacific Ocean. This feature comprises seamounts, guyots, volcanic elongated ridges, and thicker plateaus that sit on top of seafloor with a varying range of ages according to the available magnetic lineations (Seton et al., 2020); from west to east seafloor ages decrease from ~155 Ma to ~110 Ma. A seamount province located to the SE of the MPM, lies between the structure and the continuation of the Line Island hotspot track (Davis et al., 2002; Pockalny et al., 2021), however, unlike the hotspot seamounts, this seamount province does not seem to have an age progressive track and their relationship with the MPM and the Line Islands remain unclear.
In the past, a series of seagoing expeditions occurring in the 70’s and 90’s targeted several locations within and around the MPM, including expeditions DSDP 17-164, -165A, -166, -167, -169 & -170, DSDP32-313, and ODP 143-865A & 866A, which drilled boreholes on top of guyots, seamounts, plateaus, ridges, and normal ocean seafloor (Fig. 1). Even though the goals of each of the cores were variable (sedimentology, paleontology, paleoclimate reconstructions, for example), in all cases the drilling continued until reaching the basaltic bedrock, penetrating a few cm to m into the rocks. In most cases, limited geochemical analyses were performed on the basalts and very few included radiogenic isotope measurements or 40Ar/39Ar dating, yielding incomplete datasets.
Thus, for the ISOSEA Project we requested samples from the IODP Gulf Coast Repository pertaining to the mentioned drilled cores (Fig. 1). In each case, we reviewed all the available report data, including photographs and descriptions of the cores to ensure that we were requesting the least altered material. From the ~60 samples received, 35 fulfill the criteria for fresh material (i.e. absence of secondary minerals, lack of filled vesicles or fractures, unaltered phenocrysts, dark grey to black groundmasses).
Prior to this study, these unique samples from the non-hotspot-related seamounts and ridges had not been comprehensively analyzed, lacking both high-resolution geochemical and geochronological data acquired using modern analytical techniques. Through the ISOSEA project, we conducted state-of-the-art analyses that resulted in critical new insights into the origin, composition, and tectonic evolution of this isolated region. These results provide an essential contribution to our understanding of Pacific plate history and offer a robust geochemical framework for interpreting intraplate volcanism in this part of the ocean basin.
References
Davis, A.S. Gray, L.B. Clague, D.A. Hein, J.R. 2002. The Line Islands revisited: New 40Ar/39Ar geochronologic evidence for episodes of volcanism due to lithospheric extension. Geochemistry, Geophysics, Geosystems 3, 1–28. https://doi.org/10.1029/2001GC000190(opens in new window)
Hoernle, K., White, J.D.L. van den Bogaard, P., Hauff, F., Coombs, D.S. Werner, R., Timm, C., Garbe-Schönberg, D., Reay, A., Cooper, A.F. 2006. Cenozoic intraplate volcanism on New Zealand: Upwelling induced by lithospheric removal. Earth and Planetary Science Letters 248, 350–367. https://doi.org/10.1016/j.epsl.2006.06.001(opens in new window)
Hofmann, A.W. 1997. Mantle geochemistry: the message from oceanic volcanism. Nature 385, 219–229.
Homrighausen, S., Hoernle, K., Hauff, F., Geldmacher, J., Wartho, J.-A. van den Bogaard, P., Garbe-Schönberg, D., 2018. Global distribution of the HIMU end member: Formation through Archean plume-lid tectonics. Earth-Science Reviews 182, 85–101. https://doi.org/10.1016/j.earscirev.2018.04.009(opens in new window)
Jackson, M.G. Becker, T.W. Konter, J.G. 2018. Evidence for a deep mantle source for EM and HIMU domains from integrated geochemical and geophysical constraints. Earth and Planetary Science Letters 484, 154–167.
Pockalny, R., Barth, G., Eakins, B., Kelley, K.A. Wertman, C., 2021. Multiple melt source origin of the Line Islands (Pacific Ocean). Geology 49, 1358–1362. https://doi.org/10.1130/G49306.1(opens in new window)
Seton, M., Müller, R.D. Zahirovic, S., Williams, S., Wright, N.M. Cannon, J., Whittaker, J.M. Matthews, K.J. McGirr, R., 2020. A Global Data Set of Present-Day Oceanic Crustal Age and Seafloor Spreading Parameters. Geochemistry, Geophysics, Geosystems 21, e2020GC009214. https://doi.org/10.1029/2020GC009214(opens in new window)
Sobolev, A.V. Hofmann, A.W. Kuzmin, D.V. Yaxley, G.M. Arndt, N.T. Chung, S.-L. Danyushevsky, L.V. Elliott, T., Frey, F.A. Garcia, M.O. Gurenko, A.A. Kamenetsky, V.S. Kerr, A.C. Krivolutskaya, N.A. Matvienkov, V.V. Nikogosian, I.K. Rocholl, A., Sigurdsson, I.A. Sushchevskaya, N.M. Teklay, M., 2007. The Amount of Recycled Crust in Sources of Mantle-Derived Melts. Science 316, 412–417. https://doi.org/10.1126/science(opens in new window)
Willbold, M., Stracke, A., 2010. Formation of enriched mantle components by recycling of upper and lower continental crust. Chemical Geology 276, 188–197. https://doi.org/10.1016/j.chemgeo.2010.06.005(opens in new window)
Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far
To address the scientific questions and goals of this project, we carried out a methodological approach consisting of an integrated petrological, geochemical, and geochronological analyses. This process was divided into the following work packages (WP):
1. WP1: Global isolated seamount database. We compiled all published data within public databases and the literature to create a global database of isolated seamounts that include their geographical coordinates, and when available, geochemical data: major and trace element and isotopic composition. We also searched for geochronological 40Ar/39Ar data; however, these were sparse. The classification of seamounts proved to be more complex than initially anticipated, due to significant variability in how seamounts, particularly isolated ones, are defined across studies. In addition, many seamounts exhibit transitional features in both their geographic location and geochemical composition. For example, some occur near hotspots but not directly along the hotspot track and display moderately enriched isotopic signatures may reflect an upper mantle source and/or distal hotspot material. These challenges and complexities highlight the reason why these types of seamounts need to be further explored. The deliverable completed during this WP is a global dataset with thousands of data from seamounts whose origin is not related to hotspot volcanism.
2. WP2: Sample request to available repositories. We requested drill-core samples from the International Ocean Discovery Program Repository (IODP) Gulf Coast Repository (GCR) from expeditions DSDP-17-164, DSDP-17-165A, DSDP-17-166, DSDP-17-167, DSDP-17-169, DSDP-17-170, DSDP-32-313, ODP-143-865A, and ODP-143-866A (Fig.1). All these sites are located in and around the Mid-Pacific Mountains massif and include samples from normal oceanic crust as well as from seamounts, guyots, and ridge-like structures. It is interesting to note that all of these expeditions happened in the 70s and 90s. For all of the cores, we explored the available information in the IODP reports. We studied the reports, the descriptions of each core, and the available pictures for each one. The intention was to request the freshest volcanic material from every site, focusing on the deepest parts of the core. This is crucial since we wanted to acquire the samples closest to the igneous basement of the guyots and seamounts. In total 64 samples were requested from the GCR.
3. WP3: Sample preparation. After the arrival of the requested core samples, a meticulous task of evaluating which samples were suitable for analyses ensued. We wanted to make sure that only the samples least affected by seafloor alteration were prepared for analysis, thus from the 64 samples, 29 needed to be excluded due to evident pervasive alteration based on thin section evaluation. The remaining 35 samples were unexpectedly fresh; thus, we further crushed, cleaned, sieved, and hand-picked the material for major and trace element analyses. As deliverables we completed the sample preparation for 35 samples for major and trace element analyses.
4. WP4: Major and trace element analyses. We measured whole rock major elements at the XRF laboratory of the University of Hamburg. Trace elements were analyzed by solution inductively coupled plasma mass spectrometry (ICP-MS) at the Institute of Geosciences, at Kiel University. Deliverables completed include the production of a high-precision major and trace element dataset for our samples.
5. WP5: Isotope geochemistry and geochronology analyses. After evaluating the results from the major and trace elements, and the significance of each sample location, we chose 18 samples for Sr-Nd-Pb-Hf Isotope analyses at the Laboratory for Radiogenic Isotope Analysis at GEOMAR using the Thermo Fisher Scientific TRITION Plus thermal ionization mass spectrometer (TIMS) and a Nu Instruments multi-collector (MC) ICP-MS. After acquiring the complete geochemical dataset, including the radiogenic isotopes, we proceeded to separate 9 samples for 40Ar/39Ar geochronology which were sent to the WiscAr Laboratory in University of Wisconsin-Madison; we have partial results for these samples, only three samples yielded plateau ages and we are waiting to re-run the remaining six. The deliverable completed in this WP is a complete dataset including radiogenic isotope geochemistry and geochronology on select samples once the analyses are finished.
6. WP6: Data evaluation and geochemical modelling. We used our new and compiled data to create geochemical models using open-source software like MELTS, GCDKit (R-based), t-Igpet, and PRIMELT2.xls. These models help us explore the possible origin of the Mid-Pacific Mountains and their relationship with the surrounding features on the seafloor. The deliverable completed in this WP are figures (geochemical plots and mixing models) presenting the results of the geochemical modeling using our new dataset.
7. WP7: Publications. We currently have a manuscript regarding the geochemistry and tectonic history of the Emperor seamount chain undergoing a round of reviews to be resubmitted to Geology. A second manuscript is in preparation with the results of the integrated petrological, geochemical, and geochronological sets of analyses from the Mid-Pacific Mountains and related features.
8. WP8: Communication and outreach. This WP was implemented throughout the duration of the project. As deliverables I gave 5 presentations at conferences and workshops, 3 invited seminars, participated in a webinar with college students from the University of Costa Rica, and gave presentations during outreach events like GEOMAR’s Science Day, and the GEOMAR’s Summer School 2024.
1. WP1: Global isolated seamount database. We compiled all published data within public databases and the literature to create a global database of isolated seamounts that include their geographical coordinates, and when available, geochemical data: major and trace element and isotopic composition. We also searched for geochronological 40Ar/39Ar data; however, these were sparse. The classification of seamounts proved to be more complex than initially anticipated, due to significant variability in how seamounts, particularly isolated ones, are defined across studies. In addition, many seamounts exhibit transitional features in both their geographic location and geochemical composition. For example, some occur near hotspots but not directly along the hotspot track and display moderately enriched isotopic signatures may reflect an upper mantle source and/or distal hotspot material. These challenges and complexities highlight the reason why these types of seamounts need to be further explored. The deliverable completed during this WP is a global dataset with thousands of data from seamounts whose origin is not related to hotspot volcanism.
2. WP2: Sample request to available repositories. We requested drill-core samples from the International Ocean Discovery Program Repository (IODP) Gulf Coast Repository (GCR) from expeditions DSDP-17-164, DSDP-17-165A, DSDP-17-166, DSDP-17-167, DSDP-17-169, DSDP-17-170, DSDP-32-313, ODP-143-865A, and ODP-143-866A (Fig.1). All these sites are located in and around the Mid-Pacific Mountains massif and include samples from normal oceanic crust as well as from seamounts, guyots, and ridge-like structures. It is interesting to note that all of these expeditions happened in the 70s and 90s. For all of the cores, we explored the available information in the IODP reports. We studied the reports, the descriptions of each core, and the available pictures for each one. The intention was to request the freshest volcanic material from every site, focusing on the deepest parts of the core. This is crucial since we wanted to acquire the samples closest to the igneous basement of the guyots and seamounts. In total 64 samples were requested from the GCR.
3. WP3: Sample preparation. After the arrival of the requested core samples, a meticulous task of evaluating which samples were suitable for analyses ensued. We wanted to make sure that only the samples least affected by seafloor alteration were prepared for analysis, thus from the 64 samples, 29 needed to be excluded due to evident pervasive alteration based on thin section evaluation. The remaining 35 samples were unexpectedly fresh; thus, we further crushed, cleaned, sieved, and hand-picked the material for major and trace element analyses. As deliverables we completed the sample preparation for 35 samples for major and trace element analyses.
4. WP4: Major and trace element analyses. We measured whole rock major elements at the XRF laboratory of the University of Hamburg. Trace elements were analyzed by solution inductively coupled plasma mass spectrometry (ICP-MS) at the Institute of Geosciences, at Kiel University. Deliverables completed include the production of a high-precision major and trace element dataset for our samples.
5. WP5: Isotope geochemistry and geochronology analyses. After evaluating the results from the major and trace elements, and the significance of each sample location, we chose 18 samples for Sr-Nd-Pb-Hf Isotope analyses at the Laboratory for Radiogenic Isotope Analysis at GEOMAR using the Thermo Fisher Scientific TRITION Plus thermal ionization mass spectrometer (TIMS) and a Nu Instruments multi-collector (MC) ICP-MS. After acquiring the complete geochemical dataset, including the radiogenic isotopes, we proceeded to separate 9 samples for 40Ar/39Ar geochronology which were sent to the WiscAr Laboratory in University of Wisconsin-Madison; we have partial results for these samples, only three samples yielded plateau ages and we are waiting to re-run the remaining six. The deliverable completed in this WP is a complete dataset including radiogenic isotope geochemistry and geochronology on select samples once the analyses are finished.
6. WP6: Data evaluation and geochemical modelling. We used our new and compiled data to create geochemical models using open-source software like MELTS, GCDKit (R-based), t-Igpet, and PRIMELT2.xls. These models help us explore the possible origin of the Mid-Pacific Mountains and their relationship with the surrounding features on the seafloor. The deliverable completed in this WP are figures (geochemical plots and mixing models) presenting the results of the geochemical modeling using our new dataset.
7. WP7: Publications. We currently have a manuscript regarding the geochemistry and tectonic history of the Emperor seamount chain undergoing a round of reviews to be resubmitted to Geology. A second manuscript is in preparation with the results of the integrated petrological, geochemical, and geochronological sets of analyses from the Mid-Pacific Mountains and related features.
8. WP8: Communication and outreach. This WP was implemented throughout the duration of the project. As deliverables I gave 5 presentations at conferences and workshops, 3 invited seminars, participated in a webinar with college students from the University of Costa Rica, and gave presentations during outreach events like GEOMAR’s Science Day, and the GEOMAR’s Summer School 2024.
Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)
Even though the Mid-Pacific Mountains and surrounding ridges are prominent geological features in the central Pacific Ocean, they remain some of most unexplored structures on the Pacific Plate. Currently, no agreement exists about the origin of the mid-Pacific Mountains (Fletcher et al., 2020; Kroenke et al., 1985; Thiede et al., 1981), in large part due to the historical inaccessibility of representative samples. Moreover, prior studies lacked geochemical and geochronological data obtained with modern analytical techniques. Thus, getting a comprehensive overview and updated analyses using state-of-the-art laboratory methods, especially, acquiring radiogenic isotope data and 40Ar/39Ar geochronological data was of utmost importance for our understanding of the tectonic processes occurring on the Pacific Plate during the Cretaceous.
The ISOSEA project addressed this critical gap by providing an integrated, high-resolution dataset for key volcanic structures within the MPM, including radiogenic isotope compositions and 40Ar/39Ar geochronology, analyzed using state-of-the-art instrumentation. This dataset now offers a foundation to understand the origin, timing, and tectonic implications of the MPM within the broader evolution of the Pacific Plate.
Our results suggest that the single plume model alone cannot sufficiently explain the observed morphology, spatial extent, and compositions of the Mid-Pacific Mountains. For instance, geochemical variations following a west to east trend (older to younger), shows that the basalts become more alkaline towards the east, yet the easternmost location (DSDP 32-313) show distinct lower values of TiO2/Yb, plotting within the shallow melting EMORB field on a Nb/Yb vs TiO2/Yb diagram (Pearce, 2008) (Fig.2A). These samples are located closest to the Necker Ridge and the Horizon Guyot, two prominent volcanic elongated ridges trending SW-NE at the eastern edge of the Mid-Pacific Mountains. Additionally, the radiogenic isotope signatures (Sr-Nd-Pb-Hf) show that these basalts are sourced from a depleted reservoir (DMM) combined with one or more enriched source (EMI, EMII). Towards the east, the samples become higher in 87Sr/86Sr at a given 206Pb/204Pb, approaching similar values to the Line Islands seamounts (Pockalny et al., 2021) (Fig. 2B).
Moreover, similar volcanic elongated ridges have been previously identified at tectonic settings where Plume-Ridge interaction occurred. During this process, melts can be channeled in the asthenosphere from the plume conduit towards a nearby mid-ocean ridge (Jiang et al., 2020; Mittal and Richards, 2017). Estimates suggest that these melts can be transported up to 400 km from the plume to the ridge (Kopp et al., 2003), nevertheless in the case of the eastern Mid-Pacific Mountains, the volcanic elongated ridges extend up to ~630 km to the Hawaiian hotspot track, for example, the Necker ridge which is the longest volcanic elongated ridge near the Mid-Pacific Mountains (Fig. 1).
Alternatively, these type of structures may form through lithospheric cracks opened during large scale tectonic plate reorganization, for instance, the reorganization that produced the Hawaiian-Emperor Bend (O’Connor et al., 2015). This extensive deformation can facilitate melting of the upper mantle unrelated to hotspot activity. In this case, the geochemical signatures of the lavas are characterized by depleted compositions similar to mid-ocean ridge basalt (MORB) or even enriched MORB.
Based on the ISOSEA results we proposed a hybrid model where the initial phase of formation of the Mid-Pacific Mountains was characterized by the emplacement of a large igneous province fed by a deep mantle plume at circa 130 Ma (Lower Cretaceous). As the massif becomes younger towards the east during the Upper Cretaceous, the interaction of the deep mantle plume wanes and the magmatism was triggered by the lithospheric decompression that resulted from the Pacific plate deformation which created fracture zones and extensional features, like a mid-ocean ridge, that facilitated the emplacement of large volcanic elongated ridges.
The MPM proved to be an excellent case studio to understand the interactions between hotspot magmatism and magmatism un-related to hotspots, in this case, magmatism driven by the large scale deformation in response to the clockwise rotation that occurred in the Pacific Plate between 150 and 100 Ma (Torsvik et al., 2019) and a later plate reorganization ca. 90 Ma (Scott and Konrad, 2024). Even though it is an excellent scenario of dynamic interaction of deep mantle magmatic processes with surface processes as deformation and interaction of magmatic regimes with mid-ocean ridges and fracture zones, it remains grossly unexplored, with many features still unsampled. Further seagoing expeditions to collect samples and performed high resolution bathymetry are needed to clearly elucidate their origin, development, and relationship with the surrounding Pacific Plate features.
References
Fletcher, M., Wyman, D.A. Zahirovic, S., 2020. Mantle plumes, triple junctions and transforms: A reinterpretation of Pacific Cretaceous – Tertiary LIPs and the Laramide connection. Geoscience Frontiers 11, 1133–1144. https://doi.org/10.1016/j.gsf.2019.09.003(opens in new window)
Jiang, Q., Jourdan, F., Olierook, H.K.H. Merle, R.E. Whittaker, J.M. 2020. Longest continuously erupting large igneous province driven by plume-ridge interaction. Geology 49, 206–210. https://doi.org/10.1130/G47850.1(opens in new window)
Kopp, H., Kopp, C., Phipps Morgan, J., Flueh, E.R. Weinrebe, W., Morgan, W.J. 2003. Fossil hot spot-ridge interaction in the Musicians Seamount Province: Geophysical investigations of hot spot volcanism at volcanic elongated ridges. Journal of Geophysical Research: Solid Earth 108. https://doi.org/10.1029/2002JB002015(opens in new window)
Kroenke, L., Kellogg, J., Nemoto, K., 1985. Mid-pacific mountains revisited. Geo-Marine Letters 5, 77–81. https://doi.org/10.1007/BF02233931(opens in new window)
Mittal, T., Richards, M.A. 2017. Plume-ridge interaction via melt channelization at Galápagos and other near-ridge hotspot provinces. Geochemistry, Geophysics, Geosystems 18, 1711–1738. https://doi.org/10.1002/2016GC006454(opens in new window)
O’Connor, J.M. Hoernle, K., Muller, R.D. Morgan, J.P. Butterworth, N.P. Hauff, F., Sandwell, D.T. Jokat, W., Wijbrans, J.R. Stoffers, P., 2015. Deformation-related volcanism in the Pacific Ocean linked to the Hawaiian-Emperor bend. Nature Geosci 8, 393–397. https://doi.org/10.1038/ngeo2416(opens in new window)
Pearce, J.A. 2008. Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust. Lithos 100, 14–48. https://doi.org/10.1016/j.lithos.2007.06.016(opens in new window)
Pockalny, R., Barth, G., Eakins, B., Kelley, K.A. Wertman, C., 2021. Multiple melt source origin of the Line Islands (Pacific Ocean). Geology 49, 1358–1362. https://doi.org/10.1130/G49306.1(opens in new window)
Scott, B., Konrad, K., 2024. Seventeen Million Years of Episodic Volcanism Recorded Within the Geologist Seamounts: Implications for Tectonic Drivers of Intraplate Volcanism. Geochemistry, Geophysics, Geosystems 25, e2024GC011806. https://doi.org/10.1029/2024GC011806(opens in new window)
Thiede, J., Dean, W., Rea, D., Vallier, T., Adelseck, C.G. 1981. The geologic history of the Mid-Pacific Mountains in the central north Pacific Ocean—a synthesis of Deep-Sea Drilling studies. Initial Reports of the Deep Sea Drilling Project 62, 1073–1120.
Torsvik, T.H. Steinberger, B., Shephard, G.E. Doubrovine, P.V. Gaina, C., Domeier, M., Conrad, C.P. Sager, W.W. 2019. Pacific-Panthalassic Reconstructions: Overview, Errata and the Way Forward. Geochemistry, Geophysics, Geosystems 20, 3659–3689. https://doi.org/10.1029/2019GC008402(opens in new window)
The ISOSEA project addressed this critical gap by providing an integrated, high-resolution dataset for key volcanic structures within the MPM, including radiogenic isotope compositions and 40Ar/39Ar geochronology, analyzed using state-of-the-art instrumentation. This dataset now offers a foundation to understand the origin, timing, and tectonic implications of the MPM within the broader evolution of the Pacific Plate.
Our results suggest that the single plume model alone cannot sufficiently explain the observed morphology, spatial extent, and compositions of the Mid-Pacific Mountains. For instance, geochemical variations following a west to east trend (older to younger), shows that the basalts become more alkaline towards the east, yet the easternmost location (DSDP 32-313) show distinct lower values of TiO2/Yb, plotting within the shallow melting EMORB field on a Nb/Yb vs TiO2/Yb diagram (Pearce, 2008) (Fig.2A). These samples are located closest to the Necker Ridge and the Horizon Guyot, two prominent volcanic elongated ridges trending SW-NE at the eastern edge of the Mid-Pacific Mountains. Additionally, the radiogenic isotope signatures (Sr-Nd-Pb-Hf) show that these basalts are sourced from a depleted reservoir (DMM) combined with one or more enriched source (EMI, EMII). Towards the east, the samples become higher in 87Sr/86Sr at a given 206Pb/204Pb, approaching similar values to the Line Islands seamounts (Pockalny et al., 2021) (Fig. 2B).
Moreover, similar volcanic elongated ridges have been previously identified at tectonic settings where Plume-Ridge interaction occurred. During this process, melts can be channeled in the asthenosphere from the plume conduit towards a nearby mid-ocean ridge (Jiang et al., 2020; Mittal and Richards, 2017). Estimates suggest that these melts can be transported up to 400 km from the plume to the ridge (Kopp et al., 2003), nevertheless in the case of the eastern Mid-Pacific Mountains, the volcanic elongated ridges extend up to ~630 km to the Hawaiian hotspot track, for example, the Necker ridge which is the longest volcanic elongated ridge near the Mid-Pacific Mountains (Fig. 1).
Alternatively, these type of structures may form through lithospheric cracks opened during large scale tectonic plate reorganization, for instance, the reorganization that produced the Hawaiian-Emperor Bend (O’Connor et al., 2015). This extensive deformation can facilitate melting of the upper mantle unrelated to hotspot activity. In this case, the geochemical signatures of the lavas are characterized by depleted compositions similar to mid-ocean ridge basalt (MORB) or even enriched MORB.
Based on the ISOSEA results we proposed a hybrid model where the initial phase of formation of the Mid-Pacific Mountains was characterized by the emplacement of a large igneous province fed by a deep mantle plume at circa 130 Ma (Lower Cretaceous). As the massif becomes younger towards the east during the Upper Cretaceous, the interaction of the deep mantle plume wanes and the magmatism was triggered by the lithospheric decompression that resulted from the Pacific plate deformation which created fracture zones and extensional features, like a mid-ocean ridge, that facilitated the emplacement of large volcanic elongated ridges.
The MPM proved to be an excellent case studio to understand the interactions between hotspot magmatism and magmatism un-related to hotspots, in this case, magmatism driven by the large scale deformation in response to the clockwise rotation that occurred in the Pacific Plate between 150 and 100 Ma (Torsvik et al., 2019) and a later plate reorganization ca. 90 Ma (Scott and Konrad, 2024). Even though it is an excellent scenario of dynamic interaction of deep mantle magmatic processes with surface processes as deformation and interaction of magmatic regimes with mid-ocean ridges and fracture zones, it remains grossly unexplored, with many features still unsampled. Further seagoing expeditions to collect samples and performed high resolution bathymetry are needed to clearly elucidate their origin, development, and relationship with the surrounding Pacific Plate features.
References
Fletcher, M., Wyman, D.A. Zahirovic, S., 2020. Mantle plumes, triple junctions and transforms: A reinterpretation of Pacific Cretaceous – Tertiary LIPs and the Laramide connection. Geoscience Frontiers 11, 1133–1144. https://doi.org/10.1016/j.gsf.2019.09.003(opens in new window)
Jiang, Q., Jourdan, F., Olierook, H.K.H. Merle, R.E. Whittaker, J.M. 2020. Longest continuously erupting large igneous province driven by plume-ridge interaction. Geology 49, 206–210. https://doi.org/10.1130/G47850.1(opens in new window)
Kopp, H., Kopp, C., Phipps Morgan, J., Flueh, E.R. Weinrebe, W., Morgan, W.J. 2003. Fossil hot spot-ridge interaction in the Musicians Seamount Province: Geophysical investigations of hot spot volcanism at volcanic elongated ridges. Journal of Geophysical Research: Solid Earth 108. https://doi.org/10.1029/2002JB002015(opens in new window)
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Mittal, T., Richards, M.A. 2017. Plume-ridge interaction via melt channelization at Galápagos and other near-ridge hotspot provinces. Geochemistry, Geophysics, Geosystems 18, 1711–1738. https://doi.org/10.1002/2016GC006454(opens in new window)
O’Connor, J.M. Hoernle, K., Muller, R.D. Morgan, J.P. Butterworth, N.P. Hauff, F., Sandwell, D.T. Jokat, W., Wijbrans, J.R. Stoffers, P., 2015. Deformation-related volcanism in the Pacific Ocean linked to the Hawaiian-Emperor bend. Nature Geosci 8, 393–397. https://doi.org/10.1038/ngeo2416(opens in new window)
Pearce, J.A. 2008. Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust. Lithos 100, 14–48. https://doi.org/10.1016/j.lithos.2007.06.016(opens in new window)
Pockalny, R., Barth, G., Eakins, B., Kelley, K.A. Wertman, C., 2021. Multiple melt source origin of the Line Islands (Pacific Ocean). Geology 49, 1358–1362. https://doi.org/10.1130/G49306.1(opens in new window)
Scott, B., Konrad, K., 2024. Seventeen Million Years of Episodic Volcanism Recorded Within the Geologist Seamounts: Implications for Tectonic Drivers of Intraplate Volcanism. Geochemistry, Geophysics, Geosystems 25, e2024GC011806. https://doi.org/10.1029/2024GC011806(opens in new window)
Thiede, J., Dean, W., Rea, D., Vallier, T., Adelseck, C.G. 1981. The geologic history of the Mid-Pacific Mountains in the central north Pacific Ocean—a synthesis of Deep-Sea Drilling studies. Initial Reports of the Deep Sea Drilling Project 62, 1073–1120.
Torsvik, T.H. Steinberger, B., Shephard, G.E. Doubrovine, P.V. Gaina, C., Domeier, M., Conrad, C.P. Sager, W.W. 2019. Pacific-Panthalassic Reconstructions: Overview, Errata and the Way Forward. Geochemistry, Geophysics, Geosystems 20, 3659–3689. https://doi.org/10.1029/2019GC008402(opens in new window)