A document by Erik van der Wiel. Click on the document to view its contents.

The 0–2.5 Ma volcanism in Easter Island (Rapa Nui) emerges just east of the East Pacific Rise on young (Pliocene, 3–4.8 Ma) ocean floor. Here, we report the finding of mantle-derived zircon grains retrieved from Easter Island beach sands and red soils that are much older than the Easter Island volcanism and its underlying lithosphere. A large population of 0–165 Myr old zircons have coherent oxygen (δ18O(zircon) 3.8– 5.9‰) and hafnium mantle isotopic signatures (εHf(t) +3.5–+12.5). These results are consistent with the crystallization of zircon from plume-related melts. In addition, a chemically diverse population with ages as old as Precambrian was also found. We thus suggest that the Easter hotspot started at least ~165 Ma ago. A large population of ~160-164 Ma zircons could signal an intense initial massive melting phase associated with the formation of a Large Igneous Province (LIP) upon the first arrival of the plume. We use plate reconstructions to show that such a LIP would have formed on the Phoenix Plate. It would have subducted below the Antarctic Peninsula around 100-105 Ma, offering a solution for the enigmatic Palmer Land deformation event, previously proposed to result from a collision with an unknown indenter. Our findings show that asthenospheric mantle-derived xenocryst zircon cargo, as recently reported from Galápagos, may not be an exception. The here-reported “ghost” of a prolonged hotspot activity suggests that the Easter hotspot and the sub-lithospheric mantle in which it is entrained remained mantle-stationary for at least 165 Ma.

This article is composed of three independent commentaries about the state of ICON principles (Goldman et al., 2021) in the Geomagnetism, Paleomagnetism, and Electromagnetism (GPE) section and discussion on the opportunities and challenges of adopting them. Each commentary focuses on a different topic: Global collaboration, reproducibility, data sharing and infrastructure; Inclusive equitable, and accessible science: Involvement, challenges, and support of early career, BIPOC, women, LGBTQIA+, and/or disabled researchers; Community engagement, citizen science, education, and stakeholder involvement. Data sharing practices and open repository use still varies strongly between GPE communities. Some have a long tradition of data sharing, others are only starting it. Globally, GPE leadership is strongly dominated by white males and diversity may increase through the creation of Science Equality Commissions. Improved global stakeholder involvement can increase research impacts and help fight inequalities. In all investigated topics we see promising beginnings but also recognize obstacles that include a lack of funding, a lack of understanding of diversity, and prioritizing short-term gain over long-term benefit. Nonetheless, we are hopeful that our community will embrace ICON science.

The dynamics of slab detachment and associated geological fingerprints have been inferred from various numerical and analogue models. These invariably use a setup with slab-pull-driven convergence in which a slab detaches below a mantle-stationary trench after the arrest of plate convergence due to arrival of continental lithosphere. In contrast, geological reconstructions show that post-detachment plate convergence is common and that trenches and sutures are rarely mantle-stationary during detachment. Here, we identify the more realistic kinematic context of slab detachment using the example of the India-Asia convergent system. We first show that only the India and Himalayas slabs (from India’s northern margin) and the Carlsberg slab (from the western margin) unequivocally detached from Indian lithosphere. Several other slabs below the Indian Ocean do not require a Neotethyan origin and may be of Mesotethys and Paleotethys origin. Additionally, the still-connected slabs are being dragged together with the Indian plate forward (Hindu Kush) or sideways (Burma, Chaman) through the mantle. We show that Indian slab detachment occurred at moving trenches during ongoing plate convergence, providing more realistic geodynamic conditions for use in future numerical and analogue experiments. We identify that the actively detaching Hindu Kush slab is a type-example of this setting, whilst a 25-13 Ma phase of shallow detachment of the Himalayas slab, here reconstructed from plate kinematics and tomography, agrees well with independent, published geological estimates from the Himalayas orogen of slab detachment. The Sulaiman Ranges of Pakistan may hold the geological signatures of detachment of the laterally dragged Carlsberg slab.

Paleomagnetic poles used to compute apparent polar wander paths (APWPs) are strongly dispersed, which was recently shown to cause a large fraction (>50%) of these poles to be statistically distinct from the APWP to which they contributed, suggesting that current statistical approaches overestimate paleomagnetic resolution. Here, we analyze why coeval paleopoles are so dispersed, using the paleopoles behind the most recent global APWP and a compilation of paleomagnetic data obtained from <10 Ma volcanic rocks (PSV10). We find that paleopoles derived from sedimentary rocks, or from data sets underrepresenting paleosecular variation (PSV), are more dispersed and more frequently displaced. We show that paleopoles based on a smaller number of paleomagnetic sites are more dispersed than poles based on larger data sets, revealing that the degree to which PSV is averaged is an important contributor to the pole dispersion. We identify as fundamental problem, however, that the amount of paleomagnetic data used to calculate a paleopole, and thus the dispersion of coeval paleopoles, is essentially arbitrary. We therefore explore a different approach in which reference poles of APWPs are calculated from site-level data instead of paleopoles, thereby assigning larger weight to larger data sets. We introduce a bootstrap-based method for comparing a collection of paleomagnetic data with a reference data set on the same hierarchical level, whereby the uncertainty is weighted against the number of paleomagnetic sites. Finally, our study highlights that demonstrating smaller tectonic displacements requires larger paleomagnetic data sets, and that such data sets can strongly improve future APWPs.

To determine a paleopole, the paleomagnetic community commonly applies a loosely defined set of quantitative data filters that were established for studies of geomagnetic field behavior. These filters require costly and time-consuming sampling procedures, but whether they improve accuracy and precision of paleopoles has not yet been systematically analyzed. In this study, we performed a series of experiments on four datasets which consist of 73-125 lava sites with 6-7 samples per lava. The datasets are from different regions and ages, and are large enough to represent paleosecular variation, yet contain demonstrably unreliable datapoints. We show that data filters based on within-site scatter (a k-cutoff, a minimum number of samples per site, and eliminating the farthest outliers per site) cannot objectively identify unreliable directions. We find instead that excluding unreliable directions relies on the subjective interpretation of the expert, highlighting the importance of making all data available following the FAIR principles. In addition, data filters that eliminate datapoints even have an adverse effect: the accuracy as well as the precision of paleopoles decreases with the decreasing number of data. Between-site scatter far outweighs within-site scatter, and when collecting paleomagnetic poles, the extra efforts put into collecting multiple samples per site are more effectively spent on collecting more single-sample sites.