Supplemental material: Plate velocities in the hotspot reference frame (original) (raw)
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Discussion of Plate velocities in the hotspot reference frame by
A difficulty arises in the plum-pudding plume model (Morgan and Phipps Morgan, this volume; Yamamoto et al., this volume) with regard to Pt-Os isotope systematics. The Os/Os ratios in the MORB-source mantle, as indicated by the isotopic compositions of abyssal peridotites (Os/Os = 0.119830 0.119838), are generally lower than in intraplate volcanic rocks (Hawaiian picrites and Gorgona komatiites; Os/Os = 0.119831 0.119850). In standard plume models, where MORB and intraplate volcanic rocks are derived from distinct isolated reservoirs, the isotopic differences are explained by the addition of approximately 0.5 weight percent outer-core material (Os/Os = 0.119870) to a plume (Brandon and Walker, 2005, and references therein).
A high-resolution model for Eurasia-North America plate kinematics since 20 Ma
Geophysical Journal International, 2008
We derive the first chronologically detailed model of Eurasia-North America plate motion since 20 Ma from ship and airplane surveys of the well-expressed magnetic lineations along this slowly spreading plate boundary, including previously unavailable dense Russian magnetic data from the southern Reykjanes Ridge and northern Mid-Atlantic ridge near the Charlie Gibbs fracture zone. From more than 7000 crossings of 21 magnetic anomalies from Anomaly 1n (0.78 Ma) to Anomaly 6n (19.7 Ma), we estimate best-fitting finite rotations and realistic uncertainties. Linear regressions of total opening distances versus their reversal ages at different locations along the plate boundary show that reversal boundaries are shifted systematically outwards from the spreading axis with respect to their idealized locations, with the outward shift ranging from more than 5 km between Iceland and the Charlie Gibbs fracture zone to ∼2 km elsewhere. This outward displacement, which is a consequence of the finite zone of seafloor accretion, degrades estimates of the underlying plate motion and is thus removed for the ensuing kinematic analysis. The corrected plate motion rotations reveal surprising, previously unrecognized features in the relative motions of these two plates. Within the uncertainties, motion was steady from 20 to 8 Ma around a pole that was located ∼600 km north of the present pole, with seafloor spreading rates that changed by no more than 5 per cent (1 mm yr −1 ) along the Reykjanes Ridge during this period. Seafloor spreading rates decreased abruptly by 20 ± 2 per cent at 7.5-6.5 Ma, coinciding with rapid southward migration of the pole of rotation and a 5 • -10 • counter-clockwise change in the plate slip direction. Eurasia-North America plate motion since 6.7 Ma has remained remarkably steady, with an apparently stationary axis of rotation and upper limit of ±2 per cent on any variations in the rate of angular rotation during this period. Based on the good agreement between seismotectonic constraints on present deformation in northeast Asia and directions of motion that are predicted by our 6.7 Ma to present pole, we hypothesize that motion has remained steady to the present and attempt to test this hypothesis with published GPS estimates for Eurasia-North America motion. We find, however, that GPS estimates that are tied to recent versions of the international geodetic reference frame and rely principally on station velocities from Europe give implausible estimates of recent motion, with the most recently published GPS model predicting convergence along the southern Gakkel Ridge and in the Laptev Sea, where seafloor spreading occurs. An alternative GPS estimate that is not tied to the international terrestrial reference frame and employs GPS station velocities from northeastern Asia is marginally consistent with our 6.7-0 Ma motion estimate.
Journal of Geophysical Research, 1978
A data set. comprising 110 spreading rates, 78 transform fault azimuths and 142 earthquake slip vectors has been inverted to yield a new instantaneous plate motion model, designated RM2. The model represents a considerable improvement over our previous estimate RM1 (Minster, Jordan, Molnar and Haines, 1974). The mean averaging; interval for the relative motion data has been reduced to less than 3 My. A detailed comparison of RM2 with angular velocity vectors which best fit the data along individual plate boundaries indicates that RM2 performs close to optimally in most regions, with several notable exceptions. The model systematically misfits data along the India-Antarctica and Pacific-India ,plate boundaries. We hypothesize that these discre^panctes are manifestations of internal deformation within the Indian plate; the data are compatible with NW-SE compression across the Ninetyeast Ridge at a rate of about 1 cm/yr. RM2 also fails to satisfy the EW-trending transform fault azimuths observed in the FAMOUS area, which is shown to be a consequence of closure contraints about the Azores triple junction. Slow movement betwgen North and South America is required by the data set, although the angular velocity vector describing this motion remains poorly constrained. The existence of a Bering plate, postulated in our previous study, is not necessary if we accept the proposal of Engdahl and others that the Aleutian slip vector data are biased by slab effects. Absolute motion models are derived from several kinematical hypotheses and compared vitb the data from hotspot traces younger than 10 My. A-1though some of the models are inconsistent with the Wilson-biorgan hypothesis, the overall resolving power of the hotspot data is poor, and the directions of absolute motion for the several slower-moving plates are not usefully constrained. 2.
On the shallow origin of hotspots and the westward drift of the lithosphere
in Foulger, G.R., Natland, J.H., Presnall, D.C., and Anderson, D.L., eds., Plates, plumes, and paradigms: Geological Society of America Special Paper 388, p. 735–749, doi: 10.1130/2005.2388(42)., 2005
Intraplate migrating hotspots, which are unrelated to rifts or plate margins in general, regardless of their origin in the mantle column, indicate relative motion between the lithosphere and the underlying mantle in which the hotspot source is located. Pacific plate hotspots are sufficiently fixed relative to one another to represent an independent reference frame to compute plate motions. However, the interpretation of the middle asthenosphere rather than the deep lower mantle as the source for intraplate Pacific hotspots has several implications. First, decoupling between the lithosphere and subasthenospheric mantle is greater than recorded by hotspot volcanic tracks (>100 mm/yr) due to undetectable shear in the lower asthenosphere below the magmatic source. The shallower the source, the larger the décollement. Second, computation of the westward drift is linked to the Pacific plate and assumes that the deep lower mantle, below the decoupling zone, sources the hotspots above. The Pacific plate is the fastest plate in the hotspot reference frame and dominates the net rotation of the lithosphere. Therefore, if decoupling with the subasthenospheric mantle is larger, the global westward drift of the lithosphere must be faster than present estimates, and may possibly vary between 50 and 90 mm/yr. In this case, all plates, albeit moving at different velocities, move westward relative to the subasthenospheric mantle. Finally, faster decoupling can generate more shear heating in the asthenosphere (even >100 °C). This amount of heating, in an undepleted mantle, could trigger scattered intraplate Pacific volcanism itself if the viscosity of the asthenosphere is locally higher than normal. The Emperor-Hawaiian bend can be reproduced when bent viscosity anisotropy in the asthenosphere is included. Variations in depth and geometry in the asthenosphere of these regions of higher viscosity could account for the irregular migration and velocities of surface volcanic tracks. This type of volcanic chain has different kinematic and magmatic origins from the Atlantic hotspots or wetspots, which migrate with or close to the oceanic spreading center and are therefore plate margin related.
Plate velocities in the hotspot reference frame
Special Paper 430: Plates, Plumes and Planetary Processes, 2007
We present a table of 57 hotspots distributed on all major plates with a short discussion of the 'present-day' (average over most recent ~5 Ma) direction and velocity for each hotspot track, with estimated errors. An electronic supplement has a discussion of each track and references to the data sources. Using the entries in Table 1, we found Pacific plate motion is a rotation about a pole at 59.33°N, 85.10°W with a rate that gives a velocity at the pole's 'equator' of 89.20 mm/yr (=-0.8029 °/Ma). The errors in this pole/rate are of the order ±2°N, ±4°W, ±3 mm/yr. The motions of other plates are then determined by NUVEL-1A. The large number of close, many very short, tracks in the Pacific superswell region precludes all hotspots being rooted near the core-mantle boundary. In general, we think asthenosphere is hotter than mantle just below it (in a potential temperature sense). Asthenosphere is very hotbrought up from the core-mantle boundary by plumes. Mantle is cooled by downgoing slabs, and a convective stability is established whereby mantle rises only at plumes and sinks only at trenches. We propose that this normal mantle geotherm is overwhelmed by much-larger-thanaverage mantle upwelling in superswell areas, making many short-lived instabilities in the upper mantle. Because soft asthenosphere so decouples plates from mantle below, instabilities in the 2 upper mantle (perhaps even above the 660-km discontinuity) are relatively 'fixed' in comparison to plate motions. With the mantle velocity contribution being minor, tracks are parallel to and have rates set by plate velocities.
Absolute plate motions and true polar wander in the absence of hotspot tracks
Nature, 2008
The motion of continents relative to the Earth's spin axis may be due either to rotation of the entire Earth relative to its spin axistrue polar wander 1,2 -or to the motion of individual plates 3 . In order to distinguish between these over the past 320 Myr (since the formation of the Pangaea supercontinent), we present here computations of the global average of continental motion and rotation through time 4 in a palaeomagnetic reference frame. Two components are identified: a steady northward motion and, during certain time intervals, clockwise and anticlockwise rotations, interpreted as evidence for true polar wander. We find 186 anticlockwise rotation about 2502220 Myr ago and the same amount of clockwise rotation about 1952145 Myr ago. In both cases the rotation axis is located at about 102206 W, 06 N, near the site that became the North American-South American-African triple junction at the break-up of Pangaea. This was followed by 106 clockwise rotation about 1452135 Myr ago, followed again by the same amount of anticlockwise rotation about 1102100 Myr ago, with a rotation axis in both cases 252506 E in the reconstructed area of North Africa and Arabia. These rotation axes mark the maxima of the degree-two non-hydrostatic geoid during those time intervals, and the fact that the overall net rotation since 320 Myr ago is nearly zero is an indication of long-term stability of the degree-two geoid and related mantle structure 5,6 . We propose a new reference frame, based on palaeomagnetism, but corrected for the true polar wander identified in this study, appropriate for relating surface to deep mantle processes from 320 Myr ago until hotspot tracks can be used (about 130 Myr ago).
The concurrent emergence and causes of double volcanic hotspot tracks on the Pacific plate
0 0 M o n t h 2 0 1 7 | V o L 0 0 0 | n A t U R E | 1 Mantle plumes are buoyant upwellings of hot rock that transport heat from Earth's core to its surface, generating anomalous regions of volcanism that are not directly associated with plate tectonic processes. The best-studied example is the Hawaiian–Emperor chain, but the emergence of two sub-parallel volcanic tracks along this chain 1 , Loa and Kea, and the systematic geochemical differences between them 2,3 have remained unexplained. Here we argue that the emergence of these tracks coincides with the appearance of other double volcanic tracks on the Pacific plate and a recent azimuthal change in the motion of the plate. We propose a three-part model that explains the evolution of Hawaiian double-track volcanism: first, mantle flow beneath the rapidly moving Pacific plate strongly tilts the Hawaiian plume and leads to lateral separation between high-and low-pressure melt source regions; second, the recent azimuthal change in Pacific plate motion exposes high-and low-pressure melt products as geographically distinct volcanoes, explaining the simultaneous emergence of double-track volcanism across the Pacific; and finally, secondary pyroxenite, which is formed as eclogite melt reacts with peridotite 4 , dominates the low-pressure melt region beneath Loa-track volcanism, yielding the systematic geochemical differences observed between Loa-and Kea-type lavas 3,5–9. Our results imply that the formation of double-track volcanism is transitory and can be used to identify and place temporal bounds on plate-motion changes.
Examine the Global Distribution Patterns of volcanoes and Tectonic Plate Boundaries
Research Article, 2024
The dynamic geological processes on Earth, especially the interactions between tectonic plate margins and volcanic eruptions, are critical in melding the Earth's topography. This research inspects and evaluates the worldwide distribution models of volcanoes linked to tectonic plate limits to gain an understanding of the dynamic geology of the Earth. Using progressions in Geographic Information System (GIS) technology and high-quality geospatial information, the study investigates the intricate relationship between volcanoes and plate boundaries, uncovering the fundamental processes that determine the arrangement of these geological highlights. The review of existing literature sheds light on prior studies about the worldwide spread of volcanoes, stressing the link with the edges of tectonic plates. The research makes use of GIS applications and shapefiles for volcanoes and tectonic plate limits, complemented by records of seismic happenings and geological diagrams for a thorough examination. Spatial procedures like overlay review and pinpointing areas of concentrated activity in QGIS uncover patterns in volcanic distribution about plate boundaries. The findings show a relationship between the names of volcanoes and tectonic plate limits, highlighting how volcanoes are distributed across regions with different levels of tectonic movement. The kinds of volcanoes also differ around plate boundaries, displaying unique geological features. Furthermore, the research illustrates volcano sites about the countries where they are located, the condition of volcanoes along plate margins, and the potential for soils to liquefy when subjected to seismic vibrations. The analysis explains the noticed patterns, emphasizing the part plate tectonics plays in volcanic events. The grouping of volcanoes along converging and diverging plate limits matches accepted geological ideas, backed up by the commonness of certain volcano varieties in each place. The existence of volcanoes along changed plate limits, represented by Deception Island in Antarctica, highlights the dynamic essence of tectonic plate connections in faraway areas.
Late Neogene motion of the Pacific Plate
Journal of Geophysical Research, 1989
Oceanic crust between 38øS and 65øS along the Pacific-Antarctic ridge records a complete history of Neogene Pacific-Antarctic motion. We have modeled magnetic stages corresponding to portions of isochrons 1, 2, 2A, 3, 3A, 4, and 5 from 17 high-quality marine magnetic traverses of the ridge to determine the Neogene finite rotation poles for this plate pair. We chose to model velocities over time intervals of about 0.5 m.y. because this greatly increased the number of estimates of Pacific-Antarctic plate velocity. Our analysis shows that a change in Pacific-Antarctic relative motion occurred between chron 2A, 3.40 Ma, and the beginning of chron 3 time, 3.86 Ma. We used 203 estimates of Pacific-Antarctic spreading velocity to calculate a 0-3.4 Ma and 3.86-10.3 Ma Euler pole. Combined with tracks of seamounts that record the passage of the Pacific plate over mantle plumes our data show that this change in relative motion corresponds to a change in the absolute motion of the Pacific plate with respect to the hotspot frame of reference. Using the these Euler poles to calculate Pacific-Antarctic-Africa-North America circuit Euler poles show that this recent change in Pacific plate absolute motion corresponds to a change from strike-slip to transpressive motion along the coastal California Pacific-North America plate boundary. Interestingly, this age of increased tectonism agrees in time with deformation in New Zealand and northem Japan. Along the boundary of the Pacific plate are the Antarctic, Pacific-Antarctic plate poles for anomalies 1, 2, 2A, 3, 3A, 4, Nazca, Cocos, North America, Juan de Fuca, Gorda, Okhotsk, and 5 to determine the age and style of the change of motion Eurasian, Philippine, and Australian plates. With a surface area between the two plates. Finally, we relate this change in of 1.08 x 10 ø km 2, the Pacific plate is the largest of the Pacific-Antarctic plate motion to a change in the absolute present-day lithospheric plates. Geologists have long recognized motion of the Pacific plate and correlate this change with tecthe importance of understanding the timing and style of changes tonic events along the margin of the Pacific plate. in motion between plates in deciphering the complex geology We will show that a change in the absolute motion, or the around the plate margins [Morgan, 1968; Hilde et al., 1977; motion of the Pacific plate relative to the hotspots, occurred Larson and Chase, 1972; Chase, 1972; Larson and Pitman, between the end of chron 2A and the beginning of chron 3 1972; Larson, 1976; Engebretson et al., 1984] It has been sug-(between 3.4 and 3.9 Ma, using the time scale of Harland et al. gested that sometime since 9.8 Ma [Stock and Molnar, 1982], at [1982]). This change in Euler pole location was sudden and 5 Ma [Cox and Engebretson, 1985], or 3 Ma [Pollitz, 1986], the probably was the result of decoupling of a slab from the Pacific motion of the Pacific plate relative to the hotspots has changed. plate beneath the North Fiji basin. The result was a major and Because of the importance of this change to circum-Pacific tec-simultaneous episode of noncollisional tectonic deformation in tonics in this paper we address the following questions; when widely separated regions of the Pacific plate margin expressed did this change in motion occur, and what was the style of the by uplift and deformation in coastal California, Japan, and New change. Did the change from an older pole occur as a "jump," where there is a series of intermediate rotation poles? Also, what were the geological consequences along segments of the Pacific plate boundary, such as coastal California, Japan, and New Zealand? First, we review the previous studies of magnetic lineafions along the Pacific-Antarctic spreading center. We then present a new method for estimating plate velocities Zealand.