Volcanic Propagation Research Articles

Triple junction kinematics accounts for the 2016 Mw 7.8 Kaikoura earthquake rupture complexity

The 2016, moment magnitude (Mw) 7.8, Kaikoura earthquake generated the most complex surface ruptures ever observed. Although likely linked with kinematic changes in central New Zealand, the driving mechanisms of such complexity remain unclear. Here, we propose an interpretation accounting for the most puzzling aspects of the 2016 rupture. We examine the partitioning of plate motion and coseismic slip during the 2016 event in and around Kaikoura and the large-scale fault kinematics, volcanism, seismicity, and slab geometry in the broader Tonga-Kermadec region. We find that the plate motion partitioning near Kaikoura is comparable to the coseismic partitioning between strike-slip motion on the Kekerengu fault and subperpendicular thrusting along the offshore West-Hikurangi megathrust. Together with measured slip rates and paleoseismological results along the Hope, Kekerengu, and Wairarapa faults, this observation suggests that the West-Hikurangi thrust and Kekerengu faults bound the southernmost tip of the Tonga-Kermadec sliver plate. The narrow region, around Kaikoura, where the 3 fastest-slipping faults of New Zealand meet, thus hosts a fault-fault-trench (FFT) triple junction, which accounts for the particularly convoluted 2016 coseismic deformation. That triple junction appears to have migrated southward since the birth of the sliver plate (around 5 to 7 million years ago). This likely drove southward stepping of strike-slip shear within the Marlborough fault system and propagation of volcanism in the North Island. Hence, on a multimillennial time scale, the apparently distributed faulting across southern New Zealand may reflect classic plate-tectonic triple-junction migration rather than diffuse deformation of the continental lithosphere.

The link between Hawaiian mantle plume composition, magmatic flux, and deep mantle geodynamics

Oceanic island basalts sample mantle reservoirs that are isotopically and compositionally heterogeneous. The Hawaiian–Emperor chain represents ∼85 Myr of volcanism supplied by a deep mantle plume. Two geographically and geochemically delineated trends, Kea and Loa, are well documented within the Hawaiian Islands. Enriched Loa compositions originate from subduction recycled or primordial material stored in deep mantle reservoirs such as the large low shear velocity province (LLSVP) below Hawai‘i. Loa compositions have not been observed along the Emperor Seamounts (>50 Ma), whereas lavas on the Hawaiian Islands (<6.5 Ma) sample both Kea and Loa sources. Lead isotopes in shield lavas along the Northwest Hawaiian Ridge (NWHR) spanning ∼42 Myr between the bend in the chain and the Hawaiian Islands record the geochemical evolution of the Hawaiian mantle plume over a time period when many geophysical parameters (volcanic propagation rate, magmatic flux, mantle potential temperature) increased significantly. Along the NWHR, the Loa geochemical component appears ephemerally, which we link to the sampling of different lower mantle compositional domains by the Hawaiian mantle plume. The plume initially sampled only the deep Pacific mantle (Kea component) from outside the LLSVP during the formation of the Emperor Seamounts. Southward migration and anchoring of the plume on the LLSVP led to entrainment of increasing amounts of LLSVP material (Loa component) along the NWHR as documented by an increase in 208Pb*/206Pb* with decreasing age. The correlation between 208Pb*/206Pb* and magmatic flux suggests source composition affects the magmatic flux, and explains why the Hawaiian mantle plume has dramatically strengthened through time.

Young tracks of hotspots and current plate velocities

Plate motions relative to the hotspots over the past 4 to 7 Myr are investigated with a goal of determining the shortest time interval over which reliable volcanic propagation rates and segment trends can be estimated. The rate and trend uncertainties are objectively determined from the dispersion of volcano age and of volcano location and are used to test the mutual consistency of the trends and rates. Ten hotspot data sets are constructed from overlapping time intervals with various durations and starting times. Our preferred hotspot data set, HS3, consists of two volcanic propagation rates and eleven segment trends from four plates. It averages plate motion over the past ≈5.8 Myr, which is almost twice the length of time (3.2 Myr) over which the NUVEL-1A global set of relative plate angular velocities is estimated. HS3-NUVEL1A, our preferred set of angular velocities of 15 plates relative to the hotspots, was constructed from the HS3 data set while constraining the relative plate angular velocities to consistency with NUVEL-1A. No hotspots are in significant relative motion, but the 95 per cent confidence limit on motion is typically ±20 to ±40 km Myr−1 and ranges up to ±145 km Myr−1. The uncertainties of the new angular velocities of plates relative to the hotspots are smaller than those of previously published HS2-NUVEL1 (Gripp & Gordon 1990), while being averaged over a shorter and much more uniform time interval. Nine of the fourteen HS2-NUVEL1 angular velocities lie outside the 95 per cent confidence region of the corresponding HS3-NUVEL1A angular velocity, while all fourteen of the HS3-NUVEL1A angular velocities lie inside the 95 per cent confidence region of the corresponding HS2-NUVEL1 angular velocity. The HS2-NUVEL1 Pacific Plate angular velocity lies inside the 95 per cent confidence region of the HS3-NUVEL1A Pacific Plate angular velocity, but the 0 to 3 Ma Pacific Plate angular velocity of Wessel & Kroenke (1997) lies far outside the confidence region. We show that the change in trend of the Hawaiian hotspot over the past 2 to 3 Myr has no counterpart on other chains and therefore provides no basis for inferring a change in Pacific Plate motion relative to global hotspots. The current angular velocity of the Pacific Plate can be shown to differ from the average over the past 47 Myr in rate but not in orientation, with the current rotation being about 50 per cent faster (1.06 ± 0.10 deg Myr−1) than the average (0.70 deg Myr−1) since the 47-Myr-old bend in the Hawaiian–Emperor chain.

Hawaiian volcanic propagation and Hawaiian swell asymmetry: evidence of northwestward flow of the deep upper mantle

Bathymetry and the geoid anomaly of the northern flank of the Hawaiian swell is broader and higher than the southern flank, and it is characterized by higher heat flow than the axis or southern flank. It is here proposed that the northern flank of the Hawaiian swell has been augmented by heat conducted from the hotspot conduit into the upper mantle then transported northward of the volcanic axis by flow in the upper mantle (∼325°) that is more northerly than Pacific plate motion (292°). By assuming that the deep upper mantle is decoupled from the Pacific plate and is flowing at 325° to the northwest, changes in direction and rate of volcanic propagation and in geochemistry along individual volcanic segments of the Hawaiian volcanic chain can be interpreted in terms of tank experiment results showing that a volcanic hotspot conduit breaks into diapirs when tilted by mantle flow. Hawaiian volcanoes are aligned in en-echelon segments, and the Hawaiian Islands are the two most recent segments. For an individual segment, older northwestern volcanoes are aligned nearly parallel to the 292° plate motion direction, and they propagated to the southeast at approximately the same rate as the 92 km/m.y. speed of northwestward plate motion. In contrast, the alignment of the younger southeastern volcanoes is close to 325°, and they show a conspicuous acceleration in propagation of volcanism marked by out-of-sequence eruptions. Within the model proposed here, diapirs rise from instability nodes that develop along the tilted conduit of a mantle hotspot plume as it is sheared in the direction of deep upper-mantle flow and each diapir gives rise to a single volcanic center. As tilting progresses, diapirs form at lower levels along the conduit in more upstream positions of the mantle flow zone, rise sequentially into the decoupled lithosphere, erupt sequentially, and are translated in the direction of plate motion (older, northwestern Hawaiian Islands). Eventually, flow in the highly tilted conduit is impeded to the degree that the remaining upstream conduit breaks into a number of diapirs that rise together into the lithosphere. These late diapirs, translated as a group aligned in the direction of horizontal mantle flow, erupt over a relatively short time span and show out-of-sequence volcanism (younger, southeastern Hawaiian Islands). At this stage, a new cycle of rising and tilting will initiate the next en-echelon segment.

Rift propagation, detachment faulting, and associated magmatism in Bransfield Strait, Antarctic Peninsula

Multichannel seismic data from Bransfield Strait, a young (&lt;4 Ma?) marginal basin located at the NW tip of the Antarctic Peninsula, reveal a complex array of rifting styles short of clearly defined seafloor spreading. The strait is undergoing basinwide extension. While enriched mid‐ocean ridge basalts have been dredged from topographic highs in the NE part of the basin, seismic evidence does not support the formation of oceanic crust there. Acoustic signatures of volcanic crust at known axial deep highs extend laterally subseafloor; their distribution and style support propagation of volcanism and associated extension from NE to SW. Active extensional structures along both margins control a strong physiographic asymmetry. The South Shetland Islands margin is composed of a few, closely spaced, large‐offset normal faults; the gentler Antarctic Peninsula margin exhibits broader, distributed extension. To the NE, normal fault polarity reversal structures (NFPRs) dominate; listric faults sole into NW dipping, low‐angle reflectors interpreted as detachments. To the SW, larger NFPRs and convex‐up geometries up to ∼20 km across suggest broad uplift rather than detachment‐based extension. Such uplift may precedes seafloor volcanism and rapid associated deflation along detachments. NW‐SE trending accommodation zones also segment the basin along‐strike. Bransfield Strait extension may result both from plate boundary tectonics at the South Shetland Trench and at the evolving Antarctic‐Scotia plate boundary. Extension was probably initiated by onset of subduction rollback at the trench, as a slab window opened from the SW. Augmented extension in the NE part of the basin may be a response to left‐lateral transtension associated with reorganization of the triple junction at the Shackleton Fracture Zone‐South Scotia Ridge intersection.

Las Hijas Seamounts—the next Canary Island?

Volcanic structures on the seafloor off the NW African coast between 25°N and 32°N were imaged by GLORIA side scan sonar and SIMRAD EM12 multibeam bathymetry. The newly discovered Las Hijas Seamounts, located 70 km south‐east of Hierro, are interpreted as young volcanic edifices. Their location is consistent with the spacing and timing of propagation of volcanism of the Canary Archipelago and may represent future sites of volcanic islands.

Links between magma‐tectonic rate balances, plutonism, and volcanism

With Smith's (1979) model of ash flow magmatism as the point of departure, quantitative regimes of crustal magmatic evolution are outlined. The average extrusive regime of ash flow magmatism operates at a rate of about 0.001 km3/yr; progressively larger episodes of increasing repose times characterize the evolution of caldera‐forming eruptions. The intrusive regime operates at an inferred average rate of about 0.01 km3/yr expressed in terms of the volumetric influx of mafic magma from the mantle, based on the record of silicic rates of extrusion and a 10:1 intrusive to extrusive ratio derived from evidence of zoned silicic systems. This rate is almost identical with the mean cumulative rate for the Hawaiian‐Emperor system of basaltic volcanism, which is determined to be 0.015 km3/yr. Fluctuations about a mean rate of 10−2 km3/yr lead to a threefold classification of magmatic regimes in terms of source power, depending on whether they are persistently greater than (HHER regime), about equal to (MHER regime), or lower than (LHER regime) the mean Hawaiian‐Emperor rate. Ash flow magmatism correlates with the MHER regime, averaged over a sufficiently long time. Thus the conditions of Hawaiian‐Emperor magmatism are identified with a characteristic power of magma transfer rates that optimize mechanisms for creation of high‐level chambers of derivative and fractionated silicic magma (terminology of Smith (1979)) within sufficiently localized regions of high residence times. These conditions represent a balance point, and a bifurcation, in dynamic paths of magmatic evolution leading to widely divergent types of plutonic‐volcanic associations. Categorical examples of the principal types of igneous path are discussed relative to continental basalt, silicic ash flow, batholithic granite, and intrusive porphyry systems. The Henry Mountains, Utah, are thought to represent an example of an intrusive porphyry generated in the LHER regime of a mafic source system lacking sufficient power for volcanic expression or significant mineralization. Long Valley, California (and possibly other systems along the eastern front of the Sierra Nevada), is an example operating at the mean rate with transient excursions to higher and lower rates. In regions of rapid extension and/or volcanic propagation (whether linear or areal) these regimes give rise to basaltic eruptions ranging from isolated cinder cones to flood basalts.

A captured island chain in the coast range of Oregon and Washington

K‐Ar and 40Ar−39Ar geochronologic data reveal the Paleocene to Eocene eruptive history of volcanic centers which produced the basaltic basement rocks of the Coast Range of Oregon and Washington. Volcanism was short lived at each center and migrated with time from the northern and southern ends toward the center, near the present mouth of the Columbia River. A plot of crystallization ages against geographic location produces a distinct V‐shaped pattern. An origin by hot spot volcanism centered on or near a spreading ridge in early Tertiary time best explains the observed age distribution. Limited geochemical data support this model, as the basalts exhibit attributes of both spreading ridge and hot spot‐related volcanism. Icelandic volcanism may be a presentday analog. Absolute motion modeling shows that the Yellowstone hot spot could have generated an island chain with approximately the correct paleoazimuth and volcanic propagation rate. Shortly after formation, this oceanic volcanic lineament collided with North America and rotated into its present marginal setting. The western edge of North America subsequently crossed over the hot spot, perhaps triggering late Eocene to Oligocene volcanism in the Coast Range, the Miocene Columbia River basalts in eastern Washington and Oregon and most recently, the basalts of the Snake River Plain and the Yellowstone area.

Geochronology and origin of the Pratt‐Welker Seamount Chain, Gulf of Alaska: A new pole of rotation for the Pacific Plate

40K‐40Ar and fission‐track dating of four seamounts near the southeast end of the Pratt‐Welker seamount chain in the Gulf of Alaska, in conjunction with previously published K‐Ar and fission‐track ages near the northwest end of the chain, documents the complex origin of this seamount chain. Transitional basalts from the adjacent guyots Hodgkins, Davidson, and Denson are dated as 14.3 to 18.2 m.y. These ages, only slightly younger than the ages of the underlying crust, indicate formation of these three seamounts at or very near a spreading center. In contrast, alkalic series lavas (alkali olivine basalts and trachytes) from Kodiak, Giacomini, Dickins, and Hodgkins fit a systematic linear age progression: 23.9±0.6 m.y., 20.9±0.4 m.y., 4.0±0.2 m.y., and 2.8±0.2 m.y., respectively. Hodgkins has apparently experienced two generically different episodes of volcanism, separated by about 12 m.y. The age progression among dated alkali basalts is consistent with the hot spot hypothesis and suggests that for the last 24 m.y. the Pacific plate has moved northwest at 4.4±0.4 cm/yr with respect to the Pratt‐Welker hot spot. This volcanic propagation rate, together with the rates from other parallel Neogene Pacific chains, allows an improved estimate of the pole and rate of rotation of the Pacific plate relative to hot spots: 70°N, 95°W, and 0.88°±0.10°/m.y. We conclude that no significant motion of the Pratt‐Welker hot spot with respect to other Pacific hot spots has yet been detected. However, the Pratt‐Welker age data may alternatively be explained by either the longitudinal roll or propagating crack hypothesis. New K‐Ar ages from Horton guyot, in the Cobb seamount chain, indicate alkalic volcanism 20.7± .0 m.y. ago, consistent with a predicted age of 20 m.y. based on the hot spot hypothesis. Guyot depths from Horton and the dated Pratt‐Welker seamounts are consistent with the K‐Ar ages and normal subsidence of oceanic crust.

Age of shield-building volcanism of Kauai and linear migration of volcanism in the Hawaiian island chain

Tholeiitic basalts of the Napali Formation comprise the bulk of the Kauai shield volcano. Potassium-argon ages measured on 16 samples from three separate areas in this formation lie in the range 5.14 ± 0.20 to 3.81 ± 0.06 m.y. The scatter in the measured ages in each area is greater than that expected from experimental error alone, and variable loss of radiogenic argon is regarded as at least partly responsible. Nevertheless an interval of eruption in the order of 0.8 m.y. is deduced for the Napali Formation. The results from the Napali Formation taken together with K-Ar ages measured earlier on basalts of the Makaweli Formation, the youngest formation of the dome-building phase, yield a mean age of 4.43 ± 0.45 m.y. for the construction of the main subaerial shield volcano of Kauai. When this result from Kauai is combined with estimates of the average age for the shield-building volcanism in 16 other volcanoes in the Hawaiian island chain, extending over a distance of more than 2800 km, the data are found to conform to migration of the centre of volcanism from north-northwest to south-southeast at a uniform rate of 9.4 (±0.3) cm/yr over the last 28 m.y. Non-linear models of propagation of volcanism in the Hawaiian chain are quite unnecessary, especially when uncertainties in the data base are taken into account. These results are consistent with an origin of the Hawaiian volcanic chain by eruption from a magma source situated below the Pacific lithospheric plate, as proposed under hot spot or plume models. Depending upon choice of the pole for the Pacific plate, rates of rotation about the pole of 0.9° to 1.0°/m.y. are derived. By extrapolation of the Hawaiian Island chain data an age estimate of 37.8 m.y. is derived for the Hawaiian-Emperor Seamount intersection.

Deep structure under Yellowstone National Park U.S.A.: A continental “hot spot”

Abstract In order to understand the origin of long-lived loci of volcanism (sometimes called “hot spots”) and their possible role in global tectonic processes, it is essential to know their deep structure. Even though some work has been done on the crustal, upper-mantle, and deep-mantle structure under some of these “hot spots”, the picture is far from clear. In an attempt to study the structure under the Yellowstone National Park U.S.A., which is considered to be such a “hot spot”, we recorded teleseisms using 26 telemetered seismic stations and three groups of portable stations. The network was operated within a 150 km radius centered on the Yellowstone caldera, the major, Quaternary volcanic feature of the Yellowstone region. Teleseismic delays of about 1.5 sec are found inside the caldera, and the delays remain high over a 100 km wide area around the caldera. The spatial distribution and magnitude of the delays indicate the presence of a large body of low-velocity material with horizontal dimensions corresponding approximately to the caldera size (40 km × 80 km) near the surface and extending to a depth of 200–250 km under the caldera. Using ray-tracing and inversion techniques, it is estimated that the compressional velocity inside the anomalous body is lower than in the surrounding rock by about 15% in the upper crust and by 5% in the lower crust and upper mantle. It is postulated that the body is partly composed of molten rock with a high degree of partial melting at shallow depths and is responsible for the observed Yellowstone volcanism. The large size of the partially molten body, taken together with its location at the head of a 350 km zone of volcanic propagation along the axis of the Snake River Plain, indicates that the volcanism associated with Yellowstone has its origin below the lithosphere and is relatively stationary with respect to plate motion. Using our techniques, we are unable to detect any measurable velocity contrast in the mantle beneath the low-velocity body, and, hence, we are unable to determine whether the Yellowstone melting anomaly is associated with a deep heat source or with any deep phenomenon such as a convection plume, chemical plume, or gravitational anchor.

Revised age for Midway volcano, Hawaiian volcanic chain

New conventional K-Ar, 40Ar/ 39Ar, and petrochemical data on alkalic basalt pebbles from the basalt conglomerate overlying tholeiitic flows in the Midway drill hole show that Midway evolved past the tholeiitic shield-building stage and erupted lavas of the alkalic suite 27.0 ± 0.6m.y. ago. The data also show that previously published conventional K-Ar ages on altered samples of tholeiite are too young by about 9 m.y. These results remove a significant anomaly in the age-distance relationships of the Hawaiian chain and obviate the need for large changes in either the rate of rotation of the Pacific plate about the Hawaiian pole or the motion of the plate relative to the Hawaiian hot spot since the time of formation of the Hawaiian-Emperor bend. All of the age data along the Hawaiian chain are now reasonably consistent with an average rate of volcanic propagation of 8.0 cm/yr and with 0.83°/m.y. of angular rotation about the Hawaiian pole.

Implications of Pacific Island and seamount ages for the origin of volcanic chains

Available age data from the Hawaiian, Marquesas, Kodiak‐Bowie, Society, Caroline, and Guadalupe chains, all WNW trending Pacific chains, follow patterns of generally increasing ages to the WNW. The inferred rates of volcanic propagation for these chains are not significantly different and apparently offer strong support for the hypothesis that volcanic chains are formed by ‘hot spots’ which do not move with respect to each other. However, age data from the Austral‐Cook chain follow no simple pattern: ages are both younger and older than would be expected from the ‘fixed hot spot’ hypothesis. Eocene and Cretaceous ages from along the Hawaiian ridge are inconsistent with the otherwise systematic age progression along this chain. The limited age data from the older NNW trending chains show little evidence of age progression. The best dated of these older chains, the Line chain, could have formed synchronously along most of its length.

Calculated geochronology and stress field orientations along the Hawaiian chain

A new method has been discovered for calculating ages of the main shield building stages of volcanoes along the Hawaiian chain from Kilauea to the Hawaiian-Emperor bend. The method is based on a graphical technique for hypothetical subtraction of distance intervals that theoretically represent regions of simultaneous volcanism along adjacent or nearly en-echelon loci of volcanism. Distances along the chain, measured from Kilauea, when progressively foreshortened by the distances of hypothetical “collapse” and plotted versus existing age data are found to give linear age-distance relationships. A calibration graph is presented that agrees closely with the measured ages in 17 of the 20 existing dated volcanoes. The criterion for simultaneous activity on different loci is based on the concept of equal azimuths of synchronous volcanic propagation within coeval segments of the chain. This is the predicted relationship when magmatic fluids inject the lithosphere along directions normal to a nearly horizontal least principal stress. It appears that the Pacific plate has been subjected to oscillatory, but principally clockwise, rotations of horizontal stress components during the last 40 m.y.

Tectonic Significance of the Kodiak-Bowie Seamount Chain, Northeastern Pacific

The hypothesis of a fixed melting spot reference frame (M) for relative plate motion is tested in the northeastern Pacific Ocean, where the Kodiak-Bowie seamount chain intersects the northern triple junction between the Pacific, American, and Juan de Fuca plates. Available age determinations on Kodiak and Giacomini Seamounts provide an estimated average rate of volcanic propagation along the chain of 6.5 cm per yr and allow estimates of plate movements relative to the melting spot. The inferred motion of the American plate relative to M is close to that observed along the Yellowstone-Snake River Plain volcanic trend and broadly supports the concept of a fixed melting spot reference frame. However, the convex northward curvature of the Kodiak-Bowie chain and of several chains to the south does not support the hypothesis. The lack of parallelism between these seamounts and the Hawaiian chain suggests slow relative movement between the Kodiak-Bowie and Hawaiian melting spots.