A Revolution in Plate Tectonics?

The new paradigm instead argues from many lines of evidence (and lack of evidence for the above) that plate motions are driven not by warmth rising from below, but by crust cooling above, and sinking more or less in place.

Planetology... a field populated by earth scientists who said, "Fukkit, this is too hard."

I could eventually cite a new publication (currently in review) that uses the term "groupthink," after defining it for geologists.

To test how magma might behave near the core, Goncharov and his colleagues squeezed a sliver of a dark, opaque glass, made from iron and silicate to mimic the composition of deep Earth magmas, between two diamonds to simulate pressures near the core. The team then shined an infrared light through the glass and measured how much light passed through. As the pressure increased, so did the amount of light the glass absorbed, and the team saw a change in the atomic structure of the glass, the researchers report online today in Nature Communications.

Goncharov says that means magmas at high pressures in the lower mantle must be sponging up heat emanating from the core. As these patches of magma around the core get hotter, they start to act as a door for heat to pass into the mantle by convection. The heated mantle rocks then move up through the planet in a massive plume until they erupt on the surface, creating large volcanoes in strange places like Hawaii, Yellowstone, Easter Island, and Mount Etna, and some of the most violent eruptions.

Dark bullsh#t...

An ophiolite is, therefore, a suite of temporally and spatially associated ultramafic, mafic, and felsic rocks that formed as the products of multiple mantle melting events and magmatic differentiation processes in a particular tectonic environment.

Broad plumes rooted at the base of the Earth's mantle beneath major hotspots

Scott W. French & Barbara Romanowicz

Nature 525, 95–99 (03 September 2015) doi:10.1038/nature14876
Received 12 November 2014 Accepted 19 June 2015 Published online 02 September 2015

Plumes of hot upwelling rock rooted in the deep mantle have been proposed as a possible origin of hotspot volcanoes, but this idea is the subject of vigorous debate. On the basis of geodynamic computations, plumes of purely thermal origin should comprise thin tails, only several hundred kilometres wide, and be difficult to detect using standard seismic tomography techniques. Here we describe the use of a whole-mantle seismic imaging technique—combining accurate wavefield computations with information contained in whole seismic waveforms—that reveals the presence of broad (not thin), quasi-vertical conduits beneath many prominent hotspots. These conduits extend from the core–mantle boundary to about 1,000 kilometres below Earth’s surface, where some are deflected horizontally, as though entrained into more vigorous upper-mantle circulation. At the base of the mantle, these conduits are rooted in patches of greatly reduced shear velocity that, in the case of Hawaii, Iceland and Samoa, correspond to the locations of known large ultralow-velocity zones. This correspondence clearly establishes a continuous connection between such zones and mantle plumes. We also show that the imaged conduits are robustly broader than classical thermal plume tails, suggesting that they are long-lived, and may have a thermochemical origin. Their vertical orientation suggests very sluggish background circulation below depths of 1,000 kilometres. Our results should provide constraints on studies of viscosity layering of Earth’s mantle and guide further research into thermochemical convection.

Scientists Link Moon’s Tilt and Earth’s Gold
By KENNETH CHANGNOV. 27, 2015

The moon’s orbit is askew, and two planetary scientists believe that they have come up with a good reason.


Intriguingly, their idea also explains why gold and platinum are found in the Earth’s crust, well within diggable reach.

The moon is believed to have formed out of a giant cataclysmic collision early in the history of the solar system when an interplanetary interloper the size of Mars slammed into Earth and lofted a ring of debris circling over the Equator. The debris coalesced into the moon.

At its birth, the moon was quite close to the Earth, probably within 20,000 miles. Because of the tidal pulls between the Earth and moon, the moon’s orbit has slowly been spiraling outward ever since, and as it does, Earth’s pull diminishes, and the pull of the sun becomes more dominant.

By now, with the moon a quarter million miles from Earth, the sun’s gravity should have tipped the moon’s orbit to lie in the same plane as the orbits of the planets.

But it has not. The moon’s orbit is about 5 degrees askew.

“That the lunar inclination is as small as it is gives us some confidence that the basic idea of lunar formation from an equatorial disk of debris orbiting the proto-Earth is a good one,” said Kaveh Pahlevan, a planetary scientist at the Observatory of the Côte d’Azur in Nice, France. “But the story must have a twist.”

Writing in this week’s issue of the journal Nature, Dr. Pahlevan and his observatory colleague Alessandro Morbidelli propose the twist.

The moon did indeed form in the Earth’s equatorial plane, the scientists said, but then a few large objects, perhaps as large as the moon, zipping through the inner solar system repeatedly passed nearby over a few tens of millions of years and tipped the moon’s orbit.

A series of computer simulations show that the idea is plausible.

“This mechanism works for a broad range of physical conditions,” Dr. Pahlevan said.

Eventually the crisscrossing mini-planets would have been tossed out of the solar system, swallowed by the sun, or slammed into the Earth or the other planets.

Robin M. Canup, a planetary scientist at the Southwest Research Institute in Boulder, Colo., who wrote an accompanying commentary in Nature, said the thousands of close passes that typically occur before an impact were a “really new realization” by Dr. Pahlevan and Dr. Morbidelli.

“While a single scattering event will only change the moon’s tilt slightly,” Dr. Canup said, “it’s the cumulative effect of these many passes that can produce this tilt.”

The scars of one or more moon-size objects hitting Earth would have long been erased by the tectonics of the shifting surface, but those impacts would explain the gold, platinum and other precious metals in the Earth’s crust but not on the moon.

Metals on the early Earth should have sunk to the interior. Thus, planetary scientists think that after the moon was created, later collisions that provided the last 1 percent or so of the Earth’s mass added a veneer of precious metals.

A dearth of lunar metals argues for a few large metal-rich objects hitting the Earth rather than many small ones.

The computer simulations show that the chances of the moon’s getting hit are low. In the simulations, if there was one object buzzing by, the moon was hit 9 percent of the time. With four objects, the chances of a lunar impact rose to 25 percent.

“Not an overly likely outcome, which is good,” Dr. Canup said.

Scientists including Dr. Canup had proposed other explanations for the tilt. “I would say those relied on certainly more complex processes and required rather narrow sets of conditions for success,” Dr. Canup said. “I think where this has really stepped in is it’s a very simple mechanism.

THE INTERACTION OF TECTONIC AND MAGMATIC PROCESSES IN THE LONG VALLEY CALDERA, CALIFORNIA

A DISSERTATION SUBMITTED TO THE DEPARTMENT OF GEOPHYSICS AND THE COMMITTEE ON GRADUATE STUDIES OF STANFORD UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

Stephanie G. Prejean February 2002

Abstract
The Long Valley caldera of eastern California is a hazardous province where tectonic and magmatic processes interact to drive on-going seismicity and deformation. The caldera is located on the boundary between the Basin and Range province and the Sierra Nevada batholith along the actively extending Sierra Nevada range-bounding normal faults. It is not clear if Basin and Range tectonic extension drives magmatic intrusion in this area or if magmatic activity is independent of regional tectonic processes. Magmatic intrusion into the caldera and extensional faulting are temporally coupled, yet it is not clear how these pro- cesses mechanically interact and potentially trigger each other.

In this dissertation, I investigate the interaction between tectonic and mag- matic processes in the Long Valley caldera over a range of scales, with the goal of developing a comprehensive model for the observed activity in the caldera. To gain a first order understanding of the mechanics by which the Long Valley area deforms, local fault geometries need to be established. To this end I relocated seismicity in the greater Long Valley area. The resulting high-resolution locations reveal a systematic fabric of faults within the caldera and in the Sierra Nevada basement rock to its south. From the focal mechanisms associated with individ- ual faults, I developed a kinematic model for seismic deformation in the Long Valley caldera. Seismicity within the caldera occurs primarily on a set of east/ west-trending right-lateral faults in the caldera's south moat. Since the south moat is located in a left step of the Sierra Nevada range-bounding normal faults, the south moat shear zone in essence forms a "transform" zone between loci of Basin and Range extension. In the Sierra Nevada block, directly south of the caldera, tectonic extension is accommodated by an east-dipping oblique-normal fault and two left-lateral strike-slip faults in its hanging wall. The location of these faults in the footwall of the Sierra Nevada range-bounding normal fault at this latitude, suggests that Basin and Range extension is potentially cutting into the Sierra Nevada batholith in this area.

To understand better the mechanical interaction of tectonic and magmatic processes at the regional scale, I performed a series of focal mechanism stress inversions in the caldera area. The inversions show that around the caldera the minimum compressive stress is perturbed from the more regional WNW–ESE direction to a NE–SW orientation. Dislocation modeling of the mapped stress field reveals that the stress perturbation cannot be explained solely by the intru- sion of magma beneath the resurgent dome, but may reflect the large-scale left- stepping offset in the Sierran range-bounding normal faults. Thus, the direction of fault slip seems to be controlled by regional tectonic processes rather than local magmatic processes. This implies that Basin and Range extension governs activ- ity in the caldera and possibly provides conduits for ascending magma.

To understand the relationship between tectonic and magmatic processes at the scale of the earthquake source, I investigate the influence of magmatic activ- ity on earthquakes by examining the source processes of earthquakes and by studying the spatial and temporal development of seismicity during a crisis epi- sode. The great majority of earthquakes in the caldera region appear to be typical "tectonic" earthquakes with source parameters similar to those observed in non- volcanic regions. However, a small number of earthquakes show magmatic sig- natures. A close examination of a seismicity swarm on November 22, 1997 in the western south moat of the caldera reveals that the swarm was triggered directly by magmatically derived fluids. Thus, although earthquakes slip in accordance with the regional tectonic stress field, magmatic activity can trigger seismicity by decreasing the effective normal stress across faults.

Rockies Mystery Solved by New Mountain-Creation Theory?
Study "challenges this idea that we understand what's going on," expert says.

1. Scientific Objectives
This proposal is to drill to the crust-mantle boundary in a tectonic window at Atlantis
Bank on the ultraslow-spreading SW Indian Ridge. There are two principle objectives:[/url]
I. Test the hypothesis that the Moho beneath Atlantis Bank is a serpentinization
front.
II. Recover the igneous lower crust and the crust-mantle transition at an average
melt flux for slow and ultraslow-spreading ridges.
From this we seek to understand:
• The igneous stratigraphy of the lower crust
• How much mantle material is incorporated into the lower crust.
• How melt is transported through and emplaced into the lower crust
• How the lower crust shapes the composition of mid-ocean ridge basalt the
most abundant magma on Earth?
• The primary modes of accretion of the lower crust.
• Lateral heterogeneity of the lower crust at magmatic time scales.
• The distribution of strain in the lower crust and shallow mantle in the shallow
lithosphere during asymmetric seafloor spreading.
• The nature of magnetic anomaly transitions in the lower crust.
• The role of the lower crust and shallow mantle in the global carbon cycle.
• Life in the lower crust and hydrated mantle.

All published tomographic models of purported deep plumes are severely flawed, but I
discuss here only Hawaii, which provides the type example for rationalization of a “plume track”
while disregarding both observed tectonic controls of magmatism and failure of geophysical
predictions in plume speculations (Anderson, in press). Pro-plume tomographers Wolfe et al.
(2009) depicted a low-velocity plume rising through much of the upper mantle beneath the
Hawaiian region, and a disconnected narrow plume rising obliquely northwestward toward it
from a depth of 1500 km in the lower mantle. Wolfe et al. modeled only steeply rising
teleseismic S waves to calculate uppermantle structure, and only steeply rising SKS waves to
calculate midmantle structure with rays that came through the liquid core via phase conversions.
The narrow seismometer spread precluded sampling deep mantle beneath the islands with
moderately and gently inclined crossfire, and Wolfe et al. did not utilize any other steeply rising S
and P rays that would have increased coverage, nor did they incorporate any surface waves,
receiver functions, or Vp/Vs derivatives to constrain depths, amplitudes, and characters of
possible anomalies.Wolfe et al. truncated their published model downward at 2000 km, but the
narrow bundle of SKS rays that alone defined their purported lower-mantle plume rose
northwestward through a poorly known lowermost-mantle region of low velocity (likely
recording high iron content and high density, not high temperature), which they acknowledged
could be modeled as their plume — but they claimed a plume to provide the “simplest”
explanation. Wolfe et al. forced their S-wave time delay deep into the upper mantle by assuming
that only moderate retardation occurred within either the crust or a shallow magma-generating
system. Leahy et al. (2010; Wolfe was second author) showed, with receiver-function analysis of
the same seismometer records, that the upper-mantle “plume” of Wolfe et al. (2009) was the
product of downward smearing of the time delay within thickened Hawaiian Swell crust. Leahy et
al. acknowledged previous observational proof that the Hawaiian region lacked plume-predicted
high heat flow.