Tectonics

This book focuses on the highly touristed, but surprisingly under-researched Lesser Antilles region. After offering a brief overview of the region’s geologic and tectonic history, as well as its basic climatology, subsequent chapters then discuss each island’s (or island set’s) geomorphology and geology, and how the settlement history, tourism, and hazards have affected their individual landscapes. Written by regional experts and replete with up-to-date information, stunning color imagery, and beautiful cartography (maps), it is the only comprehensive, scientific evaluation of the Lesser Antilles, and serves as the region’s definitive reference resource. Accessible to non-experts and amateur explorers, the book includes in-depth discussions and reference sections for each island/island set. Usable as both a textbook and guidebook, it offers readers a straightforward yet detailed assessment of an interesting and intriguing – but often-overlooked and under-appreciated – locale.

Roughly 60% of the Earth's outer surface is composed of oceanic crust formed by volcanic processes at mid-ocean ridges. Although only a small fraction of this vast volcanic terrain has been visually surveyed or sampled, the available evidence suggests that explosive eruptions are rare on mid-ocean ridges, particularly at depths below the critical point for seawater (3,000 m). A pyroclastic deposit has never been observed on the sea floor below 3,000 m, presumably because the volatile content of mid-ocean-ridge basalts is generally too low to produce the gas fractions required for fragmenting a magma at such high hydrostatic pressure. We employed new deep submergence technologies during an International Polar Year expedition to the Gakkel ridge in the Arctic Basin at 85 degrees E, to acquire photographic and video images of 'zero-age' volcanic terrain on this remote, ice-covered ridge. Here we present images revealing that the axial valley at 4,000 m water depth is blanketed with unconsolidated pyroclastic deposits, including bubble wall fragments (limu o Pele), covering a large (>10 km(2)) area. At least 13.5 wt% CO(2) is necessary to fragment magma at these depths, which is about tenfold the highest values previously measured in a mid-ocean-ridge basalt. These observations raise important questions about the accumulation and discharge of magmatic volatiles at ultraslow spreading rates on the Gakkel ridge and demonstrate that large-scale pyroclastic activity is possible along even the deepest portions of the global mid-ocean ridge volcanic system.

The emergence of intelligence is a relatively recent phenomena throughout the cosmos. The total number of habitable extraterrestrial planets within the Milky Way capable of supporting advanced, intelligent life within the next 500 Myr is <969. Most of which are earth-like orbiting around a single star with mass ranges from 0.712 to 1 solar mass. No exomoons are capable of supporting advanced life, and a negligible number of low mass binary systems (<0.712 solar mass) are habitable. The nearest extraterrestrial industrial civilization lies at least 51.85 million light years away, and possibly at least 100 million light years or beyond. No extraterrestrial civilization arises before 119 Mya within the observable universe, and no extraterrestrial civilization arises before 138 Mya within the universe by co-moving distance. Despite great distances between the nearest civilizations and the low probability of emergence within our vicinity, given the sheer size of the universe, the total number of intelligent extraterrestrial civilizations likely approaches infinity or \left(\frac{1}{4.4\cdot10^{7}}\right)^{3}\cdot3.621\cdot10^{6}\cdot10^{10^{10^{122}}} if the universe is finitely bounded. Based on incentives for economic growth, all civilizations tend to expands near the speed of light and will eventually universally connect with each other via wormhole networks. Within such a network, the farthermost distances traversable from earth can be either infinite or 3.621\cdot10^{6}\cdot10^{10^{10^{122}}}light years in radius if the universe is finitely bounded.

The Pinnacles Volcanic Formation and the Neenach Volcanic Formation originated from a series of common eruptive centers during the early Miocene. The once contiguous units were subsequently split and separated 314 km from each other by movement along the San
Andreas fault. The actual site of the eruptions has important implications for the age of the 'big bend' segment of the San Andreas fault.
If the eruptions occurred in southern California with the Pinnacles Volcanic Formation moving northward, then the big bend segment must
have been active during early Miocene time.  Alternatively, if the eruptions occurred in northern California with the Neenach Volcanic
Formation moving southward, the big bend segment of the fault need be no older than Pliocene-Pleistocene. Early Miocene paleogeographic
reconstructions which do not place the Pinnacles and Neenach areas adjacent to each other are probably not valid.

The only occurrence of monoclines along the eastern flank of the Colorado Front Range is near Llvermore at the northern end of the tten echelonrl fold-and-fault belt (Fig. l). The monocl ines I ie along the Kawuneeche-Livermore Iineament (h/ork and tlatthev,rs, in preparatlon). sedimentary rocks elsewhere along the eastern flank of the Front Range were deformed into either homoclines, anticllnes, or syn-clines during the Laramide orogeny. Erosion has removed the sedlmentary rock cover from the Precambrian basement on the western edge of the area of monoclinal folding. Thus, the area pro-vldes an unusual opportunlty for studying the role of structural basement in the formation of the monocllnes. Our study comblned detalled field work with photo-interpretation of NASA U-2 photography stereo-pa I rs. DESCR I PT ION OF I1ONOCL lNES Northeast of Llvermore, Colorado the Paleozoic and l.lesozoic strata are folded into a series of narrov't linear monoclines (Flgs. 2r3)" The monoctines separate large areas where the strata are planar and lilanuscript received, February 18, 1976; accepted, llarch 3, 1976. fhe Mowttain Geologiet u. 73, no. 2 (Aprti lszol p. 61-66 6]. ABSTMCT: Honoclinal foldlng is the dominant style of deformation in Paleozoic and }lesozolc sedimentary strata northeast of Livermore, Colorado. The markedly llnear monocllnes are narrow and bound large areas of nearly flat-lylng strata. Axes of the monoclines are not parallel, which indlcates that they did not form as a resutt of reglonal horizontal compression. Several mlles to the west, eroslon has stripped the sedimentary cover from the underlylng Precambrian basement. The basement is characterized by brittle deformation in the form of dlfferentlally upllfted fault blocks. The pre-Pennsylvanian erosion surface developed on top of the Precambrlan igneous and metamorphlc rocks Is only sllghtly tilted. Where the faults ln the basement pass under the Paleozoic sedimentary cover to the east, the sedlmentary rocks are folded into unfaulted monoclines. This suggests that the monocllnes in the area are formed by passive draping of sedimentary rocks over dlfferentially uplifted basement blocks. Such an interpretation ls conslstent with the geometrlcal relationships of the monocllnes, with burlal conditlons durlng the Laramlde orogeny, and with experimental results on the behavior of rock materlals.

Debate over the question of whether basement rocks folded or faulted during the Laramide orogeny in the Wyoming province of the Rocky Mountain foreland has raged for many years. Proponentsbl one view or the olher have drawn support for their case from theorctical arguments, from experimental laboratory results, from interpretations of seismic and subsurface borehole data, and from direct observation of surlace outcrops and subsurface miie exposu/es. An anatysis of the validity and applicability ot these various approaches included the generation of synthetic ielsmrc sections and an evaluation of balanced cross sectlons, This analysis indicated that the notion of a folded basement is supported only bl the interpretation of seismic and borehole data whereas the concept of brittle defotmation of the basementls s upportea by ilt of thes; tines of rcasoning, interprctation, and observation. The conclusion is that structural basement did not fotd during the Laramide orogeny.

Sheet intrusions supply magma to almost all eruptions. Mechanically, the erupting sheets are primarily extension fractures and of two main geometric types: dikes and inclined (cone) sheets. Regional dikes are mostly subvertical, many metres, occasionally tens of metres, thick, with strike dimensions (strike length) from kilometres to tens of kilometres (or more). By contrast, inclined sheets dip on average 30-40 • , are mostly less than one metre thick, and with strike dimension of hundreds of metres or, at most, a few kilometres. The density/frequency is also generally much greater in sheet swarms than in regional dike swarms. Forecasting the geometry and likely propagation path (including a possible eruption) of a sheet intrusion during volcanic unrest is of fundamental importance. The inferred geometry of the sheet is also an indication of the volume of magma that leaves the chamber during the unrest period. Sheet paths and geometries (including depth and opening/aperture) are commonly determined from geodetic surface data, in particular InSAR and GPS data. Standard interpretation methods of the data use mostly dislocation models that assume the volcano and the hosting crustal segment to be an elastic half space of uniform mechanical properties. By contrast, field observations of volcanoes (active and extinct) show that they are composed of a variety of layers whose mechanical properties vary widely. In particular, Young's modulus of layers and contacts in a typical active volcanic zone may vary by 2-3 orders of a magnitude. Here we provide numerical results on a dike/inclined sheet arrested at 0.5 km depth below the surface of an active volcano/volcanic zone, with several layers of varying stiffness (Young's modulus) between the tip of the dike/inclined sheet and the surface. In particular we vary the stiffness of one layer from 10 GPa to 0.01 GPa. The results show as the layer becomes more compliant (0.1-0.01 GPa) stresses and displacements (lateral and vertical) at the surface become suppressed. The results also show that the surface stresses and displacements induced by inclined sheets depend much on their dip and are generally widely different from those induced by vertical dikes. Also, the width of any dike-induced graben or zone of tension fractures is, according to the present results, roughly twice the depth to the tip of the arrested dike. In particular, the numerical results show that the surface-uplift peaks occur at locations which differ widely from those of the tensile/shear stress peaks and do not, in contrast with common interpretations, coincide with the location of the boundary faults of a dike-induce graben.

Al Shehri, A., Gudmundsson, A., 2018. Modelling of surface stresses and fracturing during dyke emplace-ment: Application to the 2009 episode at Harrat Lunayyir, Saudi Arabia. J. Volcanol. Geotherm. Res., 356, 278-303.
Bazargan, M., Gudmundsson, A., 2018. Dike-induced stresses and displacements in layered volcanic zones. J. Volcanology Geotherm. Res. (in press).

Late Oligocene–early Miocene Grand Canyon:
A Canadian connection?
James W. Sears, Dept. of Geosciences, University of Montana,
Missoula, Montana 59812, USA, james.sears@umontana.edu


By Lionel Jackson
https://www.earthmagazine.org/article/paleo-bell-river-north-americas-vanished-amazon

Within the framework of the International Continental Drilling Program (ICDP) we propose a comprehensive initiative to drill the continental crust bordering modern and ancient convergent and collisional plate boundaries. These zones host the vast majority of modern megacities and industrial installations on Planet Earth, and at the same time are loci of major earthquakes , tsunamis, volcanic eruptions and other associated great natural threats to human life and to economies. In-depth understanding of dynamic Earthprocesses at convergent and collisional plate boundaries is not possible without scientific drilling embedded into integrated research programmes. The set of scientific questions identified here is rooted in the plate tec-tonic paradigm of a dynamic Earth. Proposed studies derived from these questions target on (1) the dynamics of active subduction and collision zones, with focus on the seismogenic zone at the plate interface, and the distribution of deformation and seismicity in general, (2) the role of mantle plumes in orogeny, (3) supra-subduction magmatism in arc systems, (4) the geological manifestation of deep subduction and exhumation of the lithosphere, and (5) aspects relating to continental birth and growth through Earth history. ICDP drilling in convergent and collisional plate margins faces unprecedented challenges regarding drilling technology, drilling depth and requirements for long-term monitoring of Earth processes in downhole observatories.

Based on the earlier research, metamorphic rock in Bayah Complex and in its surrounding area are consist of various types of rock with different degrees in metamorphism (low to high grade metamorphism) and their protolith as well. The focus of this research is to determine the tectonic environment for these rocks. Methods that  used in this study are by petrographic and geochemical analysis. The petrographic analysis showed that metamorphic rock are to consist of muscovite schist, biotite schist, garnet biotite schist, actinolite schist, epidote amphibolite schist and hornblende schist. Most of them showed foliation, with poor foliation in some area. Based on mineral assemblages, they are dominated by greenschist facies to greenschist at the upper part, with some epidote amphibolite facies. Furthermore, geochemical analysis showed that metamorphic rock in study area is associated with calc – alkaline magma series,  calc – alkali basalt and oceanic island alkali basalt. Regarding to this study, metamorphic rock in Bayah Complex is interpreted have an association with subduction related magmatic origin.

Key word : protolith, degrees of  metamorphism, metamorphic facies,  calc alkali basalt, subduction

In his seminal essay “Towards a Critical Regionalism,” the architectural historian Kenneth Frampton argued that the ontological condition of architecture is found in the poetic expression of a structure’s constructional logic. This stance presupposes a certain structural stasis, one which resists or responds to the dynamic conditions within which all built structures ultimately stand. But what if no such stasis can be found? Landscape architecture, more than any other environmental design disciplines, finds itself facing this dilemma. Its primary media—water, plants, soil—behave in complex and relatively indeterminate ways. Indeed, it may well be that the ontological condition of landscape architecture is change itself, or, to paraphrase Frampton, how its “constructional logic” expresses a landscape’s transformation over space and time. This article will explore this ontological dilemma through the lens of itineration, a term used by anthropologist Tim Ingold, to describe the emergence of form as a continuous interplay between the flows of consciousness and materials.