254 research outputs found
Pull-apart basin formation and development in narrow transform zones with application to the Dead Sea Basin
Contrary to other examples, like Death Valley, California, and the Sea of Marmara, Turkey, the Dead Sea-type pull-apart basins form within a narrow transform corridor between strike-slip faults that are less than 10 km apart, much smaller than the crustal thickness of 35 km. In this paper we investigate the role of fault zone width versus thickness and rheology on the mechanics of pull-apart basins through a series of laboratory experiments. Results show that pull-apart basins that develop above a small step over (i.e., smaller than the thickness of the brittle layer") are narrow and elongated parallel to the overall motion. This is enhanced by increased decoupling along a basal ductile layer. The experiment with the highest degree of mechanical decoupling shows a striking resemblance to the Dead Sea Basin (DSB). Comparison with modeling results suggests that the DSB's flat basin floor is bordered over its full length by strike-slip faults that control the basin geometry and temporal and spatial basin migration. This is in strong contrast to Death Valley-type pull-apart basins that are highly oblique to the transform direction with transverse normal faults dominating over longitudinal strike-slip faults. Results imply that lithosphere rheology and the ratio of basin width to crustal thickness are controlling factors in the mechanics of pull-apart basin formation within transform corridors like the Dead Sea Fault. Copyright 2008 by the American Geophysical Union
Adakites from collision-modified lithosphere
Adakitic melts from Papua New Guinea (PNG) show adakitic geochemical characteristics, yet their geodynamic context is unclear. Modern adakites are associated with hot-slab melting and/or remelting of orogenic mafic underplate at convergent margins. Rift-propagation over collision-modified lithosphere may explain the PNG adakite enigma, as PNG was influenced by rapid creation and subduction of oceanic microplates since Mesozoic times. In a new (rift) tectonic regime, decompressional rift melts encountered and melted remnant mafic eclogite and/or garnet-amphibolite slab fragments in arc collisional-modified mantle, and partially equilibrated with metasomatized mantle. Alternatively, hot-slab melting in a proposed newborn subduction zone along the Trobriand Trough could generate adakitic melts, but recent seismic P-wave tomographic models lack evidence for subducting oceanic lithosphere in the adakite melt region; however they do show deep subduction zone remnants as a number of high P-wave anomalies at lithospheric depths, which supports our proposed scenario
A Method of Intervals for the Study of Diffusion-Limited Annihilation, A + A --> 0
We introduce a method of intervals for the analysis of diffusion-limited
annihilation, A+A -> 0, on the line. The method leads to manageable diffusion
equations whose interpretation is intuitively clear. As an example, we treat
the following cases: (a) annihilation in the infinite line and in infinite
(discrete) chains; (b) annihilation with input of single particles, adjacent
particle pairs, and particle pairs separated by a given distance; (c)
annihilation, A+A -> 0, along with the birth reaction A -> 3A, on finite rings,
with and without diffusion.Comment: RevTeX, 13 pages, 4 figures, 1 table. References Added, and some
other minor changes, to conform with final for
The Levantine Basin - crustal structure and origin
The origin of the Levantine Basin in the Southeastern Mediterranean Sea is related to the opening of the Neo-Tethys. The nature of its crust has been debated for decades. Therefore, we conducted a geophysical experiment in the Levantine Basin. We recorded two refraction seismic lines with 19 and 20 ocean bottom hydrophones, respectively, and developed velocity models. Additional seismic reflection data yield structural information about the upper layers in the first few kilometers. The crystalline basement in the Levantine Basin consists of two layers with a P-wave velocity of 6.06.4 km/s in the upper and 6.56.9 km/s in the lower crust. Towards the center of the basin, the Moho depth decreases from 27 to 22 km. Local variations of the velocity gradient can be attributed to previously postulated shear zones like the Pelusium Line, the DamiettaLatakia Line and the BaltimHecateus Line. Both layers of the crystalline crust are continuous and no indication for a transition from continental to oceanic crust is observed. These results are confirmed by gravity data. Comparison with other seismic refraction studies in prolongation of our profiles under Israel and Jordan and in the Mediterranean Sea near Greece and Sardinia reveal similarities between the crust in the Levantine Basin and thinned continental crust, which is found in that region. The presence of thinned continental crust under the Levantine Basin is therefore suggested. A β-factor of 2.33 is estimated. Based on these findings, we conclude that sea-floor spreading in the Eastern Mediterranean Sea only occurred north of the Eratosthenes Seamount, and the oceanic crust was later subducted at the Cyprus Arc
Structural expression of a fading rift front: a case study from the Oligo-Miocene Irbid rift of northwest Arabia
Not all continental rifts mature to form a young ocean. The mechanism and
duration of their cessation depend on the crustal structure, modifications in
plate kinematics, lithospheric thermal response, or the intensity of subcrustal
flow (e.g., plume activity). The cessation is recorded in the structure and
stratigraphy of the basins that develop during the rifting process. This
architecture is lost due to younger tectonic inversion, severe erosion, or
even burial into greater depths that forces their detection by low-resolution
geophysical imaging. The current study focuses on a uniquely preserved
Oligo-Miocene rift that was subsequently taken over by a crossing transform
fault system and, mostly due to that, died out. We integrate all geological,
geophysical, and previous study results from across the southern
Galilee to unravel the structural development of the Irbid failing rift in
northwest Arabia. Despite tectonic, magmatic, and geomorphologic activity
postdating the rifting, its subsurface structure northwest of the Dead Sea
fault is preserved at depths of up to 1 km. Our results show that a series of
basins subsided at the rift front, i.e., rift termination, across the southern
Galilee. We constrain the timing and extent of their subsidence into two main
stages based on facies analysis and chronology of magmatism. Between 20 and 9 Ma
grabens and half-grabens subsided within a larger releasing jog, following a
NW direction of a deeper presumed principal displacement zone. The basins
continued to subside until a transition from the transtensional Red Sea to
the transpressional Dead Sea stress regime occurred. With the transition, the
basins ceased to subside as a rift, while the Dead Sea fault split the jog
structure. Between 9 and 5 Ma basin subsidence accentuated and an uplift of their
margins accompanied their overall elongation to the NNE. Our study provides
for the first time a structural as well as tectonic context for the southern
Galilee basins. Based on this case study we suggest that the rift did not
fail but rather faded and was taken over by a more dominant stress regime.
Otherwise, these basins of a failing rift could have simply died out
peacefully.</p
Two-Species Reaction-Diffusion System with Equal Diffusion Constants: Anomalous Density Decay at Large Times
We study a two-species reaction-diffusion model where A+A->0, A+B->0 and
B+B->0, with annihilation rates lambda0, delta0 > lambda0 and lambda0,
respectively. The initial particle configuration is taken to be randomly mixed
with mean densities nA(0) > nB(0), and with the two species A and B diffusing
with the same diffusion constant. A field-theoretic renormalization group
analysis suggests that, contrary to expectation, the large-time density of the
minority species decays at the same rate as the majority when d<=2. Monte Carlo
data supports the field theory prediction in d=1, while in d=2 the
logarithmically slow convergence to the large-time asymptotics makes a
numerical test difficult.Comment: revised version (more figures, claim on exactnes of d=2 treatment
removed), 5 pages, 3 figures, RevTex, see related paper Phys. Rev. E, R3787,
(1999) or cond-mat/9901147, to appear in Phys. Rev.
Diffusion-Limited Aggregation Processes with 3-Particle Elementary Reactions
A diffusion-limited aggregation process, in which clusters coalesce by means
of 3-particle reaction, A+A+A->A, is investigated. In one dimension we give a
heuristic argument that predicts logarithmic corrections to the mean-field
asymptotic behavior for the concentration of clusters of mass at time ,
, for . The total
concentration of clusters, , decays as at . We also investigate the problem with a localized steady source of
monomers and find that the steady-state concentration scales as
, , and , respectively,
for the spatial dimension equal to 1, 2, and 3. The total number of
clusters, , grows with time as , , and
for = 1, 2, and 3. Furthermore, in three dimensions we
obtain an asymptotic solution for the steady state cluster-mass distribution:
, with the scaling function
and the scaling variable .Comment: 12 pages, plain Te
Lattice Kinetics of Diffusion-Limited Coalescence and Annihilation with Sources
We study the 1D kinetics of diffusion-limited coalescence and annihilation
with back reactions and different kinds of particle input. By considering the
changes in occupation and parity of a given interval, we derive sets of
hierarchical equations from which exact expressions for the lattice coverage
and the particle concentration can be obtained. We compare the mean-field
approximation and the continuum approximation to the exact solutions and we
discuss their regime of validity.Comment: 24 pages and 3 eps figures, Revtex, accepted for publication in J.
Phys.
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