3. Fracture zones and transform faults

2015 ◽  
pp. 36-52
Author(s):  
Peter Molnar
Keyword(s):  
Fracture Zones ◽  
Transform Faults ◽  
Ocean Ridges ◽  
The 1950S

‘Fracture zones and transform faults’ introduces fracture zones, huge, long linear scars in the seafloor first mapped in the 1950s, and their interpretation in terms of a new concept, transform faulting. Fracture zones are made at mid-ocean ridges, where the seafloor spreads apart. Segments of zones of spreading intersect fracture zones at right angles, along which transform faulting transfers the spreading on one spreading zone to another. As the seafloor spreads, and plates move apart at mid-ocean ridges, fracture zones grow longer. Testing this idea relied on the study of earthquakes that occurred on the transform faults, using seismographs on distant continents. This chapter introduces readers to the pertinent seismological methods by which this was achieved.

scholarly journals MAGNETIC CHARACTERISTICS OF METAMORPHIZED ULTRABASITES OF THE OCEANIC LITHOSPHERE

2019 ◽  
Vol 47 (4) ◽  
pp. 106-127
Author(s):  
K. V. Popov ◽  
A. M. Gorodnitskiy ◽  
N. A. Shishkina
Keyword(s):  
World Ocean ◽  
Oceanic Lithosphere ◽  
Structural Features ◽  
Residual Magnetization ◽  
Magnetic Characteristics ◽  
Transform Faults ◽  
Ocean Ridges ◽  
Submarine Ridge ◽  
Deep Layers ◽  
The Stability

As part of the study of the nature of magnetic anomalies associated with the deep layers of the oceanic crust, a comparative analysis was made of the petromagnetic characteristics of serpentinized mantle ultrabasic samples taken from oceanographic expeditions of the Institute of Oceanology and the Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences in various morphotectonic regions of the World Ocean. The purpose of the work is to obtain information on the composition, concentration, crystallization temperature and structural features of ferromagnetic minerals, which are formed in different conditions of the post-magmatic metamorphism of ultrabasites. Sample collections are divided into three groups. 1. Oceanic peridotites from the rift zones of the mid-ocean ridges and transform faults. 2. Peridotites of the submarine ridge Gorringe, located within the Azoro-Gibraltar zone of faults. 3. Dunites of the Pekulney complex (Chukotka) formed in the island arc system. It has been established that in all selected regions, samples of serpentinized hyperbasites have high values of natural residual magnetization, magnetic susceptibility and saturation magnetization. The highest values of magnetic parameters are the dunites of the Pekulney complex. Estimation of the dependence of the concentration of ferrimagnetic materials C% of the degree of serpentinization of the SS%. showed that it is practically of little significance. The main factors contributing to the increase in the concentration of magnetite are the increased iron content of olivine in ultrabasites and the temperature of metamorphism. The question of the period of formation of magnetites and the stability of their primary residual magnetization requires further study.

scholarly journals Refertilization of Mantle Peridotites from the Central Indian Ridge: Response to a Geodynamic Transition

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 6) ◽  
Author(s):  
A. Hazra ◽  
A. Saha ◽  
A. Verencar ◽  
M. Satyanarayanan ◽  
S. Ganguly ◽  
...  
Keyword(s):  
Mineral Chemistry ◽  
Geochemical Data ◽  
Fracture Zones ◽  
Mechanical Instability ◽  
Transform Faults ◽  
Central Indian Ridge ◽  
Oceanic Ridge ◽  
Tectonic Transition ◽  
Suprasubduction Zone ◽  
Indian Ridge

Abstract The phenomena of reactive percolation of enriched asthenospheric melts and pervasive melt-rock interactions at mid oceanic ridge-rift systems are the principal proponents for mantle refertilization and compositional heterogeneity. This study presents new mineralogical and geochemical data for the abyssal peridotites exposed along the Vema and Vityaz fracture zones of the Central Indian Ridge (CIR) to address factors contributing to the chemical heterogeneity of CIR mantle. Cr-spinel (Cr#: 0.37-0.59) chemistry classifies these rocks as alpine-type peridotites and corroborates a transitional depleted MORB type to enriched, SSZ-related arc-type magma composition. HFSE and REE geochemistry further attests to an enriched intraoceanic forearc mantle affinity. The distinct boninitic signature of these rocks reflected by LREE>MREE<HREE and PGE compositions substantiates refertilization of the CIR mantle harzburgites by boninitic melt percolation concomitant to initiation of oceanic subduction. The mineral chemistry, trace, and PGE signatures of the CIR peridotites envisage (i) replenishment of depleted sub-ridge upper mantle by impregnation of subduction-derived boninitic melts, (ii) tectonic transition from mid oceanic ridge-rift to an embryonic suprasubduction zone, and (iii) initiation of spontaneous intraoceanic subduction along submarine transform faults and fracture zones of slow-spreading CIR owing to the weakness and mechanical instability of older, denser, and negatively buoyant Indian Ocean lithosphere.

scholarly journals Marine Transform Faults and Fracture Zones: A Joint Perspective Integrating Seismicity, Fluid Flow and Life

2019 ◽  
Vol 7 ◽  
Author(s):  
Christian Hensen ◽  
Joao C. Duarte ◽  
Paola Vannucchi ◽  
Adriano Mazzini ◽  
Mark A. Lever ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Fracture Zones ◽  
Transform Faults

scholarly journals Initiation of a Proto-transform Fault Prior to Seafloor Spreading

2020 ◽  
Author(s):  
Finnigan Illsley-Kemp ◽  
JM Bull ◽  
D Keir ◽  
T Gerya ◽  
C Pagli ◽  
...  
Keyword(s):  
Plate Tectonics ◽  
Seafloor Spreading ◽  
Continental Rift ◽  
Formation Mechanisms ◽  
Transform Fault ◽  
Transform Faults ◽  
Local Seismicity ◽  
Ocean Ridges ◽  
Rifted Margins ◽  
Direct Observations

©2018. The Authors. Transform faults are a fundamental tenet of plate tectonics, connecting offset extensional segments of mid-ocean ridges in ocean basins worldwide. The current consensus is that oceanic transform faults initiate after the onset of seafloor spreading. However, this inference has been difficult to test given the lack of direct observations of transform fault formation. Here we integrate evidence from surface faults, geodetic measurements, local seismicity, and numerical modeling of the subaerial Afar continental rift and show that a proto-transform fault is initiating during the final stages of continental breakup. This is the first direct observation of proto-transform fault initiation in a continental rift and sheds unprecedented light on their formation mechanisms. We demonstrate that they can initiate during late-stage continental rifting, earlier in the rifting cycle than previously thought. Future studies of volcanic rifted margins cannot assume that oceanic transform faults initiated after the onset of seafloor spreading.

scholarly journals Seismicity characterization of oceanic earthquakes in the Mexican territory

2020 ◽  
Author(s):  
Quetzalcoatl Rodríguez-Pérez ◽  
Víctor Hugo Márquez-Ramírez ◽  
Francisco Ramón Zúñiga
Keyword(s):  
Normal Fault ◽  
B Value ◽  
Statistical Characteristics ◽  
P Value ◽  
Transform Faults ◽  
Frequency Distributions ◽  
Ocean Ridges ◽  
The Pacific ◽  
Stress Orientations ◽  
Clear Differentiation

Abstract. We analyzed the seismicity of oceanic earthquakes in the Pacific oceanic regime of Mexico. We used data from the earthquake catalogs of the Mexican National Service (SSN), and the International Seismological Center (ISC) from 1967 to 2017. Events were classified into two different categories: intraplate oceanic (INT), and transform faults zone and mid-ocean ridges events (TF-MOR), respectively. For each category, we determined statistical characteristics such as magnitude frequency distributions, the aftershocks decay rate, the non-extensivity parameters, and the regional stress field. We obtained b-values of 1.17, and 0.82 for the INT, and TF-MOR events, respectively. TF-MOR events also exhibit local b-value variations in the range of 0.72–1.30. TF-MOR events follow a tapered Gutenberg-Richter distribution. We also obtained a p-value of 0.67 for the 1 May 1997 (Mw = 6.9) earthquake. By analyzing the non-extensivity parameters, we obtained similar q-values in the range of 1.39–1.60 for both types of earthquakes. On the other hand, the parameter a showed a clear differentiation, being higher for TF-MOR events than for INT events. This implies that more energy is released for TF-MOR events. Stress orientations are in agreement with geodynamical models for transform faults zone and mid-ocean ridges zones. In the case of intraplate seismicity, stresses are mostly related to a normal fault regime.

MORGEN – The Mid Ocean Ridge GENerating algorithm

2021 ◽  
Author(s):  
Thomas van der Linden ◽  
Douwe van Hinsbergen
Keyword(s):  
Conceptual Knowledge ◽  
Smooth Curve ◽  
Weddell Sea ◽  
Plate Boundaries ◽  
Plate Tectonic ◽  
Transform Faults ◽  
Ocean Ridges ◽  
Euler Pole ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

<p>Paleo-digital elevation models (paleoDEM) based on plate tectonic and paleogeographic reconstructions use age grids of ocean floor to determine ocean bathymetry. In recent years, such age grids have also been developed for now-subducted oceans from the far geological past, as far back as the Neoproterozoic, using geology and paleomagnetism-based estimates of ocean opening. In such reconstructions, mid ocean ridges are drawn based on estimated Euler poles and rotations, and conceptual knowledge on the geometry consisting of spreading ridges and transform faults.</p><p>Current procedures to draw mid ocean ridges in plate tectonic reconstructions are laborious, as new ridges are drawn every time the Euler pole location changes. Fortunately this is also a task that can be automated. We have written an algorithm using pyGPlates that takes as input a smooth curve at the approximate position of the reconstructed mid ocean ridge at the moment of its formation, and then calculates spreading and transform segments according to their typical geometries in modern oceans, assuming symmetric spreading. The algorithm allows gradual readjustment of ridge orientations upon Euler pole changes comparable to documented cases in the modern oceans (e.g., in the Weddell Sea). The algorithm also contains modules that can convert the calculated mid ocean ridges with other plate boundaries to boundary topologies – which can be used as input for the recently published TracerTectonics algorithm, produce isochrons which can be converted to age grids, check for subduction of isochrons and subsequently create bathymetry grids. We illustrate the use of the MORGEN algorithm with recently published reconstructions of subducted, as well as future oceans.</p>

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