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

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 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.

Transforms are forever

2021 ◽  
Author(s):  
Paola Vannucchi ◽  
David Iacopini ◽  
Jason P. Morgan
Keyword(s):  
Fluid Flow ◽  
Seismic Activity ◽  
Plate Tectonics ◽  
Driving Forces ◽  
Permanent Deformation ◽  
Oceanic Lithosphere ◽  
Ocean Floor ◽  
Spreading Center ◽  
Transform Faults ◽  
Recent Earthquakes

<p>According to Plate Tectonics, fracture zones (FZs) are born at Transform Faults (TFs), which leave behind "inactive" FZs traces as scars on the seafloor that reflect their initial use as one side of a strike-slip transform fault. FZs were originally thought to "heal" as the oceanic lithosphere cooled and strengthened with time. However, the occurrence of recent earthquakes reveals that FZs can be associated with significant seismic activity (for example during the recent Mw 8.6 2012 EQ offshore Sumatra and Mw 7.9 2018 EQ offshore SE Kodiak), and also with permanent deformation that occurs well after passage through the TF.</p><p>The TF at the spreading center is known to be accompanied by the formation of the transform valley which exposes serpentinized peridotite to the ocean floor. Valley relief itself can drive fluid flow that promotes continued serpentinization, and also cooling- and volume-change-linked stress variations. Off-axis seismicity suggests that FZs remain weaker that neighbouring oceanic lithosphere. The transform valley relief in general persists as a fracture zone valley that itself can continue to be a major drive of fluid flow even in the “healed” oceanic lithosphere. After reviewing evidence for FZ activity on (normal) ocean floor we will focus on the long-lived impact of FZs at continental margins. Offshore/onshore evidence of ongoing deformation at FZs is observed through seismic activity at both the western Brazilian and eastern Ghana-Côte d’Ivoire ends of the Romanche FZ. The western Brazil end is also characterized by recent folding and faulting, both offshore across the FZ, and onshore co-linearly with FZ extensions into the continent. Seismic activity in continental Brazil is focused where the FZ intersects the continental margin. This activity suggests that FZs remain as permanent weak lithospheric heterogeneities that are able to store elastic strain.</p><p>The reasons why FZs remain active are still poorly understood. Possible causes include i) effects of serpentinization that occurs both in the TF and in the FZ through hydrothermal fluid/mantle interaction, ii) thermal stress, iii) changing tectonic stresses related to plate driving forces.</p>

Volcanism on the passive margin of Laurentia: an early Paleozoic analogue of Cretaceous volcanism on the northeastern American margin

1988 ◽  
Vol 25 (11) ◽  
pp. 1824-1833 ◽  
Author(s):  
Stephen Kumarapeli ◽  
Karen St. Seymour ◽  
Hillar Pintson ◽  
Elizabeth Hasselgren
Keyword(s):  
Volcanic Rocks ◽  
Passive Margin ◽  
Fracture Zones ◽  
Transform Faults ◽  
Middle Ordovician ◽  
Early Ordovician ◽  
Basaltic Rocks ◽  
Sedimentary Sequences ◽  
Late Cambrian ◽  
Cretaceous Volcanism

Allochthonous masses of basaltic lava flows and related tuffs are present in several localities in an approximately 30 km long segment of the western margin of the Granby Nappe, in southeastern Quebec. They occur either as numerous small blocks in the Drummondville wildflysch related to the nappe or as larger masses intercalated with sedimentary sequences of limestone and shale of probable Late Cambrian to Early Ordovician age. These latter occurrences and the associated sedimentary units form "island-like" areas within lithologies of the Granby Nappe consisting of Cambrian sediments that accumulated on the continental rise. Their overall characteristics suggest that they represent slabs derived from the shelf margin of Laurentia and incorporated into the cratonward-moving nappes during the Middle Ordovician Taconian Orogeny.The volcanic rocks are mainly transitional but include some alkali olivine basalts. There are some indications that their affinities are to basaltic rocks of seamount chains localized along leaky transform faults. The segment of the continental margin from which the volcanic rocks were derived originated in the latest Precambian times, by rifting involving a rift–rift–rift (RRR) triple junction. Thus, it was a likely location for deep-seated transverse fracture zones linked to ridge-to-ridge transform faults of Iapetus. Therefore, the best explanation of the volcanism is that it was localized along such fracture zones. This episode of Late Cambrian – Early Ordovician volcanism related to the Iapetus cycle is probably analogous to the recently documented Early Cretaceous volcanism related to the Atlantic cycle on the northeastern American margin.

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