Rift linkage processes in areas of incipient oceanic spreading: examples from Afar

2020 ◽  
Author(s):  
Carolina Pagli ◽  
Alessandro La Rosa ◽  
Finnigan Illsley-Kemp
Keyword(s):  
Seafloor Spreading ◽  
Analytical Models ◽  
Fault System ◽  
Transform Fault ◽  
Transform Faults ◽  
Ocean Ridges ◽  
Oceanic Spreading ◽  
Moderate Seismicity ◽  
Deformation Patterns ◽  
Conjugate Fault

<p>Mid-ocean ridges are segmented and offset along their length. However, the kinematics of rift linkage and the initiation of oceanic transform faults in magmatic rifts remain debated. Crustal deformation patterns from the Afar continental rift provide evidences of how rifts grow to link in an area of incipient seafloor spreading. Here we present examples of rift linkage processes in Afar integrating seismicity and geodetic (InSAR and GPS) measurements, and explained by numerical and analytical models. We show that in central Afar overlapping spreading rifts link through zones of rift-perpendicular strike-slip faulting at the tips of the spreading rifts, demonstrating that distributed extension drives rift-perpendicular shearing. Conversely, in northern Afar we identify a linkage zone between the Erta Ale and Tat Ali segments where shear is accommodated by a conjugate set of oblique slip faults. There, InSAR modelling of a M<sub>L</sub> 5.1 earthquake in 2007 show that overall right-lateral shear is accommodated primarily by oblique left-lateral slip along faults subparallel to the rift segments but an active conjugate fault system with right-lateral slip is also highlighted by low-to-moderate seismicity during 2011-2013. Thermomechanical models of transform fault formation are consistent with the presence of a proto-transform fault that may develop into a throughgoing transform in the future. Our results provide evidences that offset rift segments during continental breakup can be linked by a wide variety of strain types and proto-transform zones can form before the onset of seafloor spreading.</p>

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 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 Semibrittle seismic deformation in high-temperature mantle mylonite shear zone along the Romanche transform fault

2021 ◽  
Vol 7 (15) ◽  
pp. eabf3388
Author(s):  
Zhiteng Yu ◽  
Satish C. Singh ◽  
Emma P. M. Gregory ◽  
Marcia Maia ◽  
Zhikai Wang ◽  
...  
Keyword(s):  
High Temperature ◽  
Plate Tectonics ◽  
Thermal Structure ◽  
Depth Range ◽  
Transform Fault ◽  
Equatorial Atlantic ◽  
Transform Faults ◽  
Ocean Ridges ◽  
Equatorial Atlantic Ocean ◽  
Large Earthquakes

Oceanic transform faults, a key element of plate tectonics, represent the first-order discontinuities along mid-ocean ridges, host large earthquakes, and induce extreme thermal gradients in lithosphere. However, the thermal structure along transform faults and its effects on earthquake generation are poorly understood. Here we report the presence of a 10- to 15-kilometer-thick in-depth band of microseismicity in 10 to 34 kilometer depth range associated with a high-temperature (700° to 900°C) mantle below the brittle lithosphere along the Romanche mega transform fault in the equatorial Atlantic Ocean. The occurrence of the shallow 2016 moment magnitude 7.1 supershear rupture earthquake and these deep microearthquakes indicate that although large earthquakes occur in the upper brittle lithosphere, a substantial amount of deformation is accommodated in the semibrittle mylonitic mantle that resides at depths below the 600°C isotherm. We also observe a rapid westward deepening of this band of seismicity indicating a strong lateral heterogeneity.

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.

The geology and evolution of the Pinchi Fault Zone at Pinchi Lake, central British Columbia

1977 ◽  
Vol 14 (6) ◽  
pp. 1324-1342 ◽  
Author(s):  
I. A. Paterson
Keyword(s):  
Fault Zone ◽  
Subduction Zones ◽  
High Pressures ◽  
Metamorphic Grade ◽  
Fault System ◽  
Late Triassic ◽  
Transform Fault ◽  
The West ◽  
Early Mesozoic ◽  
Complex Fault

At Pinchi Lake, the Pinchi Fault Zone separates the early Mesozoic Takla Group to the east from the late Paleozoic Cache Creek Group to the west. Between these regions a complex fault system involves a series of elongate fault-bounded blocks of contrasting lithology and metamorphic grade. These blocks consist of: (a) highly deformed aragonite–dolomite limestone and blueschist, (b) pumpellyite–aragonite greenstone, (c) a harzburgite–gabbro–diabase–basalt ophiolite sequence, (d) serpentinized alpine ultramafite, and (e) Cretaceous (?) conglomerate. The blueschist probably formed at 8–12 kbar (8 × 105–12 × 105 kPa) and 225–325 °C during a penetrative early deformation which was closely followed by a later deformation associated with a Late Triassic uplift and cooling event. The ophiolite sequence is overlain by Late Triassic sediments which locally contain aragonite suggesting that at least part of the Takla Group may have also undergone high pressure – low temperature metamorphism.The evolution of the 450 km fault zone is discussed and a model is proposed which involves right lateral transform faulting on the Pinchi Fault and underthrusting along northerly dipping subduction zones during the Late Triassic. The blueschist formed at high pressures in such a subduction zone and leaked to the surface in zones of low pressure along an active transform fault.

THE EFFECTS OF CONTINENTAL DRIFT ON THE PETROLEUM GEOLOGY OF WESTERN INDONESIA

1972 ◽  
Vol 12 (2) ◽  
pp. 55
Author(s):  
T.S.M. Ranneft
Keyword(s):  
Oil And Gas ◽  
Continental Drift ◽  
Wide Distribution ◽  
Petroleum Geology ◽  
Fault System ◽  
Transform Faults ◽  
Traditional Concept ◽  
Hinge Line ◽  
Straight Segments ◽  
Transverse Fault

The traditional concept of western Indonesia as a sinuous island are is probably incorrect. Instead, western Indonesia seems to consist of a series of largely straight segments that are sometimes offset and that may change direction abruptly in specific hinge line areas. The segments, especially in these hinge line areas, are cut by a system of north-northeast trending transverse faults. This fault system (Bantam trend) is noted forremarkable consistency in the direction of strike,wide distribution,variety of amount and direction of movement,occasional volcanism, andvaried activity at different times during the Cenozoic period or before, probably diminishing in a northeasterly direction.The segmentation and associated transverse fault system of western Indonesia may be caused by the Australian plate and its fracture zones (extensions of "transform" faults?) and north-northeast trending Indian Ocean morphological features, being thrust beneath the Indonesian continental area. The Bantam (transverse) fault trend may have affected the petroleum geology of western Indonesia in at least two ways:it may have been responsible for the division of the backdeep and perhaps the interdeep into a series of highs and lows, resulting in silled conditions during deposition and therefore, source rock generation;it probably provided the usual north-northeast trending oil and gas producing anticlines in northern Java and in the Java Sea. As the less explored interdeep basins are closer to the edge of the subduction zone, the Bantam trend faults are likely to be particularly prominent there, a factor that should affect exploration programmes in this region.

Evolution of migrating transform faults in anisotropic oceanic crust: examples from Iceland

2019 ◽  
Vol 56 (12) ◽  
pp. 1297-1308 ◽  
Author(s):  
Jeffrey A. Karson ◽  
Bryndís Brandsdóttir ◽  
Páll Einarsson ◽  
Kristján Sæmundsson ◽  
James A. Farrell ◽  
...  
Keyword(s):  
Plate Boundary ◽  
Fault Zones ◽  
Plate Boundaries ◽  
Transform Fault ◽  
Eurasian Plate ◽  
Transform Faults ◽  
The North ◽  
Rift Propagation ◽  
Oriented Parallel ◽  
Ocean Ridge

Major transform fault zones link extensional segments of the North American – Eurasian plate boundary as it transects the Iceland Hotspot. Changes in plate boundary geometry, involving ridge jumps, rift propagation, and related transform fault zone migration, have occurred as the boundary has moved relative to the hotspot. Reconfiguration of transform fault zones occurred at about 6 Ma in northern Iceland and began about 3 Ma in southern Iceland. These systems show a range of different types of transform fault zones, ranging from diffuse, oblique rift zones to narrower, well-defined, transform faults oriented parallel to current plate motions. Crustal deformation structures correlate with the inferred duration and magnitude of strike-slip displacements. Collectively, the different expressions of transform zones may represent different stages of development in an evolutionary sequence that may be relevant for understanding the tectonic history of plate boundaries in Iceland as well as the structure of transform fault zones on more typical parts of the mid-ocean ridge system.

Sign in / Sign up

Export Citation Format

Share Document