A leaky transform fault is a

transform fault A transform fault or transform boundary, is a fault (geology), fault along a plate boundary where the motion (physics), motion is predominantly Horizontal plane, horizontal. It ends abruptly where it connects to another plate boundary, either an ...

with volcanic activity along a significant portion of its length producing new crust. In addition to the regular

strike-slip In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

motion observed at transform boundaries, an oblique extensional component is present, resulting in motion of the plates that is not parallel to the plate boundary. This opens the fault, allowing melt to break through and cool on the ocean floor, producing new crust. This extensional component can come from a slight shift in the position of a plate's Euler Pole. In order to accommodate oblique motion along the plate boundary, these leaky transform faults can break up into a series of small transforms linked by short segments of spreading ridges. These new transforms will follow small circles centred on the new Euler Pole.

Case studies

The Western Limassol Forest Complex, an

ophiolite An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle (Earth), upper mantle that has been uplifted and exposed, and often emplaced onto continental crustal rocks. The Greek word ὄφις, ''ophis'' (''snake'') is ...

assemblage on the island of

Cyprus Cyprus (), officially the Republic of Cyprus, is an island country in the eastern Mediterranean Sea. Situated in West Asia, its cultural identity and geopolitical orientation are overwhelmingly Southeast European. Cyprus is the List of isl ...

dated to the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

, is believed to have come from a leaky, left-lateral transform fault about wide. Structural deformation of dykes in the ophiolite complex indicate injection into a shearing environment; they trend N–S but are cut by E-W trending

shear zone In geology, a shear zone is a thin zone within the Earth's crust or upper mantle that has been strongly deformed, due to the walls of rock on either side of the zone slipping past each other. In the upper crust, where rock is brittle, the shear ...

s. These

intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

s are likely syn-tectonic, as they both pass through and are cut by the shear zones. The Emerald fracture zone (EMZ), located on the boundary of the

Antarctic The Antarctic (, ; commonly ) is the polar regions of Earth, polar region of Earth that surrounds the South Pole, lying within the Antarctic Circle. It is antipodes, diametrically opposite of the Arctic region around the North Pole. The Antar ...

and

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

plates to the south of New Zealand, is an ideal location to study extensional transform faults. The EMZ is proximal to the Euler Pole for Antarctic plate rotation about the Pacific, producing large effects on the boundary between the two plates as the pole migrated and relative plate velocities changed. Two main plate boundary reorganizations are evident in the EMZ, linked by large tectonic events. One at 30 My, potentially linked to the collision of India and

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

at 35 My, and a second at 6 My, potentially linked to the collision of the

Ontong Java Plateau The Ontong Java Plateau (OJP) is a massive oceanic plateau located in the southwestern Pacific Ocean, north of the Solomon Islands. The OJP was formed around (Ma), with a much smaller volcanic event around 90 Ma. Two other southwestern Pacific pl ...

with the Melanesian arc at 10 My.

Petrology

While the

petrology Petrology () is the branch of geology that studies rocks, their mineralogy, composition, texture, structure and the conditions under which they form. Petrology has three subdivisions: igneous, metamorphic, and sedimentary petrology. Igneous ...

of leaky transform faults has not been studied extensively, some detailed petrologic work has been done on the Siqueiros transform fault in the Eastern Pacific between the Pacific and Cocos plates. This region is host to young volcanic sites producing picritic basalt. These

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

s have slight chemical variations from the typical

mid-ocean ridge A mid-ocean ridge (MOR) is a undersea mountain range, seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading ...

basalts found in the area; they are more primitive (higher MgO values) and are more depleted in incompatible elements.

References

{{reflist Structural geology Plate tectonics