Subduction polarity reversal

Generally, the oceanic plate with higher density subducts beneath and the other one overrides the down-going slab.

[1] The process continues until a buoyant continental margin sitting on the top of the subducting plate is introduced into the down-going slab.

[2][4] Geologists propose various possible models to predict what will be the next step for the intra-oceanic subduction system with the involvement of buoyant continental crust.

while the stronger plastic strength and older oceanic plate prefers an “induced subduction polarity reversal.

Different models representing the subduction polarity reversal depends highly on parameters the Geologists considered.

[4] The direction of the subduction system changes since the break-off of slab creates the space, which is the major parameter of this model.

The solution is the new developing slab moves not only vertically, but also laterally leading to a deep strike-slip movement.

[16] The development of co-existence of two opposite slabs is described as a double sided subduction[19] or doubly convergent wedge.

[2] The detachment of the pre-existing fault occurs when buoyant continental margin is in contact with the overriding plate.

[2] It is because the buoyant margin resists subduction and significantly increases the frictional force in the contact region.

[2] In reality, the magmatic arc is a relatively weak zone at the overriding plate because it has a thin lithosphere and is further weakened by high heat flow[20][21] and hot fluid.

[24] This experiment is a successful analogy to subduction polarity reversal happening at Kamchatka in early Eocene[7][25] and the active example at Taiwan region[2][11] as well as at Timor.

[4] Most of models studying this phenomenon will focus on an active collision in Taiwan which appears to reveal the incipient stages of subduction reversal.

[4] The collision between two plates started at the Northern Taiwan and propagated south with the younger region at the southern part.

Each incipient stage of subduction reversal process could be studied by correlating cross-sections in various parts of Taiwan.

The concept of flipping of subduction polarity
The evolution diagram showing how the subduction reversal initiated by a break-off slab at subducting plate: Brown colour is the less dense continental crusts; White colour is the oceanic crust; 1. Two plates move towards each other; 2. The buoyant continental crust resists to subduct; 3. Mantle window is created by gravitational instability; 4. New subducting plate develops
Evolution of double convergence model: Brown colour represents the Continental plate; White colour represents the oceanic plate; C1. The plate with both continental and oceanic plate subducts beneath; 2. The continental block engage in the subduction with building orogenic wedge; 3. The new slab develops and two slabs exhibit a deep strike-slip movement (Double circle means pointing out of the screen; Cross inside the circle means pointing into the screen; 4. New slab moves further downward; 5. The old slab breaks off; 6. The new slab subducts beneath.
A. Chemenda's Experiment setup of lithosphere break-up model: White colour indicates the oceanic plate ( Higher density) ; Brown colour indicates the continental plate ( Lower density) ;Green colour shows the pre-existing fault ; The plates represented by hydrocarbons floats at the asthenosphere represented by water.
The evolution diagram showing how the subduction reversal initiated by a pre-existing fault at the overriding plate. 1: Compression pushing ; 2: New slab develops with the failure of the fault ; 3: New slab penetrates ; 4: New slab breaks the old slab
Map of Taiwan shows the location of geological cross-section and the major subuductions
1) Cross-section A-A’ [ 4 ] (Post-collision): The passive continental margin of Eurasian plate , a buoyant continental crust, overrides the Philippine sea plate .The Eurasian plate is undergoing lithospheric stretching, forming the Okinawa Trough .
2) Cross-section B-B’ : [ 4 ] The Philippine Sea Plate subducts beneath the Eurasian plate , and Ryukyu trench roll-back leads to the extensional collapse of Taiwan orogenic wedge. [ 28 ] The direction of subduction changes in cross-section C-C'.
3) Cross-section C-C’ : [ 4 ] Drastic collision between two plate creates an accretionary wedge and develops orogenic belt. Taiwan orogens reached the maximum height with an equal amount of erosion and growth rate. [ 31 ] The angle of the slab is almost 80 degrees dipping downward. [ 32 ]
4) Cross-section D-D’ : [ 4 ] The Eurasian plate is actively subducting into the Philippine Sea plate at 80mm/year along the Manila Trench. [ 28 ] The slab is penetrating into the mantle and the volume of melt in mantle wedge keeps increasing. Meanwhile, the angle of subduction slab is not as steep as in cross-section C-C'. [ 32 ] The accretionary wedge was just developed.
5) Cross-section E-E’ [ 4 ] (Pre-Collision): Slab penetrates beneath the Philippine Sea plate and brings hydrous materials to generate a mantle wedge [ 4 ] and Luzon volcanic arc .