Effects of crustal eclogitization on plate subduction/collision dynamics: Implications for India-Asia collision

Geophysical Research Letters

Kusky

Capitanio

2018

Delamination is an important mechanism of continental lithosphere removal and recycling. It has been invoked as a likely cause for the observed thinning in the eastern North China (North China Craton) and several other cratons, returning thick depleted cratonic roots to the deep mantle. However, how delamination occurred, its lateral extent, and detachment depth of delamination are still debated. Here we test this process by means of 2‐D numerical modeling and find that delamination below lower crustal depths can only initiate near cratonic margins, where thickening‐induced eclogitization can significantly destabilize the lower part of the lithosphere, allowing it to detach and leading to intraplate orogeny. When a weak midlithosphere discontinuity is present, widespread delamination can initiate near cratonic margins and easily propagate to cratonic interiors, yet without obvious intraplate deformation. We illustrate how this delamination mechanism can recycle large volumes of depleted Archean subcontinental lithospheric mantle using numerical models. Our models explain the large‐scale delamination in the North China Craton, where a midlithosphere discontinuity is inferred by geophysical studies and shows that large portions of subcontinental lithospheric mantle can be recycled in the deep mantle potentially affecting mantle heterogeneity.

Section: Discussionsupporting

confidence: 71%

On the Role of Lower Crust and Midlithosphere Discontinuity for Cratonic Lithosphere Delamination and Recycling

Geophysical Research Letters

Kusky

Capitanio

2018

“…5.4 | Implications for multistage fluid interactions between continental crust and mantle in the subduction channel Subduction zones are important sites for the exchange of mass and energy between the mantle and crust (e.g. Brown & Rushmer, 2006;Hermann et al, 2006;Huangfu, Wang, Li, Fan & Zhang, 2016;Mibe et al, 2011;Zheng, 2012). Although arc magmatism generally does not accompany continental subduction (Rumble, Liou, & Jahn, 2003;Zheng, 2012), the development of syn-exhumation and post-collisional magmatic rocks with distinct chemical signatures indicates that crust-mantle interactions nonetheless occur during continental subduction and exhumation (Dai, Zhao, Zheng, & Zhang, 2015;Guo, Fan, Wang, & Zhang, 2004;Zhao, Dai, & Zheng, 2013;Zhao et al, 2012).…”

Section: Constraints On the Formation Of The Composite Veinsmentioning

confidence: 99%

Fluid generation and evolution during exhumation of deeply subducted UHP continental crust: Petrogenesis of composite granite–quartz veins in the Sulu belt, China

Journal Metamorphic Geology

Brown

et al. 2017

Composite granite–quartz veins occur in retrogressed ultrahigh pressure (UHP) eclogite enclosed in gneiss at General's Hill in the central Sulu belt, eastern China. The granite in the veins has a high‐pressure (HP) mineral assemblage of dominantly quartz+phengite+allanite/epidote+garnet that yields pressures of 2.5–2.1 GPa (Si‐in‐phengite barometry) and temperatures of 850–780°C (Ti‐in‐zircon thermometry) at 2.5 GPa (~20°C lower at 2.1 GPa). Zircon overgrowths on inherited cores and new grains of zircon from both components of the composite veins crystallized at c. 221 Ma. This age overlaps the timing of HP retrograde recrystallization dated at 225–215 Ma from multiple localities in the Sulu belt, consistent with the HP conditions retrieved from the granite. The εHf(t) values of new zircon from both components of the composite veins and the Sr–Nd isotope compositions of the granite consistently lie between values for gneiss and eclogite, whereas δ18O values of new zircon are similar in the veins and the crustal rocks. These data are consistent with zircon growth from a blended fluid generated internally within the gneiss and the eclogite, without any ingress of fluid from an external source. However, at the peak metamorphic pressure, which could have reached 7 GPa, the rocks were likely fluid absent. During initial exhumation under UHP conditions, exsolution of H2O from nominally anhydrous minerals generated a grain boundary supercritical fluid in both gneiss and eclogite. As exhumation progressed, the volume of fluid increased allowing it to migrate by diffusing porous flow from grain boundaries into channels and drain from the dominant gneiss through the subordinate eclogite. This produced a blended fluid intermediate in its isotope composition between the two end‐members, as recorded by the composite veins. During exhumation from UHP (coesite) eclogite to HP (quartz) eclogite facies conditions, the supercritical fluid evolved by dissolution of the silicate mineral matrix, becoming increasingly solute‐rich, more ‘granitic’ and more viscous until it became trapped. As crystallization began by diffusive loss of H2O to the host eclogite concomitant with ongoing exhumation of the crust, the trapped supercritical fluid intersected the solvus for the granite–H2O system, allowing phase separation and formation of the composite granite–quartz veins. Subsequently, during the transition from HP eclogite to amphibolite facies conditions, minor phengite breakdown melting is recorded in both the granite and the gneiss by K‐feldspar+plagioclase+biotite aggregates located around phengite and by K‐feldspar veinlets along grain boundaries. Phase equilibria modelling of the granite indicates that this late‐stage melting records P–T conditions towards the end of the exhumation, with the subsolidus assemblage yielding 0.7–1.1 GPa at <670°C. Thus, the composite granite–quartz veins represent a rare example of a natural system recording how the fluid phase evolved during exhumation of continental crust. The successive avail...

“…Fluids play a key role in kinetics of eclogitization, and the two typical locations of eclogitization in a collisional orogen are (i) the subducting crust and (ii) the base of the crustal root of the overriding crust. Eclogitization of the downgoing slab crust can provide an additional negative buoyancy force that helps to drive slab detachment (Huangfu et al, ), and an example of seismic imaging of such a slab can be seen in the Lesser Antilles (Paulatto et al, ). The lesser amount water contained by eclogite‐facies metabasalts (0.8–0.0 wt %) may explain the observations of high‐Q P waves of H2 (Ko et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…How the NW propagation of PSP tore the EUP lithosphere is not addressed in the tear model, neither is how the EUP slab detached to facilitate the west movement of PSP in the breakoff model. Recently, detachment of subducting slab due to subduction/collision of continental lithosphere has been modeled numerically (Huangfu et al, 2016;Menant et al, 2016). Results suggest that the subduction/collision of the Eurasian lithosphere alone is enough to drive detachment of the subducted slab.…”

Section: 1029/2019jb018697mentioning

confidence: 99%

High‐Resolution 3‐D P Wave Velocity Structures Under NE Taiwan and Their Tectonic Implications

Chen

2019

JGR Solid Earth

First P wave arrival-time data from local earthquakes recorded by a dense geophone array deployed on the Ilan Plain and by existing permanent stations were combined to invert for high-resolution P wave velocity structures under northeast Taiwan. With relatively high resolution, we were able to examine the structures in more detail and to investigate their significance and tectonic implications. We introduce two distinct groups of proposals for mechanisms of subduction polarity flipping in Taiwan, referred to as the "tear model" and "breakoff model." While the predicted Philippine Sea Plate boundaries differ between the two models, those of the breakoff model and the related subducting indenter model are geodynamically similar. The surface junction and the west edge of the imaged high V p anomalous Philippine Sea Plate comply with those predicted by the subducting indenter model and thus favor the breakoff model over the tear model. While the observed high V p anomalous region in the mantle wedge can be explained as eclogitization of previously subducted crust, eclogitization of the overriding continental crustal roots cannot be ruled out. Those beneath the Taipei Basin and the Tatun Volcano Group exhibit a pattern potentially connected to the low V p anomalies in the mantle wedge, suggesting the involvement of the Philippine Sea slab, either by asthenospheric upwelling due to extensional collapse or by fluid migration due to slab dehydration. Those beneath the Ilan Plain exhibit a low V p pattern extending to deeper origins in the eastern offshore region, suggesting a connection with the opening of the Okinawa Trough.