Subduction Polarity Reversal Research Articles

Deciphering Subduction Polarity During Ancient Arc‐Continent Collisions

AbstractThe closure of an ancient ocean basin via oceanic arc‐continent collision has two subduction styles with opposite polarities, which may proceed via subduction polarity reversal (SPR) or a subduction zone jump (SZJ). Interpreting the geometry or kinematic evolution of ancient collisional zones, especially the original subduction polarity, can be challenging. Here we used 2D thermo‐mechanical modeling to investigate the dynamic evolution process of SPR versus SZJ. Our modeling predicts different structural, topographic, magmatic, and basin histories for SPR and SZJ, which can be compared against, and help interpret, the geologic record past sites of oceanic closure during collisional orogens. Our results match geologic observations of past collisions in Kamchatka, eastern Russia, and the Banda Arc, eastern Indonesia, and thus our results can help effectively decode the evolutionary history of past arc‐continent collisions.

The hidden link between dry ankaramitic melts and giant alkalic-type epithermal Au deposits: The Lihir Island example

The magmatic controls on the formation of giant epithermal Au deposits genetically associated with alkaline magmatic systems are not well understood. The general model, which attributes the generation of alkaline magmas to low-degree partial melting of metasomatized lithospheric mantle in a post-subduction tectonic setting cannot easily explain why some of these magmas are highly fertile for Au mineralization while others are not. This knowledge gap hampers the effective exploration of this economically important deposit type. In this study, we focused on the alkaline magmatism on Lihir Island and the Conical Seamount, Papua New Guinea, that gave birth to the Ladolam deposit and investigated the composition of silicate melt inclusions (SMIs) hosted in primitive volcanic rocks. Our findings offer important and novel insights into the early and deep magmatic processes that controlled the ore fertility of the melts that produced the largest known alkalic-type epithermal Au deposit on Earth. Olivine- and clinopyroxene-hosted primitive SMIs reveal nepheline-normative ankaramitic melt compositions derived from high-degree partial melting of metasomatized clinopyroxene-dominated lithologies, presumably amphibole-bearing clinopyroxenitic cumulates and metasomatically overprinted lithospheric mantle, both produced during earlier active subduction. These ultra-calcic parental melts are relatively low in H2O, S, and Cl, but enriched in Cu and highly oxidized. Due to their low water contents, significant clinopyroxene crystallization over a narrow temperature interval drove melt evolution from ankaramitic to alkaline compositions by strongly increasing incompatible element concentrations. Despite initially low H2O concentrations, evidence for high-temperature degassing is present in the form of low-density single-phase fluid inclusions co-existing with SMIs in clinopyroxene. This degassing event led to a strong decrease of S concentrations in the melt, whereas Cl and chloride-complexing elements remained largely unaffected. We propose that high-temperature volatile saturation as consequence of significant clinopyroxene crystallization is a key process for subsequent epithermal Au mineralization and can explain the efficient separation of Au from Cu. The complex tectonic setting of Lihir Island, marked by a reversal of subduction polarity, a tear in the slab beneath the island, and trans-lithospheric extensional structures, facilitated the generation and ascent of highly oxidized and relatively dry ankaramitic melts that ultimately exsolved a vapor-like, S- and presumably Au-rich fluid phase and might thus represent a prerequisite for alkalic-type epithermal Au mineralization.

Initial oceanic subduction triggered by arc–continent collision: An example from the convergence between the Paleo-Asian Ocean and the North China Craton

The driving mechanisms for initial oceanic subduction beneath a passive continental margin remain unclear. The Paleozoic convergence history between the North China Craton (NCC) and the Paleo-Asian Ocean provides an ideal opportunity to investigate the driving mechanisms of the onset of oceanic subduction. Our detrital zircon U–Pb dating results yield Middle Devonian to Permian ages (391–273 Ma) in Paleozoic strata within China's Aoji region, specifically in the Bainaimiao arc belt situated between the NCC and Central Asian Orogenic Belt (CAOB). Detrital zircon age spectra, εHf(t) values, and two-stage model ages of the Devonian to Permian sediments suggest zircon contributions from both the NCC and CAOB. Combined with data from various regions along the Bainaimiao arc belt, findings suggest that the Bainaimiao island arc was accreted to the northern margin of the NCC through arc–continent collision during the late Silurian, rendering the NCC margin passive until the end-Devonian. At this point, southward subduction in the Paleo-Asian Ocean beneath the NCC commenced and continued into the Permian, transforming the northern margin of the NCC from passive to active. This initial subduction (ca. 359 Ma) in the Paleo-Asian Ocean resulted from collision-induced magmatism and deformation due to the protracted convergence and also led to a reversal in subduction polarity. Subsequently, in response to Paleo-Asian Ocean subduction, the northern margin of the NCC underwent rapid uplift during the Carboniferous, which led to widespread exposure of the NCC basement rocks in the late Carboniferous.

Terrane Collision‐Induced Subduction Initiation: Mode Selection and Implications for Western Pacific Subduction System

AbstractIn the regime of plate tectonics, the subduction of an oceanic plate generally terminates with the collision and accretion of continental terranes. Then, a new subduction zone may form in the neighboring oceanic plates, which is defined as the terrane collision‐induced subduction initiation (SI). Based on the analyses of the western Pacific subduction system in the Cenozoic, three types of collision‐induced SI have been observed: subduction polarity reversal, subduction transference and far‐field subduction. However, the dynamics and controlling factors of SI mode selection after terrane collision are not clear. In this study, a multi‐terrane collision model has been conducted with variable rheological strength of continental terranes and different convergence velocities. The model results indicate that the relative strength of the terranes controls the SI mode selection, with the new subduction zone tending to form beneath weaker terranes. In addition, the higher convergence velocity can facilitate the collision‐induced SI. An analytical study of force balance has been further conducted, which provides a mechanical explanation for the numerical prediction of a weak overriding terrane as a favorable SI site. The numerical models and force balance analyses are further compared with the natural cases in the western Pacific subduction system. This indicates that subduction polarity reversal is the most favorable mode after terrane collision in the western Pacific, possibly due to the weakness of overriding plate during the preceding subduction‐induced fluid/melt activity. This comprehensive study provides systematic constraints for the dynamics of collision‐induced subduction jump, especially for the western Pacific subduction zones in the Cenozoic.

Subduction polarity reversal facilitated by plate coupling during arc-continent collision: Evidence from the Western Kunlun orogenic belt, northwest Tibetan Plateau

Abstract Subduction polarity reversal usually involves the break off or tearing of the downgoing plate (DP) along the continent-ocean transition zone, in order to initiate subduction of the overriding plate (OP) with opposite polarity. We propose that subduction polarity reversal can also be caused by DP-OP coupling and can account for the early Paleozoic geological relationships in the Western Kunlun orogenic belt in the northwestern Tibetan Plateau. Our synthesis of elemental and isotopic data reveals transient (~2 m.y.) changes in the sources of early Paleozoic arc magmatism in the southern Kunlun terrane. The early-stage (ca. 530–487 Ma) magmatic rocks display relatively high εNd(t) (+0.3 to +8.7), εHf(t) (−3.6 to +16.0), and intra-oceanic arc-like features. In contrast, the late-stage (485–430 Ma) magmatic rocks have predominantly negative εNd(t) (−4.5 to +0.3), εHf(t) (−8.8 to +0.9), and higher incompatible trace elements (e.g., Th), similar to the sub-continental lithospheric mantle beneath the Tarim craton. This abrupt temporal-spatial variation of arc magmatism, together with the detrital zircon evidence, indicate that subduction polarity reversal of the Proto-Tethys Ocean occurred in a period of ~10 m.y., consistent with the time interval reflected by ophiolite age. This rapid polarity reversal corresponds with the absence of ultrahigh-pressure (UHP) metamorphic and post-collisional magmatic rocks, features normally characteristic of slab break-off or tearing. Numerical modeling shows that this polarity reversal was caused by plate coupling during arc-continent collision. This coupling modified the normal succession of arc-continent collision events, preventing slab break-off or tearing-induced buoyant rock rebound and asthenosphere upwelling. Our model successfully explains early Paleozoic orogenesis in the Western Kunlun orogenic belt and may be applied elsewhere where post-collisional magmatic and UHP rocks are absent.

Numerical modeling of induced subduction initiation: Insights from the oceanic plateau accretion

Subduction initiation is a crucial process for plate tectonics. Two scenarios of induced subduction initiation–subduction polarity reversal and subduction transference–are primarily attributed to the accretion of oceanic plateaus. However, the factors governing these two distinct types of subduction initiation remain elusive. Here, we employ 2D thermomechanical numerical models to investigate the dynamics of induced subduction initiation during oceanic plateau accretion. Specifically, we explore the impact of the thickness, density, and rheological strength of the oceanic plateau on subduction initiation. Our results reveal three geodynamic regimes: continuous subduction, subduction transference, and subduction polarity reversal. Thin oceanic plateaus tend to subduct along with slabs into the deep mantle, while thick oceanic plateaus often accrete to the margin, triggering subduction initiation. The rheological strength and density of an oceanic plateau play a significant role in determining whether subduction transference or polarity reversal occurs. Increasing the viscosity and decreasing the density of the oceanic plateau promotes strain concentration in front of the oceanic plateau, resulting in subduction polarity reversal. Our model results provide insights into the dynamics of subduction transference in the Caroline Sea and polarity reversal in Solomon in the western Pacific Ocean.

Late Carboniferous arc-continent collision and subduction polarity reversal in southeast Altaids: New insights from provenance analysis of late Paleozoic sedimentary records

Late Carboniferous arc-continent collision and subduction polarity reversal in southeast Altaids: New insights from provenance analysis of late Paleozoic sedimentary records

Thermo‐Kinematic Evolution of the Eastern European Alps Along the TRANSALP Transect

AbstractThe eastern European Alps are shaped by the indentation of Adria into Europe. Recent tomography, depicting detached slab fragments, has been interpreted as evidence of continuous southward subduction of European lithosphere, contrary to an often‐invoked subduction polarity reversal. Orogen‐scale exhumation, driven by rock displacement along active faults, may reflect subduction polarity within the framework of doubly‐vergent Coulomb wedge theory, provided the absence of rheological contrasts across the colliding plates. Low‐temperature thermochronology can evaluate crustal cooling in response to changes in tectonic and erosional boundary conditions. This study investigates the consistency of observed crustal re‐organization, exhumation, and mantle processes in the Eastern Alps. Thermo‐kinematic forward models driven by reconstructions of crustal shortening along the TRANSALP geophysical transect were subjected to variations in shortening rates, thermophysical parameters, and topographic evolution, supplemented by new fission‐track data. The thermo‐kinematic models reproduce: (a) the orogen‐scale structural geometry, (b) the distribution of thermochronometer ages, (c) observed time‐temperature paths, and (f) the present‐day surface heat flux. Results suggest that exhumation is driven by rock displacement along active faults without the need to involve mantle‐driven buoyancy forces. Taken together, the results identify two possible scenarios: if the Tauern Ramp is a retro‐thrust and the southward shift of deformation in the Southern Alps is a response to new Coulomb‐wedge conditions, then our results support a Mid‐Miocene reversal of the subduction polarity. Alternatively, crustal deformation does not reflect mantle processes entailing a high degree of inter‐plate decoupling.

Tectonics of the Solomon Sea Basin from Vertical Gravity Gradient and Seismic Data

AbstractThe Solomon Sea Basin is a Cenozoic back‐arc spreading basin within the convergence system of the Pacific and Indo‐Australian plates. Against the background of subduction polarity reversal, the current Solomon Sea Basin gradually formed a rhombic morphology with the subduction of the basin along the New Britain Trench and the Trobriand Trough. By analyzing the vertical gravity gradient, natural earthquake and seismic reflection data, this study determines the structural characteristics of the Solomon Sea Basin. It was found that the tectonics of the basin are characterized by the original expansion structure within the central part in addition to the structure induced by the latest subduction along the basin margin. The original spreading structure of the basin presented an east–west linear graben and horst controlled by normal faults during the basin expansion period. As a result of the subduction and slab‐pull of the Solomon Sea Basin, extensional structure belts parallel to the New Britain Trench formed along the basin margin.

A review and tectonic interpretation of the Taconian–Grampian tract between Newfoundland and Scotland: diachronous accretion of an extensive forearc–arc–backarc system to a hyperextended Laurentian margin and subsequent subduction polarity reversal

Abstract The Taconian–Grampian tract was characterized by a diachronous collision of a north-facing oceanic arc–forearc terrane and associated backarc basins with an irregular Laurentian margin with hyperextended segments. Hyperextension produced outboard continental terranes, separated by exhumed subcontinental mantle from the inboard margin. The exhumed mantle facilitated continued subduction of the extended margin after it had entered the trench. Enhanced slab-rollback resulted in spreading in lenticular backarc basins, which gradually transitioned along-strike into extensional arcs where rollback was less. Obduction of the oceanic elements onto the irregular Laurentian margin was followed by diachronous slab breakoff and a subduction polarity reversal, such that south- and north-dipping subduction zones locally were coeval along-strike. The polarity flip changed the convergence obliquity from dextral to sinistral and was accompanied by shallowing of the subducting slab near the end of the Middle Ordovician. Strike-slip movements locally juxtaposed segments where tectonic events occurred at different times, producing conflicting relationships. Slab breakoff produced punctuated magmatism, largely driven by mantle-derived melts, and drove and/or enhanced metamorphism in the overlying and enveloping crustal rocks. Boninite was generated episodically over a time span of 32 myr; the oldest Cambrian phase in the Lushs Bight Oceanic Tract (LBOT) and correlatives was associated with subduction initiation.

Late extension of a passive margin coeval with subduction of the adjacent slab: The Western Alps and Maghrebides files

The evolution of the Alpine Tethys margins during the beginning of the African-Eurasian convergence was little studied compared to their evolution during the post-Pangea rifting and oceanic expansion,i.e., from the Early Jurassic to the early Late Cretaceous. The present work firstly aims to make up for this shortcoming in the case of the distal European margin of the Alpine Tethys, namely the Briançonnais domain of the Western Alps. We show that this margin was affected by strong post-rifting extension mainly in Late Cretaceous-Paleocene times and propose to make it the type of the (rare) “Late Extension Passive Margins”. Remarkably, this extension shortly preceded Lutetian times, when Briançonnais margin encroached the SE-dipping subduction zone under the Adria microplate. Secondly, we assess the post-rifting evolution of the north-Tethyan paleomargin in the Maghrebides transects,i.e., south-west of the Briançonnais transect along the same European-Iberian paleomargin. For this purpose, we consider the Triassic-Eocene series of the “Dorsale Calcaire” in the Alkapeca Blocks located along southeastern Iberia until the Eocene then transported onto the North African margin. Examination of the literature shows that the Tethyan margin of the Alboran block was strongly affected by normal faulting as early as Late Jurassic-Early Cretaceous times whereas post-rifting extension of the Kabylian blocks mainly occurred in the Late Cretaceous-Paleocene like in the Briançonnais. We propose that post-rifting extension of the Alboran block southern margin resulted from the sinistral movement of Africa relative to Iberia while the later extension of the Kabylian blocks can be related to the further convergence kinematics. Subduction of the Ligurian-Maghrebian slab under the North African margin would have occurred at that time in the southward continuation of the Alpine subduction. The overriding Adria and North African margins did not experience significant compression at that time. During the Eocene, a subduction polarity reversal occurred, which was associated with the relocation of the subduction zone along the Alkapeca block. This was the beginning of the Apenninic subduction, which triggered the back-arc opening of the Mediterranean basins.

Breaking Up Is Hard to Do: Magmatism During Oceanic Arc Breakup, Subduction Reversal, and Cessation

AbstractThe formerly continuous Vitiaz Arc broke into its Vanuatu and Fijian portions during a reversal of subduction polarity in the Miocene. Basaltic volcanism in Fiji that accompanied the breakup ranged from shoshonitic to low‐K and boninitic with increasing distance from the broken edge of the arc that, presumably, marks the broken edge of the slab. The Sr‐Pb‐Nd isotope ratios of the slab‐derived component in the breakup basalts most closely match those of the isotopically most depleted part of the Samoan seamount chain on the Pacific Plate that was adjacent to the site of breakup at 4–8 Ma, and differ from those of subsequent basalts in spreading segments of the surrounding backarc North Fiji and Lau Basins. Subduction of the Samoan Chain along the Vitiaz Trench Lineament may have controlled the limit of polarity reversal and, hence, where the double saloon doors (Martin, 2013) opened. Prior to breakup, Fijian volcanics were more similar isotopically to the Louisville Seamount Chain.

Joint Geodynamic‐Geophysical Inversion Suggests Passive Subduction and Accretion of the Ontong Java Plateau

AbstractIn this study, we for the first time applied a joint geodynamic‐geophysical inversion approach to oceanic plateau subduction models, and compared the subduction style and corresponding topography and Bouguer gravity of two representative subduction scenarios with passive or active collision. We showed that the case of passive collision of the Ontong Java Plateau (OJP) crust better explains the topography, gravity, and seismic data than the active collision scenario. This implies that the OJP did not control the regional dynamics during the collisional process. We conclude that previous studies may have overestimated the role of the OJP in triggering subduction initiation, subduction polarity reversal, and even Pacific Plate rotation.

What conditions promote atypical subduction: Insights from the Mussau Trench, the Hjort Trench, and the Gagua Ridge

Subduction zones act as interfaces for exchanging materials between the Earth’s crust and mantle. The western Pacific plate region is evolving within a convergent tectonic environment. Old oceanic plates generally subduct beneath young oceanic plates, as exemplified by the Izu-Bonin-Mariana and Tonga-Kermadec subduction zones. However, in some subduction zones, such as the Mussau Trench, the Hjort Trench, and the Gagua Ridge, young and more buoyant oceanic plates have been recognized to subduct underneath older and denser plates. What conditions promote atypical subduction, however, remain elusive. In this study we take the Mussau Trench, the Hjort Trench, and the Gagua Ridge as examples to explore the possible underlying factors that control the formation of atypical subduction. By anatomizing the tectonic features of both the Mussau Trench and the Hjort Trench, we find that atypical subduction may be feasible mainly when the plate boundary is characterized by strike-slip-dominated transpression; that is, the strike-slip component overwhelms the compression component, which may argue against the atypical subduction occurring at the Gagua Ridge, at least at present. Moreover, in light of the evolution of both the Mussau Trench and the Hjort Trench, it is further suggested that subduction polarity reversal and a strike-slip border are the keys to atypical subduction.

Collision‐Induced Subduction Polarity Reversal Explains the Crustal Structure of Northern Borneo: New Results From Virtual Deep Seismic Sounding (VDSS)

AbstractSubduction polarity reversal (SPR) is a key subduction initiation mechanism often associated with arc‐continent collision zones. Northern Borneo has long been recognized as a location where sequential but opposing subduction zones were present in the Miocene, but has not been examined in the context of SPR. Here, we exploit teleseismic data from northern Borneo to investigate crustal thickness variations using Virtual Deep Seismic Sounding (VDSS). Our results reveal a thick crustal root beneath the Crocker Range and an area of relatively thin crust in the southeast, which appears to extend northeast into the Sulu Sea, where back‐arc rifting behind the younger subduction zone developed. Overall, our findings are consistent with predictions from numerical models of SPR involving arc‐continent collision, but with several important differences—including a substantial mountain range and more limited back‐arc rifting that can be attributed to northern Borneo being an example of SPR involving continent‐continent collision.

Dynamics of Early Neoproterozoic accretion, west-central India: II ~1.65 Ga HT-LP and ~0.95 Ga LT-HP metamorphism in Godhra-Chhota Udepur, and a tectonic model for Early Neoproterozoic accretion

The N/NNE-striking Aravalli Delhi Fold Belt (ADFB) and the E-striking Central Indian Tectonic Zone (CITZ) converge at the Godhra-Chhota Udepur (GC) sector, west-central India. Analyses of mesoscale deformation structures and metamorphic phase equilibria in the basement and supracrustal rocks are integrated with geochronological-geochemical data (accompanying article) to address the dynamics of the Early Neoproterozoic CITZ-ADFB accretion. In the GC sector, ~1.65 Ga granulite facies anatectic gneisses, ~2.5 Ga and 1.03–1.02 Ga granitoids, and greenschist to amphibolite facies allochthonous supracrustal rocks constitute a tectonic mélange (D2 deformation). The lithodemic units are traversed by networks of W/WNW-striking steep-dipping transpressional shear zones with sinistral kinematics (D3). The shallow-dipping mélange with top-to-the south kinematics is intruded by post-D2 to syn-D3 0.95–0.93 Ga granitoids. Mn-NCKFMASH P-T pseudosection analyses of the anatectic gneisses with pre-D2 garnet + cordierite-bearing leucosomes suggest the rocks evolved along a clockwise P-T path in the range of 5–6 kbar and 680–720 °C. By contrast, the Early Neoproterozoic (0.95–0.93 Ga) chlorite + phengite (Si up to 3.32 apfu) + clinozoisite + quartz ± biotite ± garnet schists in the mélange attained pre/syn-D2 peak metamorphic conditions (10–12 kbar, 450–500 °C). NCKFMASH pseudosection analyses of the ~0.95 Ga phengite-bearing schists indicate the supracrustal rocks evolved along a high-P, low-T clockwise path; phengite-poor micas defining the D3 fabric (Si up to 3.04 apfu) attest to post-peak decompression in the schists. The ~2.5 Ga ADFB granites accreted with the ~1.65 Ga HT-LP anatectic gneisses, ~1.03 Ga granites, and the ~0.95 Ga LT-HP supracrustal rocks of the CITZ during D2 thrusting. The crustal convergence continued with the emplacement of post-D2 0.95–0.93 Ga granitoids that culminated with the nucleation of W/WNW-striking D3 transpressional shear zones. This broad contemporaneity among felsic plutonism , LT-HP metamorphism in the supracrustal rocks, and the D2-D3 shortening are interpreted to be the result of a switch in subduction polarity between 1.03 and 0.93 Ga during oblique ADFB-CITZ convergence. • ~1.65 Ga HT-LP clockwise granulite metamorphism in CITZ basement anatectic gneiss. • ~0.95 Ga LT-HP clockwise metamorphism in the CITZ allochthonous supracrustal rocks. • E-striking CITZ & N-striking Aravalli Delhi Fold Belt (ADFB) accreted at ~0.95 Ga. • ~0.95 Ga metamorphism coeval with crustal shortening and granitoid emplacement. • Early Neoproterozoic oblique accretion related to subduction polarity reversal.

Extremely rapid up-and-down motions of island arc crust during arc-continent collision

Mountain building and the rock cycle often involve large vertical crustal motions, but their rates and timescales in unmetamorphosed rocks remain poorly understood. We utilize high-resolution magneto-biostratigraphy and backstripping analysis of marine deposits in an active arc-continent suture zone of eastern Taiwan to document short cycles of vertical crustal oscillations. A basal unconformity formed on Miocene volcanic arc crust in an uplifting forebulge starting ~6 Ma, followed by rapid foredeep subsidence at 2.3–3.2 mm yr−1 (~3.4–0.5 Ma) in response to oceanward-migrating flexural wave. Since ~0.8–0.5 Ma, arc crust has undergone extremely rapid (~9.0–14.4 mm yr−1) uplift to form the modern Coastal Range during transpressional strain. The northern sector may have recently entered another phase of subsidence related to a subduction polarity reversal. These transient vertical crustal motions are under-detected by thermochronologic methods, but are likely characteristic of continental growth by arc accretion over geologic timescales.

Co-Evolution of Parallel Triple Subduction Systems in the New Guinea Region: A Systematic Numerical Study

A specific configuration of the global subduction system is the parallel triple subduction. The widely accepted example of parallel triple subduction is the New Guinea region, including a northward dip at the New Britain Trench (NBT), a southward dip at the Trobriand Trough (TT), and North Solomon Trench (NST). Questions regarding the parallel triple subduction system remain largely unexplored in terms of factors controlling its initiation, duration, and dynamics. Here, we used two-dimensional numerical models to study the dynamics mechanism of the parallel triple subduction system in the New Guinea region. Four possible regimes were achieved: 1) the double subduction model, which includes the forward subduction jumping model (FSJ) and the subduction polarity reversal model (SPR) and 2) the parallel triple subduction model, which includes the tendency to the forward jumping model (TFSJ) and the tendency to polarity reversal (TSPR). By evaluating the four regimes with actual seismic data, we suggest that the pre-existing rupture and length of ocean–continent transition (OCT) determine the formation of the TT, while the formation of the NBT may be the result of the rheological strength differences between the Solomon Island Arc (SIA) and Solomon Sea Basin (SSB); the initial length of the SSB can regulate the competitive relationship between the TT and NBT, which also determines the present-day inactive state of the TT. A longer SSB makes the TT and NBT initiated independently, while a narrower SSB will allow interaction during subduction initiation of the TT and NBT.

Subduction Initiation at the Solomon Back‐Arc Basin: Contributions From Both Island Arc Rheological Strength and Oceanic Plateau Collision

AbstractIt is generally accepted that the subduction polarity reversal (SPR) results from the strong collision of two plates. Yet, the SPR of the Solomon Back‐arc Basin is started in the “soft docking” stage, and the mechanism by which the “soft docking” induced subduction initiation (SI) remains elusive. We find that the mass depletion of the plateau influences the evolution of the subduction patterns during SI. And the island arc rheological strength affects the development of the shear zone between an island arc and back‐arc basin which favors SI. What's more, with the increase of the rheological strength difference, the SI is more easily to occur, and the contribution of the plateau collision to SI weakens. Hence, by combining the available geological evidence, we suggest that the Solomon Island Arc rheological strength and the Ontong‐Java plateau collision jointly controlled the SI during the “soft docking” stage.

Subduction Polarity Reversal Triggered by Oceanic Plateau Accretion: Implications for Induced Subduction Initiation

AbstractSubduction polarity reversal, an induced subduction initiation (SI), may occur frequently in geological history as exemplified by the Solomon subduction zone. However, the mechanism and dynamics of polarity reversal remain poorly understood. Here, we use 2D thermomechanical numerical models to investigate the dynamics of subduction polarity reversal during oceanic plateau accretion. Model results show that larger and lighter oceanic plateaus favor subduction polarity reversal, which is manifested by the formation of the Solomon subduction zone after the large Ontong Java Plateau collided with the former Melanesian (Manus‐North Solomon‐Vitiaz) trench. We analyze the stress state during the transient SI process and find that rapid extension of the oceanic plateau is concomitant with subduction polarity reversal, thus questioning the use of extensional structures as geological criteria for spontaneous SI.