Subduction Zone Polarity Research Articles

The history of Cenozoic magmatism and collision in NW New Guinea – New insights into the tectonic evolution of the northernmost margin of the Australian Plate

Evidence of Cenozoic magmatism is found along the length of New Guinea. However, the petrogenetic and tectonic setting for this magmatism is poorly understood. This study presents new field, petrographic, U–Pb zircon, and geochemical data from NW New Guinea. These data have been used to identify six units of Cenozoic igneous rocks which record episodes of magmatism during the Oligocene, Miocene, and Pliocene. These episodes occurred in response to the ongoing interaction between the Australian and Philippine Sea plates. During the Eocene, the Australian Plate began to obliquely subduct beneath the Philippine Sea Plate forming the Philippine–Caroline Arc. Magmatism in this arc is recorded in the Dore, Mandi, and Arfak volcanics of NW New Guinea where calc-alkaline and tholeiitic rocks formed within subduction-related fore-arc and extension-related back-arc settings from 32 to 27 Ma. Collision along this plate boundary in the Oligocene–Miocene jammed the subduction zone and caused a reversal in subduction polarity from north-dipping to south-dipping. Following this, subduction of the Philippine Sea Plate beneath the Australian Plate produced magmatism throughout western New Guinea. In NW New Guinea this is recorded by the middle Miocene (18–12 Ma) Moon Volcanics, which include an early period of high-K to shoshonitic igneous activity. These earlier magmatic rocks are associated with the subduction zone polarity reversal and an initially steeply dipping slab. The magmatic products later changed to more calc-alkaline compositions and were emplaced as volcanic rocks in the fore-arc section of a primitive continental arc. Finally, following terminal arc–continent collision in the late Miocene–Pliocene, mantle derived magmas (including the Berangan Andesite) migrated up large strike-slip faults becoming crustally contaminated prior to their eruption during the Plio–Pleistocene. This study of the Cenozoic magmatic history of NW New Guinea provides new data and insights into the tectonic evolution of the northern margin of the Australian Plate.

Tectonic evolution of Western Tethys from Jurassic to present day: coupling geological and geophysical data with seismic tomography models

ABSTRACTThe geodynamic evolution of the Western Tethys is characterized by multiple phases of rifting, seafloor spreading, subduction, and collisional events. Regional reconstructions are highly dependent on the kinematic history of the major plates bounding the Atlantic and Tethyan tectonic domains, as well as small micro-plates resulted from the fragmentation of northern Gondwanaland. The complexity of tectonic events in this area leads to major discrepancies between competing models about the timing, location, and polarity of subduction zones, for both the Cenozoic evolution and earlier phases. We focus on unravelling the Mesozoic evolution of the Western Tethys. We first reassessed kinematic models for the Early Jurassic–Late Cretaceous opening of the central, north central, and north Atlantic and used these as boundary conditions on the kinematic reconstructions of the Tethyan realm. We combined reconstructions of rifting and early seafloor spreading in northern Pangea that incorporate quantitative estimates of continental extension, and suggest a transtensional motion of Iberia relative to Europe in Early Cretaceous time to fit within the refined plate configuration of Central North Atlantic. We combined this regional framework with a recently published model for the motion of smaller blocks within the Western Tethys; from this model, we created synthetic isochrons for extinct oceanic basins and built evolving topological plate boundaries based on the new rigid plate model to derive a self-consistent and time-dependant model for the last 200 million years. We then examined the consistency of subduction history implied by the kinematic reconstructions, by comparing reconstructed plate boundary configurations to mantle velocity structure imaged by a range of seismic tomography models. Our results show that a satisfactory match can be made between Cenozoic subduction events in the Western Tethys region and observed shallow tomographic high-velocity material. However, the match is less clear for older subducted material. Correlations between surface reconstructions and deep Earth structure suggest that mid-deep mantle seismic features under present day Northeast-Central and Northwest Africa-Arabia may correspond with the Mesozoic subduction systems in the Vardar Ocean, Alpine Tethys, and Western Neotethys, respectively. These correlations support a model with intra-oceanic subduction of the Vardar Ocean from Middle Jurassic to Early Cretaceous, and mid-Early Cretaceous initiation of oceanic subduction in the Ligurian-Piemont Ocean. The results from the plate-tomography comparison suggest the existence of oceanic subduction in the Alpine Tethys Oceans in late early Cretaceous time. We investigated the uncertainties in the tectonic model in terms of absolute and relative plate motion and surface velocities and showed that choice of absolute reference frame can partially account for the lateral offset between the Vardar subduction zone and associated slab material in deep mantle; additional mismatches may be attributable to the limitations of our methodology, such as the assumption that slabs sink vertically.

The metamorphic sole of the western Tasmanian ophiolite: New insights into the Cambrian tectonic setting of the Gondwana Pacific margin

The Cambrian Ross–Delamerian Orogeny records the first phase of accretional tectonics along the eastern margin of Gondwana following breakup of the supercontinent Rodinia. Western Tasmania represents a key area for understanding the Cambrian tectonic setting of the eastern margin of Gondwana as it is one of the few places where a Tethyan-type ophiolite is preserved and contains the only known exposures of a sub-ophiolitic metamorphic sole associated with the Ross–Delamerian Orogen. This paper presents an integrated study of the field, petrographic, geochemical, and metamorphic characteristics of the metamorphic sole to the western Tasmanian ophiolite. The structurally highest levels of the metamorphic sole consist of granulite–upper amphibolite facies metacumulates and metagabbros. A transition to amphibolite and epidote–amphibolite facies conditions is recorded by metadolerites and metabasalts towards the base of the metamorphic sole. Kinematic indicators in mylonitic amphibolites suggest the metamorphic sole formed in an east-dipping subduction zone located to the east of the Proterozoic continental crust of Tasmania. Major and trace element whole rock and relict igneous spinel geochemistry indicates that the protoliths to the metamorphic sole formed at a back arc basin spreading centre. Our new data supports a model in which east-dipping subduction in Tasmania was driven by collapse of a back arc basin developed above an earlier west-dipping subduction zone outboard of the eastern margin of Gondwana. The proposed model may help to resolve a controversy related to apparent along-strike variations in subduction zone polarity during the Ross-Delamerian Orogeny and suggests a complex geodynamic setting had developed along the eastern margin of Gondwana by the Middle Cambrian. This study highlights the importance of considering the role of multiple subduction zones in generating metamorphic soles and emplacing ophiolites, which are key events associated with the construction of many orogenic belts worldwide.

Protracted garnet growth in high‐Peclogite: constraints from multiple geochronology andP–Tpseudosection

AbstractUnderstanding convergent margin processes requires determination of the onset and the termination of subduction, the duration of subduction‐zone metamorphism, and the subduction zone polarity. Garnet growth and intracrystalline zonation can be used to constrain the timing, duration and kinetics of tectonometamorphic processes. An eclogite from the Huwan shear zone in the Hong'an orogen was investigated with combined pseudosection analysis and multiple geochronologies. The pseudosection analysis illustrates that garnet growth is continuous and along an early near‐isothermal trajectory followed by a near‐isobaric heating path from 1.9 GPa/500 °C to 2.4 GPa/575 °C and subsequent near‐isothermal decompression.40Ar/39Ar dating of an amphibole inclusion in garnet from the eclogite yielded an age of 310 ± 5 Ma, which is consistent with a U–Pb age of 305 ± 3 Ma for the metamorphic zircon within uncertainty. Garnet core and rim material produced Lu–Hf ages of 296.9 ± 3.8 and 256.9 ± 3.9 Ma respectively; the latter is consistent with its Sm–Nd age of 254.3 ± 4.6 Ma for the same aliquots. Similarly, limited zircon U–Pb ages ofc. 257 Ma were obtained in zircon rims with garnet inclusions. These ages were interpreted to bracket the period of garnet growth and the difference of up toc. 40 Ma is best explained by protracted garnet growth. We propose that the rocks represent detachment of part of the downgoing slab and remained free of significant compression/decompression or heating/cooling close to the subduction channel, most likely underplating the mantle wedge, for a long time. These rocks were incorporated into the following subduction channel due to the successive entry of the buoyant materials, and exhumed at some time later thanc. 254 Ma. The increasing observations of protracted garnet growth and long‐lived subduction in various orogens worldwide demand more sophisticated geodynamic models.

Far-field contractional polarity changes in models and nature

A change in contractional polarity occurs when the direction of tectonic transport switches along strike. This switch is conditioned by lateral variations in rheology or inherited asymmetries, such as contrasts in structure or changes in the polarity of subduction zones. The parameters controlling contractional polarity changes are less understood in situations when the strain is transferred at large distances from indenters. Analysing this type of strain transfer is critical for understanding the mechanics of thrusting in fore- or back-arc settings of orogenic areas. Comparison of crustal-scale analogue modelling with the inversion of the Black Sea back-arc and the formation of the New Guinea–New Britain fore-arc suggest that far-field changes in contractional polarity are related to rheological contrasts across inherited normal faults. The initial extension creates rheological weak zones that localize the subsequent far-field contractional deformation along groups of thrusts with opposite vergence along the strike of the system. The largest amount of far-field contractional deformation is recorded in the transfer zone located between the two indenters moving in opposite directions and is particularly high when inverting oblique extensional systems.

Geodynamic evolution of the central and western Mediterranean: Tectonics vs. igneous petrology constraints

We present a geodynamic reconstruction of the Central–Western Mediterranean and neighboring areas during the last 50Myr, including magmatological and tectonic observations. This area was interested by different styles of evolution and polarity of subduction zones influenced by the fragmented Mesozoic and Early Cenozoic paleogeography between Africa and Eurasia. Both oceanic and continental lithospheric plates were diachronously consumed along plate boundaries. The hinge of subducting slabs converged toward the upper plate in the double-vergent thick-skinned Alps–Betics and Dinarides, characterized by two slowly-subsiding foredeeps. The hinge diverged from the upper plate in the single-vergent thin-skinned Apennines–Maghrebides and Carpathians orogens, characterized by a single fast-subsiding foredeep. The retreating lithosphere deficit was compensated by asthenosphere upwelling and by the opening of several back-arc basins (the Ligurian–Provençal, Valencia Trough, Northern Algerian, Tyrrhenian and Pannonian basins). In our reconstruction, the W-directed Apennines–Maghrebides and Carpathians subductions nucleated along the retro-belt of the Alps and the Dinarides, respectively. The wide chemical composition of the igneous rocks emplaced during this tectonic evolution confirms a strong heterogeneity of the Mediterranean upper mantle and of the subducting plates. In the Apennine–Maghrebide and Carpathian systems the subduction-related igneous activity (mostly medium- to high-K calcalkaline melts) is commonly followed in time by mildly sodic alkaline and tholeiitic melts. The magmatic evolution of the Mediterranean area cannot be easily reconciled with simple magmatological models proposed for the Pacific subductions. This is most probably due to synchronous occurrence of several subduction zones that strongly perturbed the chemical composition of the upper mantle in the Mediterranean region and, above all, to the presence of ancient modifications related to past orogeneses. The classical approach of using the geochemical composition of igneous rocks to infer the coeval tectonic setting characteristics cannot be used in geologically complex systems like the Mediterranean area.

Dextral shear, terrane accretion and basin formation in the Northern Andes: best explained by interaction with a Pacific-derived Caribbean Plate?

Abstract The structure, stratigraphy and magmatic history of northern Peru, Ecuador and Colombia are only adequately explained by Pacific-origin models for the Caribbean Plate. Inter-American models for the origin of the Caribbean Plate cannot explain the contrasts between the Northern Andes and the Central Andes. Persistent large magnitude subduction, arc magmatism and compressional deformation typify the Central Andes, while the Northern Andes shows back-arc basin and passive margin formation followed by dextral oblique accretion of oceanic plateau basalt and island arc terranes with Caribbean affinity. Cretaceous separation between the Americas resulted in the development of a NNE-trending dextral–transpressive boundary between the Caribbean and northwestern South America, becoming more compressional when spreading in the Proto-Caribbean Seaway slowed towards the end of the Cretaceous. Dextral transpression started at 120–100 Ma, when the Caribbean Arc formed at the leading edge of the Caribbean Plate as a result of subduction zone polarity reversal at the site of the pre-existing Trans-American Arc, which had linked to Central America to South America in the vicinity of the present-day Peru–Ecuador border. Subsequent closure of the Andean Back-Arc Basin resulted in accretion of Caribbean terranes to western Colombia. Initiation of flat-slab subduction of the Caribbean Plate beneath Colombia at about 100 Ma is associated with limited magmatism, with no subsequent development of a magmatic arc. This was followed by northward-younging Maastrichtian to Eocene collision of the trailing edge Panama Arc. The triple junction where the Panama Arc joined the Peru–Chile trench was located west of present-day Ecuador as late as Eocene time, and the Talara, Tumbes and Manabi pull-apart basins directly relate to its northward migration. Features associated with the subduction of the Nazca Plate, such as active calc-alkaline volcanic arcs built on South American crust, only became established in Ecuador, and then Colombia, as the triple junction migrated to the north. Our model provides a comprehensive, regional and testable framework for analysing the as yet poorly understood collage of arc remnants, basement blocks and basins in the Northern Andes.

Reply to comment on “The potential influence of subduction zone polarity on overriding plate deformation, trench migration and slab dip angle”

Reply to comment on “The potential influence of subduction zone polarity on overriding plate deformation, trench migration and slab dip angle”

Comment on “The potential influence of subduction zone polarity on overriding plate deformation, trench migration and slab dip angle” by W.P. Schellart

The Schellart's [Schellart, W.P., 2007, The potential influence of subduction zone polarity on overriding plate deformation, trench migration and slab dip angle. Tectonophysics, 445, 363–372.] paper uses slab dip and upper plate extension for testing the westward drift. His analysis and discussion are misleading for the study of the net rotation of the lithosphere since the first 125 km of subduction zones are sensitive also to other parameters such upper plate thickness, geometry and obliquity of the subduction zone with respect to the convergence direction. The deeper (> 125 km) part cannot easily be compared as well because E- or NE-directed subduction zones have seismic gaps between 270–630 km. Moreover the velocity of subduction hinge cannot be precisely estimated and it does not equal to backarc spreading due to accretionary prism growth and asthenospheric intrusion at the subduction hinge. It is shown here that hinge migration in the upper plate or lower plate reference frames supports a general global polarization of the lithosphere in agreement with the westward drift of the lithosphere. The W-directed subduction zones appear controlled by the slab–mantle interaction with slab retreat imposed by the eastward mantle flow. The opposite E-NE-directed subduction zones seem rather mainly controlled by the convergence rate, plus density, thickness and viscosity of the upper and lower plates. Finally, the geological and geophysical asymmetries recorded along subduction and rift zones as a function of their polarity with respect to the tectonic mainstream are not questioned in the Schellart's paper, but they rather represent the basic evidence for the westward drift of the lithosphere.

The potential influence of subduction zone polarity on overriding plate deformation, trench migration and slab dip angle

A geodynamic model exists, the westward lithospheric drift model, in which the variety of overriding plate deformation, trench migration and slab dip angles is explained by the polarity of subduction zones. The model predicts overriding plate extension, a fixed trench and a steep slab dip for westward-dipping subduction zones (e.g. Mariana) and predicts overriding plate shortening, oceanward trench retreat and a gentle slab dip for east to northeastward-dipping subduction zones (e.g. Chile). This paper investigates these predictions quantitatively with a global subduction zone analysis. The results show overriding plate extension for all dip directions (azimuth α = − 180° to 180°) and overriding plate shortening for dip directions with α = − 90° to 110°. The wide scatter in data negate any obvious trend and only local mean values in overriding plate deformation rate indicate that overriding plate extension is somewhat more prevalent for west-dipping slabs. West-dipping subduction zones are never fixed, irrespective of the choice of reference frame, while east to northeast-dipping subduction zones are both retreating and advancing in five out of seven global reference frames. In addition, westward-dipping subduction zones have a range in trench-migration velocities that is twice the magnitude of that for east to northeastward-dipping slabs. Finally, there is no recognizable correlation between slab dip direction and slab dip angle. East to northeast-dipping slabs ( α = 30° to 120°) have shallow (0–125 km) slab dip angles in the range 10–60° and deep (125–670 km) slab dip angles in the range 40–82°, while west-dipping slabs ( α = − 60° to − 120°) have shallow slab dip angles in the range 19–50° and deep slab dip angles in the range 25–86°. Local mean deep slab dip angles are nearly identical for east and west-dipping slabs, while local mean shallow slab dip angles are lower by only 4.7–8.1° for east to northeast-dipping slabs. It is thus concluded that overall, there is no observational basis to support the three predictions made by the westward drift model, and for some sub-predictions the observational basis is very weak at most. Alternative models, which incorporate and underline the importance of slab buoyancy-driven trench migration, slab width and overriding plate motion, are better candidates to explain the complexity of subduction zones, including the variety in trench-migration velocities, overriding plate deformation and slab dip angles.

Subduction zone polarity in the Oman Mountains: implications for ophiolite emplacement

Abstract Two end-member models have been proposed to account for the structure and metamorphism of rocks beneath the Semail ophiolite in the Oman mountains. Model A involves a single, continuous NE-directed subduction away from the continental margin during the late Cretaceous. The ophiolite and underlying thrust sheets of distal to proximal oceanic sediments were emplaced a minimum of 250 km SW onto the continental margin. Subduction of Triassic-Jurassic oceanic basalts to c. 10 kbar ( c. 39 km depth) led to the accretion of amphibolite-facies rocks to the base of the ophiolite. Thrusting propagated towards the continental margin and ended with subduction of the thinned continental crust to c. 20 kbar ( c. 78 km depth), choking the subduction zone. Buoyancy forces caused the rapid exhumation of eclogites, blueschists and carpholite-grade HP rocks along the NE margin of the continental plate. During the later phase of foreland-propagating thin-skinned thrusting in the SW, NE-facing backfolding and backthrusting occurred in the hinterland, with the final exhumation of the HP rocks. Model B follows recent suggestions that a nascent SW-dipping subduction zone, dipping beneath the continental margin, existed between 130 and 95 Ma, prior to formation and emplacement of the ophiolite. A major NE-facing fold-nappe structure in the pre-Permian basement rocks of Saih Hatat is interpreted as reflecting subduction beneath the margin. Two high-pressure metamorphic events have been suggested, the first predating ophiolite emplacement, the second caused by ophiolite loading. This model is untenable, being based on a misinterpretation of the NE-facing structures in northern Saih Hatat, and on some dubious older 40 Ar/ 39 Ar cooling ages from the eclogite-facies rocks of As Sifah. We conclude that all structures in northern Oman and all the reliable geochronology point to a single emplacement-obduction event lasting from Cenomanian-Turonian time ( c. 95 Ma) when amphibolites were accreted along the metamorphic sole of the ophiolite, to Campanian time, when the continental margin was subducted to the NE producing blueschists and eclogites, to the final thin-skinned emplacement of all thrust sheets, which ended before the Late Maastrichtian, at c. 68 Ma.

Proterozoic tectonic accretion and growth of western Laurentia: results from Lithoprobe studies in northern Alberta

The western Canadian Shield of northern Alberta is composed of a series of continental slivers that were accreted to the margin of the Archean Rae hinterland ca. 1.9–2.0 Ga., preserving a unique record of continental evolution for the interval 2.1–2.3 Ga. This part of Laurentia owes its preservation to the accretionary style of tectonic assembly south of the Great Slave Lake shear zone, which contrasts with indentation–escape processes that dominate the Paleoproterozoic record farther north. The Buffalo Head and Chinchaga domains form the central core of this region, comprising a collage of ca. 2325–2045 Ma crustal elements formed on an Archean microcontinental edifice, and similar age crust is preserved as basement to the Taltson magmatic zone. The distribution of magmatic ages and inferred collision and subduction zone polarity are used to indicate closure of intervening oceanic basins that led to magmatism and emplacement of continental margin arc and collisional belts that formed from ca. 1998 to1900 Ma. Lithoprobe crustal seismic profiles complement the existing geochronologic and geologic databases for northern Alberta and elucidate the nature of late stages of the accretionary process. Crustal-scale imbrication occurred along shallow eastward-dipping shear zones, resulting in stacking of arc slivers that flanked the western Buffalo Head terrane. The seismic data suggest that strain is concentrated along the margins of these crustal slivers, with sparse evidence for internal penetrative deformation during assembly. Post-collisional mafic magmatism consisted of widespread intrusive sheets, spectacularly imaged as regionally continuous subhorizontal reflections, which are estimated to extend over a region of ca. 120 000 km2. The form of such mid-crustal magmatism, as subhorizontal sheets (versus vertical dykes), is interpreted to represent a style of magma emplacement within a confined block, for which a tectonic free face is unavailable.

Anti-Atlas (Morocco) role in Neoproterozoic Western Gondwana reconstruction

Reconstruction of latest Neoproterozoic Gondwana hinges on the interpretation of the subduction and collision kinematics of Pan-African orogenic belts that rim the West African craton. The Anti-Atlas suture zone of southern Morocco has presented an enigma in this reconstruction as the inferred subduction zone polarity and age of suturing appear to be incongruous with better known West African orogens to the west (Mauretanian, Bassaride and Rokelide) and Transaharan orogens to the east (Ougarta, Tuareg, Gourma and Dahomeyan). Contrary to previous interpretations, new data from the Anti-Atlas indicate a history of late Neoproterozoic (∼750–600) north-dipping subduction culminating in the (∼600 Ma) collision of the Saghro magmatic arc to the north with the north-facing rifted margin of the West African craton. Thus, the Anti–Atlas suture links a ∼6000-km long chain of Pan-African suture zones that essentially encircle the West African craton. The suture zones demarcate the former position of subduction zones that in all cases dipped away from the West African craton. The Anti-Atlas suture links the western and eastern segments of the Pan-African orogenic belts associated with the amalgamation of Western Gondwana.