Uncertainties in the stability field of UHP hydrous phases (10-A phase and phase E) and deep-slab dehydration: potential implications for fluid migration and water fluxes at subduction zones

2020 ◽  
Author(s):  
Nestor G. Cerpa ◽  
José Alberto Padrón-Navarta ◽  
Diane Arcay
Keyword(s):  
Lithospheric Mantle ◽  
Subduction Zones ◽  
Mantle Wedge ◽  
Numerical Models ◽  
Stability Field ◽  
Fluid Migration ◽  
Water Fluxes ◽  
Water Release ◽  
The Stability ◽  
Back Arc

<p>The subduction of water via lithospheric-mantle hydrous phases have major implications for the generation of arc and back-arc volcanism, as well as for the global water cycle. Most of the current numerical models use Perple_X [Connolly et al., 2009] to quantify water release from the slab and subsequent fluid migration in the mantle wedge. At UHP conditions, the phase diagrams generated with this thermodynamic code suggest that the breakdown of serpentine and chlorite leads to the near complete dehydration of the lithospheric mantle before reaching a 200-km depth. Laboratory experiments, however, have observed the stability of the 10-Å phase and the phase E in natural bulk compositions, which may hold moderate amounts of water, beyond the stability field of serpentine and chlorite [Fumagalli and Poli, 2005; Maurice et al., 2018]. Here, using 2D thermo-mechanical models, we explore to what extent the presence of these hydrous phases may favor a deeper subduction of water than those predicted by Perple_X.</p><p>We perform end-member models in terms of slab temperature and thickness of hydrated lithospheric mantle entering at trench. The computed geotherms within the uppermost subducted mantle show that the stability field of mantle hydrous phases around 600-800°C and 6-8 GPa is crucial for predictions of water fluxes. We point out that the lack of systematic experiments at these P-T conditions, as well as the absence of 10-Å and E phases in current thermodynamic databases, prevent accurate estimates of deep water transfers. We nonetheless build a phase diagram based on current experimental constraints that includes approximations of their stability field and qualitatively discuss the potential implications for fluid migration in the back-arc mantle wedge and water fluxes.</p>

Experimental constraints on the partial melting of sediment-metasomatized lithospheric mantle in subduction zones

2020 ◽  
Vol 105 (8) ◽  
pp. 1191-1203
Author(s):  
Yanfei Zhang ◽  
Xuran Liang ◽  
Chao Wang ◽  
Zhenmin Jin ◽  
Lüyun Zhu ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Lithospheric Mantle ◽  
Subduction Zones ◽  
Mantle Wedge ◽  
The Other ◽  
Central American ◽  
Bulk Sediment ◽  
Series Of Experiments ◽  
The Stability ◽  
Subducting Slab

Abstract Sedimentary diapirs can be relaminated to the base of the lithosphere during slab subduction, where they can interact with the ambient lithospheric mantle to form variably metasomatized zones. Here, high-pressure experiments in sediment-harzburgite systems were conducted at 1.5–2.5 GPa and 800–1300 °C to investigate the interaction between relaminated sediment diapirs and lithospheric mantle. Two end-member processes of mixed experiments and layered (reaction) experiments were explored. In the first end-member, sediment and harzburgite powders were mixed to a homogeneous proportion (1:3), whereas in the second, the two powders were juxtaposed as separate layers. In the first series of experiments, the run products were mainly composed of olivine + orthopyroxene + clinopyroxene + phlogopite in subsolidus experiments, while the phase assemblages were then replaced by olivine + orthopyroxene + melt (or trace phlogopite) in supersolidus experiments. Basaltic and foiditic melts were observed in all supersolidus mixed experiments (~44–52 wt% SiO2 at 1.5 GPa, ~35–43 wt% SiO2 at 2.5 GPa). In the phlogopite-rich experiment (PC431, 1.5 GPa and 1100 °C), the formed melts had low alkali contents (~<2 wt%) and K2O/Na2O ratios (~0.4–1.1). In contrast, the quenched melt in phlogopite-free/poor experiments showed relatively higher alkali contents (~4–8 wt%) and K2O/Na2O ratios (~2–5). Therefore, the stability of phlogopite could control the bulk K2O and K2O/Na2O ratios of magmas derived from the sediment-metasomatized lithospheric mantle. In layered experiments, a reaction zone dominated by clinopyroxene + amphibole (or orthopyroxene) was formed because of the reaction between harzburgite and bottom sediment-derived melts (~62.5–67 wt% SiO2). The total alkali contents and K2O/Na2O ratios of the formed melts were about 6–8 wt% and 1.5–3, respectively. Experimentally formed melts from both mixed and reaction experiments were rich in large ion lithosphile elements and displayed similar patterns with natural potassium-rich arc lavas from oceanic subduction zones (i.e., Mexican, Sunda, Central American, and Aleutian). The experimental results demonstrated that bulk sediment diapirs, in addition to sediment melt, may be another possible mechanism to transfer material from a subducting slab to an upper mantle wedge or lithospheric mantle. On the other hand, the breakdown of phlogopite may play an important role in the mantle source that produces potassium-rich arc lavas in subduction zones.

scholarly journals Ophiolitic Pyroxenites Record Boninite Percolation in Subduction Zone Mantle

Minerals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 565 ◽  
Author(s):  
Véronique Le Roux ◽  
Yan Liang
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Mantle Wedge ◽  
Major Element ◽  
Early Stage ◽  
Diffusion Modeling ◽  
Melt Infiltration ◽  
Melt Percolation ◽  
Back Arc ◽  
Parental Melts

The peridotite section of supra-subduction zone ophiolites is often crosscut by pyroxenite veins, reflecting the variety of melts that percolate through the mantle wedge, react, and eventually crystallize in the shallow lithospheric mantle. Understanding the nature of parental melts and the timing of formation of these pyroxenites provides unique constraints on melt infiltration processes that may occur in active subduction zones. This study deciphers the processes of orthopyroxenite and clinopyroxenite formation in the Josephine ophiolite (USA), using new trace and major element analyses of pyroxenite minerals, closure temperatures, elemental profiles, diffusion modeling, and equilibrium melt calculations. We show that multiple melt percolation events are required to explain the variable chemistry of peridotite-hosted pyroxenite veins, consistent with previous observations in the xenolith record. We argue that the Josephine ophiolite evolved in conditions intermediate between back-arc and sub-arc. Clinopyroxenites formed at an early stage of ophiolite formation from percolation of high-Ca boninites. Several million years later, and shortly before exhumation, orthopyroxenites formed through remelting of the Josephine harzburgites through percolation of ultra-depleted low-Ca boninites. Thus, we support the hypothesis that multiple types of boninites can be created at different stages of arc formation and that ophiolitic pyroxenites uniquely record the timing of boninite percolation in subduction zone mantle.

scholarly journals The effect of solid solution on the stability of talc and 10-Å phase

2019 ◽  
Vol 174 (10) ◽  
Author(s):  
Harriet Howe ◽  
Alison R. Pawley
Keyword(s):  
Subduction Zones ◽  
Rheological Behaviour ◽  
Starting Material ◽  
Stability Field ◽  
Compositional Variation ◽  
Thermal Breakdown ◽  
Large Decrease ◽  
Dehydration Reactions ◽  
The Stability ◽  
Fe Substitution

Abstract Talc and 10-Å phase are hydrous phases that are implicated in fluid processes and rheological behaviour in subduction zones. Natural samples of talc show limited compositional variation away from the MgO–SiO2–H2O (MSH) endmember, with only substitution of Fe2+ for Mg occurring in significant amounts. In experiments at 2 GPa, talc containing 0.48 apfu Fe2+ begins to break down in the divariant field talc + anthophyllite + quartz at ~ 550 °C, a temperature ~ 270 °C lower than in the MSH system. At 4 GPa, Fe-bearing talc breaks down over a wide temperature interval in the divariant field talc + enstatite + coesite. The large decrease in temperature of the beginning of talc breakdown shows that Fe2+ is partitioned strongly into enstatite and anthophyllite with respect to talc. In phase reversal experiments at 6.5 GPa, the beginning of the dehydration of 10-Å phase containing 0.48 apfu Fe2+ was bracketed between 575 °C and 600 °C, a temperature ~ 100 °C lower than the MSH endmember reaction. The relative positions of the talc and 10-Å phase dehydration reactions indicate that the latter is able to accommodate greater Fe substitution, and is, therefore, more stable in Fe-bearing systems. In experiments at 6.2 GPa, 650 °C in the systems MgO–Al2O3–SiO2–H2O (MASH) and Na2O–MgO–Al2O3–SiO2–H2O (NMASH), 10-Å phase was synthesised that contains up to 0.5 apfu Al in the system MASH (compared to 0.8 in the starting material) and up to 0.4 apfu Al + 0.4 apfu Na in the system NMASH (compared to 0.7 of each of Al and Na in the starting material). Further experiments are required to determine if higher Al and Na contents in 10-Å phase are possible. The much higher Al and Na contents than found in talc indicate that, as with Fe, substitution of these elements enlarges the 10-Å phase stability field with respect to talc. In contrast to the effect of Fe, Al and Na also increase the stability of 10-Å phase relative to its thermal breakdown products enstatite + coesite.

Subduction dynamics and rheology control on forearc and backarc subsidence: Numerical models and observations from the Mediterranean  

2021 ◽  
Author(s):  
Attila Balazs ◽  
Claudio Faccenna ◽  
Taras Gerya ◽  
Kosuke Ueda ◽  
Francesca Funiciello
Keyword(s):  
Subduction Zones ◽  
Numerical Models ◽  
Accretionary Wedge ◽  
Suction Force ◽  
Continental Subduction ◽  
Backarc Basins ◽  
The Mediterranean ◽  
Forearc Basins ◽  
Back Arc ◽  
Roll Back

<p>The dynamics of oceanic and continental subduction zones is linked to the rise and demise of forearc and backarc basins in the overriding plate. Subsidence and uplift rates of these distinct sedimentary basins are controlled by variations in plate convergence and subduction velocities and determined by lithospheric rheological structure and different lithospheric thicknesses.</p><p>In this study we conducted a series of high-resolution 2D numerical models applying the thermo-mechanical code 2DELVIS (Gerya and Yuen, 2007). The model, based on finite differences and marker-in-cell techniques, solves the mass, momentum, and energy conservation equations for incompressible media; assumes elasto-visco-plastic rheologies and involves erosion, sedimentation and hydration processes.</p><p>The models show the evolution of wedge-top basins lying on top of the accretionary wedge and retro-forearc basins in the continental overriding plate, separated by a forearc high. These forearc regions are affected by repeated compression and extension phases. Higher subsidence rates are recorded in the syncline structure of the retro-forearc basin when the slab dip angle is higher and the subduction interface is stronger and before the slab reaches the 660 km discontinuity. This implies the importance of the slab suction force as the main forcing factor creating up to 3-4 km negative dynamics topographic signals.</p><p>Extensional back-arc basins are either localized along inherited crustal or lithospheric weak zones at large distance from the forearc region or are initiated just above the hydrated mantle wedge. During trench retreat and slab roll-back the older volcanic arc area becomes part of the back-arc region. Back-arc subsidence is primarily governed by crustal and lithospheric thinning controlled by slab roll-back. Onset of continental subduction and soft collision is linked to the rapid uplift of the forearc basins; however, the back-arc region records ongoing extension. Finally, during hard collision the forarc and back-arc basins are ultimately under compression.</p><p>Our results are compared with the evolution of the Mediterranean and based on the reconstructed plate kinematics, subsidence and heat flow evolution we classify the Western and Eastern Alboran, Paola and Tyrrhenian, Transylvanian and Pannonian Basins to be genetically similar forearc–backarc basins, respectively.</p>

scholarly journals Petrology of the ultra-high pressure metamorphic Kimi complex in Rhodope (NE Greece). A new insight into the Alpine geodynamic evolution of Rhodope

2002 ◽  
Vol 34 (6) ◽  
pp. 2169 ◽  
Author(s):  
E. MPOSKOS
Keyword(s):  
Continental Crust ◽  
Mantle Wedge ◽  
Spinel Peridotite ◽  
Stability Field ◽  
Slow Cooling ◽  
Garnet Porphyroblasts ◽  
Second Stage ◽  
Third Stage ◽  
Three Stages ◽  
The Stability

Structural, penological and geochronological work has revealed that the Rhodope metamorphic province is a synmetamorphic nappe-system of Alpine age. The Kimi complex representing the uppermost entity underwent UHP metamorphism in Lower Cretaceous (>119 Ma). Diamond inclusions in garnet porphyroblasts, exsolutions of quartz rods and rutile needles in garnet from Grt-Ky-Bt-gneisses constrain pressures >4 GPa (probably -7 GPa) and temperatures > 1000 °C, indicating subduction of continental crust into the asthenospheric mantle. The garnet-spinel peridotite of the Kimi area represents a segment of upwelling asthenosphere reequilibrated into the lithospheric mantle wedge at -2.5 GPa and 1235 °C. The spinel-garnet clinopyroxenites, associated with the peridotite, represent HP mantle cumulates crystallized from a melt at similar P-T conditions (i.e. P-2.4 GPa, T~1200°C). Decompression and cooling took place in the mantle wedge within the Cr-Spinel peridotite field up to -1.8 GPa and 900 °C. Subsequent isobaric cooling crossed the stability field of garnet peridotite. At this stage, the peridotite was tectonically emplaced into the educted underlying continental crust. Three stages of exhumation of the crustal assemblage occurred in the Kimi Complex. The first stage, from the maximum depth of -200- 220 Km to -60 Km (P-1.6 GPa, T-800 °C), is characterized by slow cooling rates, indicating rapid exhumation. The second stage, from -60 Km to -38 Km (P-1.05 GPa, T~640°C), is indicated by cooling at slow rates and is characterized by hydration and annealing reequilibration/recrystallization processes. The third stage of exhumation started between 73 and 65 Ma and is characterized by rapid uplift, continuous influx of water, intrusion of muscovite pegmatites at -20 Km depth, and finally by rapid cooling at shallow levels. The Kimi Complex reached the surface before 48-42 Ma.

The rheology of talc at high P-T conditions with implications for subduction-zone dynamics

2020 ◽  
Author(s):  
Yuval Boneh ◽  
Matej Pec ◽  
Greg Hirth
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Mantle Wedge ◽  
Microstructural Analysis ◽  
Stability Field ◽  
Localized Deformation ◽  
Hydrous Minerals ◽  
Regional Seismicity ◽  
Pressure Threshold ◽  
Confining Pressures

<p>Subduction-zone dynamics, kinematics, and seismicity are strongly affected by the rheology of hydrous phyllosilicates. Although there is growing evidence for hydrous minerals in the subducting plate, mantle wedge, and the interface between the plates, we are continuing to learn more about the rheological behavior of phyllosilicates at the relevant pressures. Talc is stable to depths of ≈100 km and has been found in fault rocks and subduction-zones mélanges as the product of metasomatism and/or mineral breakdown (e.g., breakdown of antigorite). The frictional strength of talc under low to intermediate pressures (up to ~400 MPa) was studied and demonstrated some of the mineral’s unique rheology; however, there is a lack of data for pressures of P > 0.5 GPa. Here we present the first rheological and microstructural analysis of experimentally deformed talc under pressure and temperature conditions relevant for the rheology of a subducted slab or mantle wedge.</p><p>We analyzed the mechanical and microstructural evolution of 15 samples of natural talc cylinders deformed using a high P-T deformation ‘Griggs’ type apparatus. We used natural samples comprise of >98 % talc and analyzed the post-mortem microstructure and chemistry of the samples using optical microscopy, scanning electron microscopy, and electron microprobe. The experiments were performed at confining pressures from 0.5 to 2 GPa and temperatures of 25 to 700°C; all within the talc stability field. Results show that the strength of talc at 25°C or 400°C is pressure-dependent up to the highest pressure tested (2 GPa). This behavior is attributed to brittle/semi-brittle mechanisms. At higher temperatures (500-700° C) and above a pressure threshold the strength becomes independent of pressure (e.g., when P > 1 GPa at T = 600 ° C), indicating that dilatant cracking is suppressed at these pressures. However, microstructural analysis indicates that fracturing is evident in all samples at all conditions examined. Interestingly, samples deformed at higher temperatures (>600°C) show more localized deformation. A synthesis of results from this study and previously published studies demonstrate that the strength of talc only becomes temperature-dependent at higher pressures. It is suggested that an increasing P-T geotherm of a subducted slab is likely to induce weakening and localization of talc-rich layers with possible implications for the mechanism to induce/hinder regional seismicity and affect the plate-coupling between the subducted and riding plates.   </p>

Lithospheric mantle, asthenosphere, slab and crustal contribution to petrogenesis of Eocene to Miocene volcanic rocks from the west Alborz Magmatic Assemblage, SE Ahar, Iran

2020 ◽  
pp. 1-32
Author(s):  
Ahmad Ahmadvand ◽  
Mohammad Reza Ghorbani ◽  
Mir Ali Asghar Mokhtari ◽  
Yi Chen ◽  
William Amidon ◽  
...  
Keyword(s):  
Lithospheric Mantle ◽  
Mantle Wedge ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
The West ◽  
Nw Iran ◽  
Enriched Mantle ◽  
Basement Rocks ◽  
Cenozoic Volcanism ◽  
Back Arc

Abstract Significant uncertainty remains regarding the exact timing and nature of subduction events during the closure of the Tethyan seas in what is now NW Iran. This study thus presents new geochemical compositions and U–Pb ages for a suite of volcanic rocks emplaced during Cenozoic volcanism in the west Alborz Magmatic Assemblage, which is commonly regarded as the back-arc of the Neotethyan magmatism in Central Iran. The subalkali basalts and andesites are dated to 57 ± 1.2 Ma, and are likely derived from a supra-subduction mantle wedge. Later, trachytic A-type rocks erupted from ~42 to 25 Ma during an anorogenic (extensional) stage triggered by slab retreat and associated asthenospheric mantle influx. A-type melts were at least partly concurrent with lithospheric mantle magmatism implied by eruption of subalkali basalts–andesites around 26–24 Ma. Next, Amp-Bt trachybasaltic volcanism with high-Nb basaltic affinity at ~19 Ma likely records slab deepening and slab partial melting, which reacted with the mantle wedge to produce the source material for the high-Nb basalts. Sr–Nd isotopic ratios for SE Ahar mafic as well as A-type rocks imply rather enriched mantle source(s). Some crustal contamination is implied by the presence of inherited zircons dominated by those derived from Neoproterozoic–Cambrian basement rocks and Carboniferous magmatism. Rhyolitic rocks with adakitic affinity probably mark the final volcanism in the study area. The adakitic rocks show crustal signatures such as high K and Th, probably formed as a consequence of higher temperature gradients, at crustal levels, imposed by both slab and mantle partial melts.

Origin of Recent alkaline lavas by lithospheric thinning beneath the northern Canadian Cordillera

2005 ◽  
Vol 42 (6) ◽  
pp. 1073-1095 ◽  
Author(s):  
Anne-Claude Abraham ◽  
Don Francis ◽  
Mireille Polvé
Keyword(s):  
Lithospheric Mantle ◽  
Mantle Peridotite ◽  
Incompatible Trace Element ◽  
Isotopic Signature ◽  
Primitive Mantle ◽  
Stability Field ◽  
Canadian Cordillera ◽  
Nd Isotopes ◽  
Ocean Ridges ◽  
The Stability

Recent alkaline lavas that have erupted across the disparate terranes of the northern Canadian Cordillera provide natural probes with which to interrogate the underlying lithosphere. The lavas range between two compositional end members, olivine nephelinite (NEPH) and hypersthene-normative olivine (Hy-NORM) basalt. The chemical signature of amphibole in the incompatible element enriched NEPH end member indicates that it is derived in the lithospheric mantle. The Hy-NORM end member is characterized by lower incompatible trace element contents but is still relatively enriched relative to primitive mantle. Although the Hy-NORM end member is always more radiogenic in Pb and Sr isotopes and less radiogenic in Nd isotopes than the NEPH end member, its isotopic signature varies with tectonic belt. In particular, Hy-NORM basalts in the Omineca Belt are strikingly more radiogenic in Sr and Pb isotopes and less radiogenic in Nd isotopes than otherwise equivalent Hy-NORM basalts in the adjacent Intermontane Belt, indicating the existence of a major lithospheric boundary between the two belts. Cordilleran and other continental Hy-NORM basalts have distinctly low Ca and high Na contents compared with their equivalents in oceanic hot spots or at mid-ocean ridges. A comparison with experimental melts of mantle peridotite indicates that these characteristics reflect smaller degrees of partial melting (<10%) in the stability field of garnet in the lower lithospheric mantle beneath the northern Cordillera. Contrary to the conclusion commonly drawn from experimental results, the Cordilleran NEPH lavas may be derived from similar or shallower depths than coeval Hy-NORM basalts.

scholarly journals Role of warm subduction in the seismological properties of the forearc mantle: An example from southwest Japan

2021 ◽  
Vol 7 (28) ◽  
pp. eabf8934
Author(s):  
Changyeol Lee ◽  
YoungHee Kim
Keyword(s):  
Subduction Zones ◽  
Mantle Wedge ◽  
Numerical Models ◽  
Thermal Structure ◽  
Free Fluid ◽  
Southwest Japan ◽  
Seismic Properties ◽  
Delay Times ◽  
Forearc Mantle ◽  
Nonvolcanic Tremors

A warm slab thermal structure plays an important role in controlling seismic properties of the slab and mantle wedge. Among warm subduction zones, most notably in southwest Japan, the spatial distribution of large S-wave delay times and deep nonvolcanic tremors in the forearc mantle indicate the presence of a serpentinite layer along the slab interface. However, the conditions under which such a layer is generated remains unclear. Using numerical models, we here show that a serpentinite layer begins to develop by the slab-derived fluids below the deeper end of the slab-mantle decoupling interface and grows toward the corner of the mantle wedge along the interface under warm subduction conditions only, explaining the large S-wave delay times in the forearc mantle. The serpentinite layer then allows continuous free-fluid flow toward the corner of the mantle wedge, presenting possible mechanisms for the deep nonvolcanic tremors in the forearc mantle.

Sign in / Sign up

Export Citation Format

Share Document