Diapiric Upwelling Research Articles

Formation of the Naxos nested domes and crustal differentiation by convection and diapirism

The Naxos dome, in the middle of the Aegean domain, exposes the former root of the Alpine orogenic belt and represents a key natural example to investigate the development of gravitational instabilities during orogenic evolution and their impact on crustal differentiation. The Naxos dome is cored by migmatites with structures depicting second order domes with a diameter of 1–2 km nested in the first order deca-kilometer scale dome that formed at the onset of orogenic collapse. Zircon grains from the migmatites record a succession of crystallization-dissolution cycles with a period of 1–2 Myr. These features have been attributed to the development of convective and diapiric gravitational instabilities, related to thermally induced and compositional buoyancy. In this paper, we test the pertinence of this model with a thermal-mechanical numerical experiment performed with a volume of fluid method (VOF) known to preserve material phase interfaces during large deformation of viscous layers. Partial melting of the crust is modeled by strain-rate and temperature dependent viscosity and temperature dependent density. Moreover, horizontal layers with density, viscosity and heat production variations mimic more felsic or more mafic lithologies in a crust of intermediate composition. With basal heating, gravitational instabilities initiate with local segregation of the buoyant versus heavier layers, followed by diapiric upwelling of buoyant pockets of aggregated less dense material. Convection starts after 5 Myr, approximately when half of the crust has a viscosity lower than 1019 Pa s. The size of the convection cells increases as the temperature rises in the crust and reaches ∼25 km in diameter after ca. 20 Myr, which defines the size of first order domes. Some of the heterogeneous material is entrained in the convection cells with a revolution period of 1 to 3 Myr. However, most of the denser material accumulates in the lower crust, while the buoyant material segregates at the top of the convection cells and forms diapirs that correspond to second order domes, of several kilometers in diameter and nested within the first order domes. This model, which reproduces the first order characteristic dimensions of the Naxos nested domes and the periodicity of their zircon geochronological record, demonstrates the efficiency of gravitational instabilities in the formation of migmatite domes and, more generally, in the multi-scale dynamics of crustal differentiation leading to a felsic upper crust, an intermediate middle crust and a mafic lower crust.

Role of crustal fluids and thermo-mechanical structure for lower crustal seismicity: The Gargano Promontory (southern Italy)

Several regions around the globe are characterized by a seismically active lower crust, at depths where lithological and thermal conditions suggest stress release by ductile flow. The Gargano Promontory (GP, southern Italy) is an example where a recently installed seismic network has recorded an intense seismic activity at depths between 20 and 30 km, i.e. in the lower crust. The GP is located in proximity of the Gargano-Dubrovnik lineament, a seismogenic zone separating the central and southern Adriatic basins. These two basins constitute sites of sediments accumulation since Tertiary times. Another important basin in the region is represented by the Apennine foredeep, that includes the Candelaro area. We analyze the possible mechanisms controlling the distribution of seismicity in the GP to identify the factors that make the lower crust seismically active. To this aim, we construct a thermo-rheological model of a layered continental crust, calibrated on the basis of geometrical, lithological and thermal constraints. The model takes into account various crustal lithologies, the presence of fluids in the crystalline basement, lateral variations of geotherm and stress field. The numerical simulations show that the presence of fluids is a key factor controlling the cluster of seismicity in the lower crust. Moreover, the presence of water in the upper crystalline basement and sedimentary cover provides a plausible explanation for upper crustal seismicity in a zone of very high heat flow SW of the GP. The distribution of the seismicity is probably affected by the composition of the crystalline basement, with mafic bodies injected into the crust during the Paleocene magmatic phase that affected the Mediterranean region. In addition, fluid accumulation and overpressure may occur along detachment levels in the lower crust, leading to clustering of the earthquakes. Based on our findings, we hypothesize that the presence of hydrous diapiric upwelling(s) in the upper mantle can feed a deep fluid circulation system, inducing lower crustal seismicity. • A thermo-rheological model to explain lower crustal seismicity in the Gargano Promontory (Italy) is presented. • Fluid presence controls the Gargano seismic activity in the lower crust. • The Gargano crust is injected by mafic bodies at various depths.

Structural Architecture and Attenuation of the Ductile Lower Plate of the Ruby Mountain‐East Humboldt Range Metamorphic Core Complex, Northeast Nevada

AbstractStrongly deformed footwall rocks exposed in metamorphic core complexes (MCC) of the North American Cordillera were exhumed via ductile attenuation, mylonitic shearing, and detachment faulting. Whether these structures accommodated diapiric upwelling or regional extension via low‐angle normal faulting is debated. The Ruby Mountains‐East Humboldt Range MCC, northeast Nevada, records top‐west normal‐sense exhumation of deformed Proterozoic‐Paleozoic stratigraphy and older basement. We conducted 1:24,000‐scale mapping of the southwestern East Humboldt Range, with integrated structural, geochemical, and geochronological analyses to characterize the geometry and kinematics of extension and exhumation of the mylonitized footwall. Bedrock stratigraphy is pervasively intruded by Cretaceous, Eocene, and Oligocene intrusions, but observations of a coherent stratigraphic section show >80% vertical attenuation of Neoproterozoic to Ordovician rocks. These rocks are penetratively sheared with top‐west kinematics. The shear zone thus experienced combined pure‐ and simple‐shear (i.e., general shear) strain. We argue that this shear zone was syn‐/post‐kinematic with respect to Oligocene plutonism because: (a) mylonitic shearing spatially corresponds with preceding Oligocene intrusions; (b) thermochronology reveals that the shear zone experienced substantial cooling and exhumation after Oligocene plutonism; and (c) the mylonites are crosscut by undated, but likely late Oligocene, leucogranite. We propose that Eocene mantle‐derived magmatism and thermal incubation led to Oligocene diapiric upwelling of the middle crust, with ductile stretching focused on the flanks of this upwarp. Regional Basin and Range extension initiated later in the middle Miocene. Therefore, the development of the East Humboldt Range shear zone was not driven by regional extension and coupled detachment faulting.

Geomorphologic exploration targets at the Zhurong landing site in the southern Utopia Planitia of Mars

On May 15, 2021, Tianwen-1's rover Zhurong landed successfully at 109.926°E, 25.066°N, in southern Utopia Planitia on Mars. The Zhurong landing site contains a wide range of geomorphic exploration targets including troughs, raised ridges, pitted cones, mesas, sand dunes and crater ejecta. Aspects of all of these features suggest formation through interactions between volatiles, sediments, and magma. Pitted cones are invaluable windows into the subsurface and intriguing astrobiology targets for Martian life considering that they potentially formed from diapiric upwelling of fine-grained sediments (i.e. mud volcanism), a process that on Earth is often associated with methane release. The ground-penetrating radar onboard Zhurong will provide fundamentally new perspectives on the presence, distribution, and abundance of subsurface water-ice, a strategic natural resource for future crewed Mars exploration.

Topography and geology of Uranian mid-sized icy satellites in comparison with Saturnian and Plutonian satellites.

Newly processed global imaging and topographic mapping of Uranus's five major satellites reveal differences and similarities to mid-sized satellites at Saturn and Pluto. Three modes of internal heat redistribution are recognized. The broad similarity of Miranda's three oval resurfacing zones to those mapped on Enceladus and (subtly) on Dione are likely due to antipodal diapiric upwelling. Conversely, break-up and foundering of crustal blocks accompanied by extensive (cryo)volcanism is the dominant mode on both Charon and Ariel. Titania's fault network finds parallels on Rhea, Dione, Tethys and possibly Oberon. Differences in the geologic style of resurfacing in the satellite systems (e.g. plains on Charon, Dione, Tethys and perhaps Titania versus ridges on Miranda and Ariel) may be driven by differences in ice composition. Surface processes such as volatile transport may also be indicated by bright and dark materials on Oberon, Umbriel and Charon. The more complete and higher quality observations of the Saturnian and Plutonian mid-sized icy satellites by Cassini and New Horizons reveal a wealth of features and phenomena that cannot be perceived in the more limited Voyager coverage of the Uranian satellites, harbingers of many discoveries awaiting us on a return to Uranus. This article is part of a discussion meeting issue 'Future exploration of ice giant systems'.

A Neoarchean K-rich granitoid belt in the northern North China Craton

The Archean metamorphic basement in the southeastern part of Eastern Hebei to Western Liaoning provinces, northern North China Craton, is dominated by Neoarchean K-rich granitoids, with a small amount of Neoarchean supracrustal rocks and Na-rich dioritic-tonalitic-trondhjemitic-granodioritic gneisses, and minor Paleo- to Mesoarchean rocks. The Paleo- to Mesoarchean lithological signatures include TTG gneisses and supracrustal rocks at the Caozhuang and Caochang areas. The Neoarchean K-rich granitoids form a ca. 350 km long belt extending in a NE direction, and primarily consist of porphyritic monzodioritic-quartz monzodioritic-granodioritic-monzogranitic (MQGM) gneisses and secondary monzogranite-syenogranites and charnockites, with minor Neoarchean TTG gneiss enclaves. Based on their major mafic mineral phases, the MQGM gneisses can be divided into an amphibole-dominated group and a biotite-dominated group. Zircon U-Pb isotopic dating reveals that the Caozhuang trondhjemitic gneisses, amphibole-dominated MQGM gneisses, and biotite-dominated MQGM gneisses were emplaced at ∼2.90 Ga, 2.55–2.53 Ga, and 2.55–2.53 Ga, respectively. The amphibole-dominated porphyritic MQGM gneisses are geochemically analogous to sanukitoids, and the sanukitoid magma was derived from the partial melting of lithospheric mantle metasomatized by dehydration fluids and melts from subducted slabs and related sediments, following the fractionation of amphibole and clinopyroxene during their magmatic evolution. The magmatic precursors of the biotite-dominated MQGM gneisses were most likely generated by the partial melting of medium- to high-K mafic-intermediate rocks and locally generated by the partial melting of metagreywackes at medium pressures. Within the K-rich granitoid belt, the 2.55–2.53 Ga porphyritic MQGM gneisses experienced 2.53–2.51 Ga E-W extension and strike-slip shearing deformation in the Jinzhou-Xingcheng structural domain, and diapiric upwelling by the formation of dome structures in the Jielingkou-Anziling-Suizhong structural domain. All these structures then suffered a top-to-the-SE-NEE thrusting in the northern margin during 2.51–2.50 Ga. The 2.53–2.51 Ga dioritic-tonalitic-trondhjemitic-granodioritic gneisses and charnockites in the Taipingzhai-Santunying-Zunhua structural domain firstly underwent diapiric upwelling during 2.51–2.50 Ga, then together with the 2.52–2.50 Ga volcanic-sedimentary rocks in the Shuangshanzi-Qian’an-Lulong structural domain overprinted by nearly N-S-striking dextral strike-slip shearing deformation during 2.50–1.80 Ga. The temporal-spatial relationships, petrogenesis, and structural patterns of these various Neoarchean lithological assemblages confirm that the Neoarchean K-rich granitoid belt in the northern North China Craton was most likely developed in an active continental margin setting, and our studies suggest this involved progressively southeastward multi-stage retreating oceanic slab subduction and collisions between an oceanic arc and an ancient continental nucleus.

Granitic gneiss domes from the Paleoproterozoic orogen in eastern Liaoning: The typical structural styles in hot orogen

中下地壳的底辟上升是地壳中物质运移和热传递的一种重要机制，由这种机制产生的一系列穹窿构造不仅为揭示区域构造环境和构造演化提供了重要的线索，而且还提供了一个了解地壳深部物质流动的窗口。辽东半岛的古元古代造山带内就发育有这样一套花岗片麻岩穹窿构造，为了深入理解这套花岗片麻岩穹窿的成因以及对造山带演化的影响，本文对其不同构造层次进行了详细的构造特点和变形演化研究。结果显示，典型的花岗片麻岩穹窿可分为三层结构：混合岩化的花岗岩内核、发育顺层韧性剪切带的幔部以及含大型构造透镜体的外壳。其中核部花岗岩塑性流动变形发育，并具有明显的交代现象。顺层韧性剪切带的变形环境由靠近岩体的角闪岩相到远离岩体的低绿片岩相，并且没有明显的退化变质特点，拉伸线理具有统一的NW-SE方向。根据年代学数据与区域构造分析，花岗片麻岩穹窿构造是在区域收缩体制下花岗岩底辟形成的产物，其出现标志着辽东古元古代造山带变为一个由垂向和横向对流作用为主导的热造山带。;Diapiric upwelling of the middle and lower crust is an important mechanism of mass transportation and thermal transmission in the crust. Gneissic domes produced by this mechanism provide not only important clues for revealing regional tectonic environment and tectonic evolution, but also a window to understand the mass flow in the deep crust. There are such a set of dome-like magmatic domes in the Paleoproterozoic orogen of Liaodong Peninsula. In order to deeply understand the origin of the granite-gneiss domes and their influence on the evolution of the orogenic belt, this paper has conducted detailed studies on structural characteristics and deformation evolution of its different tectonic levels. The results show that typical granitic gneiss domes are composed of three parts:the core of gneissic granites, the mantle of metamorphic rocks and the crust of sliding blocks. The cores are characterized by plastic flow deformation and obvious metasomatism phenomenon. The mantle of metamorphic rocks was sheared at amphibolite facies near the granite to the distal low-greenschist facies. Stretching lineations are uniformly oriented at NW-SE orientation. According to geochronology data and regional structural analyses, the granite-gneiss domes were formed by migmatitic granite diapirism under the influence of regional contraction. The occurrence of granite-gneiss domes implies that the Paleoproterozoic orogenic belt in Liaodong Peninsula was a hot orogen dominated by vertical and horizontal convection.

Crustal-scale convection and diapiric upwelling of a partially molten orogenic root (Naxos dome, Greece)

The goal of this paper is to use the structural, metamorphic and geochronological record from the migmatitic core of the Naxos dome (Greece) and its associated subdomes to address the internal dynamics of a partially molten orogenic root. U-Pb ages from ca. 24 to 16 Ma and textures of zircon in the migmatites suggest successive dissolution and precipitation cycles with a period of 1 to 2 Ma, interpreted as the timescale of convective instabilities in a ca. 20 km thick partially molten layer. Dimensional analysis indicates that convection of this root requires a viscosity lower than 1018 Pa·s, consistent with viscosity values expected for partially molten felsic rocks. Structural analysis and U-Pb geochronology of deformed granitic dikes rooting in the migmatites record the subsequent development of the Naxos dome by diapirism from ca. 16 to 13 Ma. The size of the first order migmatite dome on Naxos (5 × 12 km) requires that the unstable layer at the onset of diapirism was 5 to 10 km thick and presented a moderate viscosity contrast with its envelope. From this analysis we propose that the Naxos migmatite dome documents a two stage dynamic evolution for the partially molten root of the Aegean belt characterized by (1) crustal scale convection for at least 8 Ma and (2) diapirism for about 3 Ma during progressive thinning of the collapsing orogenic crust.

Southeast Papuan crustal tectonics: Imaging extension and buoyancy of an active rift

AbstractSoutheast Papua hosts the world's youngest ultra‐high‐pressure (UHP) metamorphic rocks. These rocks are found in an extensional setting in metamorphic core complexes. Competing theories of extensional shear zones or diapiric upwelling have been suggested as driving their exhumation. To test these theories, we analyze the CDPAPUA temporary array of 31 land and 8 seafloor broadband seismographs. Seismicity shows that deformation is being actively accommodated on the core complex bounding faults, offset by transfer structures in a manner consistent with overall north‐south extension rather than radial deformation. Rayleigh wave dispersion curves are jointly inverted with receiver functions for crustal velocity structure. They show crustal thinning beneath the core complexes of 30–50% and very low shear velocities at all depths beneath the core complexes. On the rift flanks velocities resemble those of normal continents and increase steadily with depth. There is no evidence for velocity inversions that would indicate that a major density inversion exists to drive crustal diapirs. Also, low‐density melt seems minor within the crust. Together with the extension patterns apparent in seismicity, these data favor an extensional origin for the core complexes and limit the role of diapirism as a secondary exhumation mechanism, although deeper mantle diapirs may be undetected. A small number of intermediate‐depth earthquakes, up to 120 km deep, are identified for the first time just northeast of the D'Entrecasteaux Islands. They occur at depths similar to those recorded by UHP rocks and similar temperatures, indicating that the modern seismicity occurs at the setting that generates UHP metamorphism.

Experimental petrology of peridotites, including effects of water and carbon on melting in the Earth’s upper mantle

For over 50 years, the use of high-pressure piston/cylinder apparatus combined with an increasing diversity of microbeam analytical techniques has enabled the study of mantle peridotite compositions and of magmas derived by melting in the upper mantle. The experimental studies have been guided by the petrology and geochemistry of peridotites from diverse settings and by the remarkable range of mantle-derived magma types. Recent experimental study using FTIR spectroscopy to monitor water content of minerals has shown that fertile lherzolite (MORB-source upper mantle) at ~1,000 °C can store ~200 ppm H2O in defect sites in nominally anhydrous minerals (olivine, pyroxenes, garnet and spinel). Water in excess of 200 ppm stabilizes amphibole (pargasite) at P 3 GPa, water in excess of 200 ppm appears as an aqueous vapour phase and this depresses the temperature of the upper mantle solidus. Provided the uppermost mantle (lithosphere) has H2O 500 ppm H2O) overlying the ‘depleted’ MORB source (~200 ppm H2O). From the study of primitive MOR picrites, the modern mantle potential temperature for MORB petrogenesis is ~1,430 °C. The intersection of the 1,430 °C adiabat with the vapour-saturated lherzolite solidus at ~230 km suggests that upwelling beneath mid-ocean ridges begins around this depth. In intraplate volcanism, diapiric upwelling begins from shallower depths and lower temperatures within the asthenosphere and the upwelling lherzolite is enriched in water, carbonate and incompatible elements. Magmas including olivine melilitites, olivine nephelinites, basanites, alkali picrites and tholeiitic picrites are consequences of increasing melt fraction and decreasing pressure at melt segregation. Major element, trace element and isotopic characteristics of island chain or ‘hot-spot’ magmas show that they sample geochemically distinct components in the upper mantle, differing from MORB sources. There is no evidence for higher-temperature ‘hot-spot’ magmas, relative to primitive MORB, but there is evidence for higher water, CO2 and incompatible element contents. The distinctive geochemical signatures of ‘hot-spot’ magmas and their ‘fixed’ position and long-lived activity relative to plate movement are attributed to melt components derived from melting at interfaces between old, oxidised subducted slabs (suspended beneath or within the deeper asthenosphere) and ambient, reduced mantle. In convergent margin volcanism, the inverted temperature gradients inferred for the mantle wedge above the subducting lithosphere introduce further complexity which can be explored by overlaying the phase relations of appropriate mantle and crustal lithologies. Water and carbonate derived from the subducted slab play significant roles, magmas are relatively oxidised, and distinctive primary magmas such as boninites, adakites and island arc ankaramites provide evidence for fluxing of melting in refractory harzburgite to lherzolite by slab-derived hydrous adakitic melt and by wedge-derived carbonatite.

Progressive Interaction between Dry and Wet Mantle during High-temperature Diapiric Upwelling: Constraints from Cenozoic Kita-Matsuura Intraplate Basalt Province, Northwestern Kyushu, Japan

Intra-plate Cenozoic volcanism in Kita-Matsuura, northwestern Kyushu, Japan, shows systematic spatio-temporal changes in geochemistry that can be explained by partial melting followed by melt segregation in a region of upwelling mantle.We have examined the thermal and melting history of the upwelling mantle by quantitatively estimating melt water contents and melting conditions. The water content of a spectrum of primary melts is estimated to range from 0·5 to 1·5 wt % based on a combination of a plagioclaseliquid and olivine-saturated liquid geohygrometers and MELTS calculations. The estimated melt segregation temperature ranges from 1330 to 15008C, at pressures from 1·7 to 2·8 GPa under hydrous conditions. Melting temperature and pressure decreased with time, whereas the water content of the primary melts increased. Corresponding temporal decreases in high field strength element (HFSE) abundances and HFSE/large ion lithophile element (LILE) ratios require progressive melt extraction and aggregation from a melting mantle with a continuous and gradually increasing input of H2O-rich fluid or melt into the melting system. The estimated isotope composition of influxed fluid lies on a mixing line between the sediment and altered oceanic crust of the Philippine Sea Plate, with strong affinity to the sediment composition. Based on the temporal variation of the magmas and the melting model, we propose small-scale upwelling (c. 70 km in diameter) of a dry mantle peridotite that interacts progressively with the overlying wet mantle wedge. The wet mantle wedge was previously hydrated by fluids from sediments from the subducted Philippine Sea Plate, whereas the deep and dry mantle could have been derived from the mantle beneath the subducted Pacific Plate through a slab window.

Formation of elongated granite–migmatite domes as isostatic accommodation structures in collisional orogens

The mid-Carboniferous Pelhřimov core complex, Bohemian Massif, is a crustal-scale elongated granite–migmatite dome interpreted to have formed by gravity-driven diapiric upwelling of the metapelitic middle crust. The vertical diapiric flow is evidenced by outward-dipping foliation and lineation patterns, deformation coeval with the widespread presence of melt, rapid exhumation of the dome center from depths corresponding to pressure of about 0.6GPa to shallow levels (pressure less than 0.2GPa) within 2M.y., and kinematic indicators of downward return flow of the mantling rocks. As compared to common diapirs, however, the Pelhřimov complex exhibits a more complicated inferred strain pattern with two perpendicular, irregularly alternating directions of horizontal extension in what is interpreted as the diapir head. Comparison of structural data from migmatites with anisotropy of magnetic susceptibility (AMS) data in granites also reveals that only final increments of strain are recorded in the granites. The map dimensions and gravity image of the complex suggest that the diapiric upwelling affected a large portion of the orogen's interior between two microplates brought together during continental collision. The northwesterly microplate (the upper-crustal Teplá–Barrandian unit) collapsed vertically as an ‘elevator’ at around 346–337Ma whereas the easterly microplate (Brunia) was underthrust beneath the Moldanubian rocks during ∼346–330Ma (the indentor). It is suggested that these microplates then acted as cold and rigid margins localizing mid-crustal diapirism and associated voluminous S-type granite plutons inbetween, parallel to the edge of the Brunia indentor.We conclude that bringing together soft metapelitic middle crust with two rigid lithospheric blocks during collision resulted in significant lateral temperature and strength variations across the orogen's interior. A general conclusion from these inferences is that granite–migmatite domes delineating margins of collided microplates may form as crustal-scale structures accommodating late-orogenic isostatic reequilibration.

Computer modeling of granite gneiss diapirism in the Earth’s crust: Controlling factors, duration, and temperature regime

This paper is devoted to the modeling the granite gneiss formation by means of diapiric upwelling. The natural examples of granitic diapirism in the Precambrian granite-greenstone belts and complexes of metamorphic cores are described. A new approach is proposed to describe the partial melting and development of gravity instability in the crustal granitic layer, which experienced heat impact and melting during intrusion of basaltic melt. Rheology of partially melted material and surrounding medium is regarded to be temperature-dependent, following either plasticity or creep (non-Newtonian viscosity) law. Modeling results show that crustal rheology plays a significant role in the character of diapirism (shape of upwelling bodies, duration of the process, and width of thermal aureole). The rates of upwelling within the crust behaving as elastoplastic body are orders of magnitude higher (meters to tens meters per year) than those obtained for creep (viscous) liquid model (0.8 cm/yr). Modeling results revealed that the limiting depth of upwelling of partially crystallized melt, with allowance for temperature dependence of creep, corresponds to the isotherm of 400°C.

Neoproterozoic tectonic evolution of the Hongseong area, southwestern Gyeonggi Massif, South Korea; implication for the tectonic evolution of Northeast Asia

Two types of Neoproterozoic metabasites occur together with regionally intruded arc-related Neoproterozoic granitoids (ca. 850–830 Ma) in the Hongseong area, southwestern Gyeonggi Massif, South Korea, which is the extension of the Dabie–Sulu collision belt in China. The first type of metabasite (the Bibong and Baekdong metabasites) is a MORB-like back-arc basin basalt or gabbro formed at ca. 890–860 Ma. The Bibong and Baekdong metabasites may have formed during back-arc opening by diapiric upwelling of deep asthenospheric mantle which was metasomatized by large ion lithophile element (LILE) enriched melt or fluid derived from the subducted slab and/or subducted sediment beneath the arc axis. The second type of metabasite (the Gwangcheon metabasite) formed in a plume-related intra-continental rift setting at 763.5 ± 18.3 Ma and is geochemically similar to oceanic island basalt (OIB). These data indicate a transition in tectonic setting in the Hongseong area from arc to intra-continental rift between ca. 830 and 760 Ma. This transition is well correlated to the Neoproterozoic transition from arc to intra-continental rift tectonic setting at the margin of the Yangtze Craton and corresponds to the amalgamation and breakup of Rodinia Supercontinent.

Beta Regio, Venus: Evidence for uplift, rifting, and volcanism due to a mantle plume

Geophysical data have led to the interpretation that Beta Regio, a 2000 × 25000 km wide topographic rise with associated rifting and volcanism, formed due to the rise of a hot mantle diapir interpreted to be caused by a mantle plume. We have tested this hypothesis through detailed geologic mapping of the V-17 quadrangle, which includes a significant part of the Beta Regio rise, and reconnaissance mapping of the remaining parts of this region. Our analysis documents signatures of an early stage of uplift in the formation of the Agrona Linea fracture belts before the emplacement of regional plains and their deformation by wrinkle ridging. We see evidence that the Theia rift-associated volcanism occurred during the first part of post-regional-plains time and cannot exclude that it continued into later time. We also see evidence that Devana Chasma rifting was active during the first and the second parts of post-regional-plains time. These data are consistent with uplift, rifting and volcanism associated with a mantle diapir. Geophysical modeling shows that diapiric upwelling may continue at the present time. Together these data suggest that the duration of mantle diapir activity was as long as several hundred million years. The regional plains north of Beta rise and the area east and west of it were little affected by the Beta-forming plume, but the broader area (at least 4000 km across), whose center-northern part includes Beta Regio, could have experienced earlier uplift as morphologically recorded in formation of tessera transitional terrain.

Comment on “Stratigraphic architecture of sedimentary basin induced by mantle diapiric upwelling and eustatic event” by Yamada and Nakada [Tectonophysics 415 (2006) 103–121

Yamada and Nakada (2006) examined the stratigraphic architecture of sedimentary basin induced by mantle diapiric upwelling and eustatic event. They applied their model to the Karatsu–Sasebo coalfield in northwest Kyushu, southwest Japan. In the application, a neutral stress regime was assumed during subsidence and uplift of the coalfield. The Sazagawa Thrust at the Kita-Matsuura peninsula in the coalfield Fig. 1, however, suggests that NW Kyushu would have been al least twice under the compressive stress regime (Nagahama, 1970; Kurasawa, 1970), suggesting that the assumption of a monotonous neutral stress regime is not the case for the Karatsu–Sasebo coalfield. Therefore, their application for the Karatsu–Sasebo coalfield has to be revised. In the following this issue is discussed.

Reply to the comment on “Stratigraphic architecture of sedimentary basin induced by mantle diapiric upwelling and eustatic event” by H. Mashima

Reply to the comment on “Stratigraphic architecture of sedimentary basin induced by mantle diapiric upwelling and eustatic event” by H. Mashima

Stratigraphic architecture of sedimentary basin induced by mantle diapiric upwelling and eustatic event

The stratigraphic architecture of sedimentary basin provides important constraints on the rheological structure of the upper mantle and the crust, eustatic events and tectonic movements. In this study, we examined the convective coupling between the uppermost mantle and ductile lower crust as a formation mechanism of sedimentary basins. In this mechanism, the lower crust is squeezed by the upper mantle flow associated with mantle diapiric upwelling, resulting in the surface subsidence and formation of sedimentary basin. We investigated the stratigraphic architecture by taking into account the horizontal migration of the upwelling in time and spatial domains. The sedimentary basin is characterized by both the thickness and formation period for its gross feature and the sequence stratigraphy. The decay of the upwelling causes the surface uplift, and some parts of sediments deposited during the surface subsidence are consequently eroded. The subsidence area moves as the activity of upwelling horizontally migrates, resulting in the formation of unconformity for the uplifted and eroded area over the previous upwelling. We also incorporated the effects of third order eustasy, with amplitude of ∼100 m and period of ∼1 Myr, into convective coupling model. An application of our model to Karatsu-Sasebo coalfield in the Tertiary of the northwest Kyushu, Japan, indicates that the stratigraphic architecture of sedimentary basin including two effects, i.e. convective coupling and eustasy, may provide important information about the viscosity structure of the lower crust and uppermost mantle and spatio-temporal growth and decay histories of the mantle diapiric upwelling.

Indosinian deformation of the Songpan Garzê Fold Belt, northeast Tibetan Plateau

Deformation of the Songpan Garzê Fold Belt, southwest China, occurred progressively during the Indosinian orogeny (ca. 230–200 Ma). Two phases of south-directed deformation are identified: D 1, associated with pervasive thickening of the Songpan Garzi sedimentary pile and detachment of that portion of the fold belt onlapping the Yangtze passive margin; and D 2, a localized phase of deformation associated with transpressive shortening of the fold belt's southeast margin. An arcuate form-surface in the southeast fold belt reflects the distribution of D 1 and D 2 structural phases and the diachronous migration of these phases into the fold belt. This migration accommodated lateral growth and cumulative sinistral transpression within the fold belt's eastern margin. An enigmatic metamorphic complex, the so-called Danba antiform, is constrained to have formed during the early stages of the D 2 deformation. This was associated with diapiric upwelling of buoyant migmatised basement and domal distortion of the overlying metasedimentary pile.

Emplacement of Deep Upper-Mantle Rocks into Cratonic Lithosphere by Convection and Diapiric Upwelling

Rocks containing breakdown products of majoritic garnet, derived from the deep upper mantle, occur in kimberlite xenoliths and in orogenic peridotites from Otrøy in Norway. The Otrøy peridotites are banded harzburgites and dunites with similar compositions to mantle xenoliths from Precambrian cratons and Phanerozoic supra-subduction-zone peridotites. Pressure–temperature (P–T) paths deduced for the Otrøy peridotites and kimberlite xenoliths from South Africa are consistent with emplacement of deep mantle peridotites into cratonic lithosphere by asthenosphere diapirism. Numerical thermo-convection models provide insight into the possible P–T histories of deep upper-mantle rocks. In the models, material from the base of the convecting system is transported to depths of 60–100 km by convection and small (50–100 km) diapirs. Diapir intrusion induces small-scale convection in the low-viscosity deeper part of the thermochemically defined lithosphere. Small-scale convection in the craton root can produce complex P–T paths, complex recurrent melting histories and complex compositional structure in the craton. P–T paths derived from the numerical models for asthenosphere diapirism in a hot upper mantle are consistent with the sequence of sub-solidus P–T conditions deduced for the cratonic peridotites.