Subduction Angle Research Articles

Mass balance of Neogene sediments in the Colombia basin relationship with the evolution of the Magdalena and Cauca River basins

The Colombia basin contains large volumes of sediment accumulated during the last 17 My. The use of isochore maps, exploratory wells, micropaleontological and geochronological dates has enabled us to estimate the volumes of sediment and accumulation rates in this basin. The analysis of source of sediments and exhumation data from the Northern Andes of South America led to the definition of areas and thicknesses of material eroded during the Neogene - Quaternary, to obtain volumes or material eroded from the continent that can be correlated with sediment volumes accumulated in the Colombia Basin. The analyzed sediment volumes suggest that during the last 17 My ~72.06x1015 Tons accumulated in the Colombia Basin, while ~ 7.16x1013 Tons accumulated in the continental catchment areas. The sedimentation in the Colombian Basin has occurred at variable rates, with values ranging from 55 MTons/My to 295 MTons/My, with a peak of 803 MTons/My in the early Pleistocene (between 2.4 and 2.2 Ma). The evaluation between the total volumes of sediment accumulated in the offshore and onshore, suggests that in the continental part of the basin less than 4% of the total volume of eroded sediment is trapped and, therefore, the behavior of the accumulation rates calculated in the offshore directly reflect the relief evolution of South America’s Northern Andes. It seems, at large, that the lithospheric convergence rates and subduction angle (South America vs Nazca and Meso Atlantic opening) have controlled the regional exhumation of the Northern Andes, with the exception of the Pleistocene high sedimentation event, which seems to coincide with local events such as the collision of the Panama Arch against Western Antioquia. It may be concluded that thanks to this collision, drainage systems such as those of the Magdalena and Cauca rivers were modified, which resulted in the formation of the Magdalena Submarine Fan.

Insights from the P Wave Travel Time Tomography in the Upper Mantle Beneath the Central Philippines

In this paper, we present a high resolution 3-D tomographic model of the upper mantle obtained from a large number of teleseismic travel time data from the ISC in the central Philippines. There are 2921 teleseismic events and 32,224 useful relative travel time residuals picked to compute the velocity structure in the upper mantle, which was recorded by 87 receivers and satisfied the requirements of teleseismic tomography. Crustal correction was conducted to these data before inversion. The fast-marching method (FMM) and a subspace method were adopted in the forward step and inversion step, respectively. The present tomographic model clearly images steeply subducting high velocity anomalies along the Manila trench in the South China Sea (SCS), which reveals a gradual changing of the subduction angle and a gradual shallowing of the subduction depth from the north to the south. It is speculated that the change in its subduction depth and angle indicates the cessation of the SCS spreading from the north to the south, which also implies that the northern part of the SCS opened earlier than the southern part. Subduction of the Philippine Sea (PS) plate is exhibited between 14° N and 9° N, with its subduction direction changing from westward to eastward near 13° N. In the range of 11° N–9° N, the subduction of the Sulu Sea (SS) lies on the west side of PS plate. It is notable that obvious high velocity anomalies are imaged in the mantle transition zone (MTZ) between 14° N and 9° N, which are identified as the proto-SCS (PSCS) slabs and paleo-Pacific (PP) plate. It extends the location of the paleo-suture of PSCS-PP eastward from Borneo to the Philippines, which should be considered in studying the mechanism of the SCS and the tectonic evolution in SE Asia.

Constraining the effects of dynamic topography on the development of Late Cretaceous Cordilleran foreland basin, western United States

AbstractDynamic topography refers to the vertical deflection (i.e., uplift and subsidence) of the Earth's surface generated in response to mantle flow. Although dynamic subsidence has been increasingly invoked to explain the subsidence and migration of depocenters in the Late Cretaceous North American Cordilleran foreland basin (CFB), it remains a challenging task to discriminate the effects of dynamic mantle processes from other subsidence mechanisms, and the spatial and temporal scales of dynamic topography is not well known. To unravel the relationship between sedimentary systems, accommodation, and subsidence mechanisms of the CFB through time and space, a high-resolution chronostratigraphic framework was developed for the Upper Cretaceous strata based on a dense data set integrating >600 well logs from multiple basins/regions in Wyoming, Utah, Colorado, and New Mexico, USA. The newly developed stratigraphic framework divides the Upper Cretaceous strata into four chronostratigraphic packages separated by chronostratigraphic surfaces that can be correlated regionally and constrained by ammonite biozones. Regional isopach patterns and shoreline trends constructed for successive time intervals suggest that dynamic subsidence influenced accommodation creation in the CFB starting from ca. 85 Ma, and this wave of subsidence increasingly affected the CFB by ca. 80 Ma as subsidence migrated from the southwest to northeast. During 100–75 Ma, the depocenter migrated from central Utah (dominantly flexural subsidence) to north-central Colorado (dominantly dynamic subsidence). Subsidence within the CFB during 75–66 Ma was controlled by the combined effects of flexural subsidence induced by local Laramide uplifts and dynamic subsidence. Results from this study provide new constraints on the spatio-temporal footprint and migration of large-scale (>400 km × 400 km) dynamic topography at an average rate ranging from ~120 to 60 km/m.y. in the CFB through the Late Cretaceous. The wavelength and location of dynamic topography (subsidence and uplift) generated in response to the subduction of the conjugate Shatsky Rise highly varied through both space and time, probably depending on the evolution of the oceanic plateau (e.g., changes in its location, subduction angle and depth, and buoyancy). Careful, high-resolution reconstruction of regional stratigraphic frameworks using three-dimensional data sets is critical to constrain the influence of dynamic topography. The highly transitory effects of dynamic topography need to be incorporated into future foreland basin models to better reconstruct and predict the formation of foreland basins that may have formed under the combined influence of upper crustal flexural loading and dynamic subcrustal loading associated with large-scale mantle flows.

Detrital zircon record of Phanerozoic magmatism in the southern Central Andes

Abstract The spatial and temporal distribution of arc magmatism and associated isotopic variations provide insights into the Phanerozoic history of the western margin of South America during major shifts in Andean and pre-Andean plate interactions. We integrated detrital zircon U-Th-Pb and Hf isotopic results across continental magmatic arc systems of Chile and western Argentina (28°S–33°S) with igneous bedrock geochronologic and zircon Hf isotope results to define isotopic signatures linked to changes in continental margin processes. Key tectonic phases included: Paleozoic terrane accretion and Carboniferous subduction initiation during Gondwanide orogenesis, Permian–Triassic extensional collapse, Jurassic–Paleogene continental arc magmatism, and Neogene flat slab subduction during Andean shortening. The ~550 m.y. record of magmatic activity records spatial trends in magma composition associated with terrane boundaries. East of 69°W, radiogenic isotopic signatures indicate reworked continental lithosphere with enriched (evolved) εHf values and low (<0.65) zircon Th/U ratios during phases of early Paleozoic and Miocene shortening and lithospheric thickening. In contrast, the magmatic record west of 69°W displays depleted (juvenile) εHf values and high (>0.7) zircon Th/U values consistent with increased asthenospheric contributions during lithospheric thinning. Spatial constraints on Mesozoic to Cenozoic arc width provide a rough approximation of relative subduction angle, such that an increase in arc width reflects shallower slab dip. Comparisons among slab dip calculations with time-averaged εHf and Th/U zircon results exhibit a clear trend of decreasing (enriched) magma compositions with increasing arc width and decreasing slab dip. Collectively, these data sets demonstrate the influence of subduction angle on the position of upper-plate magmatism (including inboard arc advance and outboard arc retreat), changes in isotopic signatures, and overall composition of crustal and mantle material along the western edge of South America.

Distribution of metallogenic zones of the Caucasus region originated as a result of the subduction of the lithosphere of the Tethys Paleo-Oceanic plate under the East-European Paleo-Continental plate

On the assumption that the 2D heat flux anomaly in the territory of Caucasus is provided by the convective heat transfer from the mantle wedge, the angle and velocity of subduction of the paleo-lithospheric plate Tethys (Mediterranean and East Black Sea paleo-lithospheric plates) under the East-European paleo-lithospheric plate (Caucasus region) are estimated numerically. Within the framework of the geodynamical model constructed the horizontal extent of the 2D heat flux anomaly observed in the rear of the Caucasus mountain belt corresponds to subduction velocity of ~ 40 mm per year which is close to that observed with the help of geodetic means. The upwelling convective mantle flows can transport the mantle calc-alkali magmas (containing metals) to the subsurface Earth’s crust layers, thus making the ore deposits to be attached to the upper lithospheric locations above the ascending flows of the Karig-Richter vortices.

Geodynamics of decratonization and related magmatism and mineralization in the North China Craton

The North China Craton (NCC) experienced strong destruction (i.e., decratonization) during the Mesozoic, which triggered intensive magmatism, tectonism and thermal events and formed large-scale gold and other metal deposits in the eastern part of the craton. However, how the decratonization controls the formation and distribution of large-scale of gold and other metal deposits is not very clear. Based on a large number of published data and new results, this paper systematically summarizes all the data for the rock assemblages, chronology, geochemistry and petrogenesis of Mesozoic magmatic rocks, as well as for the mineralizing ages of gold and other metal deposits and the evolution of the Mesozoic basins in the eastern NCC. The results are used to restore the extensional rates of Mesozoic to Cenozoic basins and the strike-slip distance of the Tanlu Fault, to ascertain the location of the Paleo-Pacific plate subduction zones during the Mesozoic to Cenozoic, and to reconstruct the temporal and spatial distribution of Mesozoic gold and other metal deposits and magmatic rocks in the eastern NCC. It is obtained that the magmatism and mineralization in the eastern NCC westward migrate from east to west during the Early to Middle Jurassic, but they eastward migrate from west to east during the Early Cretaceous. The metallogenesis of these deposits is genetically related to magmatism, and the magmas provided some ore-forming materials and fluids for the generation of metal deposits. The geodynamic mechanism of decratonization and related magmatism and mineralization is proposed, i.e., the westward low-angle subduction of the Paleo-Pacific slab beneath the NCC formed continental magmatic arc with plenty of porphyry Cu-Mo-Au deposits in the Jurassic, similar to the Andean continental arc in South America. The mantle wedge was metasomatized by the fluids/melts derived from the subducting slab, laying a material foundation for hydrothermal mineralization in the Early Cretaceous. While the rollback of the subducting slab with gradually increasing subduction angle and the retreat of the subduction zones during the Early Cretaceous induced strong destruction of the craton and the formation of extensive magmatic rocks and large-scale gold and other metal deposits.

Petrogenesis of coeval shoshonitic and high-K calc-alkaline igneous suites in the Eopyeong granitoids, Taebaeksan Basin, South Korea: Lithospheric thinning-related Early Cretaceous magmatism in the Korean Peninsula

The Early Cretaceous was the initial period of prolonged Cretaceous-Tertiary magmatic episode in the Korean Peninsula, during which a tectonic transition from compression to extension occurred. The Early Cretaceous Eopyeong granitoids in the Taebaeksan Basin consist of two distinct series of magmas: shoshonitic and high-K calc-alkaline series. We investigated the petrology, whole-rock major and trace element geochemistry, and Sr-Nd-Pb isotope compositions of the Eopyeong granitoids to understand their magma evolution processes and source characteristics. Sensitive high-resolution ion microprobe zircon U-Pb analysis was performed on the Eopyeong granitoids to constrain their intrusion ages. Zircon U-Pb ages of the shoshonitic and high-K calc-alkaline series are 110.63 ± 0.52 and 110.65 ± 0.66 Ma, respectively, indicating that the two series formed during the same magmatic event. The mafic mineral assemblages of the shoshonitic series change from two-pyroxene+biotite to clinopyroxene+amphibole+biotite through magma evolution, whereas those of the high-K calc-alkaline series consist of more hydrous assemblages of amphibole+biotite. The shoshonitic series is also distinguished from the high-K calc-alkaline series by its higher La/Yb ratio and negative anomalies of Rb, Ba, and Eu. Mineral geothermobarometry and hygrometry data and geochemical mass balance modeling results show that the two series evolved mainly by fractional crystallization from two distinct parental magmas containing different water contents. Primitive rocks from each series have high compatible element contents such as MgO, Cr, and Ni with high Mg# compared to crustal melts in a similar range of SiO2, suggesting their mantle origin. They also have abundant incompatible elements and ‘crust-like’ isotopic compositions [(87Sr/86Sr)i = 0.7093–0.7098; εNd(t) = −7.1 to −8.8; (206Pb/204Pb)i = 18.133–18.327; (207Pb/204Pb)i = 15.621–15.665; (208Pb/204Pb)i = 38.691–38.862] with negative Nb-Ta anomalies in the primitive mantle-normalized patterns. The enrichment in both compatible and incompatible elements can be best explained by partial melting of phlogopite-bearing lithospheric mantle metasomatized by isotopically enriched upper crustal sediment-derived melt or fluid. The two magma series may have been generated by different degrees of partial melting of the mantle sources with varying water contents. Changes in subduction angle and direction of the paleo-Pacific plate during the Early Cretaceous may have led to lithospheric thinning and upwelling of asthenospheric mantle, which triggered the partial melting of fusible domains of metasomatized lithospheric mantle. The small igneous bodies of the Early Cretaceous shoshonitic to alkaline mafic rocks occur sporadically throughout the southern part of the Korean Peninsula in close spatial association with the Cretaceous basins. They also show crust-like geochemistry and isotopic compositions, similar to the Eopyeong granitoids, implying that the lithospheric thinning-related melting of the metasomatized lithospheric mantle may have been widespread in the southern part of the Korean Peninsula.

The Role of Fluid‐Related Heterogeneous Structures in Controlling the Fault Slip Behavior in the Slow‐Earthquake Source Region Along the Nankai Subduction Zone, Southwest Japan

AbstractA seismic array observation across the slow‐earthquake source region in the eastern Kii Peninsula, southwest Japan, reveal the detailed structure and seismicity along the upper boundary of the subducted Philippine Sea Plate. Tomography analysis and earthquake reflection imaging clarify the geometry of the upper boundary of the Philippine Sea Plate with a subduction angle of ∼15° at a depth range of 22–30 km. We observe intraslab low‐frequency earthquakes (LFEs) in and around the low‐Vp and high‐Vp/Vs zones, which are located above the intraslab earthquakes that are controlled by the dehydration embrittlement of serpentine. The intraslab LFE activity may be related to fluid movement. Fluids, which are derived from both dehydration of the serpentinized oceanic mantle and crustal eclogitization, may control the fault slip behavior. Therefore, the fluid behavior around the subducting plate boundary has an important role in controlling the downdip limit of the seismogenic zone.

The great tectonic discontinuity of Bahía de Banderas, Mexico

Detachment of the Baja California peninsula from the North American plate altered the crustal region between them, including an extension of the crust between the peninsula and Mexico's mainland. In the SE portion of this region Bahía de Banderas, a 60-km indentation in the littoral of Mexico, is a boundary region across which significant changes in topography, seismicity, seismic attenuation, trench subduction angle, continental platform width, geomagnetic field, and crustal thickness have been documented. Here we identify two additional, major discontinuities: one in gravity and the second in the regional electrical resistivity to 50-km depth, both associated with the region in which the crust changes from extended to un-extended. Under the former, we ratify and extend the presence of the oceanic slab obtained elsewhere with seismological determinations. Plate rollback is also reported in the boundary region. Gravity and electrical resistivity models locate the NW and SE limits of the rolled-back portion of the oceanic slab; within this region, we identify upwelling asthenospheric material. Bahía de Banderas region represents a major tectonic discontinuity, implying the existence of a continental sliver prolonging ~160 km into the San Blas basin north of the bay, the Tres Marías sliver, independent from the Jalisco block, in which crustal fragmentation processes appear to be still in progress. We argue that this sliver is tectonically different from the Jalisco block since at least the late Miocene, when extensional tectonics stretched and thinned its corresponding crust and lithosphere.

Eastward Dipping Style of the Underthrusting Indian Lithosphere Beneath the Tethyan Himalaya Illuminated by P and S Receiver Functions

AbstractTo explore the west‐east variations in the underthrusting Indian lithosphere, we investigate the lithospheric structure using P and S receiver functions obtained from a west‐east linear array of 19 broadband stations spanning the Tethyan Himalaya at 85.5–88.5°E. Our observations of the Main Himalayan Thrust (MHT) and Moho serving as the top and bottom boundaries at depths of 42–54 km and 60–72 km, respectively, suggest that a thinning Indian lower crust with an eastward inclined geometry is underthrusting beneath the Tethyan Himalaya. An intra‐crustal low velocity zone (LVZ) immediately above the MTH at depths of 32–42 km is imaged, likely resulting from the presence of crustal dehydration partial melting. We propose that this LVZ induces the southward extrusion of melt‐weakened crustal material with itself as a channel and facilitates the development of duplexing structures, by which Indian lower crustal materials could be accreted into the Himalayan wedge along the north‐south mid‐crustal ramp in the MHT. The eastward dipping lithosphere‐asthenosphere boundary is clearly observed ranging from 90 to 126 km, which generally coincides with the changing trends of the MHT and Moho. These observations can be attributed to the eastward steepening subduction angle of the Indian lithosphere.

Lithospheric density structure of the southern Central Andes constrained by 3D data-integrative gravity modelling

The southern Central Andes (SCA) (between 27° S and 40° S) is bordered to the west by the convergent margin between the continental South American Plate and the oceanic Nazca Plate. The subduction angle along this margin is variable, as is the deformation of the upper plate. Between 33° S and 35° S, the subduction angle of the Nazca plate increases from sub-horizontal (< 5°) in the north to relatively steep (~ 30°) in the south. The SCA contain inherited lithological and structural heterogeneities within the crust that have been reactivated and overprinted since the onset of subduction and associated Cenozoic deformation within the Andean orogen. The distribution of the deformation within the SCA has often been attributed to the variations in the subduction angle and the reactivation of these inherited heterogeneities. However, the possible influence that the thickness and composition of the continental crust have had on both short-term and long-term deformation of the SCA is yet to be thoroughly investigated. For our investigations, we have derived density distributions and thicknesses for various layers that make up the lithosphere and evaluated their relationships with tectonic events that occurred over the history of the Andean orogeny and, in particular, investigated the short- and long-term nature of the present-day deformation processes. We established a 3D model of lithosphere beneath the orogen and its foreland (29° S–39° S) that is consistent with currently available geological and geophysical data, including the gravity data. The modelled crustal configuration and density distribution reveal spatial relationships with different tectonic domains: the crystalline crust in the orogen (the magmatic arc and the main orogenic wedge) is thicker (~ 55 km) and less dense (~ 2900 kg/m3) than in the forearc (~ 35 km, ~ 2975 kg/m3) and foreland (~ 30 km, ~ 3000 kg/m3). Crustal thickening in the orogen probably occurred as a result of stacking of low-density domains, while density and thickness variations beneath the forearc and foreland most likely reflect differences in the tectonic evolution of each area following crustal accretion. No clear spatial relationship exists between the density distribution within the lithosphere and previously proposed boundaries of crustal terranes accreted during the early Paleozoic. Areas with ongoing deformation show a spatial correlation with those areas that have the highest topographic gradients and where there are abrupt changes in the average crustal-density contrast. This suggests that the short-term deformation within the interior of the Andean orogen and its foreland is fundamentally influenced by the crustal composition and the relative thickness of different crustal layers. A thicker, denser, and potentially stronger lithosphere beneath the northern part of the SCA foreland is interpreted to have favoured a strong coupling between the Nazca and South American plates, facilitating the development of a sub-horizontal slab.

Trace-element and Sr and Nd isotopic geochemistry of Cretaceous bentonites in Wyoming and South Dakota tracks magmatic processes during eastward migration of Farallon arc plutons

Abstract Bentonite beds, which are clay deposits produced by the submarine alteration of volcanic tephra, preserve millions of years of volcanic products linked to magmatic systems for which records are otherwise lost through erosion and alteration. Cretaceous strata from the Bighorn Basin, Wyoming, and southwestern South Dakota contain bentonites that originated from arc magmatism produced by subduction of the Farallon plate. We analyzed the bulk major- and trace-element geochemistry, and the 87Sr/86Sr (n = 87) and 143Nd/144Nd (n = 26) isotopic compositions of individual bentonite beds from these areas spanning 40 m.y. of volcanism to recover signals of magmatic processes and to attempt to trace bentonite geochemical and isotopic signatures to contemporaneous Cordilleran plutonic rocks. Using multiple immobile elements (e.g., Zr, TiO2, Nb, Ta, and rare earth elements), distinct temporal trends show variations in the effects of mineral fractionation and changes in crustal thickness. Bentonite Sr and Nd isotopic compositions allow ash beds to be correlated with specific batholithic complexes in Idaho and western Montana. With this data set, we observed the following: (1) The volcanic arc migrated across the 0.706 isopleth between 115 and 105 Ma; (2) between 105 and 95 Ma, magmatism stalled in central Idaho and was supported through significant MASH (mixing-assimilation-storage-homogenization) processing; (3) by 85 Ma, a shallowing subduction angle resulted in the eastward migration of the volcanic front into western Montana while volcanism in Idaho diminished; and (4) around 75 Ma, evidence of Idaho volcanism is lost. Montana plutonism continued with significant assimilation of radiogenic basement and regional centers of local magma emplacement (i.e., Pioneer batholith).

Genesis of Middle Triassic high-Mg# quartz diorites from the Xiahe area, West Qinling Orogen, Central China, and their geodynamic implications

The West Qinling Orogen (WQO) features widespread Triassic granitic rocks, which are crucial to constrain the tectonic evolution of the WQO. Here, we conducted an integrated petrological, geochronological, geochemical, and Sr-Nd-Hf isotope study on quartz diorites and mafic microgranular enclaves (MMEs) from the Ren’ai and Daerzang plutons, Hezuo area, WQO. The quartz diorites and MMEs have crystallization ages between 244 and 241 Ma. The quartz diorites display intermediate SiO2, high Mg# values (62–66) and evolved S-Nd-Hf isotope compositions, indicating an origin from magma mixing process. The MMEs display mineral compositions similar to those of the host rocks, only with more mafic minerals. The The Ren’ai and Daerzang plutons were part of the early Indosinian magmatic belt mainly distributed in the western and middle parts of the northern WQO. In comparison, late Indosinian magmatic rocks are mainly exposed in the eastern WQO. The asymmetric distribution of Early Mesozoic magmatism in the WQO might have been caused by a specific subduction pattern of the A’nimaque-Mianlue oceanic crust. The western and middle WQO experienced a period of flat or low angle subduction in the early stage, followed by slab rollback of the oceanic crust, which accounted for the flare-up of early Indosinian magmatism in the northern WQO. However, the distribution of late Indosinian magmatism might have been caused by asymmetric crustal delamination in the WQO.

Integrated Cretaceous–Cenozoic plate tectonics and structural geology in southern Mexico

Abstract The structural evolution of southern Mexico is described in the context of its plate tectonic evolution and illustrated by two restored crustal scale cross-sections through Cuicateco and the Veracruz Basin and a third across Chiapas. We interpret the Late Jurassic–Early Cretaceous opening of an oblique hyper-stretched intra-arc basin between the Cuicateco Belt and Oaxaca Block of southern Mexico where Lower Cretaceous deep-water sediments accumulated. These rocks, together with the hyper-stretched basement beneath them and the Oaxaca Block originally west of them, were thrust onto the Cretaceous platform of the Cuicateco region during a Late Cretaceous–Eocene orogenic event. The mylonitic complex of the Sierra de Juárez represents this hyper-stretched basement, perhaps itself an extensional allochthon. The Chiapas fold-and-thrust belt is mainly Neogene in age. Shallowing of the subduction angle of the Cocos Plate in the wake of the Chortis Block, suggested by seismicity and migrating arc volcanism, is thought to play an important role in the development of the Chiapas fold-and-thrust belt itself, helping to explain the structural dilemma of a vertical transcurrent plate boundary fault (the Tonalá Fault) at the back of an essentially dip-slip fold-and-thrust belt.

Characteristic of the Mount Colo Volcano, Una-Una Island, Central Sulawesi Province: Tectonic Evolution and Disaster Mitigation

The Una-Una Island is in the Gulf of Tomini, Central Sulawesi Province. This island is a soliter active volcano island with Mount Colo as volcano name. The island is located between the North Arm and East Arm of Sulawesi, which are having complex tectonic regime, situated between two subduction zones. Volcanic rocks from Una-Una Island are basaltic-trachyandesite until trachydasite composition with magma affinity is calk-alkaline, high-K calk-alkaline and shoshonite. Tectonic reconstruction in this area started at Miocene (15 Ma) where the Celebes Sea Plate subducted below the North Arm of Sulawesi with a gentle slope produced adakite-type volcanic rocks. Along with the continuous subduction process and increasingly steep angle of subduction, the magma source then underwent. Intensive movement of the Banggai-Sula microcontinent, resulted in obduction of the ophiolite during collision, whereas volcanic activity in Una-Una Island and surrounding islands are still ongoing. Recent eruption of the Mount Colo in 1983 produced abundant of pyroclastic material with acid silica and still adakite type composition with mineralogical assemblages consist of hornblende-phlogophite-biotite, gives the impression that it originated from the same magma sources. According to composition of magma and eruption history which were produced magmatic explosion followed by pyroclastic surge, flow and fall, the disaster mitigation focus to eruption forecasting through visual and instrumental monitoring provide by Centre for Volcanology and Geological Hazard Mitigation, Geological Agency, Ministry of Energy and Mineral Resources Republic of Indonesia.

Regional sandstone-type uranium mineralization rooted in Oligo–Miocene tectonic inversion in the Songliao Basin, NE China

The tectonic inversion of the Songliao Basin during the Oligo–Miocene may have played an important role in controlling the development of sandstone-type uranium deposits (SUDs). Here we investigate drill holes along a southeast to northwest section in this basin based on apatite fission-track (AFT) and zircon fission-track (ZFT) techniques. We present 50 data from 15 deep boreholes at different depths between 665 and 3956 m and different structural units including grabens and horsts formed in the Early Cretaceous beneath the basin. The results of the effective AFT ages are 100 ± 11 to 2.3 ± 0.4 Ma (P(x2) > 5%) and ZFT ages are 97.5–20.4 Ma (including binomial peak ages). These results reveal that the basin underwent two distinct stages of rapid cooling after Late Cretaceous. In the first stage, during the Late Cretaceous–Early Paleogene (~80–50 Ma), tectonic uplift occurred in all of the structural units including grabens and horsts, which was marked by an unconformity between the latest Cretaceous Mingshui and the Eocene Yi'an formations. In the second stage, during the Oligo–Miocene (~40–10 Ma), tectonic uplift occurred mainly in the grabens but not in the horsts, corresponding with a few sediments of the Neogene Da'an and Taikang formations. We propose that the folds and the thrust faults mostly characterize in the second stage indicating a major tectonic inversion in the basin. The shifting of the two stages was probably in response to differences in the subduction angles and directions of motion of the Paleo-Pacific Plate from the southeast. Combined with previous information, it was demonstrated that most of the U mineralization ages are younger than 40 Ma, with a peak in the Miocene or later (<20 Ma). We thus propose that the SUDs have been redistributed and redeposited locally in successive stages during and after the Oligo–Miocene tectonic inversion.

Late Jurassic Leucogranites of Macau (SE China): A Record of Crustal Recycling During the Early Yanshanian Orogeny

The Yanshanian Orogeny consists of Jurassic to Cretaceous compressional-extensional cycles related to the subduction of the Paleo-Pacific Ocean beneath East Asia. Numerous granitic plutons were emplaced across southeast China at distinct intervals over a period of ~100 million years that migrate from the interior to the coast. A key region to help constrain the secular evolution of granitic magmatism related to the Yanshanian Orogeny is the Peal River estuary as three distinct Mesozoic magmatic belts congregate. The islands of Taipa and Coloane, Macau Special Administrative Region, are located along the western bank of the Pearl River estuary and are composed of spessartine-bearing biotite leucogranite. In situ zircon geochronology yielded Late Jurassic weighted-mean 206Pb/238U ages of 160.0 ± 2.0 Ma and 161.5 ± 2.0 Ma that correlate to the late Early Yanshanian Orogeny. Inherited zircons of Middle Triassic to Middle Jurassic age were also identified. The rocks are peraluminous, ferroan, calc-alkalic to calcic and classify as post-collisional granite. Geochemical modeling indicates that the chemical variability of the rocks is related to hydrous fractional crystallization under reducing conditions (dFMQ -1) at ~7 km depth. The Sr-Nd isotopes (ISr = 0.71156 to 0.72477; eNd(t) = -7.9 to –8.6), zircon Hf isotopes (eHf(t) = -3.8 to -8.8), incompatible trace element ratios, and whole rock composition indicate that the parental magma was derived primarily from a sedimentary source. It is likely that the islands of Taipa and Coloane form a coherent plutonic complex that may be a member of larger batholith that extends across the Pearl River estuary to Hong Kong. The emplacement of the leucogranites is attributed to decompressional melting associated with a period of crustal relaxation or tensional plate stress that occurred during the transition from low angle subduction to high angle subduction of the Paleo-Pacific plate.

Plate convergence in the Indo-Pacific region

The Indo-Pacific convergence region is the best target to solve the two remaining challenges of the plate tectonics theory, i.e., subduction initiation and the driving force of plate tectonics. Recent studies proposed that the Izu-Bonin subduction initiation belongs to spontaneous initiation, which implies that it started from extension, followed by low angle subduction. Numerical geodynamic modeling suggests that the initiation of plate subduction likely occurred along a transform fault, which put the young spreading ridge in direct contact with old oceanic crust. This, however, does not explain the simultaneous subduction initiation in the west Pacific region in the Cenozoic. Namely, the subduction initiations in the Izu-Bonin- Mariana, the Aleutian, and the Tonga-Kermadec trenches are associated with oceanic crusts of different ages, yet they occurred at roughly the same time, suggesting that they were all triggered by a major change in the Pacific plate. Moreover, low angle subduction induces compression rather than extension, which requires external compression forces. Given that the famous Hawaiian-Emperor bending occurred roughly at the same time with the onset of westward subductions in the west Pacific, we propose that these Cenozoic subductions were initiated by the steering of the Pacific plate, which are classified as induced initiation. Induced subduction initiation usually occurs in young ocean basins, forming single-track subduction. The closures of Neo-Tethys Oceans were likely triggered by plumes in the south, forming northward subductions. Interestingly, the Indian plate kept on moving northward more than 50 Ma after the collision between the Indian and Eurasian continents and the break-off of the subducted oceanic slab attached to it. This strongly suggests that slab pull is not the main driving force of plate tectonics, whereas slab sliding is.

Reappraisal of the relative importance of dynamic topography and Andean orogeny on Amazon landscape evolution

The Cenozoic landscape of northern South America evolved under the influence of different geodynamic processes, culminating in the formation of the largest drainage basin on Earth, the Amazon drainage system. The orogeny of the Andean cordillera and the increase in surface denudation induced an asymmetric influx of sediments in Amazonia, which caused an eastward propagation of the Andean sedimentary wedge, reversing the topographic gradient and driving the drainage flow towards the Atlantic Equatorial margin. The low-relief topography of lowlands in Amazonia is also a factor that propitiates this reversal. Concomitantly, variations in the subduction angle of the Nazca plate under the continental lithosphere during the Miocene also contributed to create dynamic topography that perturbed the surface and modified the drainage pattern through time. In the last decade, both surface processes during Andean orogeny and dynamic topography were invoked independently to explain the formation of the present Amazon drainage system connecting the Andes and the equatorial margin. However, hitherto these mechanisms were not considered in a single model, hampering the evaluation of the contribution of each factor on the evolution of the Amazon River. To quantify the combined effect of the different geodynamic processes, in the present work we used numerical models that integrate orogeny, surface processes, dynamic topography and flexural isostasy of the lithosphere. In our results, we present new numerical scenarios for the Cenozoic landscape evolution of Amazonia, showing that the dynamic topography may have affected the environmental evolution in western Amazonia, favoring the development of a megawetland in this region before the establishment of the Amazon River as a transcontinental river. We conclude that, although the formation of the Amazon drainage system can be explained without the influence of mantle convection, variations in dynamic topography may have anticipated the establishment of the transcontinental drainage system a few million years. Furthermore, the stratigraphic evolution and the total Cenozoic sedimentation preserved in the Solimões Basin is a function of the temporal variations in the amplitude of dynamic topography in northern South America.

Upper Plate Controls on the Formation of Broken Foreland Basins in the Andean Retroarc Between 26°S and 28°S: From Cretaceous Rifting to Paleogene and Miocene Broken Foreland Basins

AbstractMarked along‐strike changes in stratigraphy, mountain belt morphology, basement exhumation, and deformation styles characterize the Andean retroarc; these changes have previously been related to spatiotemporal variations in the subduction angle. We modeled new apatite fission track and apatite (U‐Th‐Sm)/He data from nine ranges located between 26°S and 28°S. Using new and previously published data, we constructed a Cretaceous to Pliocene paleogeographic model that delineates a four‐stage tectonic evolution: extensional tectonics during the Cretaceous (120–75 Ma), the formation of a broken foreland basin between 55 and 30 Ma, reheating due to burial beneath sedimentary rocks (18–13 Ma), and deformation, exhumation, and surface uplift during the Late Miocene and the Pliocene (13–3 Ma). Our model highlights how preexisting upper plate structures control the deformation patterns of broken foreland basins. Because retroarc deformation predates flat‐slab subduction, we propose that slab anchoring may have been the precursor of Eocene–Oligocene compression in the Andean retroarc. Our model challenges models which consider broken foreland basins and retroarc deformation in the NW Argentinian Andes to be directly related to Miocene flat subduction.