International Conference on Subduction , Volcanism and the Evolution of Oceanic and Continental Crust ( SVEOCC 2014 ) (original) (raw)
Related papers
Earth and Planetary Science Letters, 2019
(By Artemieva I.M. and Shulgin A.) Crustal structure preserves a unique record of physical and chemical conditions of its formation and later modification by geodynamic processes. The existence of broad global correlations between crustal structure and tectonic settings led to models of crustal typization by 1D crustal columns based on absolute thicknesses of crustal layers and the Moho depth. Here we propose a fundamentally different approach to typify the crust and geodynamic models of crustal evolution. We demonstrate that the relative ratio of the thicknesses of three principal crustal layers (sedimentary/felsic-intermediate/mafic in continents and Layer1/Layer2/Layer3 in oceans) is a fundamental characteristic of the crust. The relative ratio uniquely specifies the crustal structure in different tectonic settings and is independent of the absolute values of thickness of the crustal layers and the Moho depth. We analyze this new fundamental characteristic of the crust by ternary diagrams based on seismic models for continental and oceanic crustal structure in the northern Eurasia-northern Atlantics region and for selected oceanic provinces of different geodynamic origin, where seismic models for the crust are available. We present global and regional trends of crustal evolution and, as a practical application of the new approach, calculate average crustal densities in different continental and oceanic tectonic settings. These values range from ca. 2700 kg/m 3 in deep basins, to 2775 kg/m 3 in orogens and shelves, 2800 kg/m 3 in rifts and some ocean hotspots, 2800-2850 kg/m 3 in shields and platforms, 2900 kg/m 3 in back-arc basins and aseismic ridges, and may reach 2950 kg/m 3 in the Pacific hotspots.
Making and altering the crust: A global perspective on crustal structure and evolution
EPSL, 2019
Crustal structure preserves a unique record of physical and chemical conditions of its formation and later modification by geodynamic processes. The existence of broad global correlations between crustal structure and tectonic settings led to models of crustal typization by 1D crustal columns based on absolute thicknesses of crustal layers and the Moho depth. Here we propose a fundamentally different approach to typify the crust and geodynamic models of crustal evolution. We demonstrate that the relative ratio of the thicknesses of three principal crustal layers (sedimentary/felsic-intermediate/mafic in continents and Layer1/Layer2/Layer3 in oceans) is a fundamental characteristic of the crust. The relative ratio uniquely specifies the crustal structure in different tectonic settings and is independent of the absolute values of thickness of the crustal layers and the Moho depth. We analyze this new fundamental characteristic of the crust by ternary diagrams based on seismic models for continental and oceanic crustal structure in the northern Eurasia-northern Atlantics region and for selected oceanic provinces of different geodynamic origin, where seismic models for the crust are available. We present global and regional trends of crustal evolution and, as a practical application of the new approach, calculate average crustal densities in different continental and oceanic tectonic settings. These values range from ca. 2700 kg/m 3 in deep basins, to 2775 kg/m 3 in orogens and shelves, 2800 kg/m 3 in rifts and some ocean hotspots, 2800-2850 kg/m 3 in shields and platforms, 2900 kg/m 3 in back-arc basins and aseismic ridges, and may reach 2950 kg/m 3 in the Pacific hotspots.
The crustal structure from the Altai Mountains to the Altyn Tagh fault, northwest China
Journal of Geophysical Research, 2003
The origin and evolution of cratonic roots has been debated for many years. Precambrian cratons are underlain by cold lithospheric roots that are chemically depleted. Thermal and petrologic data indicate that Archean roots are colder and more chemically depleted than Proterozoic roots. This observation has led to the hypothesis that the degree of depletion in a lithospheric root depends mostly on its age. Here we test this hypothesis using gravity, thermal, petrologic, and seismic data to quantify differences in the density of cratonic roots globally. In the first step in our analysis we use a global crustal model to remove the crustal contribution to the observed gravity. The result is the mantle gravity anomaly field, which varies over cratonic areas from 3100 to +100 mGal. Positive mantle gravity anomalies are observed for cratons in the northern hemisphere: the Baltic shield, East European Platform, and the Siberian Platform. Negative anomalies are observed over cratons in the southern hemisphere: Western Australia, South America, the Indian shield, and Southern Africa. This indicates that there are significant differences in the density of cratonic roots, even for those of similar age. Root density depends on temperature and chemical depletion. In order to separate these effects we apply a lithospheric temperature correction using thermal estimates from a combination of geothermal modeling and global seismic tomography models. Gravity anomalies induced by temperature variations in the uppermost mantle range from 3200 to +300 mGal, with the strongest negative anomalies associated with mid-ocean ridges and the strongest positive anomalies associated with cratons. After correcting for thermal effects, we obtain a map of density variations due to lithospheric compositional variations. These maps indicate that the average density decrease due to the chemical depletion within cratonic roots varies from 1.1% to 1.5%, assuming the chemical boundary layer has the same thickness as the thermal boundary layer. The maximal values of the density drop are in the range 1.7^2.5%, and correspond to the Archean portion of each craton. Temperatures within cratonic roots vary strongly, and our analysis indicates that density variations in the roots due to temperature are larger than the variations due to chemical differences. ß
Cho et al Tectonophysics K-Crust DEC 10 2012
The onshore seismic experiment, KCRT2004, explored the crustal velocity structure of the southern Korean peninsula. We present an interpretation of seismic data along this 340 km long NNW-SSE trending profile. The crust was found to consist of three layers: the upper, middle, and lower crust with P-and S-wave velocities ranging 5.50 to 6.95 km/s and 2.82 to 3.91 km/s, respectively. The average P-wave velocity (6.26 km/s) and Pn velocity (7.82-7.88 km/s) are lower than the worldwide average of continental crust. Moho depths are 29.0-34.9 km, gradually thickening toward south. The Vp/Vs ratio of crustal material is estimated to be 1.73 (σ = 0.249) for the upper and middle crust and the ratio increases with the depth in the lower crust. The Gyeonggi massif in the north of the profile has a lower Vp/Vs ratio than other tectonic units. The average crustal Vp/Vs ratio of 1.74 (σ = 0.253) is remarkably lower than the average value 1.78 (σ = 0.27) for the bulk continental crust. The low average crustal Vp/Vs ratio is similar to that measured in eastern China. The empirical analysis using both P-wave velocity and Vp/Vs ratio shows that the upper and middle crust is dominantly felsic and the lower crust is intermediate in composition. The absence of the mafic material in the lower crust that is also found in eastern China contrasts with the generally accepted global model of the mafic lower crust.
How mafic is the lower continental crust?
Earth and Planetary Science Letters, 1998
Crustal structures for nine broad tectonic units in China, except the Tarim craton, are derived from seismic data for 18 geophysical refraction profiles, which include twelve geoscience transects and have a total length of 16 216 km. All the tectonic units except the Qinling orogen show a four-layered crustal structure, consisting of upper, middle, upper lower, and lowermost crust. If corrections are made to room temperature and 600 MPa, the upper lower crust has P-wave velocities of 6.7-6.8 km s 1 and the lowermost crust 7.0-7.2 km s 1. Velocities of the bulk lower crust and total crust are 6.8-7.0 and 6.4-6.5 km s 1 , respectively. They are slower by 0.2-0.4 km s 1 , than the global averages. By correlation with experimental results on velocities of typical lower crustal rocks, the upper lower crust is suggested to be intermediate, while the lowermost crust is mafic in composition. Due to dominance of the former, the bulk lower crust is still intermediate for most tectonic units. However, inter-unit compositional variations are also evident, as indicated by large variations in the thickness ratio (0.3-3.0) of the upper lower to lowermost crust. The lower crust in East China as a whole is suggested to have ¾57% SiO 2. The results contrast with generally accepted models of mafic lower crust. Our estimates of the total crust composition in central East China show a more evolved character compared to models of Rudnick and Fountain, and Taylor and McLennan and are characterized by a prominent negative Eu anomaly (Eu=Eu * D 0.80), higher SiO 2 (61.8%), and lower Sr=Nd (¾10) as well as lower Sr=Nd, Cr=Nd, Ni=Nd, Co=Nd, V=Nd and Ti=Nd ratios. This, together with slower crustal velocities and remarkably thin crustal thicknesses (34 km) for the Paleozoic-Mesozoic Qinling-Dabie orogenic belt, leads to the suggestion that lower crustal delamination played an important role in modification of the East China crust. Mass balance modeling further suggests that eclogite from the Dabie-Sulu ultrahigh pressure metamorphic belt is the most likely candidate as the delaminated material, and that a cumulative 37-82 km thick eclogitic lower crust is required to have been delaminated in order to explain the relative Eu, Sr and transition metal deficits in the crust of central East China. Delamination of eclogites can also explain the significantly higher than eclogite Poisson's ratio in the present Dabie lower crust and upper mantle and lack of eclogite in Cenozoic xenolith populations of the lower crust and upper mantle in East China.
Nature Communications, 2024
The thick crust of the southern Tibetan and central Andean plateaus includes high-conductivity, low-velocity zones ascribed to partial melt. The melt origin and effect on plateau uplift remain speculative, in particular if plateau uplift happens before continental collision. The East Anatolian Plateau (EAP) has experienced similar, more recent uplift but its structure is largely unknown. Here we present an 80 km deep geophysical model across EAP, constrained by seismic receiver functions integrated with interpretation of gravity data and seismic tomographic, magnetotelluric, geothermal, and geochemical models. The results indicate a 20 km thick lower crustal layer and a 10 km thick midcrustal layer, which both contain pockets of partial melt. We explain plateau uplift by isostatic equilibration following magmatism associated with roll-back and break-off of the Neo-Tethys slab. Our results suggest that crustal thickening by felsic melt and mafic underplate are important for plateau uplift in the EAP, Andes and Tibet.
Preface Comparative tectonic and dynamic analysis of cratons, orogens, basins, and metallogeny: A special volume to honor the career of Brian F. Windley 1. Preface Cratons, orogens, and basins of the world each show a distinctive pattern of evolution and metallogeny, and relationships to superconti-nent cycles. Some aspects of these histories have remained similar through time, yet others have changed with Earth's changing biota, heat production and flow, and atmospheric composition and temperature. To understand the similarities and differences between these cratons, orogens, and basins through time, we need systematic comparative tectonic analyses between these different elements from similar and widely different ages. One of the pioneers in comparative tectonic analysis is Brian F. Windley, whose research has spanned all of these topics, and more, for more than five decades. This special issue is a tribute to his career. Brian's career began with graduation from Liverpool in 1960, after which he went to Exeter University for his PhD studies under Ken Coe, working on the Precambrian rocks of SW Greenland, which led to a six year contract working for the Geological Survey of Greenland mapping most of the Precambrian of western Greenland. Brian enjoyed this time, but did not want to be constrained to only mapping the geology of Greenland, so moved on to Leicester University, from where he based the rest of his career. During this career Brian visited many universities around the world (see review of Brian's career in Kusky et al., 2010), and worked on problems in tectonics, mineralogy, geochemistry, geochro-nology, and metallogeny from every continent (and the moon). Brian has not slowed down in his career and is currently active in many projects in the Central Asian Orogenic Belt, India, Madagascar, China, Scotland, and other places and is currently working on a new edition of his book "The Evolving Continents" with his colleague T. Kusky. We have collected 29 papers from Brian's peers and colleagues along these themes for this special issue of Tectonophysics and summarize them from "snippits" of the papers here. The papers are organized into five themes, namely Archean Tectonics, Proterozoic Tectonics, Structural and Metamorphic Evolution of Orogens, Tethyan and Paleo-Asian Tectonics and the Central Asian Orogenic Belt, and the Supercontinent Cycle and Earth History. We hope readers enjoy reading these papers as much as the authors have enjoyed working with Brian and doing the science to prepare them. 2. Archean tectonics Five papers focus on different aspects of Archean tectonics. Peng et al. (2015) present a study of the Qingyuan high-grade granite-greenstone terrane in the North China craton, consisting of circa 2510 Ma ultramafic-mafic-felsic rocks, 2570-2510 Ma quartz diorite, a similar aged TTG suite, and a 2510-2490 Ma quartz monzonite. Using mainly petrologic and geochemical methods, Peng et al. (2015) model the petrogenesis to be related to Archean subduction in a mantle wedge-absent flat-hot-subduction system, with considerable vertical accretion of magmatic rocks. The ultramafic-mafic rocks are interpreted to be derived from the primitive mantle, whereas the meta-dacite-rhyolite originated from eclogite facies overriding crust. The quartz dio-rite is interpreted by Peng et al. (2015) as a mixture of melts from mantle and the overriding crust, the TTG was derived from the subducting slab under amphibolite to amphibole-bearing eclogite facies conditions, and the quartz monzodiorite was derived from the overriding middle-lower crust. The Qingyuan terrain represents the root of a Neoarchaean arc and its anticlockwise P-T-path records the initiation of the arc at 2570 Ma to its cession and exhumation/cratonization at~2480 Ma. Arai et al. (2015) document intermediate P/T type regional meta-morphism of the 3.7-3.8 Ga Isua Supracrustal Belt from southwest Greenland. Using a group of metabasites that range in metamorphic grade from greenschist to amphibolite facies, and they model isochemical phase diagrams with the Perple_X software. The metamor-phic pressure and temperature both increase systematically to the south from 3 kbar and 380°C to 6 kbar and 560°C. The monotonous metamor-phic P-T change suggests that the northeastern part of the ISB preserves regional metamorphism resulting from the subduction of an accretion-ary complex, although there are also Neoarchean metamorphic over-prints. Both the presence of the regional metamorphism and an accretionary complex having originating at a subduction zone suggest that the ISB may be one of the oldest Pacific-type orogenic belts in the world (see also Komiya et al., 2015, for an example of an Eoarchean (N3.95 Ga) Pacific-type orogenic belt). The metamorphic conditions are similar to extant zones of subducting young oceanic crust such as the Philippine Sea Plate in SW Japan. Since this type of metamorphism is characteristic of most Archean terranes, Arai et al. (2015) suggest that subduction of young micro-plates was common in the Archean. Polat et al. (2015) describe the Eoarchean to Neoarchean tectonic zonation of West Greenland and interpret these as a series of accreted accretionary prisms, island arcs, and fore-arcs. They compare the structures , particularly those of high-grade migmatites with those recently documented by Wang et al. (2014) from the Mesozoic Sulu orogen of China. Polat et al. (2015) document that melting of the metavolcanic rocks during tectonic thickening of arcs during collision is important in the generation of TTG's, and that the style of deformation along with partial melting in the Archean of Greenland is similar to that of the Sulu orogen that formed by subduction processes, suggesting that subduction and collision, and hence plate tectonics, also operated in the early Archean. Tectonophysics 662 (2015) 1-6 http://dx.