Thermo-mechanical controls of flat subduction: insights from numerical modeling

This study was supported by National Basic Research Program of China (2014CB440901), the Strategic Priority Research Program (B) of CAS (XDB18020104), National Science Foundation of China (41190073, 41372198 and 41304071), and NERC grant NE/J021822/1.Numerical experiments are used to investigate the thermo- mechanical controls for inducing flat subduction and why flat subduction is rare relative to normal/steep subduction. Our modeling results demonstrate that flat subduction is an end-member of a steady state subduction geometry and is characterized by a curved slab with a nearly-horizontal slab section. Intermediate cases between normal/steep and flat subduction appear to be transient in origin and evolve toward one of the stable end-members. Physical parameters inducing flat subduction can be classified into four categories: buoyancy of the subducting oceanic lithosphere (e.g., slab age, oceanic crustal thickness), viscous coupling between the overriding and downgoing plates (e.g., initial subduction angle), external kinematic conditions, and rheological properties of the subduction zone. On the basis of parameter sensitivity tests and the main characteristics of present-day flat subduction zones, positive buoyancy from either the young slab or the thickened oceanic crust are considered the primary controlling parameter. Our results show that the possibility of flat subduction is directly proportional to oceanic crustal thickness and inversely proportional to the slab age. Furthermore, oceanic crust must be thicker than 8 km to induce flat subduction, when the slab is older than 30 Ma with an initial subduction angle of ≥ 20°, and without absolute trenchward motion of the overriding plate. The lower the initial subduction angle or the thicker the overriding continental lithosphere, the more likelihood for flat subduction. The initial subduction angle is more influential for the development of flat subduction than the overriding lithospheric thickness, and a thick overriding lithosphere induces flat subduction only under the condition of an initial subduction angle of ≤ 25°, with a slab age of ≥ 30 Ma and without absolute trenchward motion of the overriding plate. However, when the initial subduction angle is increased to > 25°, no flat subduction is predicted. All the parameters are evaluated within the constraints of a mechanical framework in which the slab geometry is regarded as a result of a balance between the gravitational and hydrodynamic torque. Any factor that can sufficiently reduce gravitational torque or increase hydrodynamic torque will exert a strong effect on flat subduction development. Our results are consistent with the observations of modern flat subduction zones on Earth.PostprintPeer reviewe

Linking Pacific Plate formation and Early Cretaceous metallogenic response on the circum-Pacific continental margins

Hydrothermal mineralization along the circum-Pacific continental margin is genetically linked to the motions of the Pacific Plate. Compiled geochronological results of ore deposits, coupled with the newly reconstructed geometry of the late Early Cretaceous subduction zones in East China, North America, and the Central Andes using GPlates and I2VIS software, were applied to investigate the relationships between mineralization and Pacific Plate formation. The ∼120-m.y.-old orogenic Au provinces in East China and North America are related to transpression caused by high-rate oblique subduction with intermediate−high dip angles of the Izanagi and Farallon plates, respectively. In contrast, the ∼105-m.y.-old porphyry-epithermal belt in Southeast China was produced by oblique subduction of the Izanagi Plate with low−intermediate subduction rates and intermediate−high dip angles. In the Central Andes, the oblique subduction of the Farallon Plate with low−intermediate rates and low dip angle accounted for iron oxide−copper−gold ore (IOCG) deposit mineralization in South Peru at ca. 110 Ma; whereas the high rate and low dip-angle subduction of the paleo-Phoenix Plate, which caused mild compression, was responsible for Fe, porphyry Cu, and IOCG mineralization in North Chile at ca. 110 Ma. The late Early Cretaceous metallogenic response in the circum-Pacific region coincides with superplume events that triggered the significant growth of the modern Pacific Plate. The forward simulations reveal that different subsequent styles of subduction and associated magmatism are likely responsible for the distinct mineralization types present in the region, including orogenic Au, porphyry-epithermal, Fe, and IOCG deposits. The precise dynamics of the subduction zone determined by this study led to the improved metallogenesis models in the Pacific margin.</p

Spatiotemporal Variation of the Cretaceous‐Eocene Arc Magmatism in Lhasa‐Tengchong Terrane

Abstract It was recognized that two magmatic belts in the Lhasa‐Tengchong terrane formed due to the Mesozoic‐Cenozoic Tethyan evolution. Still, their spatiotemporal variations of magmatic flare‐ups/lulls are rarely discussed. Here we use the new U‐Pb and Lu‐Hf isotopic data of captured zircons and a comprehensive data set to show that the flare‐up of northern magmatic belt has peak ages of 110 Ma in central and northern Lhasa and 120 Ma in eastern Tengchong, possibly related to the tectonic transition from Meso‐ and Neo‐Tethyan double subduction to Neo‐Tethyan single subduction. For the southern magmatic belt, the flare‐ups at 100–85 Ma and 65–45 Ma in eastern southern Lhasa indicate obvious juvenile crustal growth, while flare‐ups at 75–45 Ma in western southern Lhasa and Tengchong record ancient crustal reworking. Such flare‐up variations in the southern magmatic belt possibly resulted from asynchronous changes in the Neo‐Tethyan slab dip

Multi-terrane structure controls the contrasting lithospheric evolution beneath the western and central-eastern Tibetan plateau

The Tibetan plateau is manifested by contrasting along-strike lithospheric structures, but its formation mechanism and the relationship with the heterogeneous multi-terrane configuration is a challenging problem. Here we conduct systematic numerical modeling to explore the roles of width, density, and rheological properties of the multiple terranes in the lithospheric evolution of the Tibetan plateau, which reveals two distinct collision modes. In Mode-I, the lithospheric mantles of both the strong and weak terranes in the Tibetan plate are completely detached, followed by the underthrusting of Indian lithosphere beneath the whole plateau. Alternatively, Mode-II is characterized by full detachment of the weak terranes, but (partial) residue of the strong terranes during collision. These two contrasting modes, broadly consistent with the lithospheric structures of western and central–eastern Tibetan plateau, respectively, are strongly dependent on the along-strike variation of the width of the strong Lhasa–Qiangtang terranes.ISSN:2041-172

dx.doi.org/10.6084/m9.figshare.24464134

Supporting information: Detailed methods, and Figure S1-S2.Table S1: U-Pb Age of captured zircons from Tengchong Cenozoic volcanics.Table S2: Lu-Hf isotope of captured zircons from Tengchong Cenozoic volcanics.Table S3: Lhasa-Tengchong magmatic database.Table S4: Compiled magmatic zircon Hf isotopic values and ages from the Lhasa-Tengchong terrane.</p