Using an approximately analytical formation, we extend the steady state model of the pure methane hydrate system to include the salinity based on the dynamic model of the methane hydrate system. The top and bottom boundaries of the methane hydrate stability zone (MHSZ) and the actual methane hydrate zone (MHZ), and the top of free gas occurrence are determined by using numerical methods and the new steady state model developed in this paper. Numerical results show that the MHZ thickness becomes thinner with increasing the salinity, and the stability is lowered and the base of the MHSZ is shifted toward the seafloor in the presence of salts. As a result, the thickness of actual hydrate occurrence becomes thinner compared with that of the pure water case. On the other hand, since lower solubility reduces the amount of gas needed to form methane hydrate, the existence of salts in seawater can actually promote methane gas hydrate formation in the hydrate stability zone. Numerical modeling also demonstrates that for the salt-water case the presence of methane within the field of methane hydrate stability is not sufficient to ensure the occurrence of gas hydrate, which can only form when the methane concentration dissolved in solution with salts exceeds the local methane solubility in salt water and if the methane flux exceeds a critical value corresponding to the rate of diffusive methane transport. In order to maintain gas hydrate or to form methane gas hydrate in marine sediments, a persistent supplied methane probably from biogenic or thermogenic processes, is required to overcome losses due to diffusion and advection. methane gas hydrate, solubility, stability of hydrate, salinity, phase equilibrium Methane gas hydrate (MGH) is an ice-like crystalline compound of water and gas molecules [1,2] that forms at low temperature and high pressure when the dissolved methane concentration exceeds the local solubility [2] . The formation of methane hydrate can extract water and methane gas reserved in porous media. Under suitable temperature and pressure conditions liquid water in pores and methane dissolved in water may transform into solid hydrate. The formation of solid hydrate can increase the strength of sediments and result in lowering porosity and permeability [3] . Reversely, when the gas hydrate system is not stable, solid hydrate can be decomposed into water and methane. It is stable under elevated or relatively high pressure and low temperature conditions such as those found in the marine sediments along continental margins and permafrost regions [4,5] . The gas hydrate stability depends on the water depth (pressure) and temperature. Decreasing pressure caused by lowering the sea level or increasing seawater temperature causes the hydrate dissociation, resulting in the geologic hazards of seafloor sloping [6] and releasing "greenhouse" gas (main methane gas) including in hydrate further resulting in the global climate change [7] . In a word, changes of temperature and pressure cause the transformation between sol...

We present a local earthquake tomography to illuminate the crustal and uppermost mantle structure beneath the southern Puna plateau and to test the delamination hypothesis. Vp and Vp/Vs ratios were obtained using travel time variations recorded by 75 temporary seismic stations between 2007 and 2009. In the upper crust, prominent low Vp anomalies are found beneath the main volcanic centers, indicating the presence of magma and melt beneath the southern Puna plateau. Beneath the Moho at around 90-km depth, a strong high Vp anomaly is detected just west of the giant backarc Cerro Galan ignimbrite caldera. This high Vp anomaly is only resolved if earthquakes with an azimuthal gap up to 300°are included in the inversion. However, we show through data subset and synthetic tests that the anomaly is robust due to our specific station-event geometry and interpret it as a delaminated block of lower crust and uppermost mantle lithosphere under the southern Puna plateau. The low velocities in the crust are interpreted as a product of the delamination event that triggered the rise of fluids and melts into the crust and induced the high topography in this part of the plateau. The tomography also reveals the existence of low-velocity anomalies that link arc magmatism at the Ojos del Salado volcanic center with slab seismicity clusters at depths of about 100 and 150 km and support fluid transport in the mantle wedge due to dehydration reaction within the subducted slab. The northern and southern Puna are separated by the northwest-trending Olacapato-Toro-Lineament (O-T-L) near 24.5°S. To the east, the boundary of the southern Puna is structurally limited by the Santa Barbara system north of 27°S and by the Sierras Pampeanas to the south. In detail, the Santa Barbara system is characterized by predominantly west verging, relatively high-angle thrust faults that are largely inverted Cretaceous normal faults and the Sierras Pampeanas are thickskinned basement uplifts that are bounded by high-angle reverse faults (Allmendinger et al., 1997; Kley & Monaldi, 1998, 2002). To the west, the southern Puna is bounded by the Andean Neogene Central Volcanic Zone (CVZ). Within the region of the southern Puna plateau, there are a series of NW-trending zones of lithospheric weakness along which the largest

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In this study, we performed receiver function profiling and fitted harmonic functions to the arrival time variations of Pms phases to calculate the crustal seismic anisotropy with delay time and fast polarization direction, using broadband seismic data obtained from 55 temporary stations in two linear profiles and 39 stations in the Lower Yangtze and adjacent region. Moreover, we determined the crustal thickness and Poisson’s ratio using a novel H-κ-c stacking method. Our results revealed that the Middle-Lower Yangtze Metallogenic Belt and the north east section of the Qinzhou-Hangzhou Metallogenic Belt are characterized by Moho upliftment (<32 km), a relatively high Poisson’s ratio (>0.26), local lithospheric thinning (<70 km), and a pattern of deep faults that connect the crust and asthenosphere and serve as conduits for magma upwelling. The NE-SW fast polarization direction was consistent with the SKS splitting results, and the average delay time was 0.45 s. Moreover, underplating of deep magma and upwelling along the weak zone caused local Moho uplift and ductile shear of the lower crust, resulting in the directional arrangement of amphibole and other minerals, which may be the controlling mechanism for the crustal anisotropy in the study area. The variations in crustal structure and anisotropy characteristics indicated that in the context of the northeastern Paleo-Pacific plate subduction, the existence of weak lithospheric zones and the northeastern asthenospheric flow are important conditions for metal supernormal enrichment in the Lower Yangtze region.