The influence of sediment blanketing on subduction-zone seismicity
EARTH AND PLANETARY SCIENCE LETTERS
Authors: McKenzie, Dan; Jackson, James
Abstract
Subduction of oceanic lithosphere is now occurring beneath the Aegean and central Caspian Seas, and beneath the Indo-Burman Ranges in NE India, generating zones of earthquakes that reach depths of more than 150 km. Their existence is surprising. In general, where the temperature of the mantle part of the oceanic lithosphere can be estimated, earthquakes are confined to material whose temperature is below 600 degrees C. In these three regions the oceanic lithosphere is overlain by sediments with low thermal conductivity whose thickness is probably 10-25 km. The temperature of the oceanic crust and upper half of the lithosphere should be considerably increased by such a thick sedimentary cover, yet there is no obvious difference between these subduction zones and those where there is little sediment on the subducting plate. Detailed thermal modelling of the temperature shows that, for the first 40 Ma, the deposition of even a thick sedimentary layer has little effect on the thickness of the region of lithosphere whose temperature is below 600 degrees C, principally because little heat is conducted across the Moho. The modest effect of sediment blanketing over a period as long as 40 Ma was quite unexpected. Over the next 200 Ma the lithospheric temperature increases, until the Moho temperature reaches similar to 600 degrees C. This behaviour has important implications for oil and gas generation in the sediments, and for the existence of large earthquakes at depths of 150 km or more beneath the Hindu Kush, Pamirs and Romania. (C) 2020 Elsevier B.V. All rights reserved.
Toxicological effects induced on early life stages of zebrafish (Danio rerio) after an acute exposure to microplastics alone or co-exposed with copper
CHEMOSPHERE
Authors: Santos, Dercia; Felix, Luis; Luzio, Ana; Parra, Susana; Cabecinha, Edna; Bellas, Juan; Monteiro, Sandra M.
Abstract
Data about the toxicological interactions of MPs and heavy metals in biota is limited, particularly in fish early life stages. This study aimed to evaluate the toxicological effects of MPs and copper (Cu), alone or combined, in zebrafish early life stages. Embryos were exposed from 2 until 96-h post-fertilization (hpf) to MPs (2 mg/L), three sub-lethal concentrations of Cu (15, 60 and 125 mu g/L) and binary mixtures containing Cu and MPs (Cu15+MPs, Cu60+MPs, Cu125+MPs). Lethal and sub-lethal parameters, histopathological changes, biochemical biomarkers, gene expression and behavior were assessed. Our findings showed that Cu and Cu + MPs decreased embryos survival and hatching rate. Increased ROS levels were observed in larvae exposed to the two lowest Cu and Cu + MPs groups, suggesting an induction of oxidative stress. An increased CAT and GPx activities were observed in Cu and Cu + MPs, implying a response of the antioxidant defense system to overcome the metal and MPs stress. The sod1 expression was downregulated in all Cu groups and in the two highest Cu + MPs exposed groups. AChE was significantly inhibited in Cu and Cu + MPs groups, indicating neurotoxicity. A disruption of avoidance and social behaviors were also noticed in the Cu125 and Cu125+MPs exposed larvae. Evidences of Cutoxicity modulation by MPs were observed in some endpoints. Overall, the findings of this study highlight that Cu alone or co-exposed with MPs lead to oxidative stress, neurotoxicity and ultimately behavioral alterations in early life stages of zebrafish, while MPs alone do not produce significant effects on zebrafish larvae. (C) 2020 Elsevier Ltd. All rights reserved.