/pdf/global-continental-and-ocean-basin-reconstructions-since-200-huopwd2ldv.pdf

Global continental and ocean basin reconstructions since 200 Ma

/pdf/phanerozoic-polar-wander-palaeogeography-and-dynamics-3fc5flnbf0.pdf

Phanerozoic polar wander, palaeogeography and dynamics

Joint determination of 40K decay constants and 40Ar∗/40K for the Fish Canyon sanidine standard, and improved accuracy for 40Ar/39Ar geochronology

Late Jurassic–Cenozoic reconstructions of the Indonesian region and the Indian Ocean

We have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self-consistent set of global isochrons and associated plate reconstruction poles. The age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading. Ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models. We have constructed an age grid with error estimates for each grid cell as a function of (1) the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid, (2) the distance of a given grid cell to the nearest magnetic anomaly identification, and (3) the gradient of the age grid: i.e., larger errors are associated with high age gradients at fracture zones or other age discontinuities. Future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere, the heat loss of the Earth, ridge-push forces through time, asymmetry of spreading, and providing constraints for seismic tomography and mantle convection models.

Digital isochrons of the world's ocean floor

Wider use of radiogenic isotopes in geosciences has been enabled by developments in massspectrometry at the beginning of the 21st century. Nowadays, radiogenic isotope geochemistry forms an integrated part of geosciences in a range of applications, starting from formation of planetary systems, genesis, and the evolution of Earth's lithosphere and associated mineral and oil deposits, as well as environmental tracers. Two primary types of information are available from radiogenic isotopes studies: age determination and isotopic source tracing. In this chapter, the range of isotope systematics currently used in geosciences and their applications are reviewed, together with progress in analytical technologies. The chapter brings together internationally recognised researchers whohave been at the forefront of analytical technologies in the field of geochemistry of radiogenic isotopes.

Application of radiogenic isotopes in Geosciences: Overview and perspectives

Isotopic Constraints on Davis Bank, Vitória-Trindade Ridge: A Revisited Petrogenetic Model

Summary: Shatter cones in Keurusselkä impact structure, Finland

Superchondritic Nb/Ta is rarely reported in terrestrial reservoirs and is usually attributed to carbonatite metasomatism or accessory rutile in the residue phase. Previously documented high Nb/Ta in rocks derived from subcontinental lithospheric mantle indicated a predominance of carbonatite metasomatism. This study evaluates Nb/Ta in conjunction with other trace elements of Neoproterozoic mafic dykes exposed in the eastern segment of the Jiangnan Orogen, where early subduction existed before the amalgamation of South China. These mafic dykes show mostly superchondritic Nb/Ta ratios from 19.6 to 24.5. Partial melting modelling suggested low-degree melting of rutile-bearing subcontinental lithospheric mantle for these mafic dykes. A literature review of Neoproterozoic mafic–intermediate rocks throughout the Jiangnan Orogen shows sporadically but coincidently superchondritic Nb/Ta near or beneath the Shuangxiwu arc, indicating rutile stability in the relict sub-arc mantle. Rutile in the lherzolite was formed sometime after Neoproterozoic subduction initiation in South China but contemporaneous with crustal thickening at c. 860 Ma. This study brings direct evidence to bear on the mechanism of rutile formation in the mantle wedge, as well as the link between crustal thickening and superchondritic Nb/Ta of mafic products derived from the metasomatized mantle. Supplementary material: Major and trace element compositions, photomicrographs of samples, and figures illustrating geochemistry, REE and incompatible trace element patterns and loss on ignition versus Nb/Ta and La/Yb are available at https://doi.org/10.6084/m9.figshare.c.5093535

Subduction-related subcontinental lithospheric mantle metasomatism and crustal thickening: origin for superchondritic Nb/Ta in mafic dykes

Rubble piles asteroids consist of reassembled fragments from shattered monolithic asteroids and are much more abundant than previously thought in the solar system. Although monolithic asteroids that are a kilometer in diameter have been predicted to have a lifespan of few 100 million years, it is currently not known how durable rubble pile asteroids are. Here, we show that rubble pile asteroids can survive ambient solar system bombardment processes for extremely long periods and potentially 10 times longer than their monolith counterparts. We studied three regolith dust particles recovered by the Hayabusa space probe from the rubble pile asteroid 25143 Itokawa using electron backscatter diffraction, time-of-flight secondary ion mass spectrometry, atom probe tomography, and 40Ar/39Ar dating techniques. Our results show that the particles have only been affected by shock pressure of ca. 5 to 15 GPa. Two particles have 40Ar/39Ar ages of 4,219 ± 35 and 4,149 ± 41 My and when combined with thermal and diffusion models; these results constrain the formation age of the rubble pile structure to ≥4.2 billion years ago. Such a long survival time for an asteroid is attributed to the shock-absorbent nature of rubble pile material and suggests that rubble piles are hard to destroy once they are created. Our results suggest that rubble piles are probably more abundant in the asteroid belt than previously thought and provide constrain to help develop mitigation strategies to prevent asteroid collisions with Earth.

Fred Jourdan

Papers

Application of radiogenic isotopes in Geosciences: Overview and perspectives

Isotopic Constraints on Davis Bank, Vitória-Trindade Ridge: A Revisited Petrogenetic Model

Summary: Shatter cones in Keurusselkä impact structure, Finland

Subduction-related subcontinental lithospheric mantle metasomatism and crustal thickening: origin for superchondritic Nb/Ta in mafic dykes

Rubble pile asteroids are forever.