We calculate physical properties of rocks in subduction zones using a compilation of mineral physical property measurements, a new set of phase diagrams and subduction-zone thermal models, and apply our results to Cascadia. Observed P-wave speeds of the Juan de Fuca plate west of the Cascadia trench are best matched by a greenschist-facies upper crust and metastable, partially hydrated lower cr...

The lack of contraction features on the Moon has been used to argue that the Moon underwent limited secular cooling, and thus had a relatively cool initial state. A cool early state in turn limits the depth of the lunar magma ocean. Recent GRAIL gravity measurements, however, suggest that dikes were emplaced in the lower crust, requiring global lunar expansion. Starting from the magma ocean sta...

It has long been recognized that mare basalts on the Moon are preferentially located both on the Earth-facing hemisphere and within large impact basins. A popular model that accounts for this observation assumes that these magmas were denser than the lunar crust, that they accumulated at the crust^mantle interface, and that eruptions occurred only when this magma chamber became overpressurized....

[1] We present a new quantitative framework to understand the process of mantle melting based on the velocity structure of igneous crust. Our approach focuses on the lower crustal section, which is expected to be least affected by porosity and seawater alteration, especially for thick igneous crust. Our methodology is thus best for constraining the origin of large igneous provinces. First, a qu...

Introduction: The South Pole-Aitken (SPA) Basin is the largest, oldest basin on the Moon. The extreme size of the basin, ≤2,500 km in diameter and a present depth of up to 13km [1,2], suggests that much of the upper crust would have been excavated during the formation/impact event, exposing the lower crust or upper mantle. Also, a large volume of impact melt breccia containing extensive lower c...

Seismic refraction, gravity, phase velocity, and magnetic data, coupled with the geologic record, are all approximately satisfied by the structure shown in Fig. 9. A 20-kilometer crust under the Coast Ranges and Great Valley thickens to more than 30 kilometers under the Sierra Nevada and parts of the Basin and Range province; this whole area is underlain by an anomalous upper mantle with a velo...

S U M M A R Y We have simultaneously inverted seismic refraction and wide-angle Moho reflection traveltimes for the 2-D crustal thickness and velocity structure of 150–300 kyr old crust along the East Pacific Rise (EPR) between the Siqueiros and Clipperton fracture zones (FZs). Our results show a strong correlation between ridge segmentation and upperand mid-crustal seismic velocities, with hig...

The Eastern California Shear Zone is bounded by the high heat flow region of the Basin and Range province and the low heat flow region of the Sierra Nevada block. This difference in thermal state influences the rheology of the lower crust/upper mantle, resulting in a viscosity contrast between the two regions. We analyze the effect of such a contrast on the kinematics and dynamics of the shear ...

The fusion crust of eight Antarctic meteorite nds show natural thermoluminescence (TL) levels about 100 times higher than the levels in the fusion crust of freshly fallen meteorites, Dhajala, Jilin and Bansur. If it is assumed that this TL is due to cosmic ray received on the surface of Antarctica, the terrestrial residence times of the meteorites is calculated to lie between 10 10 years. Stric...

[1] GPS data define a broad zone of present day deformation in the eastern Basin and Range province, western US. Using finite element models with elastic upper crust over viscoelastic lower crust/upper mantle and incorporating earthquake cycle effects, we show that these data are consistent with a model whereby most contemporary fault slip is focused on the Wasatch fault zone. Modeled rates of ...