Karin Lydia Louzada, PhD

HOME

RESEARCH

I. Lonar impact crater, India

Lonar crater, India, is the best preserved terrestrial impact crater formed in basalt and is a unique terrestrial analogue for small, simple craters on terrestrial planets and the Moon. We investigated the paleomagnetic and rock-magnetic properties of the 1.88 km diameter crater in order to understand the effect of impacts on magnetization in target rocks. The magnetization in the Lonar basalts consists of an original 65 Ma Deccan magnetization and a recent overprint.We constrained the timing of magnetization acquisition at Lonar using a combination of conglomerate tests on ejecta deposit clasts and fold tests on the overturned and jumbled rim fold. In some areas, the recumbent rim fold is preserved and can be approximated as a horizontal cylindrical fold. In other areas, substantial vertical axis rotation may have occurred where tear zones developed during folding. We observed only subtle effects from the impact on the rock-magnetic properties of Lonar materials, which include a slightly elevated coercivity in shocked ejecta blocks. We show that paleomagnetism can provide a constraint on shock heating in the absence of petrographic evidence of shock (in this case, <187±15 °C). At Lonar, viscous (and/or chemical) remanent magnetization acquired in the 50 kyr subsequent to crater formation has obscured any evidence of shock remanent magnetization. We also find no evidence of shock demagnetization or the presence of intense impact-induced or impact amplified transient magnetic fields that have been proposed around larger impact structures. [See publications tab]

II. Shock Effects on Magnetic Properties of Pyrrhotite and the Martian Crust

We performed planar shock recovery experiments on natural pyrrhotite at pressures up to 6.9 GPa. We find that high-field isothermal remanent agnetization in pyrrhotite is demagnetized up to 90% by shock due to preferential removal of low coercivity components of magnetization. Contrary to static experiments, we do not observe complete demagnetization. Post shock permanent changes in magnetic properties include increasing saturation isothermal remanent magnetization, bulk coercivity and low-temperature memory, and changes in squareness of hysteresis. These changes are consistent with an increase in the volume fraction of single domain grains. The lack of magnetic anomalies over large Martian impact basins is not expected to be solely due to shock demagnetization of the crust. We find that pyrrhotite bearing rocks and meteorites can retain records of Martian magnetic fields even if shocked to pressures approaching 7 GPa. However, some paleointensity techniques may underestimate this field. [See publications tab]

III. Effect of Planet Curvature on the Pressure Field around Large Impact Craters

We investigate the effects of planetary curvature and the crust-mantle boundary on the shock pressure field around impact basins on Mars using acoustic ray path calculations and hydrocode simulations. Planet curvature and, to a lesser extent, increasing sound speed with depth shallow the zone of wave interference, where shock pressures decay rapidly to the surface. The depth to the interference zone boundary diverges from the flat surface solution for projectile-to-Mars radius ratios greater than ~1% (transient craters greater than ~300 km); the difference increases with distance from the impact point and projectile size. In hydrocode simulations (but not the simple ray path model), the presence of the crust-mantle boundary produces nearly vertical pressure contours in the crust. Around Hellas basin, demagnetization occurs at shock pressures between 1.1 (±0.2) and 3.4 (±0.7) GPa, where the range is due to the uncertainty in the transient crater diameter. [See publications tab]

SCIENCE AND TECHNOLOGY

BIO / CURRICULUM VITAE

PUBLICATIONS

EDUCATION

PHOTOGRAPHS

Contact:
E: louzada AT post DOT harvard DOT edu
T: +1-857-998-0728