Hellebrand Eric

No Thumbnail Available
Last Name
Hellebrand
First Name
Eric
ORCID

Filters

2011 2
1 1
2
Reset filters

Settings

Search Results

Now showing 1 - 2 of 2
Thumbnail Image
Article

Drilling constraints on lithospheric accretion and evolution at Atlantis Massif, Mid-Atlantic Ridge 30°N

2011-07-19 , Blackman, Donna K. , Ildefonse, Benoit , John, Barbara E. , Ohara, Y. , Miller, D. J. , Abe, Natsue , Abratis, M. , Andal, E. S. , Andreani, Muriel , Awaji, S. , Beard, J. S. , Brunelli, Daniele , Charney, A. B. , Christie, D. M. , Collins, John A. , Delacour, A. G. , Delius, H. , Drouin, M. , Einaudi, F. , Escartin, Javier E. , Frost, B. R. , Fruh-Green, Gretchen L. , Fryer, P. B. , Gee, Jeffrey S. , Grimes, C. B. , Halfpenny, A. , Hansen, H.-E. , Harris, Amber C. , Tamura, A. , Hayman, Nicholas W. , Hellebrand, Eric , Hirose, T. , Hirth, Greg , Ishimaru, S. , Johnson, Kevin T. M. , Karner, G. D. , Linek, M. , MacLeod, Christopher J. , Maeda, J. , Mason, O..U. , McCaig, A. M. , Michibayashi, K. , Morris, Antony , Nakagawa, T. , Nozaka, Toshio , Rosner, Martin , Searle, Roger C. , Suhr, G. , Tominaga, Masako , von der Handt, A. , Yamasaki, T. , Zhao, Xixi

Expeditions 304 and 305 of the Integrated Ocean Drilling Program cored and logged a 1.4 km section of the domal core of Atlantis Massif. Postdrilling research results summarized here constrain the structure and lithology of the Central Dome of this oceanic core complex. The dominantly gabbroic sequence recovered contrasts with predrilling predictions; application of the ground truth in subsequent geophysical processing has produced self-consistent models for the Central Dome. The presence of many thin interfingered petrologic units indicates that the intrusions forming the domal core were emplaced over a minimum of 100–220 kyr, and not as a single magma pulse. Isotopic and mineralogical alteration is intense in the upper 100 m but decreases in intensity with depth. Below 800 m, alteration is restricted to narrow zones surrounding faults, veins, igneous contacts, and to an interval of locally intense serpentinization in olivine-rich troctolite. Hydration of the lithosphere occurred over the complete range of temperature conditions from granulite to zeolite facies, but was predominantly in the amphibolite and greenschist range. Deformation of the sequence was remarkably localized, despite paleomagnetic indications that the dome has undergone at least 45° rotation, presumably during unroofing via detachment faulting. Both the deformation pattern and the lithology contrast with what is known from seafloor studies on the adjacent Southern Ridge of the massif. There, the detachment capping the domal core deformed a 100 m thick zone and serpentinized peridotite comprises ∼70% of recovered samples. We develop a working model of the evolution of Atlantis Massif over the past 2 Myr, outlining several stages that could explain the observed similarities and differences between the Central Dome and the Southern Ridge.

View
Thumbnail Image
Preprint

Protracted timescales of lower crustal growth at the fast-spreading East Pacific Rise

2011-12 , Rioux, Matthew , Lissenberg, C. Johan , McLean, Noah M. , Bowring, Samuel A. , MacLeod, Christopher J. , Hellebrand, Eric , Shimizu, Nobumichi

Formation of the oceanic crust at mid-ocean ridges is a fundamental component of plate tectonics. A majority of the crust at many ridges is composed of plutonic rocks that form by crystallization of mantle-derived magmas within the crust. Recent application of U/Pb dating to samples from in-situ oceanic crust has begun to provide exciting new insight into the timing, duration and distribution of magmatism during formation of the plutonic crust1-4. Previous studies have focused on samples from slow-spreading ridges, however, the time scales and processes of crustal growth are expected to vary with plate spreading rate. Here we present the first high-precision dates from plutonic crust formed at the fast-spreading East Pacific Rise (EPR). Individual zircon minerals yielded dates from 1.420–1.271 million years ago, with uncertainties of ± 0.006–0.081 million years. Within individual samples, zircons record a range of dates of up to ~0.124 million years, consistent with protracted crystallization or assimilation of older zircons from adjacent rocks. The variability in dates is comparable to data from the Vema lithospheric section on the Mid-Atlantic Ridge (MAR)3, suggesting that time scales of magmatic processes in the lower crust may be similar at slow- and fast-spreading ridges.

View