Date:2/11/2013

n (CIB) of south-central Alaska make locating and determining the geometry of the Border Ranges fault system (BRFS), a major feature of the region, difficult. Niti Mankhemthong and colleagues use recently collected gravity data, available aeromagnetic data, and other geophysical information as constraints to develop plausible 2D cross-section models that better image the BRFS and related geologic structures of the CIB. Their models suggest the BRFS dips 50 to 70 degrees toward the west-northwest and extends to at least 15 km. Their integrated models also show a thick sequence of sedimentary rocks and volcanic rocks (6 to 20 km depth) overlying a high metamorphosed, hydrous rock body (serpentinite) at a depth of 16 to 34 km. The volcanic rocks and serpentinite are interpreted as possible sources of the south Alaska magnetic high over the CIB. The CIB's eastern boundaries are characterized by gravity and magnetic highs of the Border Range ultramafic and mafic assemblages (BRUMA), rocks high in iron and magnesium that have been derived from the lower crust and upper mantle. Formation of the BRUMA may be related to the presences of the deeper serpentinite body. A model that includes underplated sediments at the base of the crust beneath the northwestern Chugach Mountains (12 to 40 km) is consistent with an observed regional gravity low. The underplating may be associated with the process of subducting and shortening Yakutat microplate in south-central Alaska. This paper is part of the "Neogene Tectonics and Climate-Tectonic Interactions in the Southern Alaskan Orogen" series.

---

New thermochronometric constraints on the Tertiary landscape evolution of central and eastern Grand Canyon, Arizona
J.P. Lee et al., U.S. Geological Survey, Denver Federal Center MS974, Denver, Colorado 80225, USA. Posted online 5 Feb. 2013; http://dx.doi.org/10.1130/GES00842.1.

The Grand Canyo
'/>"/>

Contact: Kea Giles kgiles@geosociety.org Geological Society of America Source:Eurekalert

0 GOOD

Page: 1 2 3 4 5 6 7 8 9 10
Related biology news :

1. Understanding faults and volcanics, plus life inside a rock
2. Rubbing boulders, fossil mammal teeth, barrier islands, and a change in volcanic behavior
3. Finding life in the volcanic systems of the Antarctic Polar Front
4. Shimmering water reveals cold volcanic vent in Antarctic waters
5. NJIT, Chinas Bengbu Glass Institute sign agreement for R&D, training
6. Feel-good glass for windows
7. Glass offers improved means of storing UKs nuclear waste
8. Pulverized rocks, coral reefs, seawater chemistry, and continental collisions
9. Australia creates worlds first continental-scale mineral maps
10. Sea surface temperatures reach record highs on Northeast continental shelf
11. New grant to establish pan-continental bioinformatics research network in Africa