Feb 2009 Membership Meeting - Banded Iron Formations

Post date: Mar 05, 2010 4:0:8 PM

February Membership Meeting

Date: 2/23/2010

The February Meeting of the Madison Gem and Mineral Club will be 7 pm, Tuesday, Feb 23, at the usual location, Rm AB20 Weeks Hall, at the corner of Charter and Dayton St on the UW Campus.

The speaker is Professor Huifeng Xu, of the UW Geology Department, on "Battle between the Bands: generation mechanism of banded iron formations in the early earth ." Please see abstract below.

Two competitions! Lake Superior Agate with uncut area AND new members self-collected material or cabochon

All members are urged to bring specimens for the monthly competition. Questions may be directed to Metje Butler, Education Chairperson, at 244-3659. Cash awards: 1st place $10; 2nd place $5.

Competition Rules:

1. Only paid members of the Madison Gem and Mineral Club may enter, personally working or fabricating the material unless otherwise designated. 2. No prior-winning competition items eligible. 3. Read the competition requirements carefully. Only one entry per month, but item may be entered in other months if it qualifies (non-previous winner)

Title:

Battle between the Bands: generation mechanism of banded iron formations in the early earth

Huifang Xu: Department of Geoscience, University of Wisconsin – Madison

Will be presented on Feb. 23 (Tuesday) for Madison Minerals and Gems Club in Weeks Hall (Home of Geology Museum), 1215 West Dayton Street, Madison, Wisconsin.

Abstract

Banded iron formations or BIFs are ancient rocks formed between ~3.8 and ~1.65 billion years ago at what was then the bottoms of the ocean and sea. The stripes represent alternating layers of silica-rich chert layer and iron-rich minerals like hematite and magnetite. BIFs carry important information on the early evolution of the Earth. Unfortunately, the actual mechanism for their formation still remains controversial. Our new results show that the predominant occurrence of BIFs in the Achaean-Paleo-Proterozic period may be controlled by the compositional changes in the oceanic crust. BIF formation requires Fe-Si-rich geologic fluids. Such fluids can be generated only from the early oceanic crust (Al-poor komatiite) through hydrothermal leaching by seawater. Later enrichment of Al in the oceanic crust leads to the formation of Fe(II)-bearing chlorite during the leaching and the depletion of Fe²⁺ in leaching fluids, thus preventing BIF formation in recent geological time periods. We further show that periodic precipitation of iron and silica minerals can be induced by positive feedbacks among relevant chemical reactions as a Fe-Si-rich fluid mixes with its ambient seawater. Unlike previous hypotheses, the mechanism proposed here attributes BIF micro-bandings to the internal dynamics of the chemical system, rather than to an outside force such as surface temperature variations. Therefore, BIFs are expected to occur in both shallow and deep water environments, as observed.

Our newly developed a BIF formation model that offers a complete picture of the earth environment at the time, including interactions between rocks, water, and air. The lithosphere affects the hydrosphere, the hydrosphere affects the atmosphere, and all those eventually affect the biosphere on the early Earth.

About my research program:

Prof. Xu is a leader of Nano-geoscience Research Group at the University of Wisconsin. His research program is closely related to energy and environment issues. His current research projects include chemical reactivity of nano-phase minerals and nanopore surfaces, and uranium behaviors in earth environments, effect of mineral substrate and dissolved molecules on controlling structures and compositions of Ca-Mg-carbonate minerals (that are long-term stable carbonate forms in geological environment), and early earth environment studies, and smart materials for scavenging waste energies for hydrogen production. His new discovery about BIF generation has been published in Nature Geosciecne (2009, November issue) and reported online in several places.

. His new discoveries have resulted in two invention patents about direct transformation from mechanical energy into chemical energy, and improving efficiency of solar energy into chemical energy transformation. Prof. Xu’s research program is currently supported by National Science Foundation, U. S. Department of Energy, and NASA Astrobiology Institute.

Copyright of photos: Huifang Xu

Achaean banded iron formation in Minnesota (more than 2.5 billion of years old)

Copyright of photos: Huifang Xu

Stromatolite in a Paleo-Proterozic (~ 1.85 billion of year old) BIF.