The following announcement will appear in the April issue of GSA Today:
PENROSE CONFERENCE SCHEDULED
Precambrian High-Pressure - High-Temperature Metamorphism: A Key to
Understanding the Lower Crust and Reconstruction of Precambrian Plate Tectonics
September 23-29, 2002
Hengshan-Wutaishan and Beijing, China
Conveners:
M. Brown, Department of Geology, University of Maryland, College Park, MD
20742, USA, (301) 405-4080, fax 301-314-7970, [log in to unmask]
A. Kröner, Institut für Geowissenschaften, Universität Mainz, D-55099
Mainz, Germany, [log in to unmask]
P.J. O’Brien, Universität Potsdam, Institut für Geowissenschaften, Postfach
60 15 53, 14415 Potsdam, Germany, [log in to unmask]
C.W. Passchier, Institut für Geowissenschaften, Universität Mainz, D-55099
Mainz, Germany, [log in to unmask]
Li Jianghai, Department of Geology, Peking University, Beijing 100871,
People’s Republic of China, [log in to unmask]
Zhai Mingguo, Department of Geology & Geophysics, Chinese Academy of
Sciences, P.O. Box 9825, Beijing 100029, People’s Republic of China,
[log in to unmask]
The major goal of this conference is to discuss new approaches to
Precambrian plate tectonics in light of recent discoveries of high-pressure
- high-temperature metamorphism in Proterozoic rocks from the Canadian
Shield, the North China Craton, Tanzania, southern India, Brazil, Siberia,
and the Baltic Shield. These rocks record evidence of metamorphic pressures
of 1.7-1.0 GPa with characteristic near-isothermal decompression
pressure-temperature paths. The metamorphic and structural evolution of
these rocks, their tectonic setting, and the mechanism of their exhumation
are topics of international interest. Furthermore, the preservation of
lower crustal sections composed of high-grade gneisses and time-equivalent
upper crustal sections exposing greenstone belts makes it possible to study
the relationships between them in the same crustal section, potentially to
advance our understanding of continental crust formation and evolution. One
area where such examples are exposed is the Hengshan-Wutaishan area of
Northern China. The first part of this conference will be devoted to a
field trip to the Hengshan-Wutaishan area that will provide a template
within which to focus on the evidence for plate tectonics in the
Precambrian during the discussions in Beijing.
The Heng Mountains in northern Shanxi Province, about 250 km west-southwest
of Beijing, form part of the North China Craton and consist of ductilely
deformed late Archean to early Paleoproterozoic (ca. 2700-2100 Ma)
orthogneisses and minor paragneisses intruded by numerous mafic dykes of
gabbroic composition. The strongly deformed and boudinaged mafic rocks,
which commonly preserve primary igneous textures, underwent high-pressure
granulite metamorphism (Grt-Cpx-Pl-Qtz-Rt) at 850-900 °C and about 14 kbar,
suggesting that the entire Hengshan metamorphic assemblage experienced
high-pressure conditions equivalent to crustal depths of about 50 km. The
Hengshan metamorphic assemblage is adjacent to the low-grade late Archean
Wutai greenstone belt that consists of ca. 2.5 Ga bimodal volcanic rocks
and metasediments of arc affinity associated with coeval granitoids. The
Hengshan metamorphic assemblage may be the lower, plutonic part of a late
Archean to early Paleoproterozoic magmatic arc, the upper volcanic part of
which is represented by the adjacent Wutai greenstone belt. Virtually all
the magmatic events recorded in the Hengshan metamorphic assemblage also
are identified in the Wutai greenstone belt.
The general themes of the conference are: (1) Precambrian high-pressure -
high-temperature eclogite- and granulite-facies rocks and their evolution,
and tectonic implications for plate tectonic processes; and (2) the
structural relationship between high-grade lower crustal domains and
low-grade upper crustal domains, including the geometry and evolution of
major ductile shear zones and thrust belts. Key speakers from the fields of
metamorphic petrology, tectonics, and geodynamic modeling will address
these themes in an interdisciplinary manner. Other contributions will
address specific regional examples, where many of the details of the field
relationships provide primary information and important constraints. All
participants are encouraged to bring poster presentations, from which
additional oral presentations will be selected. It is anticipated that
about a third of the time in Beijing will be devoted to oral presentations,
about a third of the time to discussion, and about a third of the time to
viewing the posters.
The conference is limited to 80 participants. We encourage interested
graduate students to apply. The registration fee, which will cover lodging,
meals, field trips, and all other conference costs except personal
incidentals, is likely to be US$400 (US$300 for students). Participants
will be responsible for their own travel to and from Beijing.
Application Deadline: June 1, 2002
Geologists and petrologists with an interest in Precambrian high-grade
gneiss terrains and greenstone belts are encouraged to apply. Potential
participants should send a letter of application to Alfred Kröner or
Mingguo Zhai (addresses above), including a brief statement of interests,
the relevance of the applicant’s recent work to the themes of the meeting,
the subject of any proposed presentation (verbal or poster), and contact
information (particularly e-mail address for the period June - September
2002). We expect to attract a diverse group of field geologists,
metamorphic petrologists, tectonicians, and modelers. Invitations will be
e-mailed to participants by mid-June 2002.
Co-sponsors: National Science Foundation of China, Beijing, China; Chinese
Academy of Sciences, Beijing, China; and Peking University, Beijing, China.
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Michael Brown
Professor of Geology
and Chair of Department
Department of Geology [log in to unmask]
Geology Building http: www.geol.umd.edu
University of Maryland Direct line: 301 405 4080
College Park Exec. asst.: 301 405 4065
MD 20742-4211 Dept. office: 301 405 4082
USA Direct fax: 301 314 7970
Dept. fax: 301 314
9661
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LABORATORY FOR CRUSTAL PETROLOGY (Information at:
http: www.geol.umd.edu/pages/faculty/BROWN/lcp.html)
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