Cruise Plan
From: Peter Lonsdale, 29th October, 1997
The Alarcon Initiative
The purpose would be a multifarious
study of the Alarcon spreading center in the mouth of the Gulf of California, throwing
together a collegial group of Scripps scientists and students to study the origin,
geologic history and present activity (tectonic, volcanic and hydrothermal) of this important site.
Why this site is important is addressed in the attached ÒDescription of the Alarcon
Segment and its potential as a research siteÓ. This is abstracted from a note I sent
in June to 40 Scripps scientists in all the oceanographic disciplines, inviting their
participation in this project. As I reported to the last UC Ship Fund committee meeting,
this drew positive responses from a dozen geologists, geophysicists and geochemists:
P. Lonsdale, wants to use Seabeam and magnetics for studying the spreading history and risecrest geomorphology.
M. Zumberge and J. Hildebrand, surface and deep towed gravity, for risecrest structure
J. Sclater, seismic profiling for continental rifting structure and heat flow measurements for geothermal studies
J. Gieskes, near-bottom CTD tows for hydrothermal plumes
M. Kastner, coring for sediment and pore water geochemistry
K. Brown, free-vehicle for fluid discharge measurement and sampling
D. Hilton, for isotopic studies for pore fluids (from cores and free vehicles)
and magmatic volatiles (from dredged rocks).
P. Castillo, J. Hawkins, D. Macdougall and H. Staudigel, rock dredging,
for petrologic and isotopic study of risecrest and seamount basalt.
(H. Staudigel also plans to study biologically mediated rock alteration, using material from dredge or core samples).
Each of these researchers could provide a page or more of text explaining
the scientific value of their proposed work, should the committee need that.
The general themes addressed by these studies include:
(1) what is the recent history of motion between the Pacific and North American
plates, and why did Baja California rift away from Mexico
(2) what is the petrologic nature and structure of the igneous crust accreted
at a young intracontinental spreading center and
(3) what are the effects of hydrothermal processes at an unusually nearshore, rapidly sedimented risecrest.
In almost all cases we do not expect definitive answers from this short, intensive,
basically exploratory field program; we do expect to collect information that will
stimulate and help us to propose future work with extramural funding. We would plan on a
brief (in. a.m., out p.m.) intermediate stop, to change personnel (some of who would sooner
not be absent from classes and other responsibilities for more than a week), and offload
expensive unneeded techs. This would split the time between a survey leg (Seabeam, magnetics,
gravity, seismic and 3.5kHz profiling, CTD) and a sampling leg (coring, dredging, heat flow, free-vehicles).
The student-teaching element will be limited to (a) involvement, to different
degrees among the 12 investigators, of Scripps students pursuing their thesis
research, (b) designating one or other week of the cruise as part of the SIO248
Essentials of Geology class, a ÒrequiredÓ class for all 1st year Geological
Sciences students, and some Geophysics students, and commonly taken by some
Earth Sciences undergrads, (c) participation (strongly encouraged) of students
in the new Earth Sciences M.Sc. program, and (d) participation of Mexican
graduate and undergraduate students from CICESE and UBC (Ensenada). The Mexican
institutions are eager to be involved (with research as well as educational interests,
in the case of CICESE), but detailed discussions with Mexican colleagues have been postponed
until after this cruise is scheduled. We are also trying to see how we might involve
(U.S.) undergraduates, and thereby use this cruise as a student recruiting tool for
Scripps.
Internet: shipsked@ucsd.edu
WWW: http://sio.ucsd.edu/
shipsked@ucsd.edu