Fluid flow, element migration, and petrotectonic evolution of the early Mesozoic Central Klamath island arc, northwesternmost California Page: 1 of 4
2 pagesView a full description of this report.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
V
p0^£^//-^/5f —T /
STANFORD UNIVERSITY
EARTH SCIENCES
Office of the Dean
DOE/ER/14154—Tl
lu
DE92 003770
June 13, 1991
Dr. Norman Goldstein
Division of Engineering & Geosciences, ER-15
U.S. Department of Energy
19901 Germantown Road
Germantown, MD 20874
Dear Norm:
This letter represents a progress report on DOE FG03-90ER14154, entitled “Fluid
Flow, Element Migration, and Petrotectonic Evolution of the Early Mesozoic Central
Klamath Island Arc, North westernmost California.” The first year'of the award was
funded at $99,776 for the period 09/15/90 - 09/14/91. We now request support for the
second (and last) year of the grant, 09/15/91 - 09/14/92, to be funded at a level of
$101,326. The research builds on an earlier grant, DOE FG03-87ER13806 (09/10/87 -
03/09/90, $132,590).
Continuing investigations in the central Klamath Mountains by our group have
documented the presence of a polymetamorphosed suite of highly magnesian basaltic
rocks, the so-called Yellow Dog greenstones, in the Sawyers Bar terrane (=North Fork
ophiolite) of the western Triassic and Paleozoic belt. The Yellow Dog metavolcanics
display apparent komatiitic chemical affinities; if correctly interpreted, such an occurrence
could have important significance for the thermal and petrotectonic evolution of the early
Mesozoic Klamath island arc. The metabasalts were initially thought to reflect the Permo-
Triassic to Middle Jurassic overriding of an oceanic hot spot by the stable, nonsubducted
arc-capped North American lithospheric plate, but are now regarded as metamorphosed,
mildly alkalic oceanic island lavas (OIBs) and surmounting immature calc-alkaline arc
basalts (lATs). These igneous rocks are ^nterlayered with, and are interpreted to largely
overlie distal turbidites. The assemblage was laid down, altered and metasomatized during
the hypothesized collapse of a Philippine Sea-type marginal basin which brought the
westerly Sawyers Bar oceanic arc terrane into juxtaposition with the inboard, pre-existing
Stuart Fork subduction complex, in an immature island-arc setting.
Supported research has concentrated on elucidating the areal extent and
structural/stratigraphic relations of these mafic/ultramafic Yellow Dog metavolcanic units,
and has documented the insignificant degree of crustal contamination of the melts by
associated terrigenous metasediments. The physical conditions of metamorphism and of
water-rock interaction accompanying island-arc accretion have been determined as follows:
Middle Jurassic regional metamorphism of the Sawyers Bar/Stuart Fork amalgamated
terrane took place at 350-500°C and 2.5-4.5kb; contact aureoles peripheral to the mid-
Jurassic calc-alkaline plutons reached maximum physical conditions of 500-600°C at 2.0-
3.5 kb. Intrusion of the post-collisional granitoids mobilized alkalies, silicas, rare earths,
and, especially, oxygen isotopes in the sedimentary strata intimately interlayered with the
Yellow Dog greenstones, overprinting the effects of an inferred earlier seafloor alteration in
the mafic volcanics. The thermal structure and its evolution in the central Klamath
Mountains evidently reflects surfaceward advective transport of magmatic energy derived
from the partly fused downgoing oceanic slab, as well as hydrothermal fluid circulation.
DISTRIBUTION Ot- t HIS DOCUMENT IS UNLIMITED
Upcoming Pages
Here’s what’s next.
Search Inside
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
Ernst, W.G. Fluid flow, element migration, and petrotectonic evolution of the early Mesozoic Central Klamath island arc, northwesternmost California, report, June 13, 1991; California. (https://digital.library.unt.edu/ark:/67531/metadc1100580/m1/1/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.