Erling,
You are always finding interesting things!
There are Pamir eclogite-facies crustal xenoliths from 2.7 GPa and 1050C
with *some* similar features, including Fe-Mg carbonate inclusions in
K-feldspar, and multiphase barite + carbonate + K-feldspar inclusions in
garnet. I recall that there are also other inclusions, but I have not
studied them in detail.
One paper with some pictures of inclusions is:
http://www.geol.ucsb.edu/faculty/hacker/viz/Hacker05_Ultrahigh_pressure_processing_continental_crust.pdf
I also have a number of other Russian-Tajik papers (e.g., Valery Lutkov)
that I have but cannot read in detail; e.g.,
Lutkov, V.S. (2003) Petrochemical evolution and genesis of potassium
pyroxenite-eclogite-granulite association in the mantle and crustal
xenoliths from Neogene fergusites of South Pamir, Tajikistan.
Geochimia 3, 254-265.
At least one of those papers reports up to 6000 ppm Ba.
Looking forward to hearing and seeing more, Brad
At 06:06 AM 10/26/2010, you wrote:
Dear all
Apologize for multiple postings.
We are currently working on some HP carbonate-rich rocks that appear to
have intruded UHP eclogite at still high pressure. The mineral
composition of these rocks is Fe-Mg calcite ± Fe-dolomite + ternary
garnet + omphacitic pyroxene + Ti-rich phlogopite + apatite + rutile +
ilmenite ± allanite ± zircon ± monazite. Large garnet contains inclusions
of all the other phases, except from allanite and monazite. Exsolution of
Fe-dolomite in calcite and calcite in Fe-dolomite is common. Large grains
of clinopyroxene have lamellae of ilmenite in one direction and
lamellae/rods of phlogopite in apparently in two directions (see attached
BSE images a-d). The lamellae of ilmenite also show an internal
exsolution with lamellae of magnetite (BSE image c). Of special interest
are multiphase inclusions, the presence of acicular crystals of apatite
in garnet (BSE images e & f), and ilmenite with exsolved magnetite
(BSE image g). Matrix apatite (up to 5 modal %) frequently have needles
of pure SiO2 and Fe1-xS oriented parallel to the
c-axis (BSE image h and microphoto i).
The peak conditions of the UHP metamorphism has been calculated to
700-750 °C/3.35 GPa. Some of the observed features in the carbonate-rich
rock indicate, in my opinion, exsolution from higher T and possibly also
P. The multiphase inclusions in garnet and especially the appearance of
apatite are intriguing to me. I have never seen anything like this and
don’t have any clues of how such apatite is formed. I will be happy to
receive feedback on all the features shown in the attached images, as
this could help us to make some progress in understanding these
peculiarities.
As an additional information I will mention that the rocks are strongly
enriched in LREE (La 1000x chondrite) and Ba (up to 4000 ppm).
Best regards
Erling Ravna
--------------------------------------------------------------
"I have become rather like King Midas, except that everything turns
not into gold but into a circus." --Einstein
--------------------------------------------------------------
Bradley Hacker office:
Webb 2120 tel +1 805.893.7952
Professor of
Geology
dept office +1 805.893.3471
Earth Research Institute
University of California, Santa Barbara CA 93106-9630
http://www.geol.ucsb.edu/faculty/hacker
