153
Me2+/Ca DISTRIBUTION COEFFICIENTS BETWEEN CALCITES
FEOM SARDINIAN TRAVERTINES AND DEPOSITING WATERS
Sciences,
University
of
Cagliari - Italy).
The carbonatic portion of travertines from
different localities in Sardinia has been analysed with the purpose of comparing the distribution on Mg, Sr and Ba in the calcite withthe
solutions depositing this mineral in continental
natural systems.
We considered six travertines deposits connected with
springs
CHAMBER
C ~L LANOMUIR and T. PLANK.
L A M O N T - D O H ~ R T Y O-~OLOOICAL O B S E R V A T O R Y
PALISADES, ~
10964
USA
ROSA CIDU, LUCA FANFANI, PAOLA ZUDDAS AND
PIERPAOLO ZUDDAS
(Department of Earth
QUANTITATIVE R E ~ V A L U A T I O N OF M A G M A
PROCESSES A N D M E L T I N O R B G I M E m H A P E
fed by waters from different
acquifers (Cambric Limestones, Mesozoic Dolomites,
Volcanic-Sedimentary
Tertiary
Formations and
buried c~ystalline basement, seat of a thePmal
circuit).
Values of distribution coefficients DMg, DSF
and DBa are in good agreement with the empirical
ones reported by Veizer (1983) and indicate that
rlpartition process is analogous in different
geological continental environments and not influenced by chemical composition of solution.
An increase of distribution coefficients with
temperature is confirmed by travertine deposits
of Sardara thermal waters.
In all the natural systems DMg values are
consistent with that reported by Lahann and Siebert
(]982)
for nonequilibrium precipitation
situations.
This agrees with the significantly positive
saturation indices observed in the depositing
waters.
MODELLING OF SOURCE ENRICHMENT AND MELTING PROCESSES FOR THE CALCALKALINE-SHOSHONITE-L&MPROITE SUITE
FROM S.Eo SPAIN
J. HERTOGEN, J . LOPEZ-RUIZ, D, DEMAIFFE, Do I{EIS
(University of Leuven, B-3030 Leuven, Belgium)
C,m=al questions in IX~OScM~is have been whether d~-mical
v ~
~
~
p~mbins, melnng n~ch~cs or souzce
o~ Two a p l ~ h e s ~ow~d these questions that
dmmly ccmvcri~ are (1) ~
modds cons=tuned
~n~lebr~dphysical ptinciplea and by o~imaginaflons; and (2)
Is drive~ by the e ~ f l n g systema~cs of the growing dam
hue for y o u ~ voi~uic ~:cks.
' Then: is st~lg w i ~ d
~dd~
thl¢ ll~lOlailhcd map
e h a m h e ~ c a n mlmlC ~ ¢
ezffccts o~ l~Ulial m e a d n g o £ & s o m c ¢ r t g i o ~ T h e u p p e r Limit o f
~
fi'~niom~on ~ v e ~ majorel~m~n~ in such a
magma ¢h_~_m_;~'isthe same as equ/I/briumcv/stalliz~m of the
pm'cn~ magms ~c~]in$ the chsmbcr. $ ~ sys~ms dan~n,
nmh~ ~ m m a ~ y , v m - ~ m ~ m ~ m l
ma~m~ ~ ~
eurplain]ittleo~tl~vm-i~l~ityi~ tl~~aldam base, In con=aat, in
aim cty~m,atioa m ~ bmmdm7 taytas 0f closed sy~m
m a i m d,,,m~,m can p r o d ~ ~
of ~m~m~s
¢¢eed ~
!~od~cd by ¢qtfilflxi~m psrdal me.l~ngof ,.hc
source. In ~neral, Ies~-l.g=~:x:~l~ of masma chamb~ ¢'volurion
~u~leries dsm flora an ~¢olvin~ system.
The physical ma:h~n,~m of melt removal has
been known to a£Nsetc h ~ d sys~mu~s for over a decade,
T~ ~
of the z~hi~g n~gio~ hOW~', ~ ~rnost no
di~dshinf eh~rdeal ~
eon~arexlto b~ch, ~luilibrium
m d ~ g . Rx ~mple~ s ~
the Iktuidthat~z~'~cs from me
melting zone r ~ l e ~ the m e ~ ~
of reeling in.grand ov~
integntttd c ~ t a y is almo~ i n d i ~ g u i ~ l ~ from that
by ~
parl~ meiling ~o~ ~
mean extent.
"ibisxw.sultenn be inmit~l from ,he f~t thatpooled fi'~Lmional
zmlts am1~lUiliM'iammel~s have vmy ~n~hr compositions.
In gl~m'ld,~a~'ginS syW~ma@csof maum'eMmcntchemistry
from c o m ~ e ~ and divcrg¢ilt xl~'~$ can be explained by
ren~kabiy single m d ~ g m 0 d ~ ,hat ~ h ~ chetmstryto
observable earth swacun~ The sisnai dsc earehm sending may
help us ~o ~
the ~
of hou¢lessly Complex
tl~ fm~st of chm~kml regularity ~ a t ~ to global snmctum,
MID
G.O[
The Neogene, post-orogenic volcanism from the
Betic Cordillera consists of calc-alkaline (CA),
high-K calc-alkaline (KCA), shoshonitic (SHO) and
lamproitic (LAM) rock series. Concentrations of incompatible and compatible trace elements are very
variable and increase systematically in the order
CA<KCA<SHO<LAM. 87Sr/86Sr ratios are high (0.7090.722) for the whole suite and are moderately correlated with Rb/Sr ratios and concentrations of incompatible trace elements. ~ Nd values of a CA, SHO
and LAM sample are -6.4, -10.] and -10o0 respectively. Pb isotopic composition of 14 samples from
the four rock series is rather uniform and carries
an apparent crustal signature (206/204=18.75-18.92;
207/204=15.67-15.72; 208/204=38.88-39.10).
Petrogenesis of the CA-KCA-SHO-LAM suite during
post-orogenic distensive tectonic phases is ascribed to both mantle and crustal anatexis in a lithospheric wedge including a F~ dipping underthrusted
crustal segment. Detailled modelling of major and
trace element composition and isotopic data shows
that the lamproites derive from a peridotitic mantle source strongly metasomatized by melts released from subducted supracrustal material. To reproduce the peculiar REE patterns of lamproites one
needs to assume that the subducted sediments had
already lost a fraction of the most mobile trace
elements in dehydration reactions before reaching
the deep mantle sources of the lamproites. Estimated contribution of sediment-derived component to
the source regions varies from 5 % for the St-poor
(45-50 % Si02) to 50 % for the Si-rich (58-60 %
Si02) lamproites. Petrological changes of the mantle source regions were such that melt segregation
shifted to higher degrees of melting with increasing source contamination and increasing acidity of
the melts.
ATLANTtC
RIDGE
109)
GEOCIIEM[CAL
PARTIAL
MELTING
SPREADING RIDGES
DONATO,
(Laboratoire
Sabatier,
PERIDOTITES
(FROM
OUP
LEG
COHPOStT[ONS
ANU
C O N O I T I O N S OF
OF TIlE
UPPER
MANTLE
AT SLOW
M.LOUBET
de
Mineralogle,
UniversLte
Paul
Toulouse)
A geochemical
study
of pertdotltes
from the
mid-atlantic
ridge
(23*10"N),
collected
during
Leg
ODP 1 0 9
is
hereby
presented
(analysis
of
major
elements,
trace
elements,
REE, 8 7 S r / B 6 S r ) .
Mayor
features
of
these
per[doilies
correspond
to
residual
mantle
perldot|tes
wLth
characteristics
intermediate
between
sllghly
depleted
mantle
lherzolites
and highly
depleted
ophiolitic
harzburgites.
Evaluation
of conditions
of
fusion
of
these
p e r i d o t i t e s on the basis of their REE s p e c t r u m
shows
tbat
they
must
have
been
affected
by
melting processes operating a~_e~uillbrlum.
Tile
formation
of
the
different
types
of
mantle
pertdotlte
massifs,
from
the
I.OS
( L h e r z o l l t e o p h l o l l t e subtype) masslfs, to t h i s
leg 109 Mid A t l a n t i c Ridge sectlo and to the lIDS
(llarzburgite O p h i o l l t e subtype) m a s s l f s ( B O U U I E R
and
NICOLAS,
1986)
can
be
explained
as
a
consequence
of different
kinetics
of tile mantle
diapirs
rislng
to the surface.
I. tbat
frame the
Leg 1 0 9 p e r t d o t i t e s
might
be typical
of residual
mantle
rocks
formed
in
a slow
spreading
ridge
environment.
Estimations
show
that
tbe
differences
In
fusion
conditions
in
these
different
types
of
m a s s s l f s , i.e fusion in e q u i l i b r i u m for t h e s e
leg 109 p e r i d o t l t e s and fusion in d e s e q u i l i b r i u m
ophiolltlc
harzburgltes
(PRIRZOFFER
and
in
ALI.EGRE
1986)
can
also
result
from
such
a
k i n e t i c factor.
Tile m n u t l e d i a p i r rise v e l o c i t y
should
not be
h o w e v e r tile unique factor e x p l a i n i n g tlre variety
of crustal s e c t i o n s formed at o c e a n l e ridges.
Source h e t e r o g e n e i t l e s , p r e s e n c e of some water %
can
explaLn
oceanlc
ridge
sections
with
d i f f e r e n t c h a r a c t e r i s t i c s , as those i d e n t i f i e d
alo.g
the Mid A t l a n t i c Ridge.
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