Acta Mineralogica-Petrographica, Abstract Series 2, Szeged, 2003
SILICATE-CARBONATE-CO, I M M I S C I B I L I T Y IN A L K A L I N E ROCKS: E X A M P L E F R O M INCLUSIONS IN CLINOPYRÔXENE OF TRACHYTIC LATITES AT CASERIO FUENTE DE MECA, MAZARRON, SE SPAIN
S H A R Y G I N . V. V.'
1 Institute of Mineralogy and Petrography, Koptyuga prospect 3, 630090 Novosibirsk, Russia.
E-mail: sharygin@uiggm.nsc.ru
Introduction
T h e Miocene magmatic province of SE Spain is characterized by calc-alkaline/shoshonitic and lamproitic rocks. In general, lamproites are mantle-derived rocks, whereas calc-alkaline and shoshonitic rocks have a m o r e complicated origin involving both mantle and crust components (Venturelli et al., 1984; 1991). T h e origin of some rocks f r o m the southern group of the Spanish lamproite occurrences (Zeneta, Vera) is suggested to be as a result of mixing between lamproitic and shoshonitic components (Fuster, 1956; Venturelli et al., 1984). T o other side, the studies of trachytic latites f r o m Caserio Fuente d e M e c a , Mazarron showed that these rocks possibly also derived due to mixing (Venturelli et al., 1991). This work is concerning to study of unusual silicate melt inclusions in the rocks of Caserio Fuente de Meca.
Petrography of studied rocks
T h e trachytic latites contain phenocrysts of olivine altered to serpentine, phlogopite-biotite, clinopyroxenes and apatite (sizes - up to 0.5 mm). Groundmass consists of rhyolitic colorless glass, clinopyroxenes, phlogopite and apatite. In addition, large carbonate globule (up to 0.5 mm) occurs in the groundmass. T h e minute crystals of zircon and spinel s o m e t i m e s occur as single inclusions in phenocrysts and as accessory phases in the groundmass.
Silicate melt inclusions
Silicate melt inclusions are found in all phenocrystal minerals, but they are more c o m m o n for clinopyroxene. In this mineral the inclusions are mainly situated in the central parts or outline the growth zones. Their phase composition is diverse: s o m e inclusions contain rhyolitic glass, fluid and daughter/trapped phlogopite, but most inclusions consist of glass and heterogeneous fluid bubble ( C O2v a p o r , CO2Uquid, and carbonate) and rarely individual carbonate globule (Fig. 1). It should be noted that individual carbonate inclusions coexisting with melt ones are absent. T h e heterogeneity in fluid bubble is expressed in variable amount of constituent phases. Majority of fluid bubble contain mainly C O2v a p o r and C O2l i q u i d , carbonate is minor. In inclusions, in which carbonate dominates; the vapor represents the C 02 phase.
* s
(§* ^ G l
i
í •
i Wm ÊL
C O c a v
Gi %
11 9*
- - . y " .
L > co Gt 2 v
Carb
X\
GO2 lq
C " rl > CO, v
8
O a
C0
2v
! G• ' \
Carb
• • » .g
4
.S
Vf '
> • • . .V
' ~ »2 0 f i m
Figure 1. Silicate melt inclusions in clinopyroxene phenocrysts from trachytic latite, Caserio Fuente de Meca, SE Spain.
G1 -rhyolitic glass; Pht -phlogopite; C a r b - carbonate; C02 v and C02 lq - carbon dioxide vapor and liquid, respectively.
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Acta Mineralogica-Petrographica, Abstract Series 2, Szeged, 2003
Dicussion
Silicate melt i n c l u s i o n s in latites of C a s e r i o F u e n t e d e M e c a d e m o n s t r a t e a u n i q u e c a s e w h e n C 02 and c a r b o n a t e m a y coexist in silicate glass. T h i s case s h o w s an e v i d e n c e of s i l i c a t e - c a r b o n a t e - C 02 i m m i s c i b i l i t y in siliceous v o l c a n i c r o c k s . It is u n k n o w n w h a t is n a m e l y w a s main r e a s o n to a p p e a r this p h e n o m e n o n in the S p a n i s h r o c k s . P o s s i b l y , it w a s c o n t a m i n a t i o n of c a r b o n a t e r o c k s by s i l i c e o u s m a g m a within the u p p e r - m i d d l e crust. T h e s i l i c a t e - c a r b o n a t e liquid i m m i s c i b i l i t y is m o r e c o m m o n f o r e v o l u t i o n of s i l i c a - u n d e r s a t u r a t e d i g n e o u s r o c k s . F o r e x a m p l e , this p h e n o m e n o n w a s o b s e r v e d in m i n e r a l - h o s t e d m e l t i n c l u s i o n s of the U m b r i a n k a m a f u g i t i c r o c k s (Italy), t h e L e u c i t e Hill l a m p r o i t e s ( U S A ) a n d m a n t l e - d e r i v e d x e n o l i t h s of the C a n a r y I s l a n d s ( S h a r y g i n , 2 0 0 1 a , b; Frezzotti et al., 2 0 0 2 ) .
T h i s w o r k is s u p p o r t e d b y the R u s s i a n F o u n d a t i o n for B a s i c R e s e a r c h (grant no. 0 3 - 0 5 - 6 4 0 3 0 ) .
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