RETROGRADE FORMATION OF NACL-SCAPOLITE IN HIGH-PRESSURE METAEVAPORITES FROM THE CORDILLERAS-BETICAS (SPAIN)

被引:31
作者
GOMEZPUGNAIRE, MT
FRANZ, G
LOPEZ-SANCHEZ-VIZCAINO, V
机构
[1] TECH UNIV BERLIN, FACHGEBIET PETROL, D-10623 BERLIN, GERMANY
[2] UNIV GRANADA, FAC CIENCIAS, DEPT MINERAL & PETROL, E-18002 GRANADA, SPAIN
关键词
D O I
10.1007/BF00310911
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
A Permo-Triassic pelite-carbonate rock series (with intercalated metabasitic rocks) in the Cordilleras Beticas, Spain, was metamorphosed during the Alpine metamorphism at high pressures (P(min) near 18 kbar). The rocks show well preserved sedimentary features of evaporites such as pseudomorphs of talc, of kyanite-phengitetalc-biotite, and of quartz after sulfate minerals, and relicts of baryte, anhydrite, NaCl and KCl, indicating a salt-clay mixture of illite, chlorite, talc, and halite as the original rock. The evaporitic metapelites have a whole rock composition characterized by high Mg/(Mg + Ca) ratios > 0.7, variable alkaline and Sr, Ba, contents, but are mostly K2O rich (< 8.8 wt%). The F (< 2600 ppm), Cl (< 3600 ppm), and P2O5 (< 0.24 wt%) contents are also high. The pelitic member of this series is a fine grained biotite rock. Kyanite-phengite-talc-biotite aggregates in pseudomorphs developed in the high pressure stage. Albite-rich plagioclase was formed when the rocks crossed the albite stability curve in the early stages of the uplift. Scapolite, rich in NaCl (Ca/(Ca + Na) mol% 24-40) and poor in SO4, with Cl/(Cl + CO3) ratios between 0.6 and 0.8, formed as porphyroblasts, sometimes replacing up to 60% of the rock in a late stage of metamorphism (between 10 and 5 kbar, near 600-degrees-C). No reaction with albite is observed, and the scapolite formed from biotite by: Al-biotite + CaCO3 + NaCl + SiO2 = Al-poor biotite + scapolite + MgCO3 + KCl + MgCl2 + H2O Calculated fluid composition in equilibrium with scapolite indicates varying salt concentrations in the fluid. Distribution of Cl and F in biotite and apatite also indicates varying fluid compositions.
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页码:448 / 461
页数:14
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