Structural and microthermometric studies of fluid inclusions in the Gallura intrusive complex (N Sardinia)
Structural and microthermometric studies of fluid inclusions in the Gallura intrusive complex (N Sardinia) (in Proceedings of the Eleventh European symposium on Fluid inclusions research (ECROFI XI), Benedetto De Vivo (editor) and Pierfranco Lattanzi (editor))
European Journal of Mineralogy (October 1992) 4 (5): 1175-1185
A study of brittle deformation within a segment of the Hercynian intrusive complex of Gallura reveals a fairly regular network of fluid inclusion planes and open microcracks. Fluid inclusion planes and microcracks in nine oriented samples show a consistent orientation across different intrusions; two principal, almost orthogonal sets have been recognized: both consist mainly of subvertical planes. A subhorizontal set is nearly always present as healed microcracks. Microthermometric investigations on fluid inclusions show that Na dominated aqueous fluids (salinity 0.9- 12.3 eq.wt.% NaCl; T (sub h) L = 111-257 degrees C) (T (sub h) in liquid phase) circulated throughout the complex along almost all the microfracture sets during the late-stage hydrothermal history. Locally subordinate Li- or Ca-, K- and Na-bearing brines have been detected along palaeocracks. Li-bearing brines have salinities of 11-17 eq.wt.% LiCl and T (sub h) L of 74-171 degrees C; salinity in Ca-dominated brines varies from 4.9 to 21.8 eq.wt.% NaCl and T (sub h) L from 130 to 217 degrees C. The principal set directions are often shared by fluid inclusion planes and open microcracks; it is suggested that they belonged to the same brittle deformation episode, related to late Hercynian batholith coolingand uplift.