Structural Petrology of Undeformed and Experimentally Deformed Halite Samples from USERDA Site No. 7and No. 9.

摘要

Preliminary data from USERDA test holes No. 7and No. 9in the Salado Formation of southeastern New Mexico are presented. Cores consist primarily of halite (> 80modal percent),clay, polyhalite,anhydrite, celestite,iron oxide,and magnesite. Macroscopic features of undeformed core include moderately tight grain boundaries,large cavities (less than or equal to 8mm exp 2 ),fluid inclusions,rare intragranular dislocations,and coarse and bimodal textures. Petrographic examination reveals numerous secondary fluid inclusions of variable size, blebby halite and transected hopper crystals,all of which suggest mobility and recrystallization of the primary evaporite assemblages. Deformed core shows a complex group of fabric elements,including tight grain boundaries,intercrystalline lattice rotation,cavity deformation and closure,distortion of hopper crystals, polygonization,irregular lattice dislocations,glide dislocations,and climb dislocations. Grain boundaries become tight or locked with deformation,forming pinned and bulged grains. Intercrystalline lattice rotation causes grains to rotate as much as 17exp 0to develop preferred orientation. Polygonization yields fabrics analogous to prophyroclasts in cataclastic rocks. Irregular dislocations are relatively abundant. Glide dislocations are also abundant in many deformed specimens. Individual mineral components within deformed halite also exhibit deformational fabrics. Folded layers of clay and anhydrite,and bent and broken single crystals of anhydrite are present in some samples. Secondary fluid inclusions apparently migrate in response to differential stress and form along dislocations in halite,healing the dislocations by secondary crystallization and forming discontinuous or completely healed dislocation fabrics. 67figures, 9tables. (ERA citation 04:039726)