Definitions and images to illustrate geological terms, links to images and website articles

en echelon

The term 'en echelon' refers to closely-spaced, parallel or subparallel, overlapping or step-like minor structural features in rock (faults, tension fractures), which lie oblique to the overall structural trend. Conjugate deformation structures are related in deformational origin.

Extensional stresses create fractures that can infill with calcite. When rocks deform in a brittle manner, the fracture pore can subsequently infill with some form of cement, such as calcite. Typically, crystals will nucleate on the fracture wall and grow into the opening. (Sometimes apparent fracture are completely reduced by a prismatic or fibrous mineral that is oriented long axis normal to the wall. In this case, the force of crystallization of the ‘filling’ material may be the actual cause of the opening of the fracture.)

[links: images: small scale: calcite in fault, calcite filled extension fractures in limestone; en echelon dikes, Woollen Mills, NY; en echelon extension fractures in quartz, 2; conjugate pair of en echelon extension fractures; en echelon fractures, San Andreas fault; dolerite dyke filling an en echelon fracture set, Hoedjies Punt, Saldanha Bay; en-echelon dyke geometry, Paternoster; close-up: en echelon faults in Tertiary sedimentary rocks, Blacks Beach in La Jolla, California; quartz epidote pod with en echelon fracture, and close-up; close-up of dolerite dyke filling an en echelon fracture set, Hoedjies Punt, Saldanha Bay; stresses involved in formation of en echelon veins; un système de fentes en échelon matérialise une faille potentielle; large scale: en echelon folds of Raplee Ridge anticlinal Monument Upwarp in Utah; en echelon volcanic fissures, Kilauea, Hawaii; webpages: Les Failles et Microstructures associées (Associated Faults and Microstructures, translated poorly, by google, from French)]

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