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Erstellt von siobhan.quirk
vor mehr als 11 Jahre
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Frage | Antworten |
Define bed | a unit of sedimentation, which can vary considerably in thickness |
Define bedding plane | marks the break between beds. It represents a break in sedimentation, a change in composition or grain size, or a change in colour of sediments |
Define dip | the maximum inclination of a bed measured from the horizontal using a clinometer |
Define strike | the direction at right angles to the dip. There is zero dip in this direction. It is a bearing measured from north using a compass |
Define apparent dip | is a dip that is measured to be less than the maximum inclination |
Define stress | force applied to rocks |
Define stress | (change of length of line)/(the original length of line) |
Define tension | the force trying to pull rocks apart - the Earth's crust will be lengthened |
Define compression | the force trying to push rocks together - the Earth's crust will be shortened |
Define shear forces | forces which act along a plane in the rock and promote sliding along that plane |
Define competent | rocks are strong and brittles and tend to joint and fault |
Define incompetent | rocks are weak and plastic and tend to fold and develop cleavage |
Define joint | a fracture in competent rocks along which no observable movement has occurred |
Define tectonic joints | form as a result of folding and cause tension joints parallel to the axial plabne and cross joints on the limbs |
Define cooling joints | forms as a result of contraction on cooling of igneous rock |
Define unloading joints | often horizontal as well as vertical and form as a result of lower pressure near to the surface |
Define fault | a fracture in a rock along which there has been an observable amount of displacement |
Define fault plane | the surface along which movement takes place |
Define throw | the amount of vertical displacement measured vertically between the top of the same bed seen on both sides of the fault |
Define fault dip | the angle between the fault plane and the horizontal |
Define hanging wall | the side that lies above the fault plane |
Define footwall | the side that lies below the fault plane |
Define downthrow | the side of the fault that has moved down |
Define upthrow | the side of the fault that has moved up |
Define slickensides | the polishing and striations found on a fault plane indicating the direction of relative movement |
Define fault breccia | composed of fragments produced by rocks fracturing during faulting |
Define fold limb | the section of a fold between one hinge and the next, forming at the side of a fold |
Define hinge | the line along which there is a change in amount and/or direction of dip, forming the most sharply curved part of the fold |
Define crest | the highest point of a folded bed |
Define trough | the lowest point of a folded bed |
Define axial plane | a plane that joins the hinges of all the beds. It bisects the fold |
Define axial plane trace | the outcrop of the axial plane at the Earth's surface |
Define plunge | the angle of dip of the axial plane from the horizontal |
Define antiform | an upward closing fold |
Define synform | a downward closing fold |
Define cleavage | planes of weakness in a rock along which the rock will split |
Which rocks does cleavage form in? | incompetent sedimentary rocks such as shale or clay made from clay minerals |
Where does cleavage form? | perpendicular to the maximum pressure that forms a fold, so it at an angle to the bedding planes |
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