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Descrição
FlashCards por siobhan.quirk, atualizado more than 1 year ago
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Criado por siobhan.quirk
mais de 11 anos atrás
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| Questão | Responda |
| 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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