3.1 The rock Cycle

The rock components of the crust are slowly yet constantly being readjusted from one kind to another and also the processes connected are summary in the rock cycle (Figure 3.2). The rock cycle is thrust by two forces: (1) earth internal warm engine, which move material around in the core and the mantle and also leads to slow but far-ranging changes in ~ the crust, and also (2) the hydrological cycle, i m sorry is the movement of water, ice, and air at the surface, and also is powered by the sun.

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The absent cycle is still active on Earth since our main point is hot enough to keep the mantle moving, our environment is relatively thick, and also we have actually liquid water. Top top some other planets or their satellites, such as the Moon, the rock cycle is virtually dead because the core is no longer hot enough to journey mantle convection and there is no setting or fluid water.

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Figure 3.2 A schematic check out of the absent cycle.

In describing the rock cycle, we deserve to start everywhere we like, although it’s practically to start with magma. As we’ll check out in an ext detail below, magma is rock that is warm to the suggest of being completely molten. This wake up at between about 800° and 1300°C, depending on the composition and the pressure, onto the surface and also cool conveniently (within secs to years) — developing extrusive igneous absent (Figure 3.3).

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Figure 3.3 Magma creating pahoehoe basalt in ~ Kilauea Volcano, Hawaii

Magma can either cool slowly within the crust (over centuries to millions of years) — creating intrusive igneous rock, or erupt top top the surface and also cool quickly (within seconds to years) — forming extrusive igneous rock. Intrusive igneous rock generally crystallizes at depth of numerous metres to tens of kilometres below the surface. To adjust its position in the absent cycle, intrusive igneous rock needs to be uplifted and exposed by the erosion that the overlying rocks.

Through the assorted plate-tectonics-related processes of hill building, all species of rocks space uplifted and exposed at the surface. When exposed, they space weathered, both physically (by mechanical breaking that the rock) and also chemically (by weathering of the minerals), and the weathering products — mostly small rock and mineral fragments — are eroded, transported, and also then deposited as sediments. Transportation and deposition happen through the activity of glaciers, streams, waves, wind, and also other agents, and sediments are deposited in rivers, lakes, deserts, and also the ocean.


Exercise 3.1 Rock approximately the Rock-Cycle clock

Referring to the absent cycle (Figure 3.2), perform the procedures that are important to cycle some geological material starting with a sedimentary rock, which climate gets converted into a metamorphic rock, and eventually a brand-new sedimentary rock.

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A conservative estimate is the each that these steps would take approximately 20 million year (some might be less, others would certainly be more, and also some can be lot more). Just how long might it take for this entire process to be completed?


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Figure 3.4 Cretaceous-aged naval sandstone overlying mudstone, Gabriola Island, B.C.

Unless they are re-eroded and also moved along, sediments will eventually be buried by an ext sediments. At depths of thousands of metres or more, they become compressed and cemented into sedimentary rock. Again through various means, greatly resulting from plate-tectonic forces, different kinds the rocks space either uplifted, to it is in re-eroded, or hidden deeper in ~ the crust whereby they room heated up, squeezed, and changed into metamorphic rock.

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Figure 3.5 Metamorphosed and also folded Triassic-aged limestone, Quadra Island, B.C.