Historical Geology Part 2

Front 1

continental drift

Back 1

Continental drift is the idea that the Earth’s continents have
moved to their present positions after fragmentation of a
larger landmass in the geologic past.

Front 2

seafloor spreading

Back 2

Seafloor spreading - The hypothesis that ocean basins expand
by addition of new rock from spreading centers, and that
older rock is destroyed near the basin margins.

Front 3

Basin

Back 3

- A relatively depressed area of the
crust that receives sedimentary deposition.

Front 4

Continental crust

Back 4

Solid, outer part of the Earth
underlying the continents and continental shelves,
composed largely of granitic rocks.

Front 5

Oceanic crust

Back 5

Solid, outer part of the Earth
underlying the ocean basins, consisting largely
of basaltic rocks.

Front 6

Pangea

Back 6

Late Paleozoic to early Mesozoic supercontinent comprising most of the world’s continental crust.

Alfred Wegener

Front 7

Basis for Wegener’s ideas:

Back 7

Jigsaw puzzle
similar geology
Glacial striations
similarity in ancient organisms

Front 8

Triple junction

Back 8

A junction of three spreading plates

Front 9

Graben

Back 9

Elongate basin formed through downdropping of a fault block, and bounded on both sides by a normal fault

Front 10

thermal convection cells

Back 10

allows Earth’s mantle capablity of flow and rotation

Front 11

Guyot

Back 11

A sunken seamount, or undersea volcano, having a flat top due to erosion at sea level.

Front 12

Paleomagnetism

Back 12

The study of natural remnant
magnetism in rocks to determine properties of the Earth’s magnetic field in the geologic past.

Front 13

Plate boundaries

Back 13

At present, there are seven large plates (carrying the
continents and much of the Pacific Ocean), and about
20 smaller plates.

Plate motion, typically 1 to 7 cm per year, causes plates to
converge, diverge, or slide past one another, and this
movement is the source of many earthquakes. Also,
many volcanoes line up along or close to plate boundaries.

Front 14

The basic forms of tectonic boundaries

Back 14

1) Transform boundaries occur where plates slide or, perhaps more
accurately, grind past each other along transform faults.

2) Divergent boundaries occur where two plates slide apart from each
other. Mid-ocean ridges and active zones of rifting are examples.

3) Convergent boundaries (or active margins) occur where two plates slide
towards each other commonly forming either a subduction zone
(if one plate moves underneath the other) or a continental collision
(if the two plates contain continental crust).

Front 15

Passive margin

Back 15

The trailing edge of a tectonic plate, where active tectonic interaction with another plates is not occurring.

Front 16

Aulacogen

Back 16

A failed continental rift that has filled with sediment

Front 17

Subduction zone

Back 17

Long, narrow belt, usually including a
deep-sea trench, along which subduction occurs.

Front 18

subduction zone

Back 18

a slab of cool, dense oceanic crust
comes in contact with the margin of another plate, and it
descends beneath that plate, eventually reaching depths
where melting occurs under elevated temperature and
pressure conditions. The rock will be remelted into magma
and recycled.

Front 19

Subduction

Back 19

occur when one oceanic slab collides
with another or with continental crust

creates volcanoes

Front 20

Volcanic arc

Back 20

Arcuate line of active volcanoes and igneous plutons associated with a convergent plate margin where
subduction is occurring

Front 21

Orogenesis

Back 21

The process of building mountain chains and consequently deforming granitic crust (continental-type crust).

1. where continental collision occurs;

2. in volcanic arcs adjacent to subduction zones; and

3. along mid-ocean rifts.