The Rock Cycle

lameubiquityMechanics

Feb 21, 2014 (7 years and 5 months ago)

267 views

The Rock Cycle


Sedimentary Processes

1

2) & 3)
Sediments are
transported and
deposited

4

Products of weathering

Primary


Residual


Dissolved

Minerals


Minerals


Ions




Feldspar


Clay minerals


K
+
, Ca
+2
, Na
+





Aluminum hydroxide


Fe
-
Mg minerals

Hematite &


Mg
+2





Limonite


Quartz



Quartz



Silica












Primary


Solids that


Ions that are carried

Minerals



remain in soil




away in water


----------
Detrital sediments
------------------


Chemical & biochemical







sediments



Types of sediment

Detrital


mineral & rock fragments

Chemical


halite (NaCl)

crystals


that precipitate from water

Biochemical


shells made of

calcite (CaCO
3
) by organisms

that extract the ions from water

Detrital sedimentary rocks
-

classified by
grain size differences

Conglomerate

Breccia

Sandstone

Shale

All these rocks have
clastic

textures


the rocks are composed of
particles (fragments) that are cemented together

Detrital sediments are sorted by the processes of
transportation and deposition

Well sorted

Poorly sorted

Sands and sandstones can be used to interpret the erosional
history of an area and the kinds of rocks that were eroded

Well
-
sorted

Poorly
sorted

“Mature” sediments have little feldspar. This means that the sediment was
derived from weathered rocks or that the feldspar decomposed during
transportation in water.

The same
diagram is
used to
interpret the
provenance
(source rocks)
of sediments

Placer deposit


accumulation of sand or gravel containing minerals that are
highly resistant to chemical attack and economically valuable
-

gold, platinum,
ilmenite, rutile, zircon, diamond, garnet, magnetite, corundum, monazite.


These and other chemically resistant minerals are widely used to indicate the
provenance

of sediments, e.g. kyanite, sillimanite, staurolite

indicate that metamorphic rocks were eroded.

Diamonds indicate kimberlite;
gold indicates hydrothermal veins, etc.

Chemical and biochemical sedimentary rocks

Limestones


composed of calcite

Travertine

Coquina

Chalk

Deep ocean sediments

are mainly fine
-
grained biochemical
sediment called
oozes
, with some
hydrogenous

(chemical)
and
terrigenous
(wind or water borne) detrital sediment

Calcareous & siliceous ooze

Manganese nodules are
hydrogenous
-

they
precipitate from deep ocean
water when the Mn oxidizes:

Mn
+2

(dissolved) + O
2

+ 2e
-

=
MnO
2

(pyrolusite)

Banded Iron Formations



ancient (>2.5 billion year old) sedimentary deposits of iron
-
bearing minerals. These indicate that Earth’s early atmosphere was too poor in oxygen to
oxidize iron at the site of weathering. Dissolved iron was transported in water:

4Fe
+2

(dissolved) + 3O
2

= 2Fe
2
O
3

(hematite)

Phosphates form in shallow marine environments where dissolved PO
4
-
3

is carried by upwelling of deep ocean water. These areas are biologically
productive
-

many fossils are found, especially bone material.

Phosphate Mining of the Bone Valley Formation in Florida

Shallow basin with high rate of evaporation


Gulf of Mexico,
Persian Gulf, ancient Mediterranean Sea, Red Sea

Sequence is: calcite, gypsum, halite with increasing evaporation

Evaporite minerals

Evaporites

Gypsum

Halite

Seawater evaporation:


1)
Calcite

2)
Gypsum

3)
Anhydrite

4)
Halite (95% evaporation)

5)
Sylvite

6)
Other rare minerals

Dolomite may form afterward by
reaction of Mg
+2

with calcite

Continental waters:

Borax & borates

Nitrates

Salt

dome

Sulfur is
produced by
sulfate
reducing
bacteria
which
consume the
oxygen in
gypsum or
anhydrite