Metaconglomerate
Encyclopedia
Metaconglomerate is a rock
type which originated from conglomerate
after undergoing metamorphism
. Conglomerate is easily identifiable by the pebbles or larger clasts in a matrix
of sand
, silt
, or clay
. Metaconglomerate looks similar to conglomerate, although sometimes the clasts are deformed. The cement
matrix of conglomerate is not as durable
as the grains, and hence when broken, conglomerate breaks around the grains. Metaconglomerate, however, breaks through the grains, as the cement has recrystallized and may be as durable as the clasts.
The metaconglomerates of the Jack Hills
of Western Australia
are the source rocks for much of the detrital zircon
s that have been dated
to be as old as 4.4 billion years.
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
type which originated from conglomerate
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
after undergoing metamorphism
Metamorphism
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...
. Conglomerate is easily identifiable by the pebbles or larger clasts in a matrix
Matrix (geology)
The matrix or groundmass of rock is the finer grained mass of material in which larger grains, crystals or clasts are embedded.The matrix of an igneous rock consists of finer grained, often microscopic, crystals in which larger crystals are embedded. This porphyritic texture is indicative of...
of sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
, silt
Silt
Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...
, or clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
. Metaconglomerate looks similar to conglomerate, although sometimes the clasts are deformed. The cement
Cementation
Cementation may refer to:*Cementation , the process of deposition of dissolved mineral components in the interstices of sediments*Cementation , a small deposit of calcium, similar to a cyst...
matrix of conglomerate is not as durable
Durable
Durability is the ability to endure. It can refer to:*Durable goods, goods with a long usable life in economics.*Durability , one of the ACID properties.In safety and technology:*Dust resistant*Fire resistant*Rot-proof...
as the grains, and hence when broken, conglomerate breaks around the grains. Metaconglomerate, however, breaks through the grains, as the cement has recrystallized and may be as durable as the clasts.
The metaconglomerates of the Jack Hills
Jack Hills
The Jack Hills are a range of hills in Mid West Western Australia. They are best known as the source of the oldest material of terrestrial origin found to date: zircons that formed around 4.4 billion years ago...
of Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
are the source rocks for much of the detrital zircon
Zircon
Zircon is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4. A common empirical formula showing some of the range of substitution in zircon is 1–x4x–y...
s that have been dated
Radiometric dating
Radiometric dating is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates...
to be as old as 4.4 billion years.