The Birch Mountains kimberlite field is a cluster of kimberlitic volcanic pipes or diatremes in north-central Alberta,

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

that were emplaced during a period of kimberlitic volcanism in the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided by ...

. As of 2011, 8 diatremes had been discovered in the field, and

diamond Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the Chemical stability, chemically stable form of car ...

s and microdiamononds had been recovered during sampling programs.

Location and geological setting

The Birch Mountain (BM) kimberlite field was discovered in 1998 and lies about north of

Edmonton Edmonton ( ) is the capital city of the Canadian province of Alberta. Edmonton is situated on the North Saskatchewan River and is the centre of the Edmonton Metropolitan Region, which is surrounded by Alberta's central region. The city ancho ...

and northwest of Fort McMurray. It is part of the Northern Alberta kimberlite province, along with the

Buffalo Head Hills kimberlite field The Buffalo Head Hills kimberlite field is a group of kimberlitic volcanic pipes or diatremes in north-central Alberta, Canada. As of 2011, 41 kimberlite pipes, of which 28 are diamondiferous, had been identified in the field. They were emplaced ...

and the Mountain Lake cluster. The BM diatremes are hosted in the marine

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

s and silty shales of the Late Cretaceous Smoky or La Biche Group, and they are thought to have been erupted in an open marine to near shore marine setting in the Western Interior Seaway. Unconsolidated

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

sediments that reach thicknesses of more than now cover the bedrock in the area, so the diatremes were located primarily by aeromagnetic surveys followed by drilling.

Age

According to

radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares t ...

the BM diatremes were emplaced about 70 to 78 million years ago during the Campanian to

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...

stages Stage or stages may refer to: Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly British theatre newspaper * S ...

of the

. Microfossils from shales interbedded with kimberlite at some of the diatremes are consistent with a Late Cretaceous age (Late Albian to Maastrichtian).

Lithology and mineralogy

The volcanic rocks of the BM field consist primarily of

crater Crater may refer to: Landforms *Impact crater, a depression caused by two celestial bodies impacting each other, such as a meteorite hitting a planet *Explosion crater, a hole formed in the ground produced by an explosion near or below the surfac ...

-facies pyroclastic kimberlite and sedimentation, resedimented kimberlite. They include massive layers, as well as bedded and graded layers of coarse lapilli alternating with layers of finer tuff. Lapilli and olivine phenocrysts are set in a grey-green matrix of serpentine group, serpentine, carbonate minerals (calcite, Dolomite (mineral), dolomite, and magnesite) and clay minerals. Phlogopite, oxide minerals (ilmenite, perovskite and spinel), apatite and pyrite are also present. Diamonds and microdiamonds have been recovered from samples taken from the Phoenix and Legend pipes.

List of diatremes

The diatremes within the field include: *Phoenix pipe *Dragon pipe *Xena pipe *Legend pipe *Valkyrie pipe *Kendu pipe *Roc pipe *Pegasus pipe

References

{{coord, 57.0722, -115.4069, display=title, type:landmark_region:CA-AB Birch Mountains kimberlite field, Volcanic fields of Canada

Location and geological setting

Age

Lithology and mineralogy

List of diatremes

See also

References