The Buffalo Head Terrane (BHT) is a

terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its own ...

in the western

Canadian Shield The Canadian Shield (french: Bouclier canadien ), also called the Laurentian Plateau, is a geologic shield, a large area of exposed Precambrian igneous and high-grade metamorphic rocks. It forms the North American Craton (or Laurentia), the anc ...

in northern

Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...

. It is covered by of

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

and

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

sediments and its centre is intruded by the 88–86 Ma

kimberlite Kimberlite is an igneous rock and a rare variant of peridotite. It is most commonly known to be the main host matrix for diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an diamond called the Star of ...

s of the

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 ...

iferous Buffalo Head Hills kimberlite province.

Geology

Because the BHT is covered by

Phanerozoic The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 538.8 million years to the present, and it began with the Cambrian Period, when anima ...

rocks, its extent is uncertain and only known from aeromagnetic data and drill cores. To the south it is truncated by the

Snowbird Tectonic Zone The Snowbird Tectonic Zone (STZ) is a geological structure in the western Canadian Shield which forms a geophysical boundary between the Hearne Craton and the south-west arm of the Rae Craton. It is enigmatic and has been interpreted as a Prote ...

; to the north it is delimited by the Great Slave Lake Shear Zone; in the east it is separated from the

Rae Craton 250px, North America cratons and basement rock. The Rae Craton is an Archean craton located in northern Canada north of the Superior Craton. Ungava Peninsula The Ungava Peninsula, situated on the northeast portion of the Canadian Shield, is wher ...

by the 1.99–1.9 Ga

Taltson Magmatic Zone The Taltson Magmatic Zone (TMZ) is a north-trending belt of Archean to Paleoproterozoic granitic basement gneiss, amphibolite supracrustal gneissic rock and Paleoproterozoic magmatic rocks in the Canadian Shield, extending from Northern Alberta ...

; and in the west it is separated from the Nova Terrane by the magmatic rock of the Ksituan High. In its southern end the BHT is intruded by the Peace River Arch, a cratonic

uplift Uplift may refer to: Science * Geologic uplift, a geological process ** Tectonic uplift, a geological process * Stellar uplift, the theoretical prospect of moving a stellar mass * Uplift mountains * Llano Uplift * Nemaha Uplift Business * Uplif ...

active since the Proterozoic. defined the BHT as a broad, north-trending region of areomagnetic anomalies. Drill cores from this region returned Zircon ages 2.324–1.993 Ga with occurrences of metaplutonic rocks in the range 1.999–1.993 Ga. From this Ross concluded that the BHT formed 2.32–2.0 Ga and was affected by a thermal-magnetic event 2.0–1.9 Ga. The inherited age of the Proterzoic basement rocks is 2.4–2.1 Ga. The Rae Craton is of similar age and isotopic signature which suggest it and the BHT formed a single crustal entity at 2.4 Ga. 2.34 Ga mafic to ultramafic rocks between BHT och Rae indicate separation by this time. BHT was then subducted at its eastern and western margins, which resulted in the arc magmatism that produced the Taltson Magmatic Zone 1980-1920 Ma and the 1986-1900 Ma Ksituan High.

Kimberlite field

The Buffalo Head Hills kimberlite field is an atypical diamond deposit. The lack of indicator minerals such as harzburgitic

garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different s ...

suggests a mantle composition different from those of other diamond occurrences. An unusual occurrence of Type II and Type IaB diamonds is indicative of a sub-lithospheric origin, such as a subducting oceanic slab, and the presence of a lherzolitic

suggests a formation depth of some . 26 of the 38 kimberlite pipes in the Buffalo Head Hills kimberlite field are, nevertheless, diamondiferous. Drilling restricted to upper but the carrot-shaped kimberlite

diatreme A diatreme, sometimes known as a maar-diatreme volcano, is a volcanic pipe formed by a gaseous explosion. When magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the ...

s reach below the Proterzoic boundary and contain crater facies. The pipes range in size from .

References

Sources

* * * * * {{Refend Volcanism of Alberta Buffalo Head Hills kimberlite field Terranes