Yukon-Tanana Terrane
Encyclopedia
The Yukon-Tanana Terrane (YTT) is a tectonic terrane
that extends from central Alaska
through central Yukon
and into northern British Columbia
, Canada and Southeast Alaska, USA. Extending over 2000 km, the YTT is the largest tectonostratigraphic terrane in the northern North American Cordillera
. The Yukon-Tanana Upland is a physiographic province
mostly underlain by rocks of the Yukon-Tanana terrane. The YTT consists of polymetamorphosed and polydeformed metasedimentary, metavolcanic, and metaplutonic rocks of Upper Paleozoic and older ages that were deposited or emplaced near the edge of the North American continental margin. Rocks in the terrane record a variety of tectonic settings and have experienced varying amounts of tectonic transport, both before and after amalgamation of the YTT with North America. Sequences of mainly parautochthonous quartz-rich sedimentary rocks derived from the North American continent also include meta-igneous rocks with mostly continental geochemical and isotopic signatures. Structurally higher sequences contain meta-igneous rocks with arc and back-arc characteristics. The Slide Mountain/Seventymile terrane
, composed of volcanic rocks typical of seafloor and of typical seafloor sediments, is recognized as an ocean basin that divided parts of the YTT before amalgamation of the Yukon-Tanana Terrane with the continental margin.
Understanding and definition of the YTT is constantly progressing, the term "Yukon Tanana composite terrane," or "YTCT" is used by some workers, reflecting the disparate depositional and tectonic histories being recognized in rock units within the YTT. Some recent work dispenses altogether with the term Yukon-Tanana Terrane, in favor of more detailed subdivisions.
The right-lateral strike slip Tintina Fault
occurs along the suture zone between the YTT (on the south and west) and ancestral North America to the east; it forms a significant boundary between North America cratonic rocks and rocks of the YTT and associated terranes - although displaced continental rocks are found south of the Tintina Fault and pieces of the YTT occur north of the Tintina Fault. Parts of the YTT have been offset by at least 400 km along the Tintina Fault. In most of the Alaskan part of the YTT the Denali Fault
forms the modern day southern boundary of the terrane. In Yukon the ocean-basin rocks of the Windy/McKinley terrane, and the Coast Plutonic Complex (CPC) form the southern boundary of the YTT. Units assigned to the YTT also occur within the CPC; and the YTT partially encloses and is complexley related to the Intermontane Superterrane.
s with significant copper
, zinc
, lead
, silver
and gold
mineralization. Sulfide mineral
s include massive to disseminated pyrite
and pyrrhotite
with lesser amounts of chalcopyrite
, galena
, sphalerite
and arsenopyrite
. The deposits show evidence of an Early Cretaceous
, amphibolite facies event and a younger, mid-Cretaceous lower greenschist facies event which resulted from the accretion
of the Yukon-Tanana Terrane.
A belt of significant Late Triassic to Early Jurassic Cu-Au and Cu-Mo porphyry deposits, such as Highland Valley Copper and Galore, of the Stikine terrane
and Quesnel terrane extends into the Yukon-Tanana terrane in Yukon; the Minto mine is an example.
Gold mineralization associated with post-amalgamation emplacement of Cretaceous and Tertiary plutonic rocks is widespread in the YTT.
Terrane
A terrane in geology is short-hand term for a tectonostratigraphic terrane, which is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or "sutured" to crust lying on another plate...
that extends from central Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
through central Yukon
Yukon
Yukon is the westernmost and smallest of Canada's three federal territories. It was named after the Yukon River. The word Yukon means "Great River" in Gwich’in....
and into northern British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
, Canada and Southeast Alaska, USA. Extending over 2000 km, the YTT is the largest tectonostratigraphic terrane in the northern North American Cordillera
North American Cordillera
The North American Cordillera is the North American portion of the American Cordillera which is a cordillera extending up and down the western side of the Americas. The North American Cordillera covers an extensive area of mountain ranges, intermontane basins, and plateaus in western North...
. The Yukon-Tanana Upland is a physiographic province
Physiographic province
A physiographic province is a geographic region with a specific geomorphology and often specific subsurface rock type or structural elements.A continent may be subdivided into various physiographic provinces, each having a specific character, relief, and environment which contributes to its...
mostly underlain by rocks of the Yukon-Tanana terrane. The YTT consists of polymetamorphosed and polydeformed metasedimentary, metavolcanic, and metaplutonic rocks of Upper Paleozoic and older ages that were deposited or emplaced near the edge of the North American continental margin. Rocks in the terrane record a variety of tectonic settings and have experienced varying amounts of tectonic transport, both before and after amalgamation of the YTT with North America. Sequences of mainly parautochthonous quartz-rich sedimentary rocks derived from the North American continent also include meta-igneous rocks with mostly continental geochemical and isotopic signatures. Structurally higher sequences contain meta-igneous rocks with arc and back-arc characteristics. The Slide Mountain/Seventymile terrane
Slide Mountain Terrane
The Slide Mountain Terrane is a late Paleozoic terrane made of a complex of oceanic rocks in northern and southern British Columbia, Canada. These oceanic rocks were derived from the seafloor of the prehistoric Slide Mountain Ocean, the Intermontane Plate, which was subducted under the North...
, composed of volcanic rocks typical of seafloor and of typical seafloor sediments, is recognized as an ocean basin that divided parts of the YTT before amalgamation of the Yukon-Tanana Terrane with the continental margin.
Understanding and definition of the YTT is constantly progressing, the term "Yukon Tanana composite terrane," or "YTCT" is used by some workers, reflecting the disparate depositional and tectonic histories being recognized in rock units within the YTT. Some recent work dispenses altogether with the term Yukon-Tanana Terrane, in favor of more detailed subdivisions.
The right-lateral strike slip Tintina Fault
Tintina Fault
The Tintina Fault is a large strike-slip fault in western North America, extending from northwestern British Columbia, Canada to the U.S. state of central Alaska. It represents the northern extension of the Rocky Mountain Fault in the northern United States....
occurs along the suture zone between the YTT (on the south and west) and ancestral North America to the east; it forms a significant boundary between North America cratonic rocks and rocks of the YTT and associated terranes - although displaced continental rocks are found south of the Tintina Fault and pieces of the YTT occur north of the Tintina Fault. Parts of the YTT have been offset by at least 400 km along the Tintina Fault. In most of the Alaskan part of the YTT the Denali Fault
Denali Fault
The Denali Fault is a major intracontinental dextral strike-slip fault in western North America, extending from northwestern British Columbia, Canada to the U.S. state of central Alaska. It was the main fault along which the 2002 Denali earthquake occurred, which was measured as a magnitude of 7.9...
forms the modern day southern boundary of the terrane. In Yukon the ocean-basin rocks of the Windy/McKinley terrane, and the Coast Plutonic Complex (CPC) form the southern boundary of the YTT. Units assigned to the YTT also occur within the CPC; and the YTT partially encloses and is complexley related to the Intermontane Superterrane.
Metal mineralization in the YTT
In Alaska (Delta district) and Yukon (Finlayson Lake belt) the YTT contains a number of Devonian volcanogenic massive sulfide ore depositVolcanogenic massive sulfide ore deposit
Volcanogenic massive sulfide ore deposits are a type of metal sulfide ore deposit, mainly Cu-Zn-Pb which are associated with and created by volcanic-associated hydrothermal events in submarine environments....
s with significant copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
, silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
and gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
mineralization. Sulfide mineral
Sulfide mineral
The sulfide minerals are a class of minerals containing sulfide as the major anion. Some sulfide minerals are economically important as metal ores. The sulfide class also includes the selenides, the tellurides, the arsenides, the antimonides, the bismuthinides, the sulfarsenides and the sulfosalts...
s include massive to disseminated pyrite
Pyrite
The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...
and pyrrhotite
Pyrrhotite
Pyrrhotite is an unusual iron sulfide mineral with a variable iron content: FeS . The FeS endmember is known as troilite. Pyrrhotite is also called magnetic pyrite because the color is similar to pyrite and it is weakly magnetic...
with lesser amounts of chalcopyrite
Chalcopyrite
Chalcopyrite is a copper iron sulfide mineral that crystallizes in the tetragonal system. It has the chemical composition CuFeS2. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mohs scale. Its streak is diagnostic as green tinged black.On exposure to air, chalcopyrite...
, galena
Galena
Galena is the natural mineral form of lead sulfide. It is the most important lead ore mineral.Galena is one of the most abundant and widely distributed sulfide minerals. It crystallizes in the cubic crystal system often showing octahedral forms...
, sphalerite
Sphalerite
Sphalerite is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron. When iron content is high it is an opaque black variety, marmatite. It is usually found in association with galena, pyrite, and other sulfides...
and arsenopyrite
Arsenopyrite
Arsenopyrite is an iron arsenic sulfide . It is a hard metallic, opaque, steel grey to silver white mineral with a relatively high specific gravity of 6.1. When dissolved in nitric acid, it releases elemental sulfur. When arsenopyrite is heated, it becomes magnetic and gives off toxic fumes...
. The deposits show evidence of an Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
, amphibolite facies event and a younger, mid-Cretaceous lower greenschist facies event which resulted from the accretion
Accretion (geology)
Accretion is a process by which material is added to a tectonic plate or a landmass. This material may be sediment, volcanic arcs, seamounts or other igneous features.-Description:...
of the Yukon-Tanana Terrane.
A belt of significant Late Triassic to Early Jurassic Cu-Au and Cu-Mo porphyry deposits, such as Highland Valley Copper and Galore, of the Stikine terrane
Stikinia
Stikinia is the name of a tectonostratigraphic terrane in the Canadian Cordillera of British Columbia, Canada. It was formed in a volcanic arc environment during the Paleozoic and Mesozoic periods...
and Quesnel terrane extends into the Yukon-Tanana terrane in Yukon; the Minto mine is an example.
Gold mineralization associated with post-amalgamation emplacement of Cretaceous and Tertiary plutonic rocks is widespread in the YTT.