The Brooks Range formed by amalgamation of many tectonic terranes. Although the configuration of the terranes is less complicated than in the Canadian Cordillera or southern Alaska, the history and boundaries of the terranes continues to be debated. The Brooks Range is a fairly pristine orogen, nearly unaffected by major strike-slip or extensional faulting over most of its history. Today, some E-W trending,
active strike-slip faults slice the range, and normal faults on the southern margin of the Range also appear to be active. Luckily, tectonic forces have not quite succeeded in wrenching the Range apart; geologists got there first and appear to be winning the race for understanding. The apparent simplicity of the tectonic structure of the Brooks Range may be partly due to the relative paucity of work done in the area. The more any orogen (or anything) is subjected to study, the more complex the hypotheses of formation become. This is a reflection of the advancement of ideas and techniques in the geosciences, and the integration of data gleaned from multiple approaches such as isotope geochemistry, reflection and refraction seismology, paleomagnetism, neotectonic geodesy, and computer modeling.Knowledge gained by various disciplines is discussed
elsewhere in this site. However, this part of the site may be the most important. Here, you can get an understanding of the paleogeography and tectonics of northern Alaska, which will give you a framework for understanding and placing the bits of information gleaned from various geoscience disciplines. The purpose of these four pages is to walk through a plausible tectonic history of the Brooks Range, with an illustration at each time step showing a possible geographic configuration. This is done both in map view and partly in cross section; see the links below.The construction of this tectonic history is only possible thanks to over 100 years of work by Brooks Range geoscientists of every stripe, and the history continues to change with each new piece of information we obtain. That is to say, the following reconstructions are a work in progress.
Before we jump into reconstructions, a word about time and the non-uniqueness of paleotectonic interpretations:
The Factor of Time
One "law" of geology (or any observational science) is that
"With each step we take back in time, we know exponentially less about the geology of the period"
(If you like, read more about this
law.)This fact is clearly illustrated in the following sequence of figures outlining the tectonic evolution of the Brooks Range; recent figures are most complex and detailed and become more simple and schematic as we step back in time. Also, as we step back in time, we find the available geological data supports equally well several tectonic histories. Because of this, tectonic reconstructions are non-unique.
The tectonic history of the rocks of the Brooks Range is still debated. It must be pointed out that the "Tectonic Evolution" sequence of figures represent only one of at least four possible, distinct reconstructions. These four reconstructions are summarized in the following figure.
Figure from Moore et al., 1994 in The Geology of Alaska
Briefly, the four suggested possibilities are:
A) In situ origin: Arctic Alaska is not translated or rotated
B) Yukon origin: Arctic Alaska is translated north by dextral strike-slip from a position in the northern Canadian Cordillera and then is again offset to the west by dextral strike-slip
C) Barents shelf origin: Arctic Alaska is translated west by sinistral strike-slip from a position near Greenland (making the Brooks Range part of the Caledonian or Innuitian orogens)
D) Canadian Arctic Islands Origin: Arctic Alaska is rifted away from the margin of North America along the current Canadian Arctic Islands, and then is rotated counter clockwise (model illustrated in "Tectonic Evolution" sequence).
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