Hi Mohamed,

A good review paper of Alaskan-type intrusions is Himmelberg and Loney 1995 (USGS Prof. paper 1564; available online, see below). Some more recent references and distinguishing criteria of Alaskan-type intrusive rocks (e.g. clinopyroxene mineral chemistry) are cited in Deng et al. (2013; Geoscience Frontiers; see link for online edition).

Tom Skulski

Himmelberg et al: http://137.229.113.30/webpubs/usgs/p/text/p1564.pdf

Deng et al.: http://www.sciencedirect.com/science/article/pii/S1674987113001370

Thanks so much Thomas

I wish I can receive comments and reply for field and tectonic discrimination based on field experience

Actually it is hard to tell whether a suite is originally Alaskan type or it was a layered intrusion and due to later tectonic activities it appears to be as Alaskan type. But still you can see for any evidence of deformation in and around the region. If they appears to be synchronous then may be the suite is Alaskan type, and if the deformation appears to be post-genetic, then it can be a layered suite.

Its hard to differenciate these kind of intrusions only by fieldwork observations given that many alaskan-type intrusions are incomplete or have only one lithology such as hornblendite or even have inverse zonation. Their cumulatic nature where there are no acess direct to the magma composition the best way to work is by mineral chemistry in clinopyroxenes and spinels. Its important denote that alaskan-type intrusion have genetic link with subduction zones and proximity with accreted terranes whereas layered intrusion are anorogenic. One implication are that in alaskan-type because of their origin in hydrous magma have mineral assemblage like that Clinopyroxenes, horblende, biotite and layered intrusion have annydrous mineralogy such as ortopyroxene.

I agree with Geysson A Lages. I think that the distinction between the two types is not so simple either in the field or even geochemically. In general, the Alaskan-type is commonly related to subduction regime, while the layered intrusions are generally of non-orogenic setting. Therefore it is important to be considered within the framework of the regional geology of the area, not only on the ultramafic-mafic intrusion scale. It is difficult to advocate that the collected samples are really representing the parent magma due to common fractionation processes. Hence, plotting different samples from the same parent magma could lead to conflicting tectonic setting results.

The primitive clinopyroxenes would have low Al and high Si, i.e they would plot in the HMA field in the cpx Si vs Mg# plot of Kamei et al( 2004)

Kamei et al (2004); Lithos 75 (2004) 359– 371