I am not familiar with "complexly amalgamated" as a formal term.  It is most likely informal and descriptive.  To amalgamite means to merge, combine, or unite.  I would think it is safe to say that most orogens consist of complexly amalgamated terranes.

I do not study about ' complexly amalgamated'. Best wishes.

David understand my point.

Elaborating upon David's description which I fully agree with; This combined (complexely amalgamated words....) term refers to a terminology of the late seventies which tried to capture/describe the mosaic of fragments of tectonic plates which is visible along the edges of the main and minor Plates; being made up of elements that belonged to both bounding plates and to plates that had long disappeared, it became in-vogue to speak of "terranes". The terminology is based on the concept that each of these "terranes" shows it's own unique (tectono-)stratigraphy. Later on it was recognized that this may be an oversimplification of reality and a too-rigid way of trying to define the geological reality.

How big these "terranes" are is not really clear, so the concept can be applied on various scales (hm, km). It can still be useful for descriptive purposes, especially when we look at plate boundaries characterized by a large horizontal component where different structural blocks are now facing each other in a completely unique way with respect to their origins. But then we could simply use the word "block". When we look at overthrusting it is obvious that different structural units by definition show a unique stratigraphy so the terminology is not really useful in that case according to many authors. So here we talk about "thrust sheets" or "nappes".

Obviously what is "complex" depends of our view of the world. That can be very personal and subjective if "complex" becomes synonymous of "most people do not understand it". Which can then be followed by "but I do, instead", or by "neither do I". ;-)