Hi Richard,

Since the advance of Plate Tectonic model, the greenstone-basement relationship has been generally explained by thrust tectonic, as illustrated by the attached Fig. 1. However, Plate Tectonic is assumed to work well from >2.5 Ga (e.g. Rollinson, 2007), but for early Archean times a lot of discussion still on it, and other explanations for the structures in Archean granite-greenstone terranes adopt the plume and/or dome-and-keel models (e.g. Gorman et al., 1978; Rollinson, 2007; Wymen, 2013). For example, the formation of the dome-and-keel structure could be viewed as a diapiric process driven by a density inversion, as illustrated by the Fig. 2.

So far, both models can explain high-grade basement and low-grade greenstone relationships, and if you are working at late Precambrian (>2.5 Ga) to Phanerozoic terranes, thrust tectonic can be applied easily. But if you are working on early Archean domains, I guess you will need to choose one of these models that better fits to the rocks/place where you are ….

Cheers,

Felipe

References:

Gorman, B.E., Pearce, T.H., Birkett, T.C., 1978. On the structure of Archean greenstone belts, Precambrian Research, 6 (1), 23-41.

Rollinson, H., 2007. When did plate tectonics begin? Geology Today, 23, 186-191.

Wyman, D.A., 2013. A critical assessment of Neoarchean “plume only” geodynamics: Evidence from the Superior Province. Precambrian Research, 229, 3-19.

The Dabie mountains of China and the Mederes Massif of western Anatolia (Turkey) display such relationships. Low temperature high pressure metamorphic rocks (blueschists) occur as thrust sheets above cores of granulite-bearing gneisses. Final emplacement (after overthrusting) was as mantled gneiss domes (aka metamorphic core complexes) from deep crustal or even upper mantle depths by buoyancy uplift.

Thanks fellows for your contributions. I would particularly would like to better understand Paleoproterozoic province relationships such as in North America.

I suspect that:

* Felipe's model applies to the Archean.(Sharkov & Bogatikov 2010).

* Roger's cases apply to thrusting of Phanerozoic rocks.

In northern Canada there are Paleoproterozoic granulite-gneiss belts adjacent to Archean provinces and to Wopmay low-grade Paleoproterozoic accretionary orogen. Between the Archean Wyoming and Superior provinces there is the low-grade Paleoproterozoic Trans-Hudson Province (Mints 2015, 2007). The low-grade Penokean Province has Superior Province on its northern side and the Great Proterozoic Orogen on its southern side.

Attached is a figure modified from Mints2015 to show the spatial setting of these provinces in North America. I find the relationships of the Proterozoic granulite-gneiss belts to be intriguing.

Always depend upon what part of crust you are looking at if these different facies rocks belong to the same terrane. Otherwise, they may be ascribed to different terranes or domains but now are juxatopose together by tectonics. d