Page 379 - Global Tectonics

362 CHAPTER 11

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Selected exposures of Archean and early Early Proterozoic crust
Selected exposures of late Early Proterozoic and Middle Proterozoic crust

2.1–1.8 Ga orogenic belt
Antarctica Phanerozoic cover or ice of subcontinental scale preventing access to
Antarctica
cratonic basement
19 Other crust, mostly younger than 1.8 Ga

Fig. 11.12 Global distribution of 2.1–1.8 Ga orogenic belts showing selected areas of Archean and Early Proterozoic
basement (after Zhao et al., 2002, with permission from Elsevier). Orogens labeled as follows: 1, Trans-Hudson; 2,
Penokean; 3, Taltson-Thelon; 4, Wopmay; 5, Cape Smith–New Quebec; 6, Torngat; 7, Foxe; 8, Nagssugtoqidian; 9,
Makkovikian–Ketilidian; 10, Transamazonian; 11, Eburnian; 12, Limpopo; 13, Moyar; 14, Capricorn; 15, Trans-North
China; 16, Central Aldan; 17, Svecofennian; 18, Kola-Karelian; 19, Transantarctic.

A comparison of igneous rocks in Archean and This compositional trend from basalt to tonalite to
Proterozoic belts indicates a progressive change in granite generally is attributed to an increase in the
the bulk composition of the crust through time importance of subduction and crustal recycling during
(Condie, 2005b). During the Early Archean, basaltic the transition from Late Archean to Early Proterozoic
rocks were most abundant (Section 11.3.2). Later, the times.
partial melting of these rocks in subduction zones or Large swarms of mafic dikes were emplaced into

at the base of oceanic plateaux produced large volumes Archean cratons and their cover rocks during the Late
of TTG suite granitoids (Sections 11.3.2, 11.3.3). By Archean–Early Proterozoic and onwards. One of the
3.2 Ga granites first appeared in the geologic record best exposed examples of these is the 1.27 Ga MacKen-

and were produced in large quantities after 2.6 Ga. zie dike swarm of the Canadian Shield, which exhibits