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This paper reviews current thinking with respect to the main issues concerning the nature and evolution of the North China Craton (NCC). Because literature on the NCC is so voluminous, it of necessity focuses on specific aspects that have wider applicability to the nature of Precambrian cratons in general. The assembly of the craton is examined and opposing views evaluated. The overall distribution of Precambrian rocks is placed within the favoured model for subdividing the craton, and recent advances in determining the ages of key lithological associations are presented. The more controversial topic of where the NCC was placed in the Nuna/Columbia and Rodinia supercontinents is canvassed, although no definitive conclusions can be drawn. Finally, the removal of continental lithosphere from beneath the eastern part of the craton in the Phanerozoic is briefly examined, since this phenomenon has wider implications for the global preservation of Precambrian crust.

Scapolite is an important mineral in the metamorphism of calc-silicates, marbles, amphibolites, and metagabbros in the Lufilian–Zambezi belt of Zambia. Both field and petrographic studies on granite gneisses, amphibolites, and metagabbros from the Munali hills area, in the southern part of the Lufilian–Zambezi belt indicated that scapolitization was due to metasomatism. The scapolite occurs as a pervasive replacement of plagioclase in the Munali hills granite gneiss, amphibolites, and metagabbros, and is associated with mineral assemblages that are indicative of amphibolite-facies metamorphism. Results of mineral analyses show that all the scapolites have calcian–marialite compositions, which range from 27 to 47 Me % and XCl contents of 0.37–0.50 a.p.f.u. The anorthite equivalent (31–46 EqAn %) of the scapolites overlaps with that of coexisting plagioclase (21–48 XAn %). The composition of scapolite is similar to that of the Copperbelt region of Zambia, where there is documented evidence of evaporite horizons. Moderate to high NaCl salinities, which range from 0.2–0.5 mol, and high contents of Cl in scapolite indicate that metamorphism in the belt was accompanied by metasomatic introduction of NaCl-rich fluids, which were derived from evaporite horizons that existed in the metasedimentary succession in the belt. This study shows that evaporites, from which NaCl-rich fluids were derived, were widespread in the Lufilian–Zambezi belt and played an important role in the metamorphic history of the belt.

Archaean terranes, worldwide, typically comprise remnants of low metamorphic-grade, supracrustal rocks, dominated by mafic and ultramafic volcanics with lesser but variable volumes of sediments, preserved in a sea of granitoids. Age relations of the oldest granitoid gneisses and supracrustal remnants are commonly equivocal. Recent geochronological data from Swaziland provide support for the conclusion that certain layered, tonalitic/leucotonalitic gneisses pre-date extrusion of mafic and ultramafic lavas of the Barberton (formerly Swaziland) Sequence. The purpose of this paper is to demonstrate that subdivision of the granitoids into three so-called cycles is an oversimplification. Evidence is accumulating that sodic and potassic granitoid magmas were emplaced repeatedly over a period of at least 1000 Ma. The supracrustal remnants preserved in the granitoid sea reflect complex thrusting and reclined folding. Synsedimentary tectonism resulted in accumulation of clastic sediments in fault-bounded depositional basins. On a regional scale, this deformation resulted in progressive northward uplift of the crust to the south of the Barberton supracrustal remnant. The Barberton Sequence was, in part, obducted onto sialic crust lying to the northwest as a result of horizontal compression and lateral shortening (up to 50%). New tonalitic magmas were generated and older tonalitic/leucotonalitic crust deformed and metamorphosed. Preservation of clasts composed of potassic granite in the upper sedimentary member of the Barberton Sequence implies that potassic as well as sodic granitic magmas were generated at ≈ 3480 Ma. Synchronous with this later deformation was intrusion of tabular leucotonalitic batholiths south of Barberton, generated by partial melting of tectonically intersliced metavolcanic remnants and older sialic crust. Thick sialic crust resulted from a combination of tectonic interslicing and the emplacement of the tabular potassic Lochiel granite at ≈ 3000 Ma as a consequence of partial melting of old sialic crust. The Lochiel granite batholith is confined to the southeastern flank of Barberton supracrustal remnant. It is proposed that this granite was generated at a continental margin following closure of the ocean in which the Barberton Sequence was generated. Deformation of the Pongola Sequence and subsequent intrusion of post-Pongola granitoids were the final events of Archaean age in Swaziland and adjacent areas to the south.

The 10–14 km thick Archean volcano-sedimentary sequence in the Chibougamau region is composed of two mafic to felsic cycles, and of two thick, predominantly epiclastic, sedimentary sequences. The supracrustal suite is isoclinally folded along east-west axes, and punctuated by syn-volcanic, syn-kinematic and post-kinematic plutons. Tonalitic basement occurs along the northern margin, in a central horst, and as large rafts in later batholiths. Events affecting the supracrustal rocks are recorded in the tectono-magnetic history of the basement gneiss superimposed on the events related to basement formation.

The Kapuskasing uplift provides a window on the deep crust of the Superior Province. Evidence in support of an exposed oblique crustal cross section includes: a systematic easterly increase in metamorphic grade from 3 kbar greenstones at Wawa to 8 kbar Kapuskasing granulites; structural and paleomagnetic data on gneisses and dykes indicating 10–15° of east-side-up block rotation; seismic refraction and reflection data tracing the high-velocity Kapuskasing zone from surface down dip at 15 °W to about 20 km; and progressively slower cooling rates with paleodepth. The composite cross-section derived from the oblique exposure comprises an upper, 2–3 kbar greenstone- granite megalayer (2.89–2.67 Ga), an intermediate, 5–6 kbar tonalite gneiss megalayer (2.72–2.67 Ga) and a lower, 7–9 kbar, heterogeneous granulite gneiss megalayer (2.76–2.60 Ga). Regional cooling and uplift preceded thrust uplift along the Ivanhoe Lake fault 2.2–1.95 Ga ago. Steep normal faults transecting the uplift possibly reflect topographic collapse and are cut by 1.88 Ga carbonatites. Regional NW-SE shortening of about 70 km during the 2.2–1.88 Ga Kapuskasing event was accomodated above a mid-crustal decollement by 15 km of brittle uplift of granulites along a 15°-dipping fault and below it by 10–15 km of ductile thickening of the present lower crust over a 200-km-wide zone.

Early Precambrian basic rocks occur throughout a large part of the USA (Peterman, 1979; Harrison and Peterman, 1984). Archaean complexes outcrop in two major provinces, one forming the southwestern tip of the Superior Province in northern Minnesota and Wisconsin, and the other comprising the Wyoming craton, outcropping in the mountain ranges of Wyoming and its neighbouring states (Figure 9.1). Both of these provinces have significant plutonic, hypabyssal and volcanic basic components, ranging in age from early to late Archaean. In addition, early to mid-Proterozoic hypabyssal basic intrusions occur in virtually all of the Archaean cratonic regions, while early to mid-Proterozoic metavolcanic suites occur throughout western central USA (Condie, 1986).

The elements Rb, Sr, Sm, Nd, U and Pb are all redistributed during the movement of fluids associated with regional metamorphism. The effect of this redistribution on the isotopic systems commonly used for age determination depends on several factors. Rb, U and Pb are lost on a regional scale during prograde metamorphism to granulite facies assemblages and are regained during retrogression. Sr is redistributed on a cm scale during both prograde and retrograde metamorphism and is mobile on a scale of tens of meters during retrogression associated with shearing. As Rb is markedly more mobile than Sr, Rb/Sr ratios of individual samples can be modified without homogenisation of Sr on outcrop scale. Addition of Rb to a sample suite will displace an original Rb-Sr isochron to the right, giving rise to an anomalously low intercept 87Sr/86Sr ratio. Loss of Rb has the opposite effect. A high amount of Rb movement is required before isochron relationships are totally destroyed. Redistribution of Sm and Nd takes place on outcrop scale in response to the formation of partial melts and new mineral assemblages. This can lead to local resetting of the Sm-Nd whole rock isotopic system at the time of high grade metamorphism. The effect of regional metamorphism on the redistribution of the REE on a larger scale is not well constrained by bulk rock analyses. Addition of LREE is recorded in tonalitic gneisses up to tens of meters from adjacent granite sheets and pegmatites. This results in both changes in bulk REE patterns and in changes in the Nd isotopic signatures depending on the isotopic composition of the Nd introduced. Basic rocks and ironstones with low primary REE contents from the 3.8 Ga Isua supracrustal belt show variable amounts of LREE addition during late Archaean and Proterozoic metamorphism. Estimates of crustal residence times or early Archaean mantle compositions based on initial end values from individual samples of these polymetamorphic rocks must be evaluated using field constraints. U loss during granulite facies metamorphism will arrest the radiogenic evolution of Pb. Straightforward interpretation of the resulting “palaeoisochrons” without allowing for secondary U loss leads to spuriously high ages and µ1 values. U loss during granulite facies metamorphism is commonly accompanied by Pb loss, and in some examples by partial isotopic homogenisation of the remaining Pb. Addition of U to rocks with approximately isotopically homogenous Pb (for example during retrogression from granulite facies) will yield ages close to that of U addition. The effect of Pb addition is more complex as it depends on the isotopic composition of the introduced Pb itself depending on the source of the Pb. Under certain circumstances mixing of Pb from different sources can give rise to Pb-Pb pseudoisochrons.

As we have seen in the previous chapter, it becomes progressively more difficult to interpret the structure of orogenic belts as we look further back in time, beyond the period when accurate continental reconstructions can be made from oceanic palaeomagnetic data. This difficulty is magnified in the Precambrian because of the inherent inaccuracies of continental palaeomagnetic reconstructions, and is compounded by other problems. The familiar stratigraphic certainties conveyed by accurate palaeontological dating in the Phanerozoic are absent throughout much of the Precambrian. The widely-used radiometric dating methods cannot yet give the same precision in subdividing and correlating stratigraphic sequences.