Insights into the tectonic evolution of the North China Craton through comparative tectonic analysis: A record of outward growth of Precambrian continents

Archean cratons have map patterns and rock associations that are diagnostic of the Wilson Cycle, and therefore they can be used to distinguish the principal components of of plate tectonic evolution. The North China Craton (NCC) consists of several distinctly different tectonic units, but the delineation and understanding of the significance of individual sutures and the rocks between them has been hampered by inappropriate definitions of orogens, cratonic blocks, arcs, trapped plateaus, sedimentary basins, accretionary prisms and orogens, and different generations and types of magmatic rocks. The most widely used tectonic division of the craton has been based nearly entirely on the interpretation of metamorphic P-T-t paths and recrystallized zircon morphology, and ignores other familiar elements of the Wilson Cycle. We propose an actualistic tectonic division of the North China Craton based on Wilson Cycle analysis that uses a multi-disciplinary (geology, geochemistry, geochronology, and geophysics) approach to define sutures, their ages, and the nature of the rocks between them, to determine their mode of formation and means of accretion or exhumation, and to propose appropriate modern analogues. The eastern unit of the craton consists of several different small blocks that resemble fragments of accreted arcs from an assembled archipelago similar to those in the extant SW Pacific. These different blocks were assembled between 2.6 and 2.7 Ga ago, although they contain older crustal material dating back to at least 3.8 Ga. A thick Atlantic-type margin developed on the western side of the newly assembled Eastern Block by 2.6-2.5 Ga. A >1,300 km long arc and accretionary prism collided with the margin of the Eastern Block at 2.5 Ga, obducting ophiolites and ophiolitic mélanges onto the block, and depositing a thick clastic wedge in a foreland basin farther into the Eastern Block. This was followed by an arc-polarity reversal, which led to a short-lived injection of mantle wedge-derived melts to the base of the crust that led to the intrusion of mafic dikes and arc-type granitoid (TTG) plutons with associated metamorphism. By 2.43 Ga, the remaining open ocean west of (present geometry) the accreted arc closed with the collision perhaps of an oceanic plateau now preserved as the Western Block with the collision-modified margin of the Eastern Block, causing further deformation to give rise to what has become known as the Central Orogenic Belt. Rifting at 2.4-2.35 Ga of the newly amalgamated continental block led to a rift preserved along its center, and new oceans within the other two rift arms, which removed a still-unknown continental fragment from its (present geometry) northern margin. By about 2.3 Ga an arc collided with a new Atlantic-type margin developed over the rift sequence on the northern margin of the craton, and thus was converted to an Andean margin through arc-polarity reversal. Andean margin tectonics affected much of the continental block from 2.3 to 1.9 Ga, giving rise to a broad E-to-W swath of continental margin magmas, and retro-arc sedimentary basins including a foreland basin superimposed on the passive northern margin. The horizontal extent of these tectonic components is similar to that across the present-day Andes in South America. From 1.88 to 1.79 Ga a granulite facies metamorphic event was superimposed across the entire continental block with high-pressure granulites and eclogites in the north, and medium-pressure granulites across the whole craton. The scale of this event is similar to that of the present day India-Asia collision, which has an across-strike width of 1,000 km, and a duration (~90 Ma), which is similar to that of the on-going Alpine-Himalayan collision that has been active for the last ~50 Ma. The deep crustal granulites and mapped volcanic rocks interpreted to be anatectic melts from deep crustal granulites on the surface today are similar to those that are considered to be presently forming at mid-crustal levels beneath Tibet, with high-grade metamorphism and the generation of partial melts. Analysis of structural fabrics in lower-crustal migmatites related to this event reveals that they flowed laterally parallel to the collision, much like what is hypothesized to be happening in the deep crust of the Himalayan/Tibetan foreland. We relate this continent-continent collision to the collision of the North China Craton with the postulated Columbia (Nuna) Continent. The NCC broke out of the Columbia Continent between 1753-1673 Ma, as shown by the formation of a suite of anorthosite, mangerite, charnockite, and alkali-feldspar granites in an ENE-striking belt across the north margin of the craton, whose intrusion was followed by the development of rift and graben systems, mafic dike swarms, and eventually an Atlantic-type marginal sequence that signaled the beginning of a long period of tectonic quiescence and carbonate deposition for the NCC during Sinian times which persisted into the Paleozoic. The style of tectonic accretion in the NCC changed at circa 2.5 Ga, from an earlier phase of accretion of arcs presently preserved in horizontal lengths several hundred kilometers long, to the accretion and preservation of linear arc blocks several thousand kilometers long with associated oceanic plateaus, microcontinents, and accretionary prisms. The style of progressively younger outward accretion of different tectonic elements is reminiscent of the style of accretion in the Superior Craton, and may signal the formation of progressively larger landmasses at the end of the Archean (perhaps into the time of the Kenorland Continent), then into the Paleoproterozoic, culminating in the assembly of the Columbia (Nuna) Continent at 1.9-1.8 Ga.