Growth of continental crust in intra-oceanic and continental-margin arc systems: Analogs for Archean systems

Abstract

Earth's continental crust has grown and been recycled throughout geologic history along convergent plate margins. The main locus of continental crustal growth is in intra-oceanic and continental-margin arc systems in Archean time. In arc systems, oceanic lithosphere is subducted to the deeper mantle, and together with its overlying sedimentary sequence is in some cases off-scraped to form accretionary prisms. Fluids are released from the subducting slab to chemically react with the mantle wedge, forming mafic-ultramafic metasomatites, whose partial melting generates mafic melts that rise up to form arcs. In intraoceanic arcs, they produce dominantly basaltic lavas, with a mid-crust that includes variably-developed vertically-walled intermediate plutons and higher-level dikes and sills. In continental-margin arcs, different petrogenetic processes cause assimilation and fractionation of basaltic magmas, partial melting/reworking of juvenile basaltic rocks, and mixing of mantle-and crust-derived melts, so they produce andesitic calc-alkaline melts but still have a mid-crust dominated by vertically-walled felsic plutons, which form 3-D dome-and-basin structures, akin to those in some Archean terranes such as parts of the Pilbara and Zimbabwe cratons. Notably, the continental crust of Archean times is dominated by tonalite-trondhjemite-granodiorite (TTG) plutons, similar to that of the mid-crust of these arc systems, suggesting that early continental crust may have formed largely by the amalgamation of multiple arc systems. The patterns of magmatism, in terms of petrogenesis, rock types, duration of magmatic and accretionary events, and the spatial scales of deformation and magmatism have remained essentially the same throughout geological history, demonstrating that plate tectonic processes characterized by subduction and arc magmatism have been in operation at least as long as recorded by the preserved geologic record, since the Eoarchean. However, the early Earth was dominated by accretionary orogens and oceanic arcs, that gradually grew thicker through multiple accretion events to form early continental-margin arcs by 3.5-3.2 Ga, and accretionary orogens. Slab melting and warmer metamorphism was more common in Archean arc systems due to higher mantle temperatures. These early arcs were further amalgamated into large emergent continents by ~3.2-3.0 Ga, allowing large-scale processes such as lithospheric rifting and continental collisions, and the start of the supercontinent cycle. Further work should apply the null hypothesis, that plate tectonics explains the geologic record, to test for differences in the style of plate tectonics and magmatism through time, based on the fundamental difference in planetary heat production and the evolution of rotational dynamics of the Earth-Sun-Moon system.

Comparative orotomy of the Archean Superior and Phanerozoic Altaid orogenic systems

“…1 ) contain hundreds to thousands of kilometer-scale belts of magmatic arcs, subduction accretion complexes and older ribbon continents, sliced by strike-slip faults associated with late transtensional and transpressional basins. Within and between these belts, large irregular areas characterized by intense orogenic deformation, typically containing many small ophirags, are intruded by multiple generations of plutonic rocks, and deformed into complex patterns including the classic ‘dome-and-basin’ pattern that typifies deeply eroded arc roots of all ages [ 7 , 8 ]. In this contribution, we show that the overall map patterns, lithological make-up, structural patterns and the characteristic shredding of the former ophiolite suite into the presently preserved ophirags in these orogenic collages, is no different in the Altaids than in the Superior Province, or in other Archean cratons or orogens.…”

“…While commonly contentious, it has been recognized since [ 51 ] that oceanic-type fragments of former ophiolites are found in many Archean terranes, such as the Slave [ 52 ], Superior [ 44 ], Kaapvaal [ 53 , 54 ] and many other cratons [ 23 , 55 , 56 ]. In many cases, only the upper crustal sections of ophiolites may be preserved, a characteristic of Archean ophiolites, which likely were scraped off from a thicker oceanic crustal section [ 8 , 44 , 52 , 57 ].…”

“…[ 2 ] to correlate the different tectonic belts (using a terrane analysis approach) on both the eastern and western sides of Hudson Bay into one domain, or block, that they considered continental in aspect at the time of its collision with the Berens River arc at 2720 Ma. We note that arc magmatism was continuing through the time of the collision, so suggest alternatively that the Hudson Bay block was a continental-margin arc system, with older relicts of its former history embedded in a sea of arc plutons, as is common in continental-margin arc systems [ 8 ].…”

“…A similar scenario has recently been proposed for the Pilbara Craton, where dome-and-basin structures have for some years been thought to indicate that the Mesoarchean was dominated by vertical drip and antidrip tectonics, but were then shown by T Kusky et al . [ 7 ] to be nothing more than vertically intruding and re-folded plutons in the root of an accretionary-to-continental-margin arc system, much like the Altaids [ 7 , 8 ]. The Winnipeg River ribbon microcontinent is apparently oroclinally folded into an isocline (Fig.…”

“…6 ) hosts a late Archean continental-margin-style plutonic belt (e.g. [ 8 ]), with several suites of 2760–2710 Ma low-K TTG, 2730–2680 Ma hornblende-quartz monzodiorite and granodiorites and granite, 2730–2710 Ma pyroxene granites, and 2720–2700 Ma mafic-ultramafic plutons [ 147 , 148 ]. These plutonic belts cut across the boundaries of the older subduction/accretion belts, and have been identified as a continental-margin magmatic arc suite generated by N-dipping subduction [ 149 ] followed by younger melts formed during collision.…”