A Ca. 2.8‐Ga Plume‐Induced Intraoceanic Arc System in the Eastern North China Craton

Abstract

The conversion of Archean tectonic regimes from mantle plume to plate tectonic and the mechanism of subduction initiation are two crucial issues in the current Earth sciences. A typical komatiite‐tholeiite sequence consisting of ~2,850–2,800‐Ma komatiites and ~2,780–2,710‐Ma basaltic and andesitic to dacitic volcanic rocks is well preserved in the Archean Western Shandong terrane of the eastern North China Craton. These volcanic rocks were derived from the partial melting of a depleted mantle source with subsequent fractional crystallization, a metasomatized subarc mantle wedge, and a descending oceanic slab. Structural and kinematic observations suggest that the Qixingtai‐Yanlinguan‐Panchegou granite‐greenstone belt experienced ~2.85–2.80‐Ga extensional deformation (D1) by upwelling of a mantle plume and NE‐SW‐oriented shortening (D2) during ~2.78–2.71 Ga. The petrogenesis of the Mesoarchean to early Neoarchean metamorphosed volcanic rock series and regional deformation indicate that a plume‐induced self‐sustaining intraoceanic arc system with SW‐dipping subduction polarity operated ~2.8 Ga, followed by the evolution from initial to mature subduction. An increasing pull caused by the descending slab generated gravitational instability in the surrounding oceanic lithosphere and formation of a new initial subduction zone adjacent to the preexisting arc system. Similar to the process in the Western Shandong terrane, plume activity generally culminated in subduction events in many other Archean greenstone belts, revealing that plume‐arc interaction may have been a crucial mechanism for global Archean tectonic regime conversion from mantle plume to initial plate subduction in the crust of the early Earth.

Thermal state and evolving geodynamic regimes of the Meso- to Neoarchean North China Craton

“…On the other hand, the mantle cooling also promote lithosphere strengthening. Integrated with petrological and structural data for a corresponding change through this interval from komatiite to calc-alkaline volcanic rock, and a changing structural style from extension to compression 26 , these newly obtained data indicate that plate tectonics were already a dominant geodynamic mechanism in the Neoarchean. However, the style of Archean plate tectonics (for example, subduction rate and subducted angle of oceanic slab) in North China may have been different from that of modern day cold plate tectonics due to its slightly higher mantle temperature on the basis of the thermomechanical numerical modeling results, and is often referred to as "hot subduction" 38,39 .…”

“…Recent investigations suggest that the magmatic precursors of the TTG gneisses may be derived from (1) fractionation of primary basaltic or dioritic magmas (namely, "crystal mush model") 19-21 ; (2) partial melting of hydrated mafic rocks at the base of the Earth's crust 22,23 ; or, (3) partial melting of fluid fluxed mantle (namely, "slab melting model") [24][25][26] . The most prominent features of TTG melts derived from partial melting of thickened lower crust are lower MgO content (generally less than 2.0 wt.%) and transition elements of Cr, Ni, Co and V concentrations with Mg# values (Mg# = Mg 2+ /(Mg 2+ +Total Fe 2+ ) × 100) lower than 45 based on the results of experimental petrology 27 .…”

Neoarchaean subduction tectonics in Western Shandong Province, China: Evidence from geochemistry and zircon U–Pb–Hf isotopes of metabasalts

“…Many studies have shown that volcanic rocks with low values of LOI (<2 wt%) and Ce anomalies (δCe ratios between 0.9 and 1.1, δCe = Ce N /Sqrt (La N × Pr N )) could be designated as the least altered samples (Polat et al, 2006;Polat, Hofmann, & Rosing, 2002 S177-1 S177-3 S177-4 S177-5 S177-6 S177-7 S177-8 S177-9 S177-10 in both the rims and cores, which reflect the mobility of these elements during alteration. Accordingly, the Al 2 O 3 /TiO 2 ratio is generally considered an alteration-insensitive index and displays linear relationships with the unaltered major elements in their binary diagrams Gao, Liu, & Zhang, 2019;Guo et al, 2016;Guo, Liu, & Zhang, 2015; scatter, suggesting their mobility ( Figure 4).…”

“…Both ∼2.8-2.7 and ∼2.6-2.5 Ga tectonothermal events have been identified in the WSP granite-greenstone belt (Wan et al, 2010. The ∼2.8-2.7 Ga supracrustal rocks are mainly exposed in the central part of the WSP, including the komatiite-tholeiite sequence consisting of 2,850-2,800 Ma komatiites and the~2,780-2,690 Ma basaltic and andesitic to dacitic volcanic rocks (Gao, Liu, & Zhang, 2019;Polat et al, 2006;Wan et al, 2014;Wang et al, 2013). The~2.6-2.5 Ga supracrustal rocks are mainly composed of minor mafic to felsic volcanic rocks.…”

“…As a result, fluids and melts derived from the partial melting of the oceanic slab were able to metasomatize or interact with the overlying peridotitic mantle at various depths. The partial melting of the mantle wedge that FIGURE 14 Simplified model of the tectonic evolution of the 2.6-2.5 Ga metabasalts and associated rocks of the WSP [Colour figure can be viewed at wileyonlinelibrary.com] had been metasomatized by aqueous fluids and melts would have produced IATs and associated groups of volcanic rocks (Figure 14;Peng et al, 2012;Gao, Liu, & Zhang, 2019; this study). The processes of slab-wedge interaction and lateral accretion gradually became the dominant mechanism and played a crucial role during the 2.6-2.5 Ga crustal growth and evolution.…”