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Rapid Endogenic Rock Recycling in Magmatic Arcs ✉ Jun-Yong Li1,2, Ming Tang2,3, Cin-Ty A

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Rapid Endogenic Rock Recycling in Magmatic Arcs ✉ Jun-Yong Li1,2, Ming Tang2,3, Cin-Ty A ARTICLE https://doi.org/10.1038/s41467-021-23797-3 OPEN Rapid endogenic rock recycling in magmatic arcs ✉ Jun-Yong Li1,2, Ming Tang2,3, Cin-Ty A. Lee 2, Xiao-Lei Wang 1 , Zhi-Dong Gu4, Xiao-Ping Xia 5, Di Wang1, De-Hong Du1 & Lin-Sen Li1 In subduction zones, materials on Earth’s surface can be transported to the deep crust or mantle, but the exact mechanisms and the nature of the recycled materials are not fully understood. Here, we report a set of migmatites from western Yangtze Block, China. These migmatites have similar bulk compositions as forearc sediments. Zircon age distributions and 1234567890():,; Hf–O isotopes indicate that the precursors of the sediments were predominantly derived from juvenile arc crust itself. Using phase equilibria modeling, we show that the sediments experienced high temperature-to-pressure ratio metamorphism and were most likely trans- ported to deep arc crust by intracrustal thrust faults. By dating the magmatic zircon cores and overgrowth rims, we find that the entire rock cycle, from arc magmatism, to weathering at the surface, then to burial and remelting in the deep crust, took place within ~10 Myr. Our findings highlight thrust faults as an efficient recycling channel in compressional arcs and endogenic recycling as an important mechanism driving internal redistribution and differentiation of arc crust. 1 State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, China. 2 Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX, USA. 3 School of Earth and Space Sciences, Peking University, Beijing, China. 4 Research Institute of Petroleum Exploration and Development, Beijing, China. 5 State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, ✉ Chinese Academy of Sciences, Guangzhou, China. email: [email protected] NATURE COMMUNICATIONS | (2021) 12:3533 | https://doi.org/10.1038/s41467-021-23797-3 | www.nature.com/naturecommunications 1 ARTICLE NATURE COMMUNICATIONS | https://doi.org/10.1038/s41467-021-23797-3 agmatic arcs witness the interplay between endogenous leucosome veins. The stromatic migmatites have a NNW-dipping fi and exogenous processes, including magmatism, crustal foliation (S1) (~355°/48°) de ned by oriented biotite or feldspar M fi thickening, uplift, erosion, sedimentation and burial of augen. The S1 foliation is parallel to bedding planes de ned by the detritus1–4. Magmatism produces new crust, which later interacts metapelite (Supplementary Fig. 2c) and is folded locally by syn- with the hydrosphere and atmosphere through erosion and anatectic deformation on varying scale (Supplementary Fig. 2e, f). – weathering. On the other hand, crustal materials from the surface The fold axial planes (S2) generally display E W striking, S- are recycled to Earth’s interior. This chain of processes in mag- dipping orientation. Besides, the study area was superimposed by matic arcs play important roles in driving much of the mass massive high-angle, S-verging thrust faults (Supplementary exchange between Earth’s interior and surface. The inward Fig. 2g), which should be linked with post-Mesozoic structural transport of surface materials, including volatiles, has profound tectonics17. influence on the cycling of carbon, oxygen, sulfur, etc. on Earth’s Six stromatic migmatite and one leucosome samples in the surface and may alter the chemical and physical properties of the Huangshuihe Group were collected in this study (Supplementary deep crust and even mantle. Fig. 1d). The main minerals in migmatite are plagioclase, biotite, Nearly every Phanerozoic arc in the world exhibit crustal sig- K-feldspar, quartz and muscovite (Supplementary Fig. 3). Ana- natures in geochemistry, suggesting pervasive crustal recycling in texis of primary mineral assemblage led to prevalent zircon the formation of arc crust. Conventional views link crustal overgrowth and muscovite-rimmed biotite in the migmatite recycling processes to slab subduction, including sediment sub- (Supplementary Figs. 3 and 5–7). Entrainment of peritectic phase, duction and subduction erosion (± relamination) have been which consists of small spessartine-rich garnet grains, biotite, widely invoked to explain the crustal signatures seen in most arc muscovite, quartz, plagioclase, K-feldspar and Fe-oxides, was magmas5,6. Yet the recent work on continental arcs hints at thrust found in 16YX-1-1 (Supplementary Fig. 3 and Supplementary 7–10 “ + faults as potential recycling channels . Data 4). The reaction of biotite MnO, Al2O3, SiO2 (from melt) Here, we examined a suite of migmatites from a Neoproter- = garnet + muscovite”18 may control garnet paragenesis. These ozoic magmatic arc in western China. We used combined pet- observations are indicative of near-solidus partial melting with rologic, geochronologic and geochemical studies of these samples local melt segregation. to understand the nature of the recycled materials and evaluate how thrust faults may contribute to rock recycling in compres- sional arc settings. Zircon U–Pb–Hf–O isotopes. Most zircon grains in the Peng- guan migmatites have core-rim structures. The zircon core domains, presumably derived from arc magmatic detritus, show Results limited variation in their ages, concentrating at ~830–870 Ma, Geological setting and samples. The Yangtze Block in Eastern with few at ~930 Ma (Fig. 1a), and have mantle-like to slightly δ18 ‰ ε Asia consists of Archean–Paleoproterozoic crystalline basement elevated O values (5.3 to 7.4 ) (Fig. 1b). Their Hf(t) values surrounded by Neoproterozoic fold belts. It is bounded by the vary from –3to+13, with most being positive, indicative of Tibetan Plateau to the west, the North China Block to the north heterogeneous but generally juvenile sources. Zircon overgrowth and the Cathaysia Block to the southeast. It was placed in a rims are slightly younger than the maximum depositional age for marginal position in Rodinia supercontinent and has underwent a each sample, with U − Pb dates generally ranging from ~815 Ma long-term evolution and complex tectonic-magmatic processes in to ~860 Ma (Supplementary Data 3). The overgrowth rims a continental margin setting during Neoproterozoic11–13. The have significantly higher δ18O values (9.3 to 13.3‰) compared ε western margin of the Yangtze Block became tectonically active with those of core domains, despite their similar Hf(t) range since the early Neoproterozoic; it started with intra-oceanic arc (–3to+8 except one analysis of –9) as core domains (Supple- magmatism before 971 ± 16 Ma (ref. 14) and then transitioned to mentary Data 2). Zircon grains from the leucosome sample show Andean-type magmatism at ca. 870 Ma (ref. 15). This ancient homogeneous δ18O values (11.1 to 13.4‰) with a large range of fl ε – + ε subduction relic was lately imaged by deep seismic re ection Hf(t) values ( 6.9 to 8.4) (Supplementary Data 2). All Hf(t) profile16. The prolonged magmatic history gave rise to linearly values were calculated to t = 850 Ma in order to facilitate distributed Neoproterozoic arc magmatic rocks spanning over comparison. 800 km (Supplementary Fig. 1a). The Longmenshan Thrust Belt to the northwestern margin of the Yangtze Block exposed abundant Neoproterozoic plutonic complexes due to the major Anatexis P-T conditions. We reconstructed the metamorphic P- Miocene extrusion and thrust process17, of which the largest one T conditions for the Pengguan migmatites using Perple_X 6.9.0 is known as the Pengguan Complex, comprising voluminous (http://www.perplex.ethz.ch). The bulk rock composition of 860–750 Ma plutonic rocks (Supplementary Fig. 1b, c). The sample 16YX-1-1 was chosen for calculation because this sample Huangshuihe Group in the core region of the Pengguan Complex clearly documents: (1) mineral-melt interaction; (2) coexistence exists as a huge roof pendant of the plutonic rocks and of minerals (Mn-rich garnet + biotite + muscovite + quartz + consists of metamorphic rocks of schist, metapelite, quartzite and plagioclase + K-feldspar + Fe-oxides) and; (3) minor partial meta-pyroclastic rock. Ductile deformation, faults, mylonite with melting with no evident melt migration. In the calculated P-T S-C fabric, and migmatitic lineation are extensive in the pseudosection, the mineral assemblage of the Pengguan migma- sequences. tite falls in a narrow domain (domain 1 in Fig. 2a) near the Two main types of migmatites were identified in the field solidus. Using Si pfu in muscovite from 16YX-1-1 (3.08 to 3.14, in (Supplementary Fig. 2): the inhomogeneous migmatites (or moles per formula unit; Supplementary Data 4), which is sensitive diatexite) contain abundant blocks of melanosome and associated to pressure in the K-feldspar + phlogopite + quartz system19,we aplite vein; the stromatic migmatites preserve a regular layered further constrained the anatexis P–T conditions to ~670 °C and structure and are characterized by centimeter-thick, foliation- 5.9−8.1 kbar (Fig. 2). The low anatexis temperature is also con- parallel leucosome, melanosome and mesosome. Patch-shaped sistent with the extremely low Th/U ratios of the zircon over- neosomes are abundant in stromatic migmatites and formed growth rims (Fig. 1a). At near-solidus temperatures, Th during incipient partial melting. Large leucosomes (~50 cm in concentration in the melt is largely buffered by Th-rich accessory width) occur occasionally and are usually fed by a few small minerals (such as monazite and allanite)20. 2 NATURE COMMUNICATIONS | (2021) 12:3533 | https://doi.org/10.1038/s41467-021-23797-3 | www.nature.com/naturecommunications NATURE COMMUNICATIONS | https://doi.org/10.1038/s41467-021-23797-3 ARTICLE 10 16YX-1-1 b C. R. C. R. C. R. a Core domain 16YX-1-1 16YX-4-1 15PG-32-1 16YX-1-2 1 +15 DM at ~860 Ma 0.1 Th/U=0.1 +10 Rim domain s i e 0.01 g +5 D A Anatex M 0.001 16YX-4-1 Core domain 0 CHUR y it l 1 bi Hf ε Ma) (t=850 a b Rim domain -5 o 0.1 r Th/U Th/U=0.1 e p v -10 Mantle zircon ati 0.01 l 5.3±0.6 ‰ Re MD Age MD Anatexis 0.001 -15 15PG-32-1 5 6 7 8 9 10 11 12 13 14 15 Core domain Ζircon δ18 O (‰) 1 0.1 Th/U=0.1 Rim domain 0.01 atexis n A MD Age MD 0.001 750 800 850 900 950 1000 Zircon U-Pb date (Ma) 18 Fig.
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