Is the Songshugou Complex, Qinling Belt, China, an Eclogite Facies Neoproterozoic Ophiolite?

• Published in: Journal of earth science (Wuhan, China) Vol. 30; no. 3; pp. 460 - 475
• Main Authors: Bader, Thomas, Zhang, Lifei, Li, Xiaowei
• Format: Journal Article
• Language: English
• Published: Wuhan China University of Geosciences 01.06.2019; Springer Nature B.V; Key Laboratory of Orogenic Belts and Crustal Evolution,Ministry of Education,School of Earth and Space Sciences,Peking University,Beijing 100871,China; State Key Laboratory of Geological Processes and Mineral Resources,School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China%Key Laboratory of Orogenic Belts and Crustal Evolution,Ministry of Education,School of Earth and Space Sciences,Peking University,Beijing 100871,China%State Key Laboratory of Geological Processes and Mineral Resources,School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China
• Subjects: Accretion; Amphibolites; Biogeosciences; Cambrian; Continental crust; Coronas; Deposition; Devonian; Earth and Environmental Science; Earth Sciences; Eclogite; Evolution; Garnet; Geochemistry; Geochronology; Geochronometry; Geology; Geotechnical Engineering & Applied Earth Sciences; Magma; Magnesium aluminum silicates; Ophiolites; Ordovician; Orogenic Magmatism and Metamorphism Dedicated to IGCP 649: Diamonds and Recycled Mantle; Phase equilibria; Plagioclase; Rocks; Sedimentary facies; Special Issue on Ophiolite; Subduction; Subduction (geology); Subduction zones; Ultramafic rocks; Uplift; China; Qinling belt; eclogite; garnet isopleth thermobarometry; Early Paleozoic; Songshugou Complex; Early Pa-leozoic
• ISSN: 1674-487X; 1867-111X
• DOI: 10.1007/s12583-019-1221-1

Ophiolites play a key role in understanding subduction-accretion-collision processes. Herein, we discuss origin and metamorphic evolution of an enigmatic, Neoproterozoic ophiolite candidate—the mafic-ultramafic Songshugou Complex, Qinling belt, China—summarizing published thermobarometry, U/Pb geochronology, and geochemistry and presenting new phase equilibrium modeling. Garnet, rarely preserved in amphibolites of the Songshugou Complex, has prograde zoning and low-pyrope cores [Alm 54−71 (Grs+And) 25−30 Prp 1−6 Sps 5−12 ]. It formed at quartz eclogite facies conditions of 1.93–2.54 GPa, 462–542 °C. During exhumation, garnet first was mantled by plagioclase-rich coronas at about 0.7–1.2 GPa, 660–710 °C. During an isothermal uplift to 0.5–0.8 GPa, these coronas evolved widely into σ-shaped aggregates and eventually into whitish ribbons oriented with a steeply southwest dipping mineral stretching lineation. The exhumation into middle-upper crustal levels proceeded till the Late Devonian. The oceanic protoliths of the eclogites were emplaced into continental crust in the Neoproterozoic and dragged into a subduction zone in North Qinling in the Cambrian. The ultramafic rocks of the Songshugou Complex were not subducted with the mafic rocks in a coherent block given the absence of garnet but ubiquitous occurrence of spinel implies a P maximum of ≈1.7 GPa. Rather, mafic and ultramafic rocks belonged to downgoing and overriding plate, respectively. They were juxtaposed at 0.8–1.7 GPa at Early Ordovician time.