Volcanic succession, petrology, and geochemistry of the Sujiagou komatiite from the North China Craton

Abstract

The~2.7-GaTaishan greenstone belt from the Eastern Block of the North China Craton has well-exposed komatiite sections. The komatiite outcrops at Sujiagou have wellpreserved primary volcanic texture although they have experienced amphibolitefacies metamorphism. Two komatiite lava flows are identified in the Sujiagou outcrops: "Flow Ι," with a thickness of 55 m, is characterized by poly-sutured crust at the top, spinifex texture in the middle, and olivine cumulates at the flow bottom. "Flow ΙΙ" consists of abundant pahoehoe lava lobes with no interstitial materials. These volcanic characteristics, as well as the interbedding with terrestrial sediments, suggest that the Sujiagou komatiite erupted in a subaerial continental environment. The olivinechromite geothermometer gives peak metamorphic temperatures from 684°C to 764°C. Phase equilibria modelling suggests that the mineral proportions and mineral compositions are consistent with a retrograde temperature of~488°C, at which the komatiite would have low olivine Fo (79-89) and high bulk-rock Mg # (83-90). Linear mixing of the in situ trace element compositions of the metamorphic olivine, augite, tremolite, serpentine, and chlorite from Sujiagou komatiite samples can reproduce the trace elements of representative komatiite compositions, suggesting that later metamorphism and fluid-rock interactions played key roles in trace element variationsin the bulk-rock komatiite samples. These results also imply that the "arc signature" of the Sujiagou komatiite may be an overprint from posteruption fluid alteration rather than a primary subduction geochemical feature. Therefore, the Sujiagou komatiites may belong to a part of the global plume-related greenstone belts at~2.7 Ga.

Channelized CO2-Rich Fluid Activity along a Subduction Interface in the Paleoproterozoic Wutai Complex, North China Craton

“…The USGS and Chinese National standards BHVO-2 and GSR-2 were chosen for element concentration calibration. Other details are described in [43].…”

Formation Age of the Sujiagou Komatiites in Western Shandong: Further Constraints from SHRIMP U‐Pb Zircon Dating on Granitic Dykes

“…1, Zhang et al, 1998Zhang et al, , 2001 or, spinifex komatiite, brecciated komatiite and serpentinized cumulus komatiite (Polat et al, 2006). Yang et al (2020) divided the spinifex komatiite into random-spinifex komatiite and platyspinifex komatiite. Spinifex structure is well preserved locally ( Fig.…”