首页|Concurrent MORB-type and ultrapotassic volcanism in an extensional basin along the Laurentian Iapetus margin: Tectonomagmatic response to Ordovician arc-continent collision and subduction polarity flip

Concurrent MORB-type and ultrapotassic volcanism in an extensional basin along the Laurentian Iapetus margin: Tectonomagmatic response to Ordovician arc-continent collision and subduction polarity flip

扫码查看
原文链接
  • NSTL
Arc-continent collision,followed by subduction polarity flip,occurs during closure of oceanic basins and contributes to the growth of continental crust.Such a setting may lead to a highly unusual association of ultrapotassic and mid-ocean ridge basalt(MORB)-type volcanic rocks as documented here from an Ordovician succession of the Scandinavian Caledonides.Interbedded with deep-marine turbidites,pillow basalts evolve from depleted-MORB(eNdt 9.4)to enriched-MORB(eNdt 4.8)stratigraphically upward,reflecting increasingly deeper melting of asthenospheric mantle.Intercalated intermediate to felsic lava and pyroclastic units,dated at ca.474-469 Ma,are extremely enriched in incompatible trace elements(e.g.,Th)and have low eNdt(-8.0 to-6.6)and high S^(0.7089-0.7175).These are interpreted as ultrapotassic magmas derived from lithospheric mantle domains metasomatized by late Paleoproterozoic to Neoproterozoic crust-derived material(isotopic model ages 1.7-1.3 Ga).Detrital zircon spectra reveal a composite source for the interbedded turbidites,including Archean,Paleo-,to Neoproterozoic,and Cambro-Ordovician elements; clasts of H0londa Porphyrite provide a link to the H0londa terrane of Laurentian affinity.The entire volcano-sedimentary succession is interpreted to have formed in a rift basin that opened along the Laurentian margin as a result of slab rollback subsequent to arc-continent collision,ophiolite obduction and subduction polarity flip.The association of MORBs and ultrapotassic rocks is appar-ently a unique feature along the Caledonian-Appalachian orogen.Near-analogous modern settings include northern Taiwan and the Tyrrhenian region of the Mediterranean,but other examples of strictly concurrent MORB and ultrapotassic volcanism remain to be documented.

Fernando Corfu、Deta Gasser、Tor Grenne

展开 >

Department of Geosciences and CEED,University of Oslo,PO Box 10~47,Blindern,0316 Oslo,Norway

Department of Environmental Sciences,Western Norway University of Applied Sciences,R0yrgata 6,6856 Sogndal,Norway

Geological Survey of Norway,PO Box 6315,Torgarden,7491 Trondheim,Norway

2022

10.1130/B36113.1

Geological Society of America Bulletin

Geological Society of America Bulletin

SCI
ISSN：0016-7606
年,卷(期)：2022.134(7/8)
  • 6
  • 137