『Abstract
This paper reviews localities of intraplate basalts of the Paleo-Asian
and Paleo-Pacific Oceans, which occur as fragments of former oceanic
islands, seamounts and plateaus in accretionary complexes of Altao-Sayan,
Russian Far East and Southwest Japan. Special emphasis is given
to their relationships with associated rocks of oceanic plate
stratigraphy (OPS), major and trace element chemistry and criteria
for their identification in structurally complex orogenic belts.
Accretionary complexes (ACs) host the Late Neoproterozoic-Early
Cretaceous OPS units of the two paleo-oceans, which have a number
of features in common: i) similar succession of oceanic sediments
(pelagic chert - hemipelagic terrigenous slope facies - reef carbonates);
ii) intraplate basalts occur at the bottom of the sedimentary
sections and are usually overlain by a carbonate “cap”; iii) typical
OIB-type chemistry of basalts is characterized by LREE-Nb-Ti enrichment.
There is a 100 Ma time gap in the evolution of the oceanic intraplate
magmatism, which is probably a result of our insufficient knowledge
of other ACs of Central Asia. The study of intraplate magmatism
and OPS of paleo-oceans is very important because it is an integral
part of the study of orogenic belts incorporating many commercially
valuable mineral deposits. Identification of intraplate OPS units
should be based on a combination and mutual correlation of geological,
lithological and geochemical features of basalts and their associated
sediments. OPS units, both magmatic and sedimentary, provide a
full geological record of the evolution of paleo-oceans from their
opening, through subduction and formation of accretionary complexes,
and finally to their closure accompanied by active tectonics,
orogeny and ore mineralization.
Keywords: Basalt; Geochemistry; Mantle plume; Sedimentary rocks;
Accretionary complex; Paleo-Asian ocean; Paleo-Pacific ocean』
1. Introduction
2. Geology and tectonics of OPS units and intraplate basalts
2.1. Paleo-Asian Ocean (Late Neoproterozoic to Carboniferous)
2.2. Paleo-Pacific Ocean (320-140 Ma)
3. Petrography and geochemistry of intraplate basalts
3.1. Petrography
3.2. Geochemistry of intraplate basalts
3.2.1. Major element compositions
3.2.2. Trace element compositions
4. Discussion
4.1. Recognizing OPS units
4.2. Criteria for identification of intraplate basalts
4.3. Geochemical variability of intraplate basalts
4.4. The 〜100 Ma time gap of the PAO intraplate magmatism
4.5. OPS-hosted mineral deposits
5. Conclusions
Acknowledgments
References