Ni. Filatova et Pr. Fedorov, Cenozoic magmatism of extension zones in continental margins: An example of the Korea-Japan area, PETROLOGY, 9(5), 2001, pp. 450-476
Cenozoic volcanic rocks of extension zones in the eastern margin of the Eur
asian continent display lateral and temporal variability depending on the i
ntensity of extension. The sequence of postsubduction volcanics in the cont
inental margin begins with Oligocene shoshonites, which gave way to Miocene
-Holocene rocks, predominantly alkaline basalts of the within-plate type. T
he Paleogene shoshonites are characterized by high K concentrations and sho
w some features of calc-alkaline rocks. The Lower Miocene basalts of Korea
are highly alkaline and contain a subduction-related component (lower conce
ntrations of Ti, Ta, and Nb). The HFSE richest Middle Miocene and Pliocene-
Holocene alkaline basalts of Korea additionally include single tholeiite fl
ows similar to E-MORB, and, more rarely, N-MORB. In the southeast of the Ko
rea Peninsula and in the Sea of Japan, the Early Miocene interval correspon
ds to tholeiites, whose depletion degree increases with decreasing age. The
evolution of the postsubductional Cenozoic magmatism was caused by the eff
ects of several sources. The Oligocene lavas, which were produced in an env
ironment of the initial extension of a continental margin, were derived fro
m shallow sources of the EMU type of the subcontinental lithosphere, which
had been extensively metasomatized in connection with subduction during the
earlier, Mesozoic-Paleocene stage. The genesis of the Miocene-Holocene alk
aline basalts, whose Nd and Pb isotopic signatures suggest relations with E
MI compositions, was most probably controlled by a lower-mantle plume. The
Lower Miocene tholeiites in the southeastern Korea Peninsula, adjacent to t
he opening Sea of Japan were related to an asthenospheric source. The conti
nental extension-zone tholeiites seem to be heterogeneous, and the causes o
f their calc-alkaline features are different.