The Late Yanshanian spilitic basalts (ca. 85～95 Ma) occurred in northeastern Hunan province, whose eruption was controlled by the Changsha-Pingjiang fault, which could be regarded as southward extension of the Tan-Lu fault zone. These rocks had a main mineral assemblage of albite + chlorite + epidote, with the presence of minerals olivine and pyroxene generally as porphyroblasts, typically showing the characteristics of spilites. The geochemistry of the spilitic rocks was characterized by high in Na but low in K, slightly enriched in LREE, Th, U, Ti and Hf but relatively depleted in HREE, Y, Yb, Zr, P, Nb and Ta. However, the contents of LILEs were relatively variable. The Nd isotopic composition (εNd(t)= -0.66～-1.29) revealed that the parental melts could not have been derived from an asthenospheric mantle. Considering the Mesozoic tectonic development of the South China, and particularly regional evolution of the Jiangnan orogen, these rocks might have been generated in a withinplate setting, in which their parental magma was induced by low-degree melting of a slightly enriched, sub-continental lithospheric mantle. We suggested that the Yanshanian intracontinental orogenic event induced by activation of Paleo-surtures and/or Paleo-faults in the amalgamated South China due to the Late-Triassic collision between the Yangtze and North China Blocks, probably had played a key role in the generaton of the Mesozoic magmatism in northeastern Hunan province, where the Late Yanshanian spilitic basalts might mark the recommence of lithospheric detachment and extension of the Yanshanian orogenic belt before ～90 Ma in South China.
Xu Deru,He Zhuanli,Li Pengchun et al. DISCOVERY OF THE LATE YANSHANIAN SPILITIC BASALTS IN NORTHEASTERN HUNAN PROVINCE AND ITS GEOLOGICAL IMPLICATIONS[J]. Chinese Journal of Geology, 2006, (2): 311-332.