The Meso-Neoproterozoic volcanic-intrusive rocks from Hunan in west section of Jiangnan orogen show very different geochemistry features. The Mesoproterozoic volcanic-intrusive rocks have narrow SiO2 contents varying from 49.95% to 53.91%. They are mainly sub-alkaline basalts with low TiO2 and Zr/Y ratios, high MgO, Ni, Cr, and Al2O3/TiO2 ratios. They have different types of REE patterns, and display characteristics of arc volcanic rocks. The Neoproterozoic volcanic-intrusive rocks are alkaline and sub-alkaline basalts with broad SiO2 varying 45.56% to 60.37%. They have high Zr/Y ratios and low MgO, Ni, Cr. Among them, the Neoproterozoic basic rocks are mostly alkaline basalts, with high TiO2 contents and low Al2O3/TiO2 ratios. They are obviously enriched in HFSE and show typical patterns of OIB, similar to the rift-basalts. Mesoproterozoic basalts from Nanqiao exhibit typical N-MORB features with high εNd (t) values (6.86∼8.98 , and may represent the residual slab, which provides a new important evidence for Jiuling Island Arc in the middle section of Jiangnan orogen. Mesoproterozoic basalts from Yiyang show enrichment in Th and depletion in Nb and Ti with low εNd (t) values (1.56 ∼1.76), similar to arc island volcanic rocks. On the other hand, they are enriched in MgO, Ni, and Cr with komatiitic basalts signatures, implying that they might be a product of interaction between the plume induced by subduction and the arc in the area. Early Neoproterozoic andesites from Yiyang are enriched in Th, La, Sm and Nd and depleted in Nb, Ti, Zr and Hf showing arc volcanic features. They suggest that they are the products of Grenville orogeny. Patterns normalized by primitive mantle of Neoproterozoic volcanic-intrusive rocks from Qianyang, Guzhang and Gaoqiao are similar to OIB, the εNd (t) of basic rocks from Qianyang and Guzhang are 1.69∼1.05, indicating that they might be originated from asthenospheric mantle. The geochemistry of these Meso-Neoproterozoic volcanic-intrusive rocks give some implications for the evolvement of Rodinia from colliding to rifting in this area.
|Number of pages||12|
|Journal||Acta Petrologica Sinica|
|Publication status||Published - 2003|
- Meso- Neoproterozoic
- Volcanic-intrusive rocks