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Trace Elements and Sr, Nd Isotope Geochemistry of the Lajimiao Norite‐Gabbro from the North Qinling Belt 1
Author(s) -
Shuguang Li,
Yizhi Chen,
Zongqing Zhang,
Xiaojing Ye,
Guowei Zhang,
Anlin Guo,
Hart S. R.
Publication year - 1994
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.1994.mp7002003.x
Subject(s) - norite , gabbro , geology , geochemistry , magma chamber , ophiolite , basalt , magma , tectonics , paleontology , volcano
The Lajimiao norite‐gabbro complex, as a part of the ophiolites on the southern side of the North Qinling belt, consists of gabbro and norite‐gabbro. They were derived from different magma series: the gabbro was derived from tholeiitic magma series with higher TiO 2 , REE abundance and Fe 3+ / Fe 2+ ratio; norite‐gabbro was derived from calc‐alkali magma series with lower TiO 2 , Fe 3+ / Fe 2+ ratio and REE abundance and much lower HREE abundance, which suggests that the source of the norite‐gabbro magma was deeper and controlled by eclogite facies. Geochemical characteristics of both plutonic rocks are similar to those of island‐arc basalts, such as relatively high contents of Ba, Pb and Sr and relatively low contents of Nb, Zr and Ni. The Sr, Nd isotopic characteristics of the Lajimiao norite‐gabbro complex are similar to those of ophiolites. Its 8 Nd values are constant, about +2; whereas 8 Sr values have wide variation from — 6.4 to +31.2 and positively correlate with Na 2 O, H 2 O + and CO 2 contents and the Fe 3+ / Fe 2+ ratio. The ɛ Nd —Nd / Th, ɛ Nd —La/Nb and ɛ Nd —Ba/Nb diagrams clearly show that there were significant components of terrigenous sediments in the mantle source of the Lajimiao norite‐gabbro complex. It suggests that large amount of sediments had been carried into the mantle by the subducted ancient Qinling sea plate during the Palaeozoic.