Geochemical Characteristics and Tectonic Setting of the Laohushan Basalts, North Qilian Mountains |
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作者姓名: | QIAN Qing and ZHANG Qi Institute of Geology and Geophysics CAS P. O. Box Beijing |
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作者单位: | QIAN Qing and ZHANG Qi Institute of Geology and Geophysics,CAS,P. O. Box 9825,Beijing 100029 |
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摘 要: | The Ordovician Laohushan ophiolite, located in the eastern part of the North Qilian Mountains, is mainly composed of meta-peridotites, gabbros and basalts alternating with sediments. The sediments are mainly turbidites, including sandstones, siltstones, cherts etc. Major elements show that the basalts are subalkaline tholeiites and may be analogous to ocean-floor basalts. Except a few N-MORBs, most of the basalts are E-MORBs as indicated by incompatible element ratios such as (La/Ce)N, La/Sm, Ce/Zr, Zr/Y and Zr/Nb. Negative Nb anomaly is common but negative Zr, Hf and Ti anomalies are quite rare. Based on the geochemical characteristics, it is suggested that the Laohushan basalts were formed in a back-arc basin. εNd (t) of the basalts ranges between +3.0 and +8.9 and (87Sr/86Sr), ranges between 0.7030 and 0.7060, indicating a depleted mantle source which was mixed with more or less enriched mantle components. Furthermore, the petrography of the sandstones and geochemistry of the cherts suggest that the
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Geochemical Characteristics and Tectonic Setting of the Laohushan Basalts, North Qilian Mountains |
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Authors: | QIAN Qing and ZHANG Qi Institute of Geology and Geophysics CAS P O Box Beijing |
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Abstract: | Abstract The Ordovician Laohushan ophiolite, located in the eastern part of the North Qilian Mountains, is mainly composed of meta‐peridotites, gabbros and basalts alternating with sediments. The sediments are mainly turbidites, including sandstones, siltstones, cherts etc. Major elements show that the basalts are subalkaline tholeiites and may be analogous to ocean‐floor basalts. Except a few N‐MORBs, most of the basalts are E‐MORBs as indicated by incompatible element ratios such as (La/Ce)N, La/Sm, Ce/Zr, Zr/Y and Zr/Nb. Negative Nb anomaly is common but negative Zr, Hf and Ti anomalies are quite rare. Based on the geochemical characteristics, it is suggested that the Laohushan basalts were formed in a back‐arc basin. ENd (t) of the basalts ranges between +3.0 and +8.9 and (87Sr/86Sr), ranges between 0.7030 and 0.7060, indicating a depleted mantle source which was mixed with more or less enriched mantle components. Furthermore, the petrography of the sandstones and geochemistry of the cherts suggest that the sediments were deposited near a continental margin. |
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Keywords: | North Qilian Mountains Laohushan basalts sediments geochemistry |
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