Chemical and isotopic data of the lava samples dredged in the southern Bach Ridge and the northern Italian Ridge of the Musicians Seamounts province, northeast of Hawaii. Although most of the samples analyzed are gene...Chemical and isotopic data of the lava samples dredged in the southern Bach Ridge and the northern Italian Ridge of the Musicians Seamounts province, northeast of Hawaii. Although most of the samples analyzed are generally altered, a few are fresh. The latter exhibits similar geochemical and isotopic characteristics to normal MORB （Mid-Ocean Ridge Basalts）. There are systematic geochemical trends from hotspot to mid-ocean ridge in the province. Incompatible element and isotopic variations suggest that the flow field had at least two distinct parental magmas, one with higher and one with lower MgO concentrations. The two parental magmas could be related by a magma mixing model. The major and trace element modeling shows that the two parental magmas could not have been produced by different degrees of melting of a homogeneous mantle source, but they are consistent with melting of a generally depleted mantle containing variable volumes of embedded enriched heterogeneity enriched interbeds.展开更多
The Chagangnuoer deposit is a typical submarine volcanic rock-hosted skarn iron deposit, where orebodies mainly occur in andesitic rocks of the Dahalajunshan Formation （DF） with skams well developed around orebodies...The Chagangnuoer deposit is a typical submarine volcanic rock-hosted skarn iron deposit, where orebodies mainly occur in andesitic rocks of the Dahalajunshan Formation （DF） with skams well developed around orebodies. The volcanic rocks of the DF in the Chagangnuoer deposit display calc-alkaline characteristics. The ore-bearing andesitic rocks have high ^87Sr/^86Sr（i） （0.7058-0.7117） and low εNd（t） （-3.51 to 1.67）. They probably formed through mixing of basaltic melts and the induced crustal melts. LA-ICP-MS U-Pb zircon ages of 250 and 305 Ma are obtained for the granite and granodiorite in the Chagangnuoer deposit, respectively, which are signifi- cantly younger than the timing of the skarn formation （316 Ma）. These age data indicate that the granitoids have no contribution to the skarn and associated iron mineralization. This paper proposes a new genetic model for submarine volcanic rock-hosted skam iron deposits, in which the iron mineralization, skarn formation and volcanic magmatism are necessary aspects of the same system; the iron separates and concentrates from the silicate magma in the form of Fe（II） carbonate complex. While this conceptual model is largely based on observations on the Chagangnuoer deposit, it may have general significance for skam-type iron deposits associated with submarine volcanic rock sequences and warrants further testing and improvement.展开更多
基金Supported by the major program of Knowledge Innovation Project of the Chinese Academy of Sciences (No.KZCX2-YW-211)the National Natural Science Foundation of China (No.40776030)
文摘Chemical and isotopic data of the lava samples dredged in the southern Bach Ridge and the northern Italian Ridge of the Musicians Seamounts province, northeast of Hawaii. Although most of the samples analyzed are generally altered, a few are fresh. The latter exhibits similar geochemical and isotopic characteristics to normal MORB （Mid-Ocean Ridge Basalts）. There are systematic geochemical trends from hotspot to mid-ocean ridge in the province. Incompatible element and isotopic variations suggest that the flow field had at least two distinct parental magmas, one with higher and one with lower MgO concentrations. The two parental magmas could be related by a magma mixing model. The major and trace element modeling shows that the two parental magmas could not have been produced by different degrees of melting of a homogeneous mantle source, but they are consistent with melting of a generally depleted mantle containing variable volumes of embedded enriched heterogeneity enriched interbeds.
基金supported by two geological survey projects of China Geological Survey Departments and Offices (1212011121092, 1212011220928)
文摘The Chagangnuoer deposit is a typical submarine volcanic rock-hosted skarn iron deposit, where orebodies mainly occur in andesitic rocks of the Dahalajunshan Formation （DF） with skams well developed around orebodies. The volcanic rocks of the DF in the Chagangnuoer deposit display calc-alkaline characteristics. The ore-bearing andesitic rocks have high ^87Sr/^86Sr（i） （0.7058-0.7117） and low εNd（t） （-3.51 to 1.67）. They probably formed through mixing of basaltic melts and the induced crustal melts. LA-ICP-MS U-Pb zircon ages of 250 and 305 Ma are obtained for the granite and granodiorite in the Chagangnuoer deposit, respectively, which are signifi- cantly younger than the timing of the skarn formation （316 Ma）. These age data indicate that the granitoids have no contribution to the skarn and associated iron mineralization. This paper proposes a new genetic model for submarine volcanic rock-hosted skam iron deposits, in which the iron mineralization, skarn formation and volcanic magmatism are necessary aspects of the same system; the iron separates and concentrates from the silicate magma in the form of Fe（II） carbonate complex. While this conceptual model is largely based on observations on the Chagangnuoer deposit, it may have general significance for skam-type iron deposits associated with submarine volcanic rock sequences and warrants further testing and improvement.
