The genetic relationship between Habo alkaline intrusion and its surrounding deposits,Yunnan Province,China: geological and S–Pb isotopic evidences

The Habo alkaline intrusion, which is located in the south of the Sanjiang area, Yunnan Province, China, is a typical Cenozoic alkaline intrusion. There are a series of small to medium-sized Au and Pb–(Zn) deposits around this intrusion. Those deposits are spatially associated with the Habo alkaline intrusion.(1) The d~(34) S values of sulfides from Au deposits range from-1.91 % to 2.69 %, which are similar to those of Pb–(Zn) deposits(-3.82 % to-0.05 %) and both indicate a much greater contribution from magma.(2) The Habo alkaline intrusion has relatively homogeneous Pb isotopic compositions with~(206)Pb/~(204) Pb ranging from 18.608 to 18.761,~(207)Pb/~(204) Pb from 15.572 to15.722 and~(208)Pb/~(204) Pb from 38.599 to 39.110. These Pb isotope ratios are similar to those of Au deposits, whose~(206)Pb/~(204) Pb range from 18.564 to 18.734,~(207)Pb/~(204) Pb from15.582 to 15.738 and~(208)Pb/~(204) Pb from 38.592 to 39.319.Pb ratios in both the intrusion and Au deposits suggest that Pb mainly derived from the depth, probably represents a mixture of mantle and crust. Pb–(Zn) deposits, however,show a decentralized trait, and most of them are similar to that of the alkaline intrusion with~(206)Pb/~(204) Pb ranging from18.523 to 18.648,~(207)Pb/~(204) Pb from 15.599 to 15.802, and~(208)Pb/~(204) Pb from 38.659 to 39.206.(3) In the plumbotectonic diagram~(207)Pb/~(204) Pb versus~(206)Pb/~(204) Pb, almost all of Au and Pb–(Zn) deposits have the same projection area with the Habo alkaline intrusion, which indicates that thosedeposits almost share the same source with the alkaline intrusion.(4) Isotopic age of the Habo alkaline intrusion is36–33 Ma, which is similar to that of Beiya, whose orerelated alkaline porphyries age is 38–31 Ma and molybdenite Re–Os age is 36.9 Ma. Therefore, along with S–Pb isotope traits, we suggest that the Habo Au and Pb–(Zn)deposits should be typically Ailaoshan-Red River Cenozoicalkaline-related deposits and ore-forming ages of these deposits should be later than that of the Habo alkaline intrusion.     

Space–time relationships between volcanic associations of different alkalinities: The Belogolovskii Massif,Sredinnyi Range,Kamchatka. Part II. Geochemistry of volcanic rocks and magma sources

Data are presented relating to volcanic series in the Belogolovskii Massif, Sredinnyi Range, Kamchatka. We discuss new geochronologic data, the distributions of rare elements and platinum elements in the rocks, and list the isotope characteristics of volcanic series with normal and moderate alkalinities. We show that the Late Pliocene to Early Pleistocene rocks that belong to the moderate alkaline series of the Belogolovskii volcanic massif are different from rocks in the normally alkaline series of the Late Miocene to Middle Pliocene volcanogenic basement in having higher concentrations of the HFSE and LILE components. We propose a model for the generation of moderate alkaline magmas involving a heterogeneous depleted and a heterogeneous enriched source of material. According to the isotope data, one of these sources may be the subducted oceanic lithosphere of the Pacific and the Commander-Islands type, while the other source was recycled material of the Indian MORB type.     

Constraints on processes affecting the origin of oceanic crust: Geochemical evidence from the 0–35 M. Y. age basalts,between 30°N and 40°N,MAR

DSDP Leg 82 sampled the oceanic crust, at 9 sites, west of the MAR between 33°N and 38°N, i.e., from the Azores “mantle plume” to south of the Hayes Fracture Zone. A specific aim of this DSDP Leg was to determine if the origin, and spatial and temporal evolution of oceanic mantle heterogeneity in the vicinity was related in a predictable manner to the “mantle plume”. Our approach in evaluating this question has been to select samples on the basis of trace element characteristics and age, for radiogenic isotope determinations.Isotopic and trace element heterogeneity occur both within between sites. While there is a crude correlation between trace element and isotopic characteristics, it is difficult to establish a detailed set of guidelines which would describe either trace element-isotope interrelationships. This difficulty is highlighted by the occurrence of basalts in one hole (H558) with trace element characteristics ranging from enriched to depleted, which can have identical or different isotopic characteristics.The origin, and spatial and temporal distribution of the heterogeneity cannot be reconciled with any simple models. A complicated scenario, involving mantle plums or blobs, recent local heterogeneity and complex mixing models, is required.