This work studies new petrological and geochemical data and zircon U-Pb ages for bimodal intrusive rocks from Xinglong re- gion, Hainan Island. Zircon U-Pb dating yields mean 238U/26pb ages of 238 ± 2 Ma and 234&...This work studies new petrological and geochemical data and zircon U-Pb ages for bimodal intrusive rocks from Xinglong re- gion, Hainan Island. Zircon U-Pb dating yields mean 238U/26pb ages of 238 ± 2 Ma and 234±2 Ma for diabasic and granitic phases, respectively, representing the Middle Triassic emplacement. The diabase and granite bodies were formed from discrete mafic and acidic magma sources that experienced local mechanical mixing at their mutual contacts. Although SiO2 content of intrusions is bimodal, trace element ratios indicate that both were formed in a post-orogenic extensional setting. Sr-Nd isotopic composition reflects a shared EMII type enriched mantle source component, possibly influenced by subduction-fluid metaso- matism.展开更多
Measurements of anisotropy of magnetic susceptibility (AMS) were performed on a gabbro pluton and 7 diabase dykes in the Wanning area, southeast Hainan Island. Rock magnetism showed that pseudo-single domain (PSD) to ...Measurements of anisotropy of magnetic susceptibility (AMS) were performed on a gabbro pluton and 7 diabase dykes in the Wanning area, southeast Hainan Island. Rock magnetism showed that pseudo-single domain (PSD) to multidomain (MD) Ti-poor magnetite carries the magnetic fabric in the gabbro pluton whereas MD Ti-poor magnetite carries the magnetic fabric in the diabase dykes. The corrected anisotropy degree (Pj ) in most specimens was found to be less than 1.2 which is indicative of a possible flow-related magnetic fabric. The AMS eigenvectors within each site are generally well grouped. The maximum susceptibility axes (K1 ) of the gabbro pluton are inclined towards the north at low angles (< 30°). K1 axes of the diabase dykes are inclined towards the NNW and SSE with dip angles of ≤ 30°. From this study, it appears that the emplacement mode of the gabbro pluton was characterized by intrusion from the north to the south at a low angle whereas the diabase dykes were emplaced from the NNW to the SSE at low to moderate angles. This was verified by comparison of the rock fabric to the magnetic fabric. All of this evidence leads to the conclusion that the Wanning gabbro pluton and diabase dykes were the products of pulsative intrusion from the same magma chamber in the area far to the north of Wanning, which suggests that basic rocks may exist beneath the Indosin- ian granite in the area to the north of Wanning.展开更多
Himalayan remagnetization in the Tarim Basin was found to be widespread in Paleozoic, Mesozoic and Ce-nozoic rocks. Rock magnetism was performed to study the magnetic carriers. The authors believe that tectonic fluid ...Himalayan remagnetization in the Tarim Basin was found to be widespread in Paleozoic, Mesozoic and Ce-nozoic rocks. Rock magnetism was performed to study the magnetic carriers. The authors believe that tectonic fluid in the Himalayan stage caused the rock remagnetization. The framboidal pyrites in bitumen and hydrocarbon-rich rocks may transform to framboidal magnetite in the later alkali environment, which leads to remagnetization.展开更多
基金supported China Postdoctoral Science Foundation (Grant No. 2011M500991)Basic Scientific Research Specific Foundation of Second Insitute of Oceanography, SIO (Grant No. JT1104)
文摘This work studies new petrological and geochemical data and zircon U-Pb ages for bimodal intrusive rocks from Xinglong re- gion, Hainan Island. Zircon U-Pb dating yields mean 238U/26pb ages of 238 ± 2 Ma and 234±2 Ma for diabasic and granitic phases, respectively, representing the Middle Triassic emplacement. The diabase and granite bodies were formed from discrete mafic and acidic magma sources that experienced local mechanical mixing at their mutual contacts. Although SiO2 content of intrusions is bimodal, trace element ratios indicate that both were formed in a post-orogenic extensional setting. Sr-Nd isotopic composition reflects a shared EMII type enriched mantle source component, possibly influenced by subduction-fluid metaso- matism.
基金supported by the National Basic Research Program of China(2007CB411706)the National Natural Science Foundation of China(40274014)
文摘Measurements of anisotropy of magnetic susceptibility (AMS) were performed on a gabbro pluton and 7 diabase dykes in the Wanning area, southeast Hainan Island. Rock magnetism showed that pseudo-single domain (PSD) to multidomain (MD) Ti-poor magnetite carries the magnetic fabric in the gabbro pluton whereas MD Ti-poor magnetite carries the magnetic fabric in the diabase dykes. The corrected anisotropy degree (Pj ) in most specimens was found to be less than 1.2 which is indicative of a possible flow-related magnetic fabric. The AMS eigenvectors within each site are generally well grouped. The maximum susceptibility axes (K1 ) of the gabbro pluton are inclined towards the north at low angles (< 30°). K1 axes of the diabase dykes are inclined towards the NNW and SSE with dip angles of ≤ 30°. From this study, it appears that the emplacement mode of the gabbro pluton was characterized by intrusion from the north to the south at a low angle whereas the diabase dykes were emplaced from the NNW to the SSE at low to moderate angles. This was verified by comparison of the rock fabric to the magnetic fabric. All of this evidence leads to the conclusion that the Wanning gabbro pluton and diabase dykes were the products of pulsative intrusion from the same magma chamber in the area far to the north of Wanning, which suggests that basic rocks may exist beneath the Indosin- ian granite in the area to the north of Wanning.
基金This work was supported by the National Natural Science Foundation of China (Grant No. 49974016).
文摘Himalayan remagnetization in the Tarim Basin was found to be widespread in Paleozoic, Mesozoic and Ce-nozoic rocks. Rock magnetism was performed to study the magnetic carriers. The authors believe that tectonic fluid in the Himalayan stage caused the rock remagnetization. The framboidal pyrites in bitumen and hydrocarbon-rich rocks may transform to framboidal magnetite in the later alkali environment, which leads to remagnetization.
