SHRIMP U-Pb Dating of Zircons from the Late Mesozoic Basalts in Eastern Zhejiang Province and Its Geological Significance
SHRIMP U-Pb Dating of Zircons from the Late Mesozoic Basalts in Eastern Zhejiang Province and Its Geological Significance
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发表时间：
2010
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通讯作者：
Hu Li-hai
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作者：
Hu Li-hai
用SHRIMP法测定了浙东地区晚中生代喷发的8块玄武岩的锆石U-Pb年龄，命名为上、下部岩系(LRSURS)。来自LRSURS的玄武岩的206Pb/238U加权平均年龄为(120±1)Ma，Th/U比值为0.65~2.44。Th/U值在0.57~3.03之间。这些数据表明，两个岩系中的锆石均为岩浆成因，代表了LRS和URS玄武岩的形成时代。因此，URS和LRS的形成时间明显不同，年龄数据与前人的研究相一致。LRS玄武岩中的大多数锆石年龄相对均匀，只有少数古锆石残留物。部分锆石颗粒呈核缘结构，核心年龄约为132 Ma，边缘年龄约为120 Ma，表明继承颗粒来自岩浆源区，暗示LRS岩浆活动期间在地幔或地壳边界存在130 Ma左右形成的岩浆岩。来自URS玄武岩的岩浆锆石很少，碎屑颗粒的年龄几乎覆盖了中国地块南部所有的岩浆活动，这表明URS玄武岩受到了碎屑岩的混染，其中含有不同时代的碎屑颗粒。
The zircon U-Pb ages were dated by SHRIMP method for eight basaltic rocks occurred in the eastern area of Zhejiang Province,which were erupted during the Late Mesozoic and named as Lower and Upper rock series(LRSURS).The weighted average 206 Pb/238 U age of the basalts from LRS is(120±1)Ma with Th/U ratios ranging from 0.65 to 2.44.The weighted average 206 Pb/238 U age of the basalts from URS is(103±2)Ma,with Th/U ratios ranging from 0.57 to 3.03.These data suggest that the zircons from both rock series are of magmatic origin and represent the formation times of the basalts of LRS and URS.Thus,it can be concluded that the formation time of the URS and LRS is significantly different,and the age data are consistent with the previous researches.It can also be found that most of the zircons from the LRS basalts have a relatively homogeneous ages with only a few ancient zircon relicts,which indicates that they have little crustal contamination during petrogenesis.Some zircon grains show core-rim structure with a core age of about 132 Ma and a rim age of about 120 Ma,which may indicate that the inherited grains were captured from the magma source,and imply that there exist magmatic rocks formed at about 130 Ma in the mantle or mantle-crustal boundary during the LRS magma activity.The magmatic zircons from URS basalts are very few,many detrital grains were dated with the ages covering almost all of the magmatic events in the South China block.It is suggested that the URS basaltic rocks were contaminated by clastic rocks which contained the detrital grains with different ages.