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定结日玛那穹窿位于高喜马拉雅带中段,由花岗片麻岩、变泥质岩、变基性岩及大量淡色花岗岩等组成,经历了角闪岩-麻粒岩相变质作用。为厘定淡色花岗岩的形成机制以及与高级变质岩的关系,我们对淡色花岗岩和高级变质岩进行了全岩元素和Sr和Nd同位素组成和SHRIMP锆石U-Pb地质年代学测试。全岩元素和Sr-Nd同位素测试结果揭示淡色花岗岩具有以下特征:(1)高SiO2(>72%),高Al2O3(>12%)和高A/CNK比值(>1·0);(2)高Rb,低Sr,高Rb/Sr比值(>1·0);(3)高∑REE和明显的负Eu异常;(4)高Sr同位素初始比值(0·7621~0·8846)和低εNd(t)值(-13·0~-20·2)。淡色花岗岩的高Rb/Sr比值和Sr-Nd同位素系统特征表明其形成机制为主要为白云母脱水部分熔融作用,源区为由花岗片麻岩和变泥质岩组成的混合源区。SHRIMP锆石U-Pb年代学研究揭示出定结地区淡色花岗岩具有21·0±0·7Ma和15·8±0·1Ma2期年龄,花岗片麻岩的锆石变质增生边年龄为22·2±1·4Ma,与该区的榴辉岩退变质年龄一致。这些数据共同表明,花岗片麻岩和变泥质岩在22~21Ma发生高级变质和深熔作用,形成早期淡色花岗岩岩浆,在~16Ma进一步深熔,形成晚期淡色花岗岩岩浆。
Set at the center of the high Himalayan zone, the fixed knot Mauna Dome consists of granitic gneisses, metamorphic argillaceous rocks, metamorphic rocks and a large amount of light-colored granite, which underwent amphibolite-granulite facies metamorphism. In order to determine the formation mechanism of pale granite and its relationship with the high-grade metamorphic rocks, we conducted whole-rock elements, Sr and Nd isotopic compositions and SHRIMP zircon U-Pb geochronological tests on the pale-grained granites and high-grade metamorphic rocks. The results of the whole rock element and Sr-Nd isotope test reveal that the pale granite has the following characteristics: (1) the ratio of high SiO2 (> 72%), high Al2O3 (> 12%) and high A / CNK (> 1.0) ) High Rb, low Sr and high Rb / Sr ratios (> 1.0); (3) high ΣREE and significant negative Eu anomalies; (4) high Sr isotope initial ratios (0 · 7621 ~ 0 · 8846) and Low εNd (t) values (-13.0 to -20.2). The high Rb / Sr ratios and Sr-Nd isotopic characteristics of pale-colored granites suggest that the formation mechanism is mainly the partial melting of the dehydrated muscovite, and the source area is a mixed source zone composed of granitic gneisses and metamorphic argillaceous rocks. SHRIMP zircon U-Pb dating reveals that the pale-colored granites in the Dingjie area have ages of 21.0 ± 0.7Ma and 15.8 ± 0.1Ma2, and the gneiss ages of granitic gneiss are 22 · 2 ± 1.4Ma, consistent with the degenerated age of eclogite in this area. Together, these data suggest that the granitic gneiss and metamorphic metamorphic and diagenetic metamorphism advanced between 22 and 21 Ma, forming early pale-granite magma and further deep-melting at ~ 16 Ma, forming later pale-pale-granite magma.