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首页> 外文期刊>Journal of Asian earth sciences >Pb, Sr and Nd isotope systematics of metavolcanic rocks of the Hutti greenstone belt, Eastern Dharwar craton: Constraints on age, duration of volcanism and evolution of mantle sources during Late Archean
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Pb, Sr and Nd isotope systematics of metavolcanic rocks of the Hutti greenstone belt, Eastern Dharwar craton: Constraints on age, duration of volcanism and evolution of mantle sources during Late Archean

机译：东达哈尔克拉通Hutti绿岩带的准火山岩中的Pb，Sr和Nd同位素系统：太古宙晚期的年龄，火山作用时间和地幔源演化的限制

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The Hutti greenstone belt, hosting major gold mines, is made up of tholeiitic basalts, felsic volcanic rocks and sediments metamorphosed to amphibolite facies and surrounded by granitoid rocks, predominantly of granodiorite in composition. The granitoid rocks show intrusive contact relationship at places along the eastern and northern margins of the belt while such relationships could not be observed along the western margin as it is covered by soil. The tholeiitic basalts have flat to moderately LREE-enriched chon-drite normalized REE patterns and show depletion in Nb relative to MORB. The Hutti metabasalts define a collinear array in the Rb-Sr isotope evolution diagram with a slope corresponding to an age of 2706 ±130 Ma. The higher uncertainty is due to scatter caused by mobility of Rb and Sr during metamor-phism and low temperature hydrothermal alteration. In the ~(206)Pb/~(204)Pb vs. ~(207)Pb/~(204)Pb diagram the metabasalts define a collinear array corresponding to an age of 2637 ±150 Ma with significant scatter indicating that Pb was also mobilized by the post-crystallization alteration processes. The Sm-Nd isotope system in the Hutti metabasalts has been least disturbed giving an isochron age of 2662 ± 81 Ma which is suggested as the age of formation of their precursors. Combined with the published U-Pb SHRIMP ages on zircons from the felsic volcanic rocks it is inferred that the Hutti greenstone belt formed over a period of ≥86 Ma. The major greenstone belts of the eastern Dharwar craton have evolved coevally at ca. 2700 Ma ago and are older than the surrounding granitoid rocks. The metabasalts have ε_(Nd) values of+1.4 to +3.0 and ε_(Sr) values of -23.4 to +2.0 and plot close to the mantle array. They were derived from long-term LREE depleted mantle source. The felsic volcanic rocks have ε_(Nd) values of-1.3 and -1.4 and ε_(Sr) values of -30.6 and +89.3, respectively. Their magmas were derived from older continental crustal sources.
机译：赫蒂（Hutti）绿岩带拥有主要的金矿，由玄武岩，玄武质火山岩和沉积物变质为闪石岩相，周围环绕着花岗岩类岩石，主要成分是花岗闪长岩。花岗岩岩石在该带的东部和北部边缘处显示出侵入式接触关系，而在西部边缘则由于土壤覆盖而无法观察到这种接触关系。玄武岩玄武岩具有平坦至中等程度的富含LREE的绒头岩归一化REE模式，并且相对于MORB表现出Nb耗竭。 Hutti玄武岩在Rb-Sr同位素演化图中定义了共线阵列，其斜率对应于2706±130 Ma的年龄。较高的不确定性是由于在变质作用和低温热液蚀变过程中Rb和Sr的迁移引起的分散。在〜（206）Pb /〜（204）Pb与〜（207）Pb /〜（204）Pb图表中，玄武岩定义了一个共线阵列，对应于2637±150 Ma的年龄，且具有明显的分散性，表明Pb也是由后结晶改变过程动员。 Hutti玄武岩中的Sm-Nd同位素系统受到的干扰最小，其等时年龄为2662±81 Ma，这被认为是其前体形成的年龄。结合已发表的长英质火山岩锆石上的U-Pb SHRIMP年龄，可以推断Hutti绿岩带形成于≥86 Ma的时期。东部Dharwar克拉通的主要绿岩带已在约公元前期演化。距今2700 Ma，比周围的花岗岩岩石还老。玄武岩的ε_（Nd）值为+1.4到+ 3.0，ε_（Sr）值为-23.4到+2.0，并且绘图接近地幔阵列。它们来自长期的LREE耗尽地幔来源。长英质火山岩的ε_（Nd）值为-1.3和-1.4，ε_（Sr）值为-30.6和+89.3。他们的岩浆来自较古老的大陆地壳来源。

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