Geodynamic studies have shown that mantle convection is like a giant blender to make the original heterogeneous mantle mixing and homogenizing. However, some models, especially from geochemical data show that the mode...Geodynamic studies have shown that mantle convection is like a giant blender to make the original heterogeneous mantle mixing and homogenizing. However, some models, especially from geochemical data show that the modem mantle may still contain a number of reservoir bodies with different chemical composition. Then, the modern mantle is homogeneous？ Authors have defined a box replacement degree of convective mantle mixing and pervasion degree of convective mantle mixing （that equals to initial density of tracing elements divided by final density of tracing elements） to investigate the mantle mixing. The previous results have shown that after four billion years the mantle is basic uniform and the box replacement of the convective mantle is more than 80% in steady-state convection models. This paper calculates and discusses the pervasion degree of convective mantle mixing in detail. For the initial state we will set some 10°× 10°（spacing 0.25°） tracing boxes, which includes 1 681 tracer, at the top and bottom of the mantle, and then track the motions of these tracers, and investigate the convective mixed pervasions. The results show that at the initial stage though the convective mixing pervasions are very different from mode to mode, after running for some time, the convective mixing pervasions for most modes are going to be a constant and the tracers are more evenly distributed in the whole mantle.展开更多
Cenozoic basaltic volcanic rocks of various ages from the Tertiary to Pleistocene in Jiangsu, Anhui and Shandong are widely distributed. In the Paleocene they are mainly tholeiitic eruption and in the Neogene alkalic ...Cenozoic basaltic volcanic rocks of various ages from the Tertiary to Pleistocene in Jiangsu, Anhui and Shandong are widely distributed. In the Paleocene they are mainly tholeiitic eruption and in the Neogene alkalic basalt. In the Pleistocene, they consist of alkalic basalt, basanite展开更多
华南西南部博白-岑溪多金属成矿带是华南地区重要成矿带。在该带中先后发现的米场、油麻坡、三叉冲等中大型钨钼矿与晚中生代白垩纪花岗岩关系密切。本文选择了该区典型岩体——三叉冲岩体进行研究,通过对其特征及成因的研究对该地区成...华南西南部博白-岑溪多金属成矿带是华南地区重要成矿带。在该带中先后发现的米场、油麻坡、三叉冲等中大型钨钼矿与晚中生代白垩纪花岗岩关系密切。本文选择了该区典型岩体——三叉冲岩体进行研究,通过对其特征及成因的研究对该地区成矿作用提供指示意义。三叉冲岩体由斑状中粒黑云母花岗岩和细粒二云母花岗岩组成。LA-ICP-MS锆石U-Pb同位素定年表明,斑状中粒黑云母花岗岩形成于101-104 Ma,细粒二云母花岗岩形成于103-105 Ma。两种花岗岩都具有较大的化学成分变化,但具有相似的Nd同位素组成,εNd（t）值分别为–7.5-–6.5和–7.8-–6.7。我们认为中粒黑云母花岗岩为中元古界中-高钾玄武岩成分基底部分熔融,并与幔源基性岩浆发生岩浆混合作用形成的。在中粒黑云母花岗岩的演化过程中有角闪石＋少量斜长石的分离结晶作用。细粒二云母花岗岩具有明显不同于中粒黑云母花岗岩的Na2O和K2O演化趋势；且具有更高的 CaO 和 Sr 含量；同时,细粒二云母花岗岩具有高得多的 La/Lu 比值,这些证据都表明细粒二云母花岗岩并非中粒黑云母花岗岩通过分离结晶形成的。细粒二云母花岗岩为中元古界长英质麻粒岩＋少量拉斑玄武岩成分部分熔融产生中酸性岩浆,并与幔源岩浆发生混合作用形成的。幔源岩浆贡献的挥发分F使得细粒二云母花岗岩朝更富Na2O的方向演化。在细粒二云母花岗岩的演化过程中以黑云母＋钾长石＋斜长石的分离结晶为主。野外地质调查、岩石学及地球化学数据表明,细粒二云母花岗岩与三叉冲钨钼成矿作用的关系更为密切。晚中生代,受太平洋板块的俯冲作用的影响,桂东南地区处于拉张构造环境。软流圈上涌及玄武质岩浆底侵为基底的部分熔融提供了必要的热源,同时也为三叉冲岩体的形成提供了物质来源。展开更多
基金supported by National Natural Science Foundation of China (40574043)
文摘Geodynamic studies have shown that mantle convection is like a giant blender to make the original heterogeneous mantle mixing and homogenizing. However, some models, especially from geochemical data show that the modem mantle may still contain a number of reservoir bodies with different chemical composition. Then, the modern mantle is homogeneous？ Authors have defined a box replacement degree of convective mantle mixing and pervasion degree of convective mantle mixing （that equals to initial density of tracing elements divided by final density of tracing elements） to investigate the mantle mixing. The previous results have shown that after four billion years the mantle is basic uniform and the box replacement of the convective mantle is more than 80% in steady-state convection models. This paper calculates and discusses the pervasion degree of convective mantle mixing in detail. For the initial state we will set some 10°× 10°（spacing 0.25°） tracing boxes, which includes 1 681 tracer, at the top and bottom of the mantle, and then track the motions of these tracers, and investigate the convective mixed pervasions. The results show that at the initial stage though the convective mixing pervasions are very different from mode to mode, after running for some time, the convective mixing pervasions for most modes are going to be a constant and the tracers are more evenly distributed in the whole mantle.
文摘Cenozoic basaltic volcanic rocks of various ages from the Tertiary to Pleistocene in Jiangsu, Anhui and Shandong are widely distributed. In the Paleocene they are mainly tholeiitic eruption and in the Neogene alkalic basalt. In the Pleistocene, they consist of alkalic basalt, basanite
文摘华南西南部博白-岑溪多金属成矿带是华南地区重要成矿带。在该带中先后发现的米场、油麻坡、三叉冲等中大型钨钼矿与晚中生代白垩纪花岗岩关系密切。本文选择了该区典型岩体——三叉冲岩体进行研究,通过对其特征及成因的研究对该地区成矿作用提供指示意义。三叉冲岩体由斑状中粒黑云母花岗岩和细粒二云母花岗岩组成。LA-ICP-MS锆石U-Pb同位素定年表明,斑状中粒黑云母花岗岩形成于101-104 Ma,细粒二云母花岗岩形成于103-105 Ma。两种花岗岩都具有较大的化学成分变化,但具有相似的Nd同位素组成,εNd（t）值分别为–7.5-–6.5和–7.8-–6.7。我们认为中粒黑云母花岗岩为中元古界中-高钾玄武岩成分基底部分熔融,并与幔源基性岩浆发生岩浆混合作用形成的。在中粒黑云母花岗岩的演化过程中有角闪石＋少量斜长石的分离结晶作用。细粒二云母花岗岩具有明显不同于中粒黑云母花岗岩的Na2O和K2O演化趋势；且具有更高的 CaO 和 Sr 含量；同时,细粒二云母花岗岩具有高得多的 La/Lu 比值,这些证据都表明细粒二云母花岗岩并非中粒黑云母花岗岩通过分离结晶形成的。细粒二云母花岗岩为中元古界长英质麻粒岩＋少量拉斑玄武岩成分部分熔融产生中酸性岩浆,并与幔源岩浆发生混合作用形成的。幔源岩浆贡献的挥发分F使得细粒二云母花岗岩朝更富Na2O的方向演化。在细粒二云母花岗岩的演化过程中以黑云母＋钾长石＋斜长石的分离结晶为主。野外地质调查、岩石学及地球化学数据表明,细粒二云母花岗岩与三叉冲钨钼成矿作用的关系更为密切。晚中生代,受太平洋板块的俯冲作用的影响,桂东南地区处于拉张构造环境。软流圈上涌及玄武质岩浆底侵为基底的部分熔融提供了必要的热源,同时也为三叉冲岩体的形成提供了物质来源。
