Influences of marine floor hydrothermal activity on organic matter abundance in marine carbonate rocks——A case study of middle-upper Proterozoic in the northern part of North China

FOR A LONG TIME, RESEARCHERS HAVE BEEN REGARDING THE BIOLOGICAL PRODUCTIVITY, THE SEDIMENTATION RATE, THE DEPOSITION ENVIRONMENT, AND THE PRESERVATION CONDITION OF THE DEPOSITIONAL ORGANIC MATTER AS THE CONTROLLING FACTORS OF ORGANIC MATTER ABUNDANCE IN T…     

河北兴隆中元古代硫化物黑烟囱群发现及其地质成因

报道了河北兴隆高板河中元古代硫化物矿床中保留完好的古海底黑烟囱群.高板河古海底黑烟囱群呈柱状、锥状、圆丘状、尖顶状及复合状等形态,显示良好的热水通道,一些烟囱顶部还保留明显的喷口以及放射状纹理,记录了海底成矿热水以多种活动方式喷溢.它们的形态和组成类似现代洋底黑烟囱及世界其他地区发现的古海底黑烟囱.研究认为,该区黑烟囱发育于地堑深水盆地,与海底同沉积断裂活动密切相关.结构构造对比分析表明,含矿热水与海水作用形成黑烟囱外壁,通道内含矿热水持续运移及圈闭造成烟囱内部分带性及交代结晶过程.该区保留了不同形态和结构的烟囱类型,表明海底成矿过程中涉及含矿热水的集束喷溢及弥散喷溢.     

Nd isotopic characteristics of post-Archean sediments from the Eastern Nanling Range： Evidence for crustal evolution

A systematic Sm-Nd isotopic study was carried out for sediments and metasediments of different ages from Mesoproterozoic to early Mesozoic era in southwestern Fujian, Eastern Nanling Range. The results show that Nd model age (tDM) and εNd(t) value of most sediments are closely similar to those of Paleoproterozoic Mayuan Group, indicating that they may mainly be the recycling product of Paleoproterozoic crustal materials. However, the Nd model age significantly decreases with a corresponding increase in the εNd(t) value at Neoproterozoic (ca. 0.8-0.7 Ga) and Late Paleozoic (ca. 0.25 Ga), respectively. This is manifested by prominent vales and apexes on the diagrams of tDM VS. tStr. (stratum age) and εNd(t) VS. tstr. The decrease in tDM and the increase in εNd(t) are explained as a result of the significant incorporation of juvenile crustal materials that originated from depleted mantle due to strong lithospheric extension during both periods. It appears that tectonic magmatism in the Neoproterozoic and the Late Paleozoic is of prominent importance in affecting the geochemical nature of sediments in South China.     

龙门山中段映秀地区花岗岩单元特征

映秀地区花岗岩属龙门山推覆构造带“彭灌杂岩”南段之组成部分，岩石类型以二长花岗岩、英云闪长岩为主，少量花岗闪长岩。按照同源岩浆演化序列的观点，根据岩石学、岩石化学及地球化学、接触关系等特征，将该区花岗岩划分为８个花岗岩单元。其岩石为稀土总量偏低、具负铕右倾型式的钙碱性次铝及过铝型酸性侵入岩，分属造山前陆弧Ｉ型花岗岩的成分演化序列及造山晚期Ｓ型花岗岩的结构演化序列，其形成时代为中─晚元古代。     

Paleoproterozoic lower crust beneath Nushan in Anhui Province： Evidence from zircon SHRIMP U-Pb dating on granulite xenoliths in Cenozoic alkali basalt

Zircon SHRIMP U-Pb dating was carried out for an intermediate granulite xenolith in Cenozoic alkali basalt from Nushan. The results suggest that the lower crust beneath Nushan may have formed at about 2400—2200 Ma, and have been subjected to granulite-facies metamorphism at 1915 27 Ma. The old age of the Nushan lower crust is consistent with the geochemical similarities between Nushan granulite xenoliths and Archean-Paleoproterozoic granulite terrains in the North China craton, but it is not distinguishable from high-grade metamorphic rocks in the Yangtze craton where such old ages were also reported. Significant Pb-loss occurs in the Nushan zircons, implying important influence of widespread Mesozoic to Cenozoic underplating in East China on the lower crust beneath Nushan.     

浙西南早元古代花岗岩、伟晶岩的单颗粒锆石U-Pb年龄

胡雄健等曾首次于浙西南龙泉地区发现早元古代变质变形的花岗岩侵入体,现得到单颗粒锆石U-Pb法测年资料的进一步证实。     

赣北元古代地体拚贴带中高压变质矿物的发现及其构造意义

本文介绍了在赣北怀玉山地区首次发现的兰闪石等高压矿物详细特征,讨论了其产出环境和构造背景,论证了中晚元古代二个地体碰撞拼贴带和高压变质作用的存在,初步恢复了古板块构造的演化历史。     

鄂尔多斯盆地基底变质岩与花岗岩锆石SHRIMP U-Pb定年

通过对采自鄂尔多斯盆地基底西部石榴夕线黑云斜长片麻岩与东部片麻状二云母花岗岩的钻孔样品进行SHRIMP锆石U-Pb定年,分别获得了203110和203510Ma的207Pb/206Pb年龄.两件样品的锆石都显示清楚的韵律环带,具岩浆锆石特征.其中石榴夕线黑云斜长片麻岩中的部分锆石具有较薄的变质增生边,由3个增生边获得的年龄范围约为1850～1630Ma.该岩石的矿物组合显示原岩为泥质-长英质岩石,但其锆石主体为岩浆成因,可能说明其源区为单一的花岗质岩体或火山沉积岩区.因此,鄂尔多斯基底与邻近剥露区域一样,在古元古代2035～2030Ma左右曾有大规模的花岗岩浆侵位,表明存在古元古代活动构造带,这对揭示华北克拉通西部陆块的性质和特征具有重要的意义.     

宜昌圈椅埫A型花岗岩锆石U-Pb年龄和Hf同位素与扬子大陆古元古代克拉通化作用

对侵位于湖北宜昌崆岭杂岩中的圈椅埫花岗岩进行了主量元素、微量元素、锆石U-Pb年龄和Hf同位素分析. 结果表明, 圈椅埫花岗岩富硅、碱, 贫钙、镁, 富集Ga, Y, Zr和Nb, 亏损Sr和Ba, 表现出后造山A型花岗岩(A2型)的特征. 圈椅埫A型花岗岩的锆石90%是谐和的, 并给出平均1854 Ma的古元古代岩体结晶年龄. 古元古代锆石初始(¹⁷⁶Hf/¹⁷⁷Hf)_i比值为0.280863~0.281134, ε_Hf(t)均为负值(最低为-26.3), 亏损地幔模式年龄是2.9~3.3 Ga (平均3.0 Ga), 平均地壳模式年龄高达3.6~4.2 Ga (平均3.8 Ga). 表面年龄为中太古代(2859 Ma)的锆石有略高的亏损地幔模式年龄(3.4 Ga)但相似的平均地壳模式年龄(3.8 Ga). 这些数据表明形成圈椅埫A型花岗岩的初始物质非常古老, 至少老于2.9 Ga, 甚至可以追溯到冥太古代. 与圈椅埫A型花岗岩形成有关的古元古代地壳熔融事件记录着扬子大陆克拉通化过程, 可能与Columbia超大陆聚合后-裂解前的伸展作用所引起的深部太古宙地壳拉张垮塌有关.