东秦岭陡岭杂岩中存在新太古代物质组成——SHRIMP锆石U—Pb和Sm—Nd年代学证据

出露于豫、陕交界处的陡岭杂岩是秦岭造山带中一个不大的构造岩块 ,它可能是在 1.95～ 2 .10Ga期间由于构造作用将不同时代、不同源区的岩石组合叠置在一起而形成的。出露在其西部的透辉变粒岩的 TDM为 2 .6 7～ 2 .76 Ga,残余锆石 SHRIMP年龄为 2 .5～ 2 .6 Ga,表明透辉变粒岩的物质主要来自新太古代 ,基本没有或少有太古宙以后的陆壳物质混合 ,同时也说明透辉变粒岩的原岩形成时在其附近应该有新太古代岩块存在。     

Geology of the summit limestone of Mount Qomolangma (Everest) and cooling history of the Yellow Band under the Qomolangma detachment

Abstract   Newly discovered peloidal limestone from the summit of Mount Qomolangma (Mount Everest) contains skeletal fragments of trilobites, ostracods and crinoids. They are small pebble-sized debris interbedded in micritic bedded limestone of the Qomolangma Formation, and are interpreted to have been derived from a bank margin and redeposited in peri-platform environments. An exposure of the Qomolangma detachment at the base of the first step (8520 m), on the northern slope of Mount Qomolangma was also found. Non-metamorphosed, strongly fractured Ordovician limestone is separated from underlying metamorphosed Yellow Band by a sharp fault with a breccia zone. The ⁴⁰Ar–³⁹Ar ages of muscovite from the Yellow Band show two-phase metamorphic events of approximately 33.3 and 24.5 Ma. The older age represents the peak of a Barrovian-type Eo-Himalayan metamorphic event and the younger age records a decompressional high-temperature Neo-Himalayan metamorphic event. A muscovite whole-rock ⁸⁷Rb–⁸⁶Sr isochron of the Yellow Band yielded 40.06 ± 0.81 Ma, which suggests a Pre-Himalayan metamorphism, probably caused by tectonic stacking of the Tibetan Tethys sediments in the leading margin of the Indian subcontinent. Zircon and apatite grains, separated from the Yellow Band, gave pooled fission-track ages of 14.4 ± 0.9 and 14.4 ± 1.4 Ma, respectively. These new chronologic data indicate rapid cooling of the hanging wall of the Qomolangma detachment from approximately 350°C to 130°C during a short period (15.5–14.4 Ma).     

Petrogenesis and significance of early Yanshanian syenite-granite complex in eastern Nanling Range

According to the statistics for granitoid distribution map of 1/2000000 Nanling region[1], the granitoids in the Nanling region sum up an area of more than 170000 km2, occupying about one fifth of the entire Nanling region. Granitoid rocks in the Nanlingregion are mainly composed of monzogranites (occu- pying more than 84%), granodiorites (about 11%) and syenogranites (about 3%)[2]. There also exists a small amount of syenites (0.12%) with a sum area of about 94 km2[2]. However, nearly half …     

西昆仑新藏公路118～323km段基性、酸性岩脉K—Ar年龄

在西昆仑西段新藏公路沿线广泛发育数量众多的岩脉，野外出露有煌斑岩脉、辉绿岩脉、闪长岩脉、花岗岩脉。对以上岩脉进行了全岩K-Ar同位素测年，其侵位年龄与该区的地质构造事件有很好的对应关系：辉绿岩脉273～280Ma的侵位年龄对应着弧后扩张的时间，闪长岩脉和花岗岩脉230～244Ma的侵位年龄对应着碰撞造山的时间。     

Cosmogenic nuclide chronology of pre-last glacial maximum moraines at Lago Buenos Aires, 46°S, Argentina

At Lago Buenos Aires, Argentina, ¹⁰Be, ²⁶Al, and ⁴⁰Ar/³⁹Ar ages range from 190,000 to 109,000 yr for two moraines deposited prior to the last glaciation, 23,000–16,000 yr ago. Two approaches, maximum boulder ages assuming no erosion, and the average age of all boulders and an erosion rate of 1.4 mm/10³ yr, both yield a common estimate age of 150,000–140,000 yr for the two moraines. The erosion rate estimate derives from ¹⁰Be and ²⁶Al concentrations in old erratics, deposited on moraines that are >760,000 yr old on the basis of interbedded ⁴⁰Ar/³⁹Ar dated lavas. The new cosmogenic ages indicate that a major glaciation during marine oxygen isotope stage 6 occurred in the mid-latitude Andes. The next five youngest moraines correspond to stage 2. There is no preserved record of a glacial advance during stage 4. The distribution of dated boulders and their ages suggest that at least one major glaciation occurred between 760,000 and >200,000 yr ago. The mid-latitude Patagonian glacial record, which is well preserved because of low erosion rates, indicates that during the last two glacial cycles major glaciations in the southern Andes have been in phase with growth and decay of Northern Hemisphere ice sheets, especially at the 100,000 yr periodicity. Thus, glacial maxima are global in nature and are ultimately paced by small changes in Northern Hemisphere insolation.     

长江三角洲（江南）地区第四纪海侵层的划分及时代归属

依据多年积累的钻孔剖面、微体生物化石、孢子花粉、古地磁和“C测年等资料综合分析研究，本区第四系有5个主要海侵层，从老到新为第V海侵层（宝山海侵）、第Ⅳ海侵层（嘉定海侵）、第Ⅲ海侵层（昆山海侵）和第Ⅱ海侵层（涌湖海侵）、第1海侵层（镇江海侵），其时代分别为早更新亚世中期（1．8-2．0Ma B．P．）、中更新亚世早期（0．78-0．45MaB．P．）、晚更新亚世早期（126～70Ka B．P．）、晚更新亚世晚期（40-20Ka B．P．）、全新世（始于10Ka B．P．）。     

甘肃北山红尖兵山钨矿床的40Ar-39Ar同位素年代学研究

文章对红尖兵山钨矿云英岩中的白云母进行了40Ar-39Ar同位素年代学研究,获得的坪年龄为(216.6±1.6)Ma(2σ),等时线年龄为(215.2±2.8)Ma,MSWD=0.47,40Ar/36Ar初始比值为333±47。等时线年龄与坪年龄在误差范围内完全一致,可认为该结果近似代表了黑钨矿的形成时代,即红尖兵山的黑钨矿形成于印支期。     

新疆哈密镜儿泉伟晶岩型稀有金属矿床40Ar-39Ar年龄及其地质意义

文章通过对哈密镜儿泉伟晶岩型稀有金属矿床中白云母的40Ar/39Ar同位素定年研究,测得该矿床的同位素年龄数据,其坪年龄为(243±2)Ma。这一结果显示,镜儿泉的含稀有金属伟晶岩脉是在印支期形成的,并且在形成之后没有再受到后期地质事件的影响。与阿尔泰成矿省相似,东天山在印支期也发生了伟晶岩型稀有金属的成矿作用。这表明,东天山地区的成矿演化与阿尔泰地区具有可比性,从而为2个地区的地质找矿指出了新的方向。     

中国西北干旱环境的形成时代与成因探讨*

西北干旱环境的形成时代是我国古环境研究的重要问题。干旱环境的存在可据地层中风成沉积、风化沉积、水成沉积、古生物等信息综合确定。对塔里木、准噶尔、柴达木、河西走廊、陕甘宁等盆地的中、新生界干旱环境沉积记录分析表明,我国西北干旱沉积及其时代可上溯到晚侏罗世初期(约160Ma以来),其间可分为三大阶段:1)晚侏罗世至古近纪(约160~24Ma),以红色干旱沉积与亚热带干旱环境为主; 2)晚第三纪(约24.0~2.5Ma),以红色干旱沉积与亚热带干旱环境向灰、黄色干旱沉积与温带干旱环境逐渐过渡为特征;3)第四纪(约2.5Ma以来),以灰、黄色干旱沉积与温带干旱环境为主。干旱环境在晚侏罗世的大范围出现主要是侏罗纪全球气温回升、北亚热带北界北推引起的。相比可见,新近纪温带干旱环境的形成主要与古特提斯海关闭、青藏高原及盆地外围山脉的隆升等构造运动引起内陆盆地干旱效应的加强有关。进而推知,我国西北在新近纪出现的温带内陆干旱环境既是盆地外围高原、山脉隆升的重要直接结果,也是亚洲季风系统的重要直接形成因素。     

Metamorphic zircon from Xindian eclogite,Dabie Terrain: U-Pb age and oxygen isotope composition

~~Metamorphic zircon from Xindian eclogite,Dabie Terrain: U-Pb age and oxygen isotope composition@E. Deloule$CRPG-CNRS Nancy,54501,France1. Vavra, G, Gebauer. D., Schmid. R. et al., Multiple zircon growth and recrystallization during polyphase Late Carboniferous to Tri-assic metamorphism in granulites of the Ivrea Zone (Southern Alps): an ion microprobe (SHRIMP) study, Contrib. Mineral Petrol., 1996, 122:337-358 2. Vavra, G, Schmid, R., Gebauer, D., Internal morphology, ha…