Diachroneity of continental subduction and exhumation: Constraints from the Permian-Triassic HP metamorphic terrane in the Tongbai orogen, central China

High-pressure （HP） metamorphic terrane in the Tongbai orogen comprises two HP slices （I and II） and a tectonic m61ange zone in the northeast and a blueschist-greenschist zone in the southwest. HP slice I is represented by the northern and southern eclogite zones on the two sides of the Tongbaishan antiform. HP slice II is represented by retrograded eclogite-bearing metamorphic en- claves in Cretaceous gneissic granites in the Tongbai Complex. U-Pb, Lu-Hf, Rb-Sr and 4Ar/39Ar multichronometric data indi- cate that the peak metamorphism of HP slice I took place at -255 Ma, whereas the metamorphic ages of HP slice II are as young as 232-220 Ma. By contrast, the tectonic melange zone near the suture was metamorphosed at -256 Ma. Such a diachroneity of dif- ferent slices across the direction of the orogen in the Hong＇an-Dabie-Sulu HP/UHP terrane is ubiquitous, and it can be interpreted by a syn-subduction detachment/exhumation model. Furthermore, the metamorphic age of HP slice I in the Tongbai orogen is older than that of the equivalent HP slice in the Hong＇an orogen by ~15 Ma, suggesting that the diachroneity may have also ex- isted along the direction of the orogen. A seesaw-type subduction/exhumation model is proposed to explain this age disparity and the subduction of the South China Block becomimg shallower towards the west.     

农家安全贮种“十防”

防潮。种子的吸湿性很强，在较阴暗潮湿的条件下，种子易吸水返潮。种子越干燥，吸湿性就越强．返潮也就越厉害，往往会造成种子含水量大，致使种子遭冻或发霉变质，发芽率降低。预防措施是：把种子存放在干燥的库房内，并且用木料垫起来不能把种子堆放在豆腐房、粉坊、厨房和饲料房等场所。     

Impact-derived features of the Xiuyan meteorite crater

Up to now, 176 meteorite impact craters have been found on the Earth. Among these craters, none of them lies in China. The Xiuyan crater is located in the Liaodong Peninsula of China. This bowl-shaped crater has a diameter of 1.8 km and depth of about 150 m. The impact-derived features include planar deformation features （PDFs） in quartz, shatter cones, impact breccia, and radial valleys on the wall of rim. It is the first confirmed meteorite impact crater in China.     

北祁连山含镁纤柱石高压泥质岩及其对古大洋俯冲的意义

北祁连山发育有缝合带是一条典型的早古生代大洋型俯冲带。针对该缝合带中首次发现的含镁纤柱石高压泥质片岩进行了详细的岩石学和矿物学研究。根据平衡矿物组合,利用THERMORCAL(V3.23)计算出镁纤柱石+石榴石+硬绿泥石+多硅白云母组合稳定的温压条件为P=2.2～2.5GPa,T=530～580℃。利用纤柱石和硬绿泥石的稳定范围,确定了北祁连山早古生代大洋冷俯冲的地热梯度的范围为6.5～7.5℃/km。该研究结果对于了解早古生代时期大洋俯冲带的热结构及其高压变质岩石的脱水过程有重要意义。     

大王山动力变质带中蠕英石的特征和成因

文章根据大王山糜棱片麻岩中蠕英石的形态特征、分布规律、以及与岩石有限应变状态之间的几何关系等,说明蠕英石是在钾长石变形时形成且受到压应力方向的控制。文中对糜棱片麻岩中蠕英石的形成机理进行了探讨。     

绳子下落问题教学法探讨

本文以绳于下落的力学问题为例,采用一题多解的形式.与学生展开讨论的教学方法,以求激发学生积极思维,提高分析问题的能力,进而促进教学质量的提高.     

齐次马氏随机过程中突变质体遗传规律研究中的应用

以Ｍａｒｋｏｖ链为工具研究了突变质体分裂后随细胞分裂而传递的规律，并对含突变质体细胞的纯合概率及其在生物学，育种学上的意义进行了探讨。     

陕西省煤种分布及其地质背景分析

陕西省煤炭资源丰富，含煤地层众多，煤种较为齐全，煤种地域分布严格受区域地质三分性区划控制。明显可分为秦巴山腐泥无烟煤区、渭北高变质烟煤区和陕北高原低变质烟煤区，煤变质程度由南向北依次递降，聚煤作用强度则随时间推移由南而北逐渐增强；层位分布与区域地质背景息息相关，明显受制于各地质单元的地质发展历史、地质结构特征和变质因素。     

汽车自动检测系统：安全行车的保障

汽车检测,是为确定汽车技术状况或工作能力的检查。汽车在使用过程中,随着使用时间的延长（或行驶里程的增加）,其零件逐渐磨损、腐蚀、变形、老化,以及润滑油变质等,致使配合副间隙变大,引起运动松旷、振动、发响和漏气、漏水、漏油等,造成汽车技术性能下降。     

华北太古宙退变质榴辉岩的发现及其含义

1993年,Smelov等报道在西伯利亚阿尔丹地盾奥列克玛晚太古代花岗绿岩区内有退变质为麻粒岩和角闪岩的榴辉岩.1994年,Williams等又在加拿大地盾晚太古代斯垂汀-阿斯巴斯卡花岗糜棱岩带发现原称为麻粒岩的岩石是榴辉岩.这是早前寒武纪地质研究的重大进展.1 地质概况晋冀蒙交界地区的太古宙变质岩石出露区可以划分为3个岩石构造单元,即(1)出露于