Yangshan Gold Deposit: The Largest Carlin and Carlin-like Type Gold Deposit in China

Gold Headquarter of the CAPF has discovered the Yangshan super large-scale gold depositin Gansu Province, which is a great breakthrough of gold exploration and prospecting in WesternQiniing Mountains of China. The gold resources of this deposit achieved 308 tons with increasingpotentials. Preliminary geological investigations indicate that the Yangshan gold deposit is located inthe intra-continental collision orogenic belt; and the deposit was formed during the continent-continentcollision orogenic processes. The geological characteristics of the deposit are similar to that of thetypical Carlin-type gold deposits, while differences still exist. The ore-forming background is notablydifferent from the Carlin gold deposit province in the United States; and the ore-forming fluids aresimilar with that of the orogenic-type gold deposit. Accordingly, the Yangshan gold deposit is atransitional type between the Carlin-type and the orogenic type gold deposits. At present, the Yangshangold deposit is the largest Carlin and Carlin-like type gold deposit that is ever discovered in China.Researches on metaliogeny, metaliogenic model and ore-enrichment regularities of the Yangshan golddeposit are crucial to meet the pressing needs of the current geological investigation and oreexploration of the deposit.     

Tectonics of the Simplon massif and Lepontine gneiss dome: deformation structures due to collision between the underthrusting European plate and the Adriatic indenter

This study presents a review of published geological data, combined with original observations on the tectonics of the Simplon massif and the Lepontine gneiss dome in the Western Alps. New observations concern the geometry of the Oligocene Vanzone back fold, formed under amphibolite facies conditions, and of its root between Domodossola and Locarno, which is cut at an acute angle by the Miocene, epi- to anchizonal, dextral Centovalli strike-slip fault. The structures of the Simplon massif result from collision over 50 Ma between two plate boundaries with a different geometry: the underthrusted European plate and the Adriatic indenter. Detailed mapping and analysis of a complex structural interference pattern, combined with observations on the metamorphic grade of the superimposed structures and radiometric data, allow a kinematic model to be developed for this zone of oblique continental collision. The following main Alpine tectonic phases and structures may be distinguished:

印度板块和亚洲大陆在何时何地碰撞

印度板块和亚洲大陆的初始碰撞时间是所有相关的喜马拉雅-西藏造山体系演化模式的主控条件,并严重影响到对众多与青藏高原隆升和东亚大陆挤出相关的地质过程速率的解释,以及对新生代全球气候变化的理解。尽管印度板块和亚洲大陆汇聚的速率在55Ma突然减缓被广泛地认为是初始碰撞的标志,但这次碰撞所造成的主要构造效应直到20多个百万年以后才显现出来。对印度板块和亚洲大陆相对位置的重新估算,表明它们在55Ma时并没有达到可以彼此发生碰撞的距离。基于来自西藏新的野外证据和对已有数据的重新评估,认为初始碰撞发生在始新世—渐新世之交（约34Ma）,并对55Ma时发生的地质事件提出了另一种解释     

The origin of accretionary lapilli

Experimental investigations in a recirculating wind tunnel of the mechanisms of formation of accretionary lapilli have demonstrated that growth is controlled by collision of liquid-coated particles, due to differences in fall velocities, and binding as a result of surface tension forces and secondary mineral growth. The liquids present on particle surfaces in eruption plumes are acid solutions stable at 100% relative humidity, from which secondary minerals, e.g. calcium sulphate and sodium chloride, precipitate prior to impact of accretionary lapilli with the ground. Concentric grain-size zones within accretionary lapilli build up due to differences in the supply of particular particle sizes during aggregate growth. Accretionary lapilli do not evolve by scavenging of particles by liquid drops followed by evaporation — a process which, in wind tunnel experiments, generates horizontally layered hemispherical aggregates. Size analysis of particles in the wind tunnel air stream and particles adhering to growing aggregates demonstrate that the aggregation coefficient is highly grain-size dependent. Theoretical simulation of accretionary lapilli growth in eruption plumes predicts maximum sizes in the range 0.7–20 mm for ash cloud thicknesses of 0.5–10 km respectively.     

大别山榴辉岩一片麻岩杂岩的成因

大别山榴辉岩由辉长岩、大陆拉斑玄武岩和少量泥灰质经高压变质作用形成。大别地块可划分出四个形成条件不同的榴辉岩区,它们代表一种构造－岩石组合体。片麻岩杂岩中各种高压变质岩类的发现证明它们与榴辉岩一起经历了原地高压变质过程。二者变质作用Ｐ－Ｔ参数的差异归因于抬升过程中退变质反应速度的不同。不同地区榴辉岩退变质组合及Ｐ－Ｔ条件与围岩的一致性表明,大别杂岩现今所展示的“递增”变质带是由榴辉岩相退变质作用形成的。高压榴辉岩－片麻岩杂岩的产生是印支期扬子与华北两个大陆板块碰撞的结果。     

“全新特提斯洋”概念与广义特提斯构造域

特提斯最初是指欧亚大陆南缘的古海洋，后逐渐引申出从元古宙、古生代到中生代的一系列位于劳亚大陆与冈瓦纳大陆之间的古大洋，如原特提斯洋、古特提斯洋和新特提斯洋，不同大洋在时间上前后交叠。如今横亘在冈瓦纳大陆(南极洲)和欧亚大陆之间的是印度洋，是新特提斯洋的继承者，可以另称为“全新特提斯洋”。这一概念的引申直接体现了印度洋与特提斯构造域一脉相承的关系，有助于将今论古、由此及彼，更直观地了解特提斯构造域的演化过程。本文按时间序列梳理了印度洋的大地构造演化和岩浆作用过程，识别了印度洋在155 Ma、120 Ma、90~84 Ma、76 Ma、65 Ma、52 Ma、45 Ma、38 Ma等关键时期的异常海底扩张记录，这些扩张事件将为标定新特提斯构造域的演化提供参照。其中155 Ma可能指示了新特提斯洋的鼎盛期，90 Ma指示了新特提斯洋的洋中脊俯冲，76~52 Ma是非洲- 阿拉伯大陆与欧亚大陆初始碰撞- 主碰撞(即新特提斯洋西部关闭)的时期，65~45 Ma是印度次大陆与欧亚大陆初始碰撞- 主碰撞(即新特提斯洋中部关闭)的时期，38 Ma是澳大利亚北部大洋开始净俯冲(即新提斯洋东部开始消减)的时间。印度洋扩张历史的研究为理解新特提斯洋消亡提供参考标尺。站在“后方”印度洋的角度，可以更清晰地透视“前线”特提斯构造域的演化过程，为理解板块构造活动规律提供支撑。     

杨山晚古生代沉积盆地成因类型及其与桐柏-大别造山带关系的探讨

杨山晚古生代沉积盆地位于桐柏-大别山北麓,它具有明显的前陆盆地沉积特点,由早期(D₂?—C₁)的复理石建造到晚期(C₁—P?)的磨拉石建造;古生物地理分析表明其与华北、扬子陆块都有密不可分的联系,其间不可能有古洋盆的存在,因而它应当是桐柏一大别造山带碰撞造山过程中形成的前陆盆地。杨山晚古生代前陆盆地的形成说明,扬子陆块和华北陆块的陆-陆碰撞起始于晚泥盆世之前(S₃—D₂),而桐柏-大别造山带中生代的构造事件则可能代表一次大规模陆内逆冲-推覆作用。     

Paleoproterozoic accretion in the Northeast Siberian craton: Isotopic dating of the Anabar collision system

Geochronological database considered in the work and characterizing the Anabar collision system in the Northeast Siberian craton includes coordinated results of Sm-Nd and Rb-Sr dating of samples from crustal xenoliths in kimberlites, deep drill holes, and bedrock outcrops. As is inferred, collision developed in three stages dated at 2200–2100, 1940–1760, and 1710–1630 Ma. The age of 2000–1960 Ma is established for substratum of mafic rocks, which probably originated during the lower crust interaction with asthenosphere due to the local collapse of the collision prism. Comparison of Sm-Nd and Rb-Sr isochron dates shows that the system cooling from ≈700 to ≈300°C lasted approximately 300 m.y. with a substantial lag relative to collision metamorphism and granite formation. It is assumed that accretion of the Siberian craton resulted in formation of a giant collision mountainous structure of the Himalayan type that was eroded by 1.65 Ga ago, when accumulation of gently dipping Meso-to Neoproterozoic (Riphean) platform cover commenced.     

鄂尔多斯盆地石炭纪中央古隆起形成机制

将鄂尔多斯盆地简化为受南北挤压的等厚各向同性弹性薄板模型进行应力—应变场数值模拟,力图揭示鄂尔多斯地区石炭纪出现的细腰状中央古隆起的形成机制。模拟中Z轴方向应变(εz)正值区对应于盆地内部的隆起区,zε正等值线形态对应于隆起形态;单轴挤压条件下,εz正等值线总会呈现沿应力轴方向延伸的细腰状形态;点作用力产生的zε正等值线范围局限,而线作用力产生的εz正值区分布较广。模拟结果表明鄂尔多斯盆地石炭纪细腰状隆起是在南北边界受挤压条件下,应力—应变在盆地内部传递过程中所必然出现的结果,南北向点作用力比南北向线作用力产生的zε等值线形态更接近于鄂尔多斯盆地中央古隆起形态;点作用力可能代表了石炭纪微板块间的点碰撞或者弧—陆碰撞。     

大别山-苏鲁碰撞造山带构造几何学、运动学和岩石变形分析

按照构造几何学特点和运动学特征我们把大别山-苏鲁造山带的分为三个构造单元:南部,中部和北部。造山带南部为一套构造堆叠体系;中部为一个混合岩穹窿,浅变质的砂岩、板岩和片岩构成了大别山-苏鲁造山带的北部构造单元。造山带南部的构造堆叠体系主要由前陆褶皱带构成:未变质的新元古代-早三叠世的沉积地层;由“宿松群”北部和苏北地区的“海州群”构成的高压变质岩石单元及含柯石英和金刚石的超高压变质岩石单元。造山带中部的混合岩穹隆由大别山地区的罗田穹隆和苏鲁地区的莱西-栖霞穹隆构成。同样大别山北部的浅变质“佛子岭-卢镇关群”和胶东地区浅变质的“蓬莱群”构成了造山带北部的构造堆叠体系。同时大别山和苏鲁两个构造地体均经历了相似的多期构造变形:沿 NW-SE 向矿物拉伸线理发育的上部指北的剪切变形代表着造山带主变形期的变形;早期向南逆冲的韧性剪切变形和沿中部混合岩穹隆边缘发育的重力滑脱变形体系,后者代表了混合岩穹隆形成时的垂向缩短作用。正是由于构造几何学和多期变形的可对比性决定了这两个变质地体具有相同的地球动力学背景。