大山片麻岩地质特征及侵位机制研究

大山片麻岩的原财为奥长化岗石,呈不规则状侵入柳树河子片麻岩中,年龄２７亿年左右,太古代阜平运动晚期侵位的。侵位与当时区域上大规模的韧性剪切作用密切相关。由于剪切带各相关位置的位移量的差异,形成空间,给岩浆被动就位了有利场所,形成大山片麻岩古深成岩体。     

Sunrise Hill unconformity: A newly discovered regional hiatus between Archaean granites and greenstones in the northeastern Pilbara Craton

Contacts between Archaean granites and greenstones in the northeastern part of the Pilbara Craton have been described as intrusive and tectonic. New field observations in the Shay Gap region demonstrate that greenstones of the Gorge Creek Group unconformably overlie the Muccan and Warrawagine batholiths. Regionally, the unconformity is marked by a persistent but relatively thin basal clastic sequence, locally with a granite boulder conglomerate, overlain by ore‐bearing banded iron‐formation, fine‐grained clastic rocks and chert. The granite basement is dated at 3443 ± 6 Ma. The precise age of the hiatus is unknown but its maximum effect might have been the removal of a substantial thickness of Early to Middle Archaean strata.     

滇西“三江”地区临沧花岗岩基中三叠世碱长花岗岩的发现及其意义

在野外调研的基础上,对滇西“三江”地区临沧花岗岩基中勐库碱长花岗岩体的年代学、岩石学和地球化学开展了较系统的研究。结果显示,勐库岩体的锆石LA-ICP-MS U-Pb年龄为236.2±3.7 Ma,表明岩体应形成于中三叠世,而非前人认为的新生代。全岩主、微量元素,Sr同位素和锆石微量元素特征显示岩体属于S型花岗岩系列,来自于与临沧花岗岩基相类似的地壳沉积物源区的部分熔融,并经历了高程度的结晶分异作用。以勐库岩体为代表的碱长花岗岩与临沧花岗岩基形成时代一致,表明碱长花岗岩应为临沧花岗岩基的重要组成部分。除已报道的黑云母二长花岗岩类和黑云母花岗闪长岩类外,临沧花岗岩基还应包括较广泛分布的碱长花岗岩类。本文同时揭示,由于临沧花岗岩基中以勐库岩体为代表的碱长花岗岩并非早前认为的新生代岩体,“三江”南段特别是临沧地块前人划分的新生代岩体分布范围和规模可能需要重估。     

内蒙古京格斯台晚石炭世碱性花岗岩年代学及地球化学特征——岩石成因及对构造演化的约束

京格斯台碱性花岗岩出露于内蒙古东乌旗西北部的中蒙边境一带,是准噶尔-南蒙古-内蒙古碱性花岗岩带的一部分,为一套含钠铁闪石碱性花岗岩类。锆石LA-MC-ICPMS U-Pb测年获得了301.3±1.5Ma(n=21,MSWD=1.3)的年龄,表明侵位时代为晚石炭世。全岩地球化学分析显示样品具有高SiO2(75.16%~76.96%)、高碱(K2O=4.61%~5.04%,Na2O=3.98%~4.24%)、贫CaO(0.08%~0.25%)、MgO(0.07%~0.1%),低FeOt(1.05%~2.05%),高的FeOt/MgO比值(12.85~29.66),属于弱过铝质系列;富集Rb、Th、U、K等大离子亲石元素及Zr、Hf等高场强元素,弱亏损Nb、Ta,强烈亏损Ba、Sr、P、Ti等;稀土元素总量较低[ΣREE范围为(70.19~193.93)×10~(-6),平均值为126.82×10~(-6)],轻稀土略富集,具有明显的Eu负异常(δEu=0.03~0.07),呈类似"海鸥"型稀土配分模式。岩石学及地球化学特征表明京格斯台碱性花岗岩属于碱质A型花岗岩。锆石原位Hf同位素和全岩Nd同位素分析显示其具有亏损的Hf-Nd同位素组成εHf(t)和εNd(t)均为正值,Hf地壳存留模式年龄范围为385~1605Ma,并且多数集中于600~900Ma,二阶段Nd模式年龄范围为582~650Ma,这表明源岩为幔源新生地壳物质,代表了新元古代一次地壳增生。综合岩石学、岩石地球化学和同位素地球化学数据,我们认为京格斯台碱性花岗岩是由新生地壳,在晚石炭世贺根山洋闭合后的后造山伸展阶段,在上涌软流圈的加热及减压作用下部分熔融形成的,形成于后造山构造环境。     

Evolution of the Mesozoic Granites in the Xiong''ershan-Waifangshan Region,Western Henan Province,China,and Its Tectonic Implications

Based on the new data of isotopic ages and geochemical analyses, three types of Mesozoic granites have been identified for the Xiong'ershan-Waifangshan region in western Henan Province: high-Ba-SrⅠ-type granite emplaced in the early stage (～160 Ma),Ⅰ-type granite in the middle stage (～130 Ma) and anorogenic A-type granite in the late stage (～115 Ma). Geochemical characteristics of the high-Ba-SrⅠ-type granite suggest that it may have been generated from the thickened lower crust by partial melting with primary residues of amphibole and garnet. Gradual increase of negative Eu anomaly and Sr content variations reflect progressive shallowing of the source regions of these granites from the early to late stage. New 40Ar/39Ar plateau ages of the early-stage Wuzhangshan granite (156.0±1.1 Ma, amphibole) and middle-stage Heyu granite (131.8±0.7 Ma, biotite) are indistinguishable from their SHRIMP U-Pb ages previous published, indicating a rapid uplift and erosion in this region. The representative anorogenic A-type granite, Taishanmiao pluton, was emplaced at～115 Ma. The evolution of the granites in this region reveals a tectonic regime change from post-collisional to anorogenic between～160 Ma and～115 Ma. The genesis of the early- and middle-stageⅠ-type granites could be linked to delamination of subducted lithosphere of the Qiniing orogenic belt, while the late-stage A-type granites represent the onset of extension and the end of orogenic process. In fact, along the Qiniing -Dabie-Sulu belt, the Mesozoic granitoids in western Henan, Dabieshan and Jiaodong regions are comparable on the basis of these temporal evolutionary stages and their initial 87Sr/86Sr ratios, which may suggest a similar geodynamic process related to the collision between the North China and Yangtze cratons.     

朝鲜~19亿年侵入岩的岩石类型与构造背景初探

朝鲜半岛北部广泛发育~19亿年侵入岩,这些岩浆岩可以分为三个系列,分别为似斑状花岗岩系列(多为I型,以妙香山岩体为代表,年龄1900~1840Ma)、S型花岗岩系列(以嘉山岩体为代表,本文获得1862±5Ma锆石U-Pb年龄)和正长岩系列(以龙浦岩体为代表,本文获得1857±2Ma锆石U-Pb年龄)。似斑状花岗岩系列(I型花岗岩)大致对应朝鲜地质学家定义的Myohyangsan(妙香山)杂岩,以发育钾长石巨斑为特征,与麻粒岩相变质的火山岩-沉积岩系关系密切;S型花岗岩系列大致对应Ryonhwasan(莲花山)杂岩,以发育石榴石和堇青石等矿物为特征,与麻粒岩相变质的副变质岩共生:这说明前者可能与变质火山岩系相关,而后者可能和副变质岩相关。正长岩系列,朝鲜地质学家称为Sakju(朔州)杂岩,分布较为局限,仅见于朔州以及博川-定州之间,也见于邻区辽东,多为岩株。这三个系列岩浆岩稍早或者同期于角闪岩相-麻粒岩相变质(本文获得甑山"群"变质锆石U-Pb年龄1844±2Ma)。邻区辽东-吉南及胶东地区也发育这三个系列岩浆岩,但这两个地区~21亿年岩浆作用更为广泛。朝鲜半岛南部发育大量同期岩浆岩,但岩石类型以似斑状花岗岩为主,并发育紫苏花岗岩和斜长岩。我们推测,朝鲜半岛南北两侧基底属性存在差异,可能对应不同的古陆(华北与华南古陆)。综合分析表明,朝鲜~19亿年前广泛发育I型和S型花岗岩,并有幔源岩浆作用,同时发育正长岩类,并且这些岩浆活动与区域高级变质作用时代接近。考虑到本区存在太古宙基底,我们推测本区在古元古代可能处于类似现今活动大陆边缘弧背景。     

辽东地区连山关岩体锆石U-Pb一致线年龄特征及其意义

本文以连山关花岗岩体为例，指出该区古老花岗岩体2种锆石可以作出3组U-Pb一致线交点年龄，分析了这3组年龄间的相互关系及其所代表的意义，并提出一种可能求出岩体上限年龄的方法。     

从哥伦比亚超大陆裂解事件论古/中元古代的界限

国际前寒武纪地层表中始终把古/中元古代的界线置于1. 6Ga,我国则一直将这一界线置于1. 8Ga。存在认识分歧的根本原因是对1. 8Ga前后时期地质事件及其性质的理解与认识的差异或偏颇。本文通过阐述1. 8～1. 6Ga期间地质事件及其性质,重点分析和讨论古/中元古代(界)界限的划分及相关地质事件的标志与意义。大量的地质资料显示,超大陆从1. 8～1. 75Ga开始裂解,形成一系列的陆内盆地,如北美(劳伦古陆)的Thelon盆地、澳大利亚北部的Leichhardt超级盆地、南美巴西圣弗兰西斯科盆地、华北南缘的熊耳裂谷盆地以及扬子地块西南缘的东川盆地等。在这些盆地形成的早期沉积了冲积扇相、河流相的碎屑岩,之后伴有较广泛的火山岩喷发,中晚期从河流相、湖相碎屑岩沉积过渡到浅海碳酸盐台地沉积,反映一个拉伸裂解的过程。在复原的哥伦比亚超大陆内,广泛分布有1. 78～1. 72Ga的非造山花岗岩,包括AMCG组合(斜长岩、纹长二长岩、紫苏花岗岩和花岗岩)、环斑花岗岩、A型花岗岩等,以及广泛分布的基性岩墙群。这些岩浆岩都反映了拉伸裂解的地球动力学背景。在1. 8～1. 6Ga,不论是沉积事件还是岩浆事件,绝大部分与超大陆的拉伸裂解有关,并未显示造山作用、大陆固结和克拉通化的特点,用固结纪来概括这一阶段地质事件的性质并不合适。哥伦比亚超大陆上的许多盆地在1. 6Ga左右经历了一次广泛的抬升,使沉积作用短时间间断,之后原有盆地继续发展,接受了更广泛的沉积,这种沉积作用可以一直延续到1. 4～1. 3Ga左右。与裂解有关的岩浆事件也以幕式方式从1. 78Ga一直断续持续到1. 4～1. 32Ga左右。从1. 8Ga(或1. 78Ga)到1. 4～1. 3Ga,不论是盆地的沉积事件还是与裂解有关的岩浆事件,基本是连续的。以1. 6Ga作为年代界线划分古/中元古代,人为地隔断了连续的沉积事件和岩浆事件,显然与"尽可能少地截断沉积作用、火成侵位或造山运动的主要序列"的前寒武纪地层划分原则相悖。连续的裂谷盆地沉积事件和非造山岩浆事件可以追溯到1. 8Ga(或1. 78Ga)。因此,我们建议将古/中元古代的界线置于1. 8Ga或1. 78Ga。考虑到裂谷作用的本质是在已有超大陆或克拉通的基础上盖层的发育过程,因此我们建议将～1. 8Ga或1. 78～1. 4Ga都归入盖层系。     

K-Ar Ages of Granitic Magmatism and Related Pegmatite Formation at the Umanotani-Shiroyama Mine, Shimane Prefecture, SW Japan and Their Bearings on Cooling History

Abstract. The Umanotani-Shiroyama pegmatite deposits, the largest producer of K-feldspar and quartz in Japan, are of typical granitic pegmatite. Ilmenite-series biotite granite and granite porphyry, hosting the ore deposits, and biotites separated from these rocks yielded K-Ar ages ranging from 89.0 to 81.4 Ma and 95.2 to 93.7 Ma, respectively. Muscovite and K-feldspar separated from the ore zone yielded K-Ar ages with the range of 96.2 to 93.1 Ma and 87.3 to 80.7 Ma, respectively. Muscovites from quartz-muscovite veins in the ore zone and in the granite porphyry yielded K-Ar ages of 90.4 and 76.3 Ma, respectively. K-feldspar is much younger in age than coexisting muscovite. It is noted that the K-Ar ages of biotite separates and the whole-rock ages are identical to those of muscovite and K-feldspar in the ore zone, respectively. These time relations, as well as field occurrence, indicate that the formation of the pegmatite deposits at the Umanotani-Shiroyama mine is closely related in space and time to a series of granitic magmatism of ilmenite-series nature. Using closure temperatures of the K-Ar system for biotite and K-feldspar (microcline), cooling rate of the pegmatite deposits is estimated to be about 82C/m.y. at the beginning, but slowed down to about 15C/m.y. in the later period.     

花岗岩的成岩时代、地球化学特征和成因青海祁漫塔格地区虎头崖矿床Ⅵ矿带

利用 LA ICP MS 锆石 U Pb 法,测得与成矿有关的青海祁漫塔格地区虎头崖矿床Ⅵ矿带花岗岩的成岩年龄为(233.6±1.8)Ma(MSWD=1.2,n=17)。地球化学特征显示：花岗岩属高钾钙碱性、弱过铝质花岗岩;样品的稀土元素组成以总体右倾,轻、重稀土分异明显和具明显的负铕异常为特征;微量元素具有富集 Rb、Th、U、La、Nd 等大离子亲石元素,亏损 Ba、Sr、Nb、P、Ti 等元素的特点。Sr Nd 同位素组成特征显示,花岗岩的源区可能是富集岩石圈地幔。初步研究认为,虎头崖矿床Ⅵ矿带花岗岩可能形成于中、晚三叠世碰撞后碰撞的构造背景下。