Zircon U–Pb age and trace element evidence for Paleoproterozoic granulite-facies metamorphism and Archean crustal rocks in the Dabie Orogen

Zircon U–Pb ages and trace elements were determined for granulites and gneiss at Huangtuling, which are hosted by ultrahigh-pressure metamorphic rocks in the Dabie Orogen, east-central China. CL images reveal core–rim structure for most zircons in the granulites. The cores show oscillatory zoning, relatively high Th/U ratios, and HREE enriched patterns, consistent with a magmatic origin. They gave a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 2766 ± 9 Ma, interpreted as dating magma emplacement of the protolith. The rims are characterized by sector or planar zoning, low Th/U ratios, negative Eu anomalies and flat HREE patterns, consistent with their formation under granulite-facies metamorphic conditions. Zircon U–Pb dating yields a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 2029 ± 13 Ma, which is interpreted to record a metamorphic event, possibly during assembly of the supercontinent Columbia. The gneiss has a protolith age of 1982 ± 14 Ma, which is younger than the zircon age of the granulite-facies metamorphism, suggesting a generally delay between HT metamorphism and the intrusion of post-collisional granites. A few inherited cores with igneous characteristics have ²⁰⁷Pb/²⁰⁶Pb ages of 2.90, 3.28 and 3.53 Ga, suggesting the presence of Mesoarchean to Paleoarchean crustal remnants in the Yangtze Craton. A few Cretaceous metamorphic ages were also obtained, suggesting the influence of post-collisional collapse in response to Cretaceous extension of the Dabie Orogen. It is inferred that the recently discovered Archean basement of the Yangtze Craton occurs as far north as the Dabie Orogen.     

天山冰达坂和拉尔敦达坂花岗片麻岩SHRIMP锆石年代学特征及其地质意义

西天山冰达坂和拉尔敦达坂地区出露前寒武纪花岗片麻岩,具有变余花岗结构和眼球状构造,表明经历了明显的动力变质作用;SHRIMP锆石U-Pb年代学测试表明它们分别形成于（926±8）Ma和（948±8）Ma,代表了9～10亿年左右的一次重要地质热事件,其中冰达坂花岗片麻岩分析数据中有一颗锆石的年龄为1．4Ga,与前人所报道的天山地区更古老的一期岩浆作用时代相同,可能代表了古老地壳物质的残留锆石。结合前人研究成果认为,天山地区普遍存在这一时期的岩浆作用,可能与Rodinia超大陆聚合过程中的Grenville造山运动有关。     

北秦岭造山带西段早古生代榴辉岩相变质岩石的发现及其地质意义SCIEI北大核心CSCD

西秦岭地处中国中央造山系东西转换衔接部位,随着东秦岭以及祁连、柴北缘和东昆仑早古生代高压-超高压变质岩石的陆续发现和深入研究,西秦岭造山带变质作用研究吸引了大家的普遍关注。本文在大范围野外地质调查基础上,在北秦岭造山带西段天水南部的秦岭岩群长英质片麻岩中发现了一套石榴子石斜长角闪岩(榴闪岩),并开展了详细的锆石形貌和内部结构、微区微量元素和U-Th-Pb同位素研究。CL图像显示榴闪岩锆石普遍具有核-幔-边或核-边结构,部分存在原岩残留锆石。定年结果得到榴闪岩原岩残留锆石年龄为710±52Ma,同时得到497±3Ma、452±3Ma和423±7Ma三期变质年龄。其中497±3Ma变质年龄来自锆石核部并显示出轻稀土亏损、重稀土平坦且没有明显负Eu异常的稀土配分曲线特征,表明该时期的矿物组合中有石榴子石但没有斜长石,与榴辉岩相变质锆石特征一致;452±3Ma变质年龄来自锆石幔部或边部,对应测点重稀土元素的分异加大,并出现弱的负Eu异常,说明此时石榴子石被消耗且出现少量斜长石;423±7Ma变质年龄来自锆石的最边部,对应稀土配分曲线表现出更明显的负Eu异常和更大的重稀土元素分异特征,指示此时岩石中石榴子石含量更少,斜长石含量更多。上述结果表明该榴闪岩可能经历了~500Ma的榴辉岩相变质作用,并在~450Ma和~420Ma叠加了两期退变质改造。天水地区榴闪岩无论是其野外产状,还是变质锆石的形貌和内部结构、稀土配分曲线特征及其所记录的原岩和三期变质年龄都与北秦岭造山带东段大陆俯冲型高压-超高压变质榴辉岩近乎一致,指示早古生代时期,北秦岭造山带西段与东段经历了相似的大陆(深)俯冲和折返过程,它们共同构成一条统一的早古生代高压-超高压变质岩带。     

The Tectonic Implications of the Hongliuhe-Xichangjing Ophiolitic Mélanges Belt in the Central Region of the Beishan Orogen, NW China — Constrained by the U-Pb Ages of Detrital Zircons of the Metasandstones

The tectonic attributes of different blocks within orogenic belts are of great significance for the study of accretionary processes and the evolution of Earth. The Hongliuhe-Niujianzi-Baiyunshan-Xichangjing ophiolitic mélange belt(HXOMB) is distributed in the heart of the Beishan Orogen, the Shuangyingshan and Minshui-Hanshan blocks being distributed in the south and north of the HXOMB respectively, and a large number of Early Paleozoic geological units are exposed on the blocks. According to the zircon age populations of the metasandstones in the Baiyunshan area recovered in this paper, when compared with the zircon age populations of the Paleozoic metasandstones reported in the Niujuanzi and Hanshan areas, we found that the metasandstones of the Shuangyingshan Block have age peaks at c. 598 Ma, 742 Ma, 828 Ma, 941 Ma, 990 Ma, 1168 Ma, 1636 Ma, 2497 Ma with non-significant age populations of 1500–1300 Ma, showing a possible affinity with the Tarim Craton; the metasandstones of the Minshui-Hanshan Block have age peaks at c. 606 Ma, 758 Ma, 914 Ma, 1102 Ma, 1194 Ma, 1304 Ma, 1672 Ma with significant age populations of 1500-1300 Ma, showing a possible affinity with the Chinese Central Tianshan Block. Therefore, the HXOMB of the Beishan Orogen is of great significance in plate segmentation, which separates the Tarim Craton in the south and the Chinese Central Tianshan Block in the north. Based on the evolutionary process of the Hongliuhe-Xichangjing ocean in the Beishan Orogen, we believe that break-up and convergence can be recognized as having occurred twice between the Chinese Central Tianshan Block and the Tarim Craton since the Mesoproterozoic in the Beishan area. This was related firstly to the break-up of the Columbia Supercontinent and the convergence of the Rodinia Supercontinent, mainly during the Middle Mesoproterozoic to Early Neoproterozoic, and secondly to the opening and closing of the Hongliuhe-Xichangjing ocean, mainly during the Early Paleozoic.     

河南银洞沟银金钼矿床铼-锇同位素定年和加里东期造山-成矿事件

河南内乡银洞沟银金钼矿床是夏馆银多金属矿田新发现的造山型矿床,赋矿地层为新元古代-早古生代弧后盆地堆积的二郎坪群火山-沉积岩系,二郎坪群在志留纪或加里东运动中遭受区域变形和变质.矿床5件辉钼矿Re-Os同位素模式年龄介于423.4±4.4～432.2±3.4Ma,加权平均年龄为429.3±3.9Ma(MSWD=0.73),指示秦岭地区存在显著的加里东期造山-成矿事件.     

西昆仑东段苏巴什洋向北俯冲:来自早—中二叠世火山岩的证据

西昆仑东段苏巴什蛇绿构造混杂岩带南侧卡拉勒塔什群以大面积分布的酸性和中基性火山岩为特征,本次对卡拉勒塔什群弧火山岩代表性的岩石组合进行了LA-ICP-MS锆石U-Pb年龄、地球化学及锆石Lu-Hf同位素研究。研究结果表明,LA-ICP-MS锆石U-Pb测年获得酸性晶屑凝灰岩、蚀变玄武岩²⁰⁶Pb/²³⁸U加权平均年龄为(284.2±1.6) Ma和(262.6±2.0) Ma,表明研究区卡拉勒塔什群火山岩形成于早—中二叠世。卡拉勒塔什群火山岩具有富铝、钠、铁,富集大离子亲石元素K、Rb、Ba和亏损高场强元素Sr、Ta、Nb、Ti的地球化学特征。其中,基性火山岩属钙碱性-拉斑玄武岩系列,岩石稀土元素配分模式接近大洋拉斑玄武岩,Nd/Th和La/Nb比值为8.91~13.76和0.39~2.28,Lu-Hf同位素ε_Hf(t)值为-0.15~4.95,表现为地幔物质来源,但加入了地壳组分。酸性火山岩属于钙碱性系列,相对亏损P和Zr元素,Nd/Th和La/Nb比值为1.92~4.10和2.52~3.39,Lu-Hf同位素ε_Hf(t)值分别为0.94~3.78和8.26~12.45,二阶段模式年龄分别为1.07~1.25 Ga、0.51~0.78 Ga,表明酸性火山岩物质来源为古老地壳和新生地壳物质重熔后的混合物。卡拉勒塔什群总体地球化学特征表现为岛弧环境。卡拉勒塔什群岛弧火山岩与北侧苏巴什蛇绿构造混杂岩带在形成时代、空间分布以及基性岩地球化学特征均表现成对关系,与苏巴什蛇绿构造混杂岩带内发育的硫磺达坂砂岩组深水复理石建造共同构成造山带沟-弧-盆体系,表明苏巴什洋盆由南向北的俯冲极性,说明苏巴什蛇绿构造混杂岩形成于岛弧偏向于海沟的弧前盆地构造背景。     

勉略构造带庄科岩片洋壳型变玄武岩锆石U-Pb年龄和Lu-Hf同位素特征:新元古代勉略洋盆存在的直接证据

庄科岩片位于南秦岭南缘勉略构造带.前人系统的岩石地球化学研究表明,庄科岩片变玄武岩属拉斑玄武岩系列,整体表现出N-MORB特征,为勉略洋盆残余,但一直未获得高精度的测年数据.本文首次获得庄科岩片洋壳型变玄武岩LA-ICP-MS锆石U-Pb年龄为999±4Ma(MSWD=0.08,n=25)、991±6Ma(MSWD=1...     

华北克拉通中部造山带中条山地区绛县群地层划分与构造背景

中条山地区是华北克拉通中部造山带的重要组成部分,保存了中部造山带演化的重要记录。绛县群划分为横岭关亚群和铜矿峪亚群,横岭关亚群为一套由石英岩和绢云片岩组成的变质碎屑岩;铜矿峪亚群则以酸性、基性火山岩为主,夹有正常沉积碎屑岩的“双峰式”火山岩。本文对绛县群岩石组合及地层特征开展详细调查研究,经过对绛县群火山岩、侵入岩和碎屑锆石同位素年龄的综合分析,认为绛县群的形成年龄大约在2200~ 2120Ma之间,时代为古元古代。结合碎屑岩、火山岩的地球化学特征和华北克拉通中部造山带的演化过程,推测绛县群形成的构造环境很可能为古活动大陆边缘。其中,横岭关亚群沉积在活动大陆边缘盆地,而铜矿峪亚群则形成于活动大陆边缘火山弧环境。     

河南商城地区石门冲组时代归属及其构造背景

分布于桐柏-大别造山带北缘的石门冲组,由一套片岩、石英岩、大理岩等变质岩系组成,厚约1000 m。该地层的时代、构造归属一直存在较大争议。通过岩石组合、碎屑锆石同位素年代学和地球化学研究,进一步明确了石门冲组地层时代,恢复了原岩类型和沉积环境。最年轻的碎屑锆石年龄为449±12 Ma(YSG),表明石门冲组属于上奥陶统凯迪阶(钱塘江阶)。原岩主要为石英砂岩-长石砂岩-岩屑砂岩-页岩-白云岩组合,形成于滨-浅海环境。碎屑锆石最小年龄、年代相和沉积环境可以与佛子岭群下部祥云寨组相对比,应该属于原商城群的一部分。石门冲组形成于被动大陆边缘构造背景,物源区主要为类似于北秦岭奥陶纪岛弧、新元古代的扬子基底以及秦岭地块的中元古代基底等。