华北陆块南缘熊耳群形成时代讨论

分布于豫、晋、陕3省的熊耳群火山岩系不整合覆盖于太古界及下元古界结晶基底之上,其上被汝阳群、官道口群等陆源碎屑岩-碳酸盐岩地层不整合覆盖.已有的各种熊耳群年龄资料为1.40～1.85 Ga,故常认为其形成标志着中元古代的开始,并将它与蓟县剖面的长城系对比.豫西熊耳山地区马家河组顶部的流纹斑岩和侵入于鸡蛋坪组的辉石闪长岩的单颗粒锆石U-Pb和激光探针等离子体质谱(LP-ICPMS)年龄表明:熊耳群形成于古元古代1.75～1.95 Ga,早于长城系;火山喷发开始于1.95 Ga±,中心可能在豫西的熊耳山或崤山地区,形成豫西崤山、熊耳山、外方山地区的许山组和鸡蛋坪组;大约在1.85 Ga±,火山活动可能以崤山地区为中心呈三叉裂谷系分别向西、东和北3个方向发展,形成覆盖全区的马家河组;末期(1.75 Ga±)可能仅在豫西地区形成次火山-侵入岩——辉石闪长岩类.不整合覆盖于熊耳群之上的汝阳群云梦山组和官道口群高山河组的形成时代相当于长城系.     

苏南晚二叠世末期双峰次火山岩的发现和单颗粒锆石U－Pb年代学意义

苏南晚二叠世末期双峰次火山岩的发现和单颗粒锆石Ｕ－Ｐｂ年代学意义方中，李惠民，夏邦栋，楚雪君，刘寿和，王学锋（南京大学地球科学系，江苏南京，２１０００８；天津地质矿产研究所，天津，３００１７０）关键词晚二叠世，双峰火山岩，同生锆石，捕虏晶锆石，Ｕ－Ｐ...     

苏南晚二叠世末期双峰次火山岩的发现和单颗粒锆石U－Pb年代学意义

苏南晚二叠世末期双峰次火山岩的发现和单颗粒锆石Ｕ－Ｐｂ年代学意义方中，李惠民，夏邦栋，楚雪君，刘寿和，王学锋（南京大学地球科学系，江苏南京，２１０００８；天津地质矿产研究所，天津，３００１７０）关键词晚二叠世，双峰火山岩，同生锆石，捕虏晶锆石，Ｕ－Ｐ...     

秦岭造山带商南-西峡地区富水杂岩的变辉长岩中斜锆石与锆石U-Pb同位素年龄的差异

秦岭造山带富水杂岩体的一些变辉长岩含有粒度较大且U、Pb含量较高的斜锆石和锆石,是U-Pb同位素测年的极好矿物.对该杂岩体的中粗粒角闪黑云辉长岩中的斜锆石和锆石分别进行了SHRIMP法和TIMS法U-Pb同位素年龄测定,获得斜锆石和锆石的U-Pb同位素年龄分别为501.4 Ma±1.2 Ma和480.0 Ma±3.4Ma,两者相差约20 Ma.对该岩石中部分斜锆石向锆石转化的现象及锆石的成因进行了初步研究,认为斜锆石的U-Pb同位素年龄应解释为秦岭富水杂岩中基性岩石的形成时代,而锆石的成因及其U-Pb同位素系统在变质作用过程中的变化比较复杂,对其U-Pb同位素年龄地质意义的合理解释需做进一步的研究.     

山东招掖金矿带花岗岩类单颗粒锆石U—Pb年代学研究及其意义

在占我国最著名的金矿域－胶北金矿域的金矿储量８６．３％的招掖金矿带内,广泛分布的燕山期花岗岩类与金矿化作用密切相关。然而,这些花岗岩类的形成时代却是长期困扰地学界的棘手问题,并一直阻碍着有关金矿化问题的探讨。精确的单颗粒锆石Ｕ－Ｐｂ年代学研究表明,招掖金矿带内花岗岩类：玲珑型花岗岩和廓家岭花岗闪长岩均形成于１４５Ｍａ（分别为１４５．９±０．５Ｍａ和１４４．１±０．８Ｍａ）左右的燕山早期（晚侏罗世）     

从第30届国际地质大会看同位素地质年代学的最新发展

本文从同位素地质年代学的实验技术和应用领域两方面，概述同位素地质年代学的最新进展，供参考。     

U-Pb isotopic geochemistry of the post-collisional mafic-ultramafic rocks from the Dabie Mountains——Crust-mantle interaction and LOMU component

Geochronological studies of mafic-ultramafic intrusions occurrence in the northern Dabie zone (NDZ) suggest that these pyroxenite-gabbro intrusions formed 120—130 Ma ago should be post-collisional magmatic rocks[1—4]. These mafic-ultramafic rocks provid…     

Time and tectonic setting of the Xixiang Group: Constraints from zircon U-Pb geochronology and geochemistry

The present paper reports the research development in the timing and tectonic setting of the Xixiang Group, northwestern margin of the Yangtze block. U-Pb concordant ages of (946 ± 18) Ma and (904±18) Ma of zircons were obtained from the upper and lower units of the Xixiang volcanic succession, respectively. Elemental and Nd isotope characteristics show that the volcanic suite has the affinities of arc island magmatism as well as an evolution trend of tectonic setting from front-arc to back-arc. The volcanic rocks suffered from some extensive post-stage tectono-thermal events, resulting in the resetting of their Rb-Sr isotopic system.     

U-Pb dating of early Mesozoic granodioritic intrusions in southeastern Hunan Province, South China and its petrogenetic implications

The NE-trended Mesozoic granodioritic intrusions are spatially and temporally associated with the copper multi-metal mineralization in southeastern Hunan Province, South China. U-Pb dating result of single-grained zircons of four samples respectively from Shuikoushan, Baoshan, western Tongshanling and eastern Tongshanling intrusions reveals that their crystallization age spans a range from 172 Ma to 181 Ma, which also represents the oldest age of the regional copper multi-metal mineralization. Some of the zircon grains give an upper intercept age of about 1753 Ma and ²⁰⁷Pb/²⁰⁶Pb apparent age of (1752 ± 4) Ma, implying the involvement of the pre-Cambrian metamorphic (possible Middle Proterozoic) basement in their genesis. The presence of such a kind of zircon grains in these granodiorites indicates either that the parental magmas were assimilated by basement rocks during magma ascent or that lower/middle crustal rocks were one of the important components during the melting process.     

大别山北部漫水河灰色片麻岩的锆石UPb年龄及其地质意义

北大别杂岩主要由灰色片麻岩和斜长解闪岩组成。通过对大别山北部霍山漫水河花岗闪长片麻岩的锆石U-Pb年龄测定，得到中元古代、早三叠世和晚侏罗世3组年龄数据。中元古代的年龄老于灰色片麻岩集中在新元古代的锆石U-Pb上交点年龄，指示漫水河北部片麻岩中有古老锆石捕掳晶；早三叠世年龄指示该片麻岩中有印支期变质作用形成的锆石；晚侏罗世年龄表明灰色片麻岩中有燕山早期形成的岩浆锆石。根据北大别杂岩的构造背景、变质作用及地球化学特征，认为北大别杂岩中的部分灰色片麻岩形成于燕山早期的花岗闪长岩，它们可能源自或混染了经过早三叠世变质作用的扬子陆块俯冲基底。本文的结果表明，北大别杂岩既不是形成于白垩纪的岩浆杂岩，也不完全是形成于新元古代的TTG岩系，其中的部分灰色片麻岩为形成于燕山早期的花岗闪长岩，即在白垩纪大规模岩浆作用前的燕山早期，北大别曾有过一次岩浆作用。