川西龙门山彭灌杂岩地球化学特征:岩石成因与构造意义

对位于扬子地块西缘龙门山逆冲推覆构造带中的彭灌杂岩进行了岩石地球化学研究，重点讨论了岩石成因、成岩物质来源及其构造意义。彭灌杂岩为一新元古代侵入的杂岩体，主要由中酸性侵入岩组成，其地球化学特征表现为SiO2含量变化范围较大（57.70％-71.90％），Na2O〉K2O（K2O／Na2O=0.31-0.85），里特曼指数δ=1.33-2.28，A／CNK=0.93-1.08，彭灌杂岩主体属于准铝质到弱过铝质的钙碱性花岗岩类；稀土总量不高（∑REE=76.25×10^-6-139.80×10^-6），轻重稀土分异程度差别较大（Lan／Ybn=3.86-35.23），弱负到正Eu异常（δEu=0.70-1.86）；富集大离子亲石元素（LILE）Rb、Sr、Ba、K等，亏损高场强元素（HFSE）Nb、Ta、P和Y。与正常壳源钙碱性花岗岩相比，彭灌杂岩显示出更高的Mg#值（多数〉45）和Sr／Y比值（多数20.03-111.34）。通过与其毗邻的埃达克质雪隆包杂岩的比较，表明彭灌杂岩可能是底侵的幔源岩浆与下地壳熔融产物混合的结果。结合其它研究成果，认为扬子西缘新元古代大面积分布的岩浆岩形成于俯冲汇聚和火山弧构造环境。

扬子陆块及周缘地质矿产调查工程进展与规划

中南地区锡、锰、铅锌、金、稀土等资源找矿潜力大,成矿条件有利,中国地质调查局组织实施了扬子陆块及周缘地质矿产调查工程和七个二级项目,全力支撑找矿突破战略行动锰、锡等重点矿种勘查目标的实现。扬子工程近两年来新发现大量矿化点,圈定了一批找矿靶区,总结了区域成矿规律,在扬子古陆核及其东南缘、北缘、华夏陆块群等构造演化等成矿地质背景研究取得较多进展,一批地质调查项目圈定的有利找矿靶区转入矿产勘查。依据国土资源部及地质调查局的工作部署,本文提出下一阶段工作的初步规划,继续在成矿区带开展1∶5万地质矿产调查和科技创新工作,聚焦华南陆块聚散过程中的资源效应和资源潜力评价,助力华南大宗矿种与战略性新兴矿种资源新格局和重要矿产资源基地建设。

扬子地块西南缘前寒武纪铜多金属矿床及成矿系列

文章在分析扬子地块西南缘与前寒武纪铜多金属矿床成矿特征及与有关的重大地质事件的基础上,研究了区域成矿作用与重大地质事件的响应,划分了区域金属成矿系列,较详细地论述了主要成矿系列的组成及成矿规律,总结了扬子地块西南缘前寒武纪铜多金属矿床及成矿系列。认为本区成矿作用属于多期次成矿,至少可以分为前期预富集作用及两次大的成矿作用(古元古代成矿作用和中元古代成矿作用),以及若干个小的成矿作用;1.7Ga—1.5Ga、1.1Ga—1.0Ga、中新生代是3次规模、强度较大的铜矿成矿作用,形成了研究区内规模较大的诸多铜多金属矿床。

Two Types of Granites in the Western Yangtze Block and Their Implications for Regional Tectonic Evolution： Constraints from Geochemistry and Isotopic Data

In the western Yangtze Block, widespread Mesoproterozoic to Neoproterozoic rocks are the key to understanding the Precambrian tectonic-magmatic evolution of the region. However, their petrogenesis and tectonic setting are still controversial. In this paper, zircon U-Pb ages, Sm-Nd isotopic and whole-rock geochemical data are reported from selected fresh samples in the southern Dechang county, southwestern China, in order to constrain their emplacement age and magma source, as well as their petrogenesis and tectonic setting. They are mainly composed of biotite monzogranite, monzonitic granite, biotite granodiorites, and quartz diorite. Two ages of 1055 ± 43 Ma and 837.6 ± 3.8 Ma were obtained through zircon U-Pb dating by LA-ICP-MS and LA-MC-ICP-MS, respectively. According to their major element compositions, the Grenville-age granites are peraluminous calc-alkaline series calcic S-type granite. In contrast, the mid-Neoproterozoic granites are metaluminous calc-aikaline series alkalic I-type granite. Furthermore, the S-type granites are enriched in LREEs relative to HREEs with （La/Yb）N ratios of 3.85-18.56 and underwent major fractionation with strongly negative Eu anomalies （Eu/Eu＊ = 0.38-0.66）. In the MORB-normalized trace element variation diagram, all the samples are enriched in Ce and large ion lithophile elements such as Rb, Th, and K, and depleted in high field strength elements such as Nb, and Ti, with negative Sr and Ti anomalies. The I-type granites are enriched in LREEs with slight negative Eu anomalies （Eu/Eu＊= 0.83-0.93）. They are characterized by the enrichment of highly incompatible elements （such as K, Rb, Ba, Th） and LREEs, relative to MORB. Neodymium isotopic data show that the S-type granites display 143Nd/144Nd values of 0.51241-0.51256, and have eNa （t = 1055 Ma） values of （-3.29） to （-3.81）. Calculated tDM ages yield values from 1.87 to 1.91 Ga with the tDM.2stg ages of 1.86 to 1.9 Ga. The I-type granites have 143Nd/144Nd ratios between 0.51192 and 0.51195, corresponding to initial eNd （t = 837 Ma） values of 1.22 to 5.63. Calculated tDM ages yield values from 1.0 to 1.38 Ga and the tDM.2stg ages yield values from 0.99 to 1.06 Ga. The S-type granites are distinguished as syn-collision granite, whereas the I-type granites were formed as arc magmas according to the Rb-（Yb＋Ta） and R1-R2 tectonic discrimination diagrams. To conclude, there are two types of spatially associated granite, the Mesoproterozoic S-type granite which were derived from re- melting of upper crustal mudstone and/or clastics and resulted from the convergence of two continental plates, and the mid-Neoproterozoic I-type granite which formed in continental arc and resulted from mantle-derived magma mixed crust material, in the western Yangtze Block. Furthermore, we suggest that collision between the Yangtze and Cathaysia blocks occurred at about 1055 Ma, and caused the S- type granite. The I-type granite related to the subduction of oceanic lithosphere eastward underneath the Yangtze Block in the mid-Neoproterozoic.

扬子地块西缘河口群的时代:来自火山岩锆石LA-ICP-MS U-Pb年龄的证据

扬子地块西缘的河口群长期以来被认为是早元古代的火山—沉积地层,这种认识缺乏高精度同位素年龄的支持。为精确标定河口群的时代,采用激光剥蚀等离子体质谱(LA-ICP-MS)对川西南拉拉铜矿区河口群中的石英角斑岩进行锆石U-Pb定年。结果表明所有锆石均为岩浆锆石,单点分析结果均为谐和年龄,锆石207Pb/206Pb加权平均年龄为1722±25Ma(2σ,MSWD=0.5,n=11)。由此认为河口群浅变质火山—沉积岩系的精确沉积时代为1722±25Ma,为早元古代晚期的火山—沉积地层。

Low-Temperature Thermochronology Constraints on the Mesozoic-Cenozoic Exhumation of the Huangling Massif in the Middle Yangtze Block, Central China

The Huangling （黄陵） massif is an important area to understand the tectonic evolution of the northern Middle Yangtze Block. Integrating previously published thermochronology data with new zircon and apatite fission track, and apatite （U-Th）/He thermochronometry, the Meso- Cenozoic exhumation history of the Huangling massif has been quantitatively studied. Based on the data and the time-temperature thermal history modelling results, the exhumation process of the Huangling massif can be divided into four stages： the slow cooling stage during 200-150 Ma; the rapid cooling event at ca. 150-80 Ma; a period of relative thermal stability during ca. 80-40 Ma, and an increase in cooling thereafter. Two rapid cooling/exhumation indicate two tectonic events in the northern Middle Yangtze Block. The rapid exhumation between ca. 150-80 Ma is likely related to a wide range Cretaceous intra-continental reactive and deformation in the eastern China. The accelerated cooling after ca. 40-30 Ma may result from a far-field effect of the India-Asia collision.