排山楼金矿床40Ar-39Ar年龄及其地质意义

采用Ar-Ar同位素测年法对辽宁排山楼金矿床矿化阶段形成的钾长石和似斑状花岗岩中的钾长石进行了测试,获得矿化阶段形成钾长石40Ar-39Ar坪年龄为(116.69±1.15)Ma,等时线年龄为(116.97±1.39)Ma,以及似斑状花岗岩中原生钾长石40Ar-39Ar坪年龄为(126.71±2.03)Ma,等时线年龄为(124.00±4.32)Ma的数据.前者代表了该矿床的形成年龄,即该矿床形成于早白垩世,后者表明金矿化不早于(126.71±2.03)Ma.这一成矿年龄与华北陆块北缘大部分金矿床的成矿年龄一致,表明华北陆块北缘绝大多数金矿床形成于中国东部中生代动力学体制发生转折的时期.     

宁芜玢岩铁矿钠长石40Ar-39Ar定年及意义

梅山铁矿主矿体下部钠长石岩带和陶村铁矿的钠长石岩带中钠长石的 40 Ar-39 Ar测定结果表明,2件样品的坪年龄分别为(122.90±0.16)和(124.89±0.30)Ma,相对应的等时线年龄分别为(122.60±0.16)和(124.90±0.29)Ma.通过对长江中下游中生代地球动力学演化分析,认为玢岩铁矿成矿亚系列形成于岩石圈大规模拆沉作用和郯庐断裂带发生强烈左行走滑的环境下,而夕卡岩型-斑岩型铜、钼、金成矿亚系列形成于应力转换期.     

西藏南部羊应乡后碰撞火山岩40Ar/39Ar年龄及其地质意义

通过西藏羊应乡地热田 4个高钾火山岩样品进行的快中子4 0 Ar/39Ar阶段升温定年结果 ,并结合其岩石地球化学研究数据 ,确定该地热田后碰撞火山作用发生在 (10 .73± 0 .0 9)～ (11.4 0±0 .11)Ma之间 ,形成与加厚下地壳 ,构造环境与岩石圈地幔减薄有关 .通过对青藏高原南部冈底斯地区新近纪火山岩同位素年龄的展布的进一步分析 ,认为后碰撞高钾火山岩在该区广泛存在 ,并有由西向东逐渐年轻的趋势 .     

福建省新生代玄武岩40Ar/39Ar年代学及地质意义

对福建省沿海至内陆出露的4件新生代玄武岩进行⁴⁰Ar/³⁹Ar年龄测试,对玄武岩中橄榄石斑晶进行电子探针测试;其中洋底和柳城玄武岩首次获得精确的⁴⁰Ar/³⁹Ar年龄数据.结果显示,闽西明溪⁴⁰Ar/³⁹Ar年龄数据为(1.44±0.11)Ma,柳城为(17.35±0.93)Ma;闽中洋底玄武岩年龄为(11.71±0.44)Ma;闽东厦门玄武岩年龄为(17.0±0.36)Ma.结合前人年龄数据,福建省新生代玄武岩整体表现出从闽东至闽西年龄逐渐减小的趋势.橄榄石斑晶电子探针数据显示闽东至闽西玄武岩碱性程度逐渐增加,可能指示岩浆熔融程度由沿海至内陆逐渐减少,岩石圈厚度由东向西逐渐增厚.最新获得的闽西柳城玄武岩⁴⁰Ar-³⁹Ar年龄为(17.35±0.93)Ma,与东部沿海玄武岩相似,推测可能是太平洋板块北西向俯冲时引起的岩浆扰动作用形成的.     

40Ar-39Ar ages of the Louzidian-Dachengzi ductile shear zone near Chifeng,Inner Mongolia and their tectonic significance

The Louzidian normal fault occurs as the eastern detachment fault of the Kalaqin metamorphic core complex. Field observations and microstructural analyses reveal that the Louzidian-Dachengzi ductile shear zone developed in its lower-plate was genetically related to sinistral strike-slips and extensional faulting. Two samples from this ductile shear zone yield 40Ar-39Ar plateau ages of 133 Ma (Bi) and 126 Ma (Kp), which are concordant with their isochron ages. The plateau age of 133 Ma (Bi) records the formation age of the ductile shear zone. The inconsistent relationship between the earlier strike-slip ductile shear zone and the later normal fault makes the Kalaqin Quasi-metamorphic core complex distinctive from Cordilleran metamorphic core complex. These ages provide important geochronological data for putting constraints on the formation age and genesis of such ductile shear zones.     

40Ar-39Ar thermochronology of two ductile shear zones from Yiwulüshan, West Liaoning Region: Age constraints on the Mesozoic tectonic events

Two ductile shear zones trending EW and NNE respectively not only controlled the tectonic framework of the northern North China, but also constrained the geodynamic background for gold mineralization in this region. Field observations and microstructural analyses reveal that the EW trending ductile shear zones are mainly contributed to dextral compressional deformation resulting from top-to- the-southeast oblique thrust shearing, whereas the NNE trending ones are genetically related to sinistral strike-slip and extensional faulting. One sample from the former yielded an 40Ar-39Ar plateau age of (219±4) Ma (Bi) and two samples from the latter gave 40Ar-39Ar plateau ages of (116±2) Ma (Bi) and (127±3) Ma (Bi). These ages provide constraints on the top-to-the-southeast oblique thrusting event occurring in Late Triassic and the sinistral extensional and strike-slip faulting event which occurred in Early Cretaceous.     

^40Ar／^39Ar geochronological constraints on syn-orogenic strike-slip movement of Tan-Lu fault zone

Two phases of sinistral strike-slip ductile shear belts occur on the eastern margin of the Dabie orogenic belt. A muscovite ~(40)Ar/~(39)Ar plateau age of 128 Ma was obtained from mylonite in the later ductile shear zone. Three muscovite samples separated from mylonites of 3 localities in the earlier ductile shear belts yield ~(40)Ar/~(39)Ar plateau ages of 192.5±0.7 Ma, 189.7±0.6 Ma and 188.7±0.7 Ma, respectively. They are interpreted as cooling ages of the earlier sinistral strike-slip deformation. It is suggested that left-lateral displacement of the Tan-Lu fault zone started in a late stage of the collision orogeny in the Dabie-Sulu orogenic belt between the North and South China plates. Therefore, the earlier Tan-Lu fault zone was syn-orogenic strike-slip tectonics. The fault zone was used again for sinistral displacement during tectonic activities of peri-Pacific regime in Early Cretaceous. It is proposed that the fault zone occurred as a transform fault during the orogenic process.     

Experiment of the ~(40)Ar/~(39)Ar dating of diagenetic illite in gas reservoirs

40Ar/39Ar dating of diagenetic illite has been performed to investigate gas reservoirs in the Sulige Gas Field of the northern Ordos Basin. A series of technical challenges were confronted, including illite purification, Ar recoil loss, and separation of diagenetic illite from detrital illite. Mineral growth ages for diagenetic illite were obtained by this experiment, from which the age of gas emplacement was deduced to be later than 169 Ma.     

40Ar-39Ar ages of the Louzidian-Dachengzi ductile shear zone near Chifeng, Inner Mongolia and their tectonic significance

The Louzidian normal fault occurs as the eastern detachment fault of the Kalaqin metamorphic core complex. Field observations and microstructural analyses reveal that the Louzidian-Dachengzi ductile shear zone developed in its lower-plate was genetically related to sinistral strike-slips and extensional faulting. Two samples from this ductile shear zone yield ⁴⁰Ar-³⁹Ar plateau ages of 133 Ma (Bi) and 126 Ma (Kp), which are concordant with their isochron ages. The plateau age of 133 Ma (Bi) records the formation age of the ductile shear zone. The inconsistent relationship between the earlier strike-slip ductile shear zone and the later normal fault makes the Kalaqin Quasi-metamorphic core complex distinctive from Cordilleran metamorphic core complex. These ages provide important geochronological data for putting constraints on the formation age and genesis of such ductile shear zones.     

Lasing on pyroclastic rocks:A case study of ~(40)Ar/~(39)Ar dating on Moshishan Group,eastern Zhejiang Province

It is difficult to date pyroclastic rocks,for almost all the dating methods,due to the multiple sources during their formation.40Ar/39Ar incremental heating results on groundmass selected from the samples show that the age spectra are meaningless geologically.However,singe crystal total fusions of CO2 lasing on the sanidine separates could yield rational 40Ar/39Ar results and distinguish their sources in this study.Timing on three formations of the Moshishan Group,after avoiding the exotic and altered grains by lasing on the single sanidine separate,was reported in this paper.The lowermost portion of the Chawan Formation gives an age of 113.7±0.3 Ma;the lower part of the Xishantou Formation was formed 116.4±0.4 Ma ago and the bottom of the Gaowu Formation took its shape at 118.4±0.4 Ma.These new ages are much younger than the previous ones,suggesting that these thick volcanic formations had been formed in very short durations.     

Subduction age of Neo-Tethys oceanic crust in southwest Yunnan, China: Laser micro-area40Ar-39Ar dating

The basic granulite, which is considered to be the MORE based on geochemistry and isotopic characteristics[1], has been discovered recently as the enclaves in the Yingjiang island-arc magmatic suite on the border of Burma and west Yunnan, east of Myitkyina suture in the eastern Burma. The laser micro-area 40Ar-39Ar technique is used to date the age of garnet and cliopyroxene that is the result of the early metamorphic event. The isochron outcome is -74.4 Ma which is induced to be the age of the suduction event of the Myitkyina oceanic crust on the basis of the Cenozoic lithosphere tectonic evolution, tectonic thermal events and the age of deformation and metamorphism. The discovery of the high-grade or high-pressure metamophic rocks in the island-arc magmatic suite by the way of studying its P-T-t paths can provide a good way to study the age and process of oceanic crust subduction, slab break-off, metamorphic terrain exhumation and the evolution of paleoocean basin.     

冀北赤城红旗营子群黑云斜长片麻岩的黑云母~(40)Ar/~(39)Ar年龄及其地质意义

探讨冀北赤城红旗营子群是否经历了印支期的构造热事件。通过对冀北赤城红旗营子群黑云斜长片麻岩样品进行的黑云母40 Ar/39 Ar年龄测定,获得其坪年龄和等时线年龄分别为(238.63±1.44)Ma和(238.77±1.71)Ma,两者基本一致。此年龄数据是黑云斜长片麻岩在晚古生代角闪岩相区域变质作用之后所经历印支期构造热事件的记录。综合分析冀北岩浆作用及其地质年代学特征,认为它可能与区域上同时期的酸性岩浆活动有关,是后者为此次构造热事件提供了必要的热源。