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1.
Ages determined with the 40Ar/39Ar isotopic system affirms the Early Cretaceous volcanic activity in the Barton Peninsula, King George Island, Antarctica. Two specimens of basaltic andesite collected from the lowermost volcanic sequence of the peninsula were irradiated and analyzed in different experiments, yielding an identical age spectrum, and two magmatic thermal events of the Early Cretaceous (120.4± 1.6 Ma, 119± 1 Ma) and Early Tertiary (53.1± 1.5 Ma, 52± 1 Ma) are distinguished. The former is interpreted to represent the primary cooling age of basaltic andesite, whereas the latter is the thermal reset age caused by the intrusion of granitic pluton. These new ages clearly indicate that volcanism was active during the Early Cretaceous on the Barton Peninsula and that intensive hydrothermal alteration and mineralization of Mesozoic volcanic rocks resulted from Tertiary magmatism. 相似文献
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Ar/Ar analyses of phengites and paragonites from the ultrahigh-pressure metamorphic rocks (zoisite–clinozoisite schist, garnet–phengite schist and piemontite schist) in the Lago di Cignana area, Western Alps were carried out with a laser probe step-heating method using single crystals and a spot dating method on thin sections. Eight phengite and two paragonite crystals give the plateau ages of 37–42 Ma with 96–100% of 39Ar released. Each rock type also contains mica crystals showing discordant age spectra with age fractions (20–35 Ma) significantly younger than the plateau ages. Phengite inclusions in garnet give ages of 43.2 ± 1.1 Ma and 44.4 ± 1.5 Ma, which are significantly older than the spot age (36.4 ± 1.4 Ma) from the matrix phengites, and the plateau ages from the step-heating analyses. Inclusion ages (43 and 44 Ma) are consistent with a zircon SHRIMP age (44 ± 1 Ma) in this area. These results suggest that the oceanic materials that underwent a simple subduction related UHPM, form excess 40Ar-free phengite and that the peak metamorphism is ca. 44 Ma or little older. We suggest that matrix phengites experienced a retrogression reaction changing their chemistry contemporaneously with deformation related to the exhumation of rocks releasing significant radiogenic 40Ar from the crystals. This has lead to the apparent ages of the matrix phengites that are significantly younger than the inclusion age. 相似文献
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Agung Harijoko Kenzo Sanematsu Robert A. Duncan Sukmandaru Prihatmoko Koichiro Watanabe 《Resource Geology》2004,54(2):187-195
Abstract. The Cibaliung deposit is a low-sulfidation type epithermal gold deposit situated about 70 km west of the Bayah dome complex. The gold-bearing quartz veins are hosted by basaltic andesite of the Honje Formation, which is comparable to the host rock of gold deposits at the Bayah dome complex.
In order to clarify the timing of the mineralization and the volcanism at the Cibaliung area, two radiometric dating methods were applied. First,40 Ar/39 Ar dating was conducted on six adularia samples to elucidate the age of mineralization. Second, K-Ar method was applied to two samples of the host rock, andesite and the Cibaliung tuff, in order to reveal the timing of volcanism.
The40 Ar/39 Ar dating determined mineralization ages in the range from 11.18 to 10.65 Ma while the K-Ar dating indicated the age of the andesite and the Cibaliung tuff to be 11.4±0.8 Ma and 4.9±0.6 Ma, respectively. These results imply that the epithermal gold mineralization in the Cibaliung area is related to the volcanic activity that produced the Honje Formation, while the Cibaliung tuff played an important role in the preservation of the Cibaliung deposit. The Cibaliung deposit is the oldest epithermal gold deposit yet discovered in western Java. 相似文献
In order to clarify the timing of the mineralization and the volcanism at the Cibaliung area, two radiometric dating methods were applied. First,
The
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陕西小秦岭华阳川韧性剪切带的特征
及其区域构造意义 总被引：1，自引：0，他引：1
陕西小秦岭华阳川韧性剪切带发育在新太古界太华群之中,野外调研和显微构造观察结果表明,该韧性剪切带是由构造片岩、眼球状片麻岩组成的深层次韧性剪切带,具有逆冲兼左行走滑的斜冲特征。对韧性剪切带构造片岩黑云母进行^40Ar／^39Ar同位素定年,获得坪年龄为419M±0．6Ma,反等时线年龄为417Ma±0．8Ma。认为华阳川韧性剪切带及其相应的小秦岭区域主导构造变形是发生于419Ma左右的秦岭加里东事件的结果。 相似文献
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新疆富蕴可可托海—二台断裂带中假玄武玻璃及其围岩的年代学研究 总被引：3，自引：0，他引：3
发育在新疆富蕴可可托海—二台断裂带中的假玄武玻璃是古地震断裂快速滑移形成的构造岩。地质产状、显微构造研究表明,这些假玄武玻璃主要由发生重结晶的玻璃质熔融体形成。假玄武玻璃基质的全岩40Ar/39Ar阶段升温方法主阶段和KAr年龄分别为282.8±3.8 Ma和276.4±7.4 Ma。假玄武玻璃所在母岩（黑云母花岗岩和钾长花岗岩）的锆石U-Pb年龄分别为390.4±1.0 Ma和396.3±0.1 Ma,表明二台断裂带中的假玄武玻璃是在二叠世早期形成的,也说明二台断裂带古地震活动至少可以追溯到晚古生代（早二叠世早期）。尽管二台断裂带是现今仍然活动的地震构造带,但目前所见到的假玄武玻璃是早二叠世时期古地震活动的产物。1931年的富蕴80级地震仅仅是沿着二台断裂带发生的多次构造活动的一次活动,与假玄武玻璃之间没有成因上的联系。 相似文献
7.
Franco PIRAJNO 《《地质学报》英文版》2007,81(2)
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. 相似文献
8.
Evolution of the Mesozoic Granites in the Xiong''ershan-Waifangshan Region,Western Henan Province,China,and Its Tectonic Implications 
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下载免费PDF全文 Franco PIRAJNO 《《地质学报》英文版》2007,81(2)
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. 相似文献
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本文报道了藏北羌塘中部才多茶卡地区晚三叠世蓝闪石片岩及蓝闪石矿物的新发现及地质意义。通过对才多茶卡构造混杂岩地质剖面的实测,在剖面第6层灰绿色变基性火山岩(绿片岩)中新发现以产蓝闪石类矿物为特征的中—高压变质岩系——蓝闪石片岩。对蓝闪石片岩的岩石学和矿物学特征进行了详细室内研究。从蓝闪石片岩中挑选出蓝闪石单矿物进行了40Ar/39Ar同位素年龄测定,结果表明,蓝闪石单矿物的坪年龄值为209±4Ma,等时线年龄值为216±4Ma,坪年龄与等时线年龄基本一致,属于晚三叠世诺利期,这与区域上羌塘中部发育的红脊山—双湖蓝闪石片岩的中—高压变质事件相吻合。由于蓝闪石类矿物的产出具有特殊的构造机制和地质意义,因此双湖以东的才多茶卡地区蓝闪石片岩的新发现及蓝闪石矿物的40Ar/39Ar同位素年代学研究进一步补充和丰富了青藏高原腹地羌塘中部龙木错-双湖构造混杂岩带的物质组成和同位素年代学信息,同时也为解决羌塘地区"龙木错-双湖构造混杂岩带是否向东延伸"等重大基础性地质问题,提供了新的重要资料。研究资料表明,羌塘中部自西向东从冈玛错、红脊山、绒马,经嘎尔错到才多茶卡地区,沿构造线方向断续分布的长达600km的含蓝闪石片岩的中—高压变质岩系,都是龙木错-双湖构造混杂岩带印支期构造活动事件的产物。 相似文献
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WU Cailai WANG Fusheng HAO Meiying SHI Rendeng Institute of Geology CAGS Beijing China WANG Zhihong Xi''''an Engineering College Xi''''an China QIAO Dewu Geological mechanics institute CAGS Beijing China 《Continental Dynamics》2000,(1)
1. Introduction Tongling district is situated in the southern part of the middle-lower reaches of the Yangtze River, Anhui province, China (Fig.1). It is one of the most important metal base in China, being rich copper material resources, also named "ancient copper capital of China". Many geologists have been working in petrology, tectonics and ore-deposits in the area for many years. Studies show none of the ore-deposits is not bound up with the intermediate-acid intrusion in the area (Ma… 相似文献
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The Haftcheshmeh porphyry Cu-Mo-Au deposit in the Arasbaran metallogenic belt(AMB) of NW Iran contains more than 185 Mt of ore, with a grade ranging from 0.3% to 0.4%. It is hosted within a porphyritic diorite to granodiorite intruded into an older gabbro-diorite intrusion. 40 Ar/39 Ar analyses of primary magmatic hornblende from the granodiorite porphyry and gabbro-diorite show plateau ages of 26.41 ± 0.59 Ma, with an inverse isochron age of 25.9 ± 1.0 Ma and a plateau age of 27.47 ± 0.17 Ma, with an inverse isochron age of 27.48 ± 0.35 Ma for these two rock types, respectively. Comparing these new age data with those from the nearby Sungun(20.69 ± 0.35 Ma) and Kighal porphyry deposits defines a northwest-southeast Cu-Mo-Au mineralization zone extending for 20 km over the time span of ~27 to 20 Ma. Geochemically, Haftcheshmeh rocks are calc-alkaline with high potassium affinities with tectonic setting in relation to volcanic arc setting. Large ion lithophile elements(LILE) such as Th, U and K show enrichment on a primitive mantle normalized diagram(specially Pb), and are depleted in high field strength elements(HFSE) such as Ti and Nb, pointing to a mantle magma source contamination with crustal materials by subducted oceanic crust. 相似文献
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秦岭岩群中两类斜长角闪岩的性质和时代及其地质意义 总被引：4，自引：2，他引：2
在北秦岭造山带核部秦岭岩群内发育两类不同产状的斜长角闪岩.一类与秦岭岩群中的大理岩紧密共生,呈规模较大的似层状或较小块体产于大理岩内,另一类则呈密集岩墙群型式侵入于秦岭岩群南段二云母石英片岩中.不同的产出状态表明两类斜长角闪岩的成因和时代存在显著差异,也具有不同的地质构造意义.地球化学上,两类不同产状的斜长角闪岩的原岩皆为玄武岩质的.侵入秦岭岩群二云母石英片岩中的斜长角闪岩墙群形成于板内拉张环境,SHRIMP锆石U-Pb测年揭示该类斜长角闪岩形成于晚奥陶世(449±11Ma),Sr-Nd同位素特征显示其岩浆源区为亏损地幔源区,40Ar/39Ar热年代学研究显示该类斜长角闪岩的角闪岩相变质作用发生于石炭纪末期(301.3±6.4Ma).地球化学和Sr-Nd同位素特征显示与秦岭岩群大理岩共生的似层状或块状斜长角闪岩的形成环境与侵入云母石英片岩中的斜长角闪岩墙群的存在显著差异,其形成于洋岛(OIB)或海山环境.40Ar/39Ar热年代学研究显示该类斜长角闪岩于晚二叠世(258.1±5.7Ma)发生了角闪岩相变质作用.不同性质、形成和变质时代、相似的变质作用等特点表明,秦岭岩群中的两类角闪岩分属不同性质的构造块体,秦岭岩群高级变地质地体可能是一个构造拼合地体.斜长角闪岩岩墙为晚奥陶世(449±11Ma)侵入秦岭岩群云英片岩中的基性岩墙群,是北秦岭晚加里东期后造山期热收缩而致的地壳伸展或岩圈拆离减薄的产物.与秦岭岩群大理岩共生的斜长角闪岩则可能是洋隆体的基性喷出岩+碳酸盐岩帽组合,是中二叠世(312～260Ma)期间构造移置而来的外来块体. 相似文献
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西藏林子宗群火山岩氩-氩年代学研究 总被引：25，自引：0，他引：25
通过对西藏冈底斯南带林周盆地中 3个岩组样品的40 Ar 3 9Ar定年 ,初步建立了该剖面林子宗群火山岩形成的同位素年代时序格架 :底部典中组的下限年龄为 6 3.32± 0 .89Ma;中部年波组为 5 4.16± 0 .49Ma;上部帕那组下限年龄为 38.7± 0 .40Ma .。指出至少在林周盆地剖面 ,林子宗群火山岩的形成时代为早第三纪 ,而非晚白垩纪。 相似文献
15.
~(40)Ar-~(39)Ar GEOCHRONOLOGY OF THE SUTURE ZONE, LADAKH, INDIA1 TalatAhmedetal.GeochemicalJournal,1999.
2 HoneggerK ,etal.EarthandPlanetaryScienceLetters,1982 ,6 0 :2 53.
3 SearleMP ,etal.GeologicalSocietyofAmericaBulletin ,1987,98:6 78.
4 SharmaK ,K .PhysicsandChemistryoftheEarth ,1990 ,17( 2 ) :133.
5 Venkatesan ,etal.EarthandPlanetSciLett,1993,119:181.… 相似文献
16.
Yuki Tohma Akira Imai Kenzo Sanematsu Kotaro Yonezu Ryohei Takahashi Masaaki Koyama Ryota Sekine Robert Duncan Koichiro Watanabe 《Resource Geology》2010,60(4):348-358
The Fukusen No. 1 vein is located in the southeastern part of the Yamada deposit, Hishikari epithermal gold deposits, southern Kyushu, Japan. 40Ar/39Ar plateau ages of adularia from the margin and the center of the Fukusen vein are determined to be 0.617 ± 0.024 Ma and 0.606 ± 0.009 Ma, respectively. The Fukusen No. 1 vein shows banding structure composed mainly of quartz, adularia and clay minerals. Colloform texture is displayed by cryptocrystalline to amorphous silica material that is associated with fine-grained electrum and sulfides near the center of the vein. Pyrite in the Fukusen No. 1 vein often shows acicular shape resulting from inversion from marcasite. Near the center of the vein, primary marcasite occurs associated with colloform texture of silica. The Fukusen No.1 vein preserves primary texture and materials which were deposited from the ore-forming hydrothermal solution. The Fukusen No. 1 vein was formed in a short period and is one of the youngest veins in the Hishikari deposits. 相似文献
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佳木斯地块南缘牡丹江地区高压变质作用：黑龙江杂岩的岩石学和地质年代学 总被引：6，自引：0，他引：6
牡丹江地区出露的黑龙江杂岩是由变质基性岩、泥质片岩、大理岩和变硅质岩系列组成的类似于蛇绿岩层序的构造混杂岩,代表了佳木斯地块西南缘碰撞增生的产物。钠长石和绿帘石变斑晶中共生的矿物组合(钠云母+蓝闪石+多硅白云母+绿帘石)的地质温压计估算结果表明,黑龙江杂岩的峰期变质的温压条件为 T=320~480℃, p=800~1600MPa,为典型的绿帘-蓝片岩相高压变质作用。黑龙江杂岩带中泥质片岩所含的多硅白云母单矿物给出的40Ar/39Ar坪年龄为164.9Ma±0.5Ma。根据白云母中K-Ar同位素体系的封闭温度(350~430℃)接近于得到的黑龙江杂岩的峰期变质温度,可以认为40Ar/39Ar坪年龄指示了这期高压变质事件的年龄,也证实了黑龙江杂岩带中普遍存在一期中侏罗世末期的变质-热事件。 相似文献
19.
Evolution of the Mesozoic Granites in the Xiong＇ershan-Waifangshan Region, Western Henan Province, China, and Its Tectonic Implications 总被引：4，自引：0，他引：4 下载免费PDF全文
下载免费PDF全文 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-Sr I-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-Sr I-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-stage I-type granites could be linked to delamination of subducted lithosphere of the Qinling orogenic belt, while the late-stage A-type granites represent the onset of extension and the end of orogenic process. In fact, along the Qinling -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. 相似文献
20.
塔里木盆地西北缘出露的辉绿岩墙的SiO2含量为44.34%～49.34%,Na2O K2O(4.32%～6.04%)和Na2O/K2O均较高(2.23～9.15),主量元素反映板内玄武岩的特点。稀土总量较低(∑REE=35.71～47.95μg/g),(La/Yb)N高达11.66～14.77,呈轻稀土强烈富集的稀土配分型式,基本不显示明显的Eu异常,具有富集地幔源的地球化学特点。对辉绿岩的40Ar/39Ar年龄测定为235.6Ma和203.7Ma。结合塔里木盆地西部,特别是西邻塔吉克盆地和卡拉库姆盆地三叠—侏罗纪沉积与构造背景的综合分析表明,塔里木盆地西部三叠—侏罗纪时期是白垩纪—古近纪强烈沉降作用的前奏,主体处于伸展背景下的隆起状态。 相似文献