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1.
构造剪切与变质角闪石中过剩Ar的引入 总被引：2，自引：0，他引：2
本文对两个北秦岭凤凤群斜长角闪岩样品进行了Ｓｍ－Ｎｄ，Ｒｂ－Ｓｒ和＾４０Ａｒ／＾３９Ａｒ测年，发现其中受构造改造轻微的黑河丹凤群工角闪岩样品的角闪石＾４０Ａ＾３０Ａｒ年龄与其人Ｒｂ－Ｓｒ，Ｓｍ－Ｎｄ矿物等时线年龄接近，而遭受强烈构造剪切作用的蒲峪丹凤群斜长角闪岩的角闪石＾４０Ａ＾３９Ａｒ年测则明显高于其Ｒｂ－Ｓｒ、Ｓｍ－Ｎｄ矿物时线年龄，指示构造剪切作用地变质角闪石中过剩氩的引入有显著影响。在利用 相似文献
2.
东秦岭陡岭群变质杂岩Sm-Nd、Rb-Sr、40Ar/39Ar、207Pb/206Pb年龄 总被引：12，自引：1，他引：12
本文用单颗粒锆石逐级蒸发２０７Ｐｂ／２０６Ｐｂ、ＳｍＮｄ、ＲｂＳｒ、４０Ａｒ／３９Ａｒ年代学方法对东秦岭陡岭群变质杂岩的形成时代、变质时期和构造归属进行了研究。结果表明：陡岭群变质杂岩形成于早元古代，年龄为２０００Ｍａ左右，在其形成后遭受了多期变质作用。片麻岩ＳｍＮｄ等时年龄１８７８±２５６Ｍａ（εＮｄ（ｔ）＝＋２．８±２．６）代表了ＳｍＮｄ同位素系统重新发生均一化作用的时间。主期变质作用发生在８３３±１７Ｍａ（角闪石４０Ａｒ／３９Ａｒ高温坪年龄）；另一期变质作用发生于４２２±１６Ｍａ（片麻岩Ｒｂ 相似文献
3.
本文给出的滹沱群下亚群青石村组玄武岩Ｒｂ－Ｓｒ、Ｓｍ－Ｎｄ全岩等时线年龄为２０４５．８±１７和２３６９±３０Ｍａ（Ｚ），角门石４０Ａｒ－３９Ａｒ坪年龄和最高视年龄为１３６４±１９和１９３２±１９Ｍａ（１）；中亚群河边村组玄武岩Ｒｂ－Ｓｒ全岩等时线年龄图的投点呈完全离散状，Ｓｍ－Ｎｄ全岩等时线年龄为２３２２±３１Ｍａ（２），角门石４０Ａｒ－３９Ａｒ坪年龄和最高视年龄为１３６０和１７４２±１７Ｍａ（１）。根据上述Ｒｂ－Ｓｒ、Ｓｍ－Ｎｄ数据与已知青石村组、河边村组单颗粒锆石Ｕ－Ｐｂ法确定的成岩年龄２４５０±１０和２４００±２０Ｍａ（２）的明显差别，４０Ａｒ－３９Ａｒ均揭示为较典型受扰动的年龄谱和较发育的透人性构造、晚期岩脉等地质证据，认为Ｒｂ－Ｓｒ、Ｓｍ－Ｎｄ是重设的同位素体系。 相似文献
4.
早元古代滹沱群玄武岩Rb—Sr,Sm—Nd同位素体系初论 总被引：6，自引：0，他引：6
王汝铮 《前寒武纪研究进展》1997,20(1):35-43
本文给出了的滹沱群下亚群青石村组玄武岩Ｒｂ－Ｓｒ、Ｓｍ－Ｎｄ全岩等时线年龄为２０４５．８±１７和２３６９±３０Ｍａ（２σ），角闪石＾４０Ａｒ＾－＾３９Ａｒ坪年龄和最高视年龄为１３６４±１９和１９３２±１９Ｍａ（１σ）；中亚群河边村组玄武岩Ｒｂ－Ｓｒ全岩等时线年龄图的投点呈完全离散状。 相似文献
5.
上海金山群斜长角闪岩Sm—Nd和Ar—Ar同位素年龄测定 总被引：2，自引：0，他引：2
上海地区经钻孔揭示的基底变质地层，即金山群中斜长角闪岩类经全岩Ｓｍ－Ｎｄ等时线法测定其年龄为１２６４±１１３Ｍａ，εｎｄ（ｔ）为１．５±１．９。而从中分选出的角闪石的＾４０Ａｒ－＾３９Ａｒ体系则反映了后期多次热事件的叠加。上述测定结果反映了本区在中元石代的壳增长及显生代期间多期改造的复杂地质演化过程。 相似文献
6.
滇西南那邦变质基性岩两其变质作用的^40Ar／^39Ar年代学研究 总被引：4，自引：3，他引：1
中缅边界那邦变质基性岩出圳于东缅著名的Ｍｏｇｏｋ带的东缘。那邦基性麻粒岩经历了早期麻粒岩相、晚期角闪岩相的两期变质作用的改造。早期变质作用的矿物石榴石和单斜辉石的＾４０Ａｒ／＾３９Ａｒ年龄谱图和等时线年龄均显示两组年龄：７４￣７６Ｍａ和２３￣２４Ｍａ。晚期变质作用矿物角闪石的Ｋ－Ａｒ法得出２３Ｍａ,角闪石和斜长石的＾４０Ａｒ／＾３９Ａｒ年龄谱图和等时线年龄均显示２３￣２４Ｍａ。晚期变质作用矿物角闪 相似文献
7.
安徽大别、苏北和山东胶南是世界上第三个发现含柯石英榴辉岩的地区。在关于苏鲁皖超高压变质带大地构造背景的学术讨论中，其时代问题成为当前争论的焦点。本文用锆石Ｕ－Ｐｂ法得到碧溪岭榴辉岩体谐和图上交点年龄２７７４．５±２４Ｍａ以及ｔ（~（２０７）Ｐｂ／~（２０６）Ｔｂ）平均表面年龄２６６２Ｍａ，提供了榴辉岩的原岩和超高压变质作用可能形成于晚太古代的信息；并用多硅白云母Ａｒ－Ａｒ法测得６６１．７±１３Ｍａ的退变质年龄，也表明本区榴辉岩可能是前寒武纪的产物；此外，还测得围岩大别群斜长片麻岩中的白云母以及榴辉岩中晚期交代的普通角闪石的Ａｒ－Ａｒ等时线年龄分别为１９２．５５±３．８５和２３０．７０±４．６１Ｍａ，代表后榴辉岩（ｐｏｓｔｅｃｌｏｇｉｔｅ）的印支期区域动力变质作用改造年龄。笔者对已报道的榴辉岩Ｓｍ－Ｎｄ年龄的地质意义进行了讨论，并指出了含石榴子石Ｓｍ－Ｎｄ矿物等时线定年法潜在的弊端。 相似文献
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11.
Coesite- and microdiamond- bearing ultra-high pressure (UHP) eclogites in the North Qinling terrane have been widely retrogressed to amphibolites. Previous geochronological studies on these UHP rocks mainly focused on the timing of peak eclogite facies metamorphism. The Kanfenggou UHP metamorphic domain is one of the best-preserved coesite-bearing eclogite occurrences in the North Qinling terrane. In this study, mafic amphibolites and host schists from this domain were collected for 40Ar/39Ar dating to constrain their retrograde evolution. Two generations of amphibole are recognized based on their mineral parageneses and 40Ar/39Ar ages. A first generation of amphibole from garnet amphibolites yielded irregularly-shaped age spectra with anomalously old apparent ages. Isochron ages of 484–473 Ma and initial 40Ar/36Ar ratios of 3695–774 are obtained from this generation of amphibole, indicating incorporation of excess argon. Second generation amphibole occurs in epidote amphibolites yielded flat age spectra with plateau ages of 464–462 Ma without evidence for excess argon. These ages suggest that the amphibolite-facies metamorphism has taken place as early as 484 Ma and lasted until 462 Ma for the North Qinling UHP metamorphic rocks. Phengite from the country-rock schists yielded 40Ar/39Ar plateau ages of 426–396 Ma, with higher phengite Si contents associated with the older the plateau ages. Based on our new 40Ar/39Ar ages and previous zircon UPb geochronological data, we construct a new detailed pressure-temperature-time (P-T-t) path illustrating the retrograde metamorphism and exhumation rate of the North Qinling eclogites and host schists. The P-T-t path suggests that these UHP metamorphic rocks experienced initial medium-to-high exhumation rates (ca. 8.7 mm/yr) during the Early Ordovician (489–484 Ma), which was mainly derived from buoyancy forces. Subsequently, the exhumation rate decreased gradually from ~0.8 to 0.3 mm/yr from 484 to 426 Ma, which was probably governed by extension and/or erosion. 相似文献
12.
《International Geology Review》2012,54(12):1114-1124
Because of a complicated metamorphic history, the isotopic systematics of the ultrahigh-pressure (UHP) metamorphic rocks in the Dabie-Sulu belt, east China, appear to be rather different from what were expected. Depending on the degree of retrograde metamorphism and on the retentivity of isotopes, the radiogenic isotopic systematics in the UHP metamorphic rocks yielded a wide range of radiometric ages. Some of these ages are geologically meaningful, but others may not be. In some fine-grained UHP metamorphic rocks, Sm/Nd isotopic systematics appear to be in equilibrium among the UHP phases, showing the best estimate for the age of peak metamorphism at 226 ± 3 Ma. On the other hand, retrograde overprinting often makes the interpretation of isotopic data more difficult. It is common to find that the Sm/Nd and Rb/Sr isotopic systematics among the UHP phases and retrograde phases are not in equilibrium. Regression of isotopic data involving both UHP and retrograde minerals in isotopic correlation diagrams often yields geologically meaningless ages. Although 40Ar/39Ar dating of UHP metamorphic rocks has been reported not to be very helpful in establishing the thermal history because of the presence of excess argon, a good correlation between excess argon and rock type in the Dabie-Sulu belt would provide a criterion in identifying the possible sources of excess argon. By taking all the possible effects into consideration, a T-t path with two rapid cooling stages for UHP metamorphic rocks from the Dabie-Sulu belt can be postulated. An initial rapid cooling stage in the period from 226 to 219 Ma may have resulted from rapid exhumation of UHP metamorphic rocks immediately after the peak metamorphism. The second rapid cooling stage, from 450°C to 300°C, may have been caused by the exhumation of the entire terrane, including UHP metamorphic units and their host gneisses, during the period from 180 to 167 Ma. 相似文献
13.
Isotopic Geochronology of the Late Paleozoic Kanggur Gold Deposit of East Tianshan Mountains, Xinjiang, NW China 总被引：1，自引：0，他引：1
Lian–chang ZHANG Tie–bing LIU Yuan–chao SHEN Guang–ming LI Jin–sheng JI 《Resource Geology》2002,52(3):249-261
Abstract: The Kanggur gold deposit lies in East Tianshan mountains, eastern section of Central Asia orogenic belt. The gold mineralization occurs on the northern margin of the Aqishan‐Yamansu Paleozoic island arc in the Tarim Plate. It was hosted mainly in Middle‐Lower Carboniferous calc‐alkaline volcanic rocks, and controlled by the distributions of syn‐tectonic intrusions and ductile shear zones. In order to determine ore‐forming age of the Kanggur deposit, samples were collected from ores, wall rocks, altered rocks and intrusions. The dating methods include Rb‐Sr isochron and Sm‐Nd isochron, and secondly 40Ar/39Ar age spectrum, U‐Pb and Pb‐Pb methods. Based on the mineral assemblage and crosscutting relationship of ore veins, five mineralization stages are identified. This result is confirmed by isotope geochronologic data. The first stage featuring formation of pyrite‐bearing phyllic rock, is mineralogically represented by pyrite, sericite and quartz with poor native gold. The Rb‐Sr isochron age of this stage is 2905 Ma. The second stage represents the main ore‐forming stage and is characterized by native gold–quartz–pyrite–magnetite–chlorite assemblage. Magnetite and pyrite of this stage are dated by Sm‐Nd isochron at 290.47.2 Ma and fluid inclusion in quartz is dated by Rb‐Sr isochron at 282.35 Ma. The third mineralization stage features native gold–quartz–pyrite vein. In the fourth stage, Au‐bearing polymetallic sulfide‐quartz veins formed. Fluid inclusions in quartz are dated by Rb‐Sr isochron method at 25821 Ma. The fifth stage is composed of sulfide‐free quartz–carbonate veins with Rb‐Sr age of 2547 Ma. The first and second stages are related to ductile‐brittle deformation of shear zones, and are named dynamo‐metamorphic hydrothermal period. The third to fifth stages related to intrusive processes of tonalite and brittle fracturing of the shear zones, are called magmato‐hydrothermal mineralization period. The Rb‐Sr isochron age of 2905 Ma of the altered andesite in the Kanggur mine area may reflect timing of regional ductile shear zone. The Rb‐Sr isochron age of 28216 Ma of the quartz‐syenite porphyry and the zircon U‐Pb age of 2757 Ma of tonalite in the north of Kanggur gold mine area are consistent with the age of gold mineralization (290‐254 Ma). This correspondence indicates that the tonalite and subvolcanic rocks may have been related to gold mineralization. The Rb–Sr, Sm‐Nd and U‐Pb ages and regional geology support the hypothesis that the Kanggur gold deposit was formed during collisional orogenesis process in Late Variscan. 相似文献
14.
An understanding of the Okcheon Metamorphic Belt (OMB) in South Korea is central to unraveling the tectono-metamorphic evolution of East Asia. Amphibole-bearing rocks in the OMB occur as calcsilicate layers and lenses in psammitic rocks, in the psammitic rocks themselves, and in the mafic volcanic layers and intrusives. Most amphiboles fail to show 40Ar/39Ar plateau ages; those that do have ages ranging from 132 to 975 Ma. The disturbed age pattern and wide variation in 40Ar/39Ar ages can be related to metamorphic grade, retrograde chemical reactions, excess Ar and amphibole composition. The oldest age (975 Ma) can be interpreted either as an old igneous or metamorphic age predating sedimentation or a false age caused by excess Ar. The youngest age of 132 Ma and the disturbed age pattern found in amphiboles from rocks located close to Jurassic granitoids are the result of retrograde thermal metamorphic effects accompanying intrusion of the granitoids. Some medium- or coarse-grained amphiboles in the calcsilicates are aggregates of fine-grained crystals. As a result, they are heterogeneous and prove to be readily affected by excess Ar. A disturbed age pattern in amphiboles from the calcsilicates occurring in the high-grade metamorphic zone may also be the product of excess Ar. On the other hand, the disturbed pattern of amphiboles present in the calcsilicates from the low-grade metamorphic zone could arise from both excess Ar and mixed ages. However, amphiboles from psammitic rocks and some calcsilicates in the high-grade metamorphic zone and in intrusive metabasites display real plateau ages of 237 to 261 Ma. The temperature conditions in the high-grade metamorphic zone were higher than the argon closing temperature for amphibole, and the amphiboles in this zone give plateau ages only when they are homogeneous in composition, lack excess Ar, and have not been thermally affected by intrusion of the granitoids. The unmodified 40Ar/39Ar ages prove rather younger than the age of the Late Paleozoic metamorphic event of 280 to 300 Ma, but they are close to muscovite K-Ar ages of 263 to 277 Ma. These 40Ar/39Ar amphibole ages are interpreted as the time of cooling that followed the main regional, intermediate-P/T metamorphic climax. The results demonstrate that interpretation of 40Ar/39Ar amphibole ages in an area subjected to several metamorphic events can be accomplished only by undertaking a thorough tectono-metamorphic study, accompanied by detailed chemical analysis of the amphiboles. 相似文献
15.
Ultra-high pressure eclogite/amphibolite grade metamorphism of the Dora Maira Massif in the western Alps is a well established
and intensively studied event. However, the age of peak metamorphism and early cooling remains controversial. The 40Ar-39Ar step-heating and laser spot ages from high pressure phengites yield plateau ages as old as 110 Ma which have been interpreted
as the time of early cooling after the high pressure event. Recent U/Pb and Sm/Nd results challenge this assertion, indicating
a much younger age for the event, around 45 Ma, and hence a radically different timing for the tectonic evolution of the western
Alps. In a new approach to the problem, samples from the undeformed Hercynian metagranite, Brossasco, were studied using an
ultra-violet laser ablation microprobe technique for 40Ar-39Ar dating. The new technique allowed selective in situ analysis, at a spatial resolution of 50 μm, of quartz, phengite, biotite
and K-feldspar. The results demonstrate the frequent occurrence of excess argon with high 40Ar-36Ar ratios (1000–10000) and a strong relationship between apparent ages and metamorphic textures. The highest excess argon
ratios are always associated with high closure temperature minerals or large diffusion domains within single mineral phases.
The best interpretation of this relationship seems to be that excess argon was incorporated in all phases during the high
pressure event, then mixed with an atmospheric component during rapid cooling and retrogression, producing a wide range of
argon concentrations and 40Ar/36Ar ratios. Step-heating analysis of minerals with this mixture would produce linear arrays on a 36Ar/40Ar versus 39Ar/40Ar correlation diagram, leading to geologically meaningless plateau ages, older than the true closure age. In the present
case, some ages in the range 60–110 Ma could be explained by the presence of excess argon incorporated around 40–50 Ma ago.
Similar results found in other high pressure terrains in the Alps may reconcile the argon geochronometer with other systems
such as Rb/Sr, U/Pb or Sm/Nd. This study therefore calls for an increasing use of high resolution in situ sampling techniques
to clarify the meaning of 40Ar/39Ar ages in many high pressure terrains.
Received: 6 January 1994/Accepted: 4 April 1995 相似文献
16.
Sonia Tonarini Igor M. Villa Felix Oberli Martin Meier David A. Spencer Ugo Pognante John G. Ramsay 《地学学报》1993,5(1):13-20
A geochronological investigation of two rocks with an eclogitic assemblage (omphacite-garnet-quartz-rutile) from the High Himalaya using the Sm/Nd, Rb/Sr, U/Pb and Ar/Ar methods is presented here. The first three methods outline a cooling history from the time of peak metamorphism at 49±6 Ma recorded by Sm/Nd in garnet-clinopyroxene to the closure of Rb/Sr in phengite at 43±1 Ma and U/Pb in rutile at 39–40 Ma. The Sm/Nd isotopic system was fully equilibrated during eclogitization and has not been disturbed since; its mineral ages may date the peak metamorphic conditions (650±50°C at 13–18 kbar: Pognante and Spencer, 1991). The Ar/Ar data reveal the presence of substantial amounts of excess 40Ar in hornblende, and yield a statistically acceptable but geologically meaningless phengite plateau age of 81.4±0.2 Ma, inconsistent with Sm/Nd, Rb/Sr and U/Pb. This questions the use of such a chronometer for the dating of high-pressure assemblages. The results imply a Late Palaeocene or Early Eocene subduction of the northern Indian plate margin in NW Himalaya. The fact that eclogites are restricted to NW Himalaya may be the result of a peculiar p-T-t path associated with a high convergence rate during the first indentation, in contrast to the later and slow subduction in Central and Eastern Himalaya. 相似文献
17.
Johannes Glodny Håkon Austrheim Anatolij I Rusin 《Geochimica et cosmochimica acta》2003,67(22):4353-4371
Rb/Sr internal mineral isochrons in the eclogite facies Marun-Keu metamorphic complex, Polar Urals, Russia, date periods of fluid-rock interaction and record the metamorphic reaction history. The Marun-Keu complex consists of Late Proterozoic to Early Ordovician, mostly igneous rocks that experienced a subduction-related, non-pervasive eclogite facies metamorphism, followed by a local decompression-related amphibolite facies overprint, during the Uralian orogeny. Field observations show that metamorphic reactions as well as ductile deformation are controlled by local availability of a free fluid phase. Isotopic data reveals that availability of fluids similarly exerts control on isotope distribution. From a relic gabbro which has never been infiltrated by free fluids, a premetamorphic Rb/Sr age of 467 ± 39 Ma was obtained. Rb/Sr isochron ages for 14 samples of eclogite and amphibolite facies assemblages, sampled from within or close to metamorphic fluid veins, range from 352 ± 5 Ma to 360 ± 3 Ma. A Sm/Nd isochron for a metagranite yields an age of 354 ± 4 Ma. Taken together, the ages for both prograde and retrograde metamorphic assemblages overlap within analytical uncertainty and yield an average value of 355.5 ± 1.4 Ma, indicating that the metamorphic evolution and incipient exhumation of the Marun-Keu complex proceeded rapidly. The results demonstrate that assemblages preserve their Rb/Sr isotopic signatures as long as they remain devoid of free fluids, and that only fluid-rock interaction may cause Sr isotope redistribution. In addition, the data suggest local fluid-rock equilibrium, low fluid-rock ratios with overall fluid deficiency, and limited fluid mobility at depth. However, some fluids must have been mobile on the km-scale since they can be traced into the suprasubduction zone mantle wedge. Metasomatic veins in the Rai-Iz ophiolite yield a Rb/Sr mineral isochron age of 373.1 ± 5.4 Ma. They are interpreted as evidence for suprasubduction zone metasomatism in an oceanic setting, prior to subduction of the East European margin and associated formation of eclogites in the Marun-Keu complex.We propose that Rb/Sr mineral-isochron ages provide hygrochronological rather than thermochronological constraints. They define the cooling history only in combination with zircon and apatite fission track data. The straightforward interpretation of Rb/Sr mineral ages as cooling ages is obsolete. 相似文献
18.
Wei Wang Ren-Xu Chen Fukun Chen Yong-Fei Zheng 《International Journal of Earth Sciences》2010,99(4):727-743
Diffusion rates of Sr and O in minerals are often comparable while Nd has a lower diffusion rate during thermal overprint(s); thus, the O isotope systems between metamorphic minerals can serve as an indicator to evaluate whether equilibrium of Rb–Sr and Sm–Nd systems has been preserved in the metamorphic minerals that experienced retrograde metamorphism. This study presents a combination of investigation on Sm–Nd, Rb–Sr, and O isotopic compositions of minerals separated from ultrahigh-pressure eclogite and gneiss that were collected from the main hole of the Chinese Continental Scientific Drilling project located in the Sulu orogen, eastern China. Oxygen isotopic compositions of minerals from gneiss and eclogite yield two temperature groups of 620–740 and 460–590°C, representing diffusion cessation of isotopic exchange during the eclogite-facies recrystallization and later amphibolite-facies retrograde overprint. Rb–Sr mineral regressions of two eclogite samples give consistent Triassic ages of 244 Ma, corresponding to eclogite-facies metamorphism, while the same minerals do not yield meaningful Sm–Nd isochron ages. This phenomenon likely suggests that Rb–Sr isotopic equilibrium was achieved during eclogite-facies metamorphism and preserved during late amphibolite-facies retrogression. In contrast, Sm–Nd isotopic equilibrium between the minerals of eclogite was not achieved under UHP metamorphic conditions. Regressions of epidote and biotite of one gneiss sample give a Triassic Sm–Nd age of 243 ± 34 Ma, corresponding to the time of the eclogite-facies metamorphism, and a Jurassic mineral Rb–Sr age of 187.5 ± 1.8 Ma. These results imply that fluids have played an important role to achievement of the Sm–Nd isotopic equilibrium during eclogite-facies metamorphism and re-equilibration of the Rb–Sr isotopic system during later retrograde overprint. 相似文献
19.
New Chronological Evidence for Indosinian Diagenetic Mineralization in Eastern Xinjiang, NW China 总被引：7，自引：2，他引：7
LI Huaqin CHEN Fuwen LU Yuanf YANG Hongmei GUO Jing MEI Yuping Yichang Institute of Geology Mineral Resources Gangyao Ro Yichang Hubei 《《地质学报》英文版》2005,79(2):264-275
1 IntroductionMineralization in E. Xinjiang constitutes an importantpart of the Mid-Asian Metallogenetic Province. A greatdeal of nonferrous, ferrous, rare and noble metaldeposits of different genetic types and ages were formedduring different crustal evolution stages and werecontrolled by regional tectonic evolution. Large-scalemineralization of metallic deposits and relatedmagmatism mainly occurred during the Carboniferous toPermian periods (Li et al., 1998; Ji et al., 1999; Mao etal., 2… 相似文献
20.
宽坪岩群位于北秦岭造山带,主要由广东坪岩组斜长角闪岩、四岔口岩组云母石英片岩及谢湾岩组的大理岩组成。通过LA-MC-ICPMS锆石U-Pb测年研究,宽坪岩群谢湾岩组碎屑锆石年龄为400~3502 Ma,其中最年轻一组的206Pb/238U年龄在380~418 Ma,结合黑云母40Ar/39Ar（370.9±2.0）Ma的变质年龄,表明谢湾岩组形成在晚泥盆世。四岔口岩组碎屑锆石年龄介于512~3598 Ma,最年轻的一组锆石206Pb/238U年龄在512~549 Ma,其黑云母40Ar/39Ar变质年龄为（370.4±1.8）Ma,表明该组形成于512 Ma（早寒武世）之后,晚泥盆世之前,主体很可能形成于早古生代。宽坪岩群是由不同时代的地层和岩片构成,应该进一步解体。宽坪岩群物源来自华北陆块、秦岭造山带和扬子陆块。其变形变质时代为晚泥盆世,代表了北秦岭造山带碰撞造山的结束时代。 相似文献