Zircon LA-ICP-MS U-Pb Dating of the Guandiping Diorite Pluton from Mianxian,South Qinling,Central China
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The Guandiping biotite diorite outcrops in the Mianlue suture zone,located in the western part of the Guangtoushan granite pluton.The biotite diorite is mainly consisted by plagioclase,bhrnblende and biotite,with slight alteration.LAICP-MS dating of zircon U-Pb yeilds a weighted mean age of 220.5Ma±3.1Ma(MSWD)=0.66,2σ),which is considered representing the crystallizing age of the Guandiping diorite pluton.This age is similar with the emplacement age of the biotite-plagioclase granite(216Ma±2Ma)from the Guangtoushan Pluton in the surroundings,it can be inferred that the Guandiping biotite diorite pluton was formed in post-collisional setting.Keywords:
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The Longyuanba pluton in the eastern Nanling Range is an important part of the Nanling granites. However, so far no reliable isotopic dating result is available for this pluton. Based on the interior structures of zircons from the Longyuanba pluton analyzed by the CL technology, in-situ zircon U-Pb dating was performed with La-ICP-MS and reliable age data were obtained. The results show that the Longyuanba pluton was formed in multi-stage magmatism spanning the Indosinian and Yanshanian periods. The main body of the pluton was formed in the Indosinian, especially in the early Indosinian. Single-grain zircon dating for the early Indosinian granites yields ages of 241.0±5.9 Ma and 241.0±1.3 Ma (two samples), for the late Indosinian granite yields 210.9±3.8 Ma, and for the Yanshanian syenite yields 149.4±4.9 Ma. The ages and geneses of the Longyuanba pluton are different from those of the Pitou—Tabei complex pluton located to its east, but are very similar to those of the Zhuguangshan pluton located to its north. When considering the prospect of uranium mineralization in the region, we should consider it with the integration of Zhuguangshan pluton and Longyuanba pluton, and should enhance the exploration on the Longyuanba pluton.
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The Xiaoheishan pluton is located in the southern Liaodong Peninsula of the eastern North China Craton,and consists of deformed diorite,granodiorite and biotite granite.LA-ICPMS zircon U-Pb dating gives the age of 174-170 Ma for diorite,174±1 Ma for granodiorite,177±2 Ma for biotite granite and 175±2 Ma for granitic pegmatitic dike,indicating that the Xiaoheishan pluton is a Jurassic intrusive complex.Geochemical,whole rock Sr and Nd isotopic and zircon Hf isotopic data indicate that the diorite,granodiorite and granite of the Xiaoheishan pluton were result of partial melting of ancient lower crustal materials at high pressures,interacted with mantle-derived magmas.The Xiaoheishan pluton and the Jurassic magmatism in the eastern North China Craton formed in a continental crustal thickening setting that may be related to subduction of the Paleo-Pacific oceanic plate,which induced partial melting of lower crustal materials of the North China Craton.
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The Guandimao and Wawutang plutons are located at the center of Hunan, South China. The former is mainly composed of biotite monzonitic granites/granodiorites and two-mica monzonitic granites, but the latter only consists of biotite monzonitic granites. The zircon ages of 203.0±1.6 Ma (biotite monzonitic granites) and 208.0±3.2 Ma (two-mica monzonitic granites) for the Guandimao pluton and 204±3 Ma for the Wawutang pluton obtained with the LA-ICP-MS U-Pb dating indicate that they were formed during the late Indosinian. In consideration of other geochronological data from Indosinian rocks of South China and adjacent regions, it is inferred that the two plutons were derived from crustal materials by decompressional melting in a post-collisional tectonic setting during spontaneous thinning of the thickened curst. Moreover, the inherited zircon age of 1273±57 Ma from the Wawutang pluton indicates that the source of the two plutons is related to the early Proterozoic crustal basement.
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The Yushenkala pluton is located in the northern part of west Junggar Basin of Xinjiang and lies along the suture zonebetween Siberia plate and Junggar plate. Petrologically, the pluton consists of gabbro, hornblende gabbro, diorite and quartz diorite which intruded in the middle Devonian Yudoukala Group. LA-ICP-MS zircon U-Pb dating shows that the age of the hornblende gabbro is 364±1Ma, which represents the formation age of the pluon. The eHf(t) values of the zircon are in the range of 4.3-11.5,with a weighted average of 9.0±1.2, suggesting that its original rock was derived from mantle materials. The one-stage Hf model ages(TDM1) are 529-827 Ma(629±95 Ma on average), indicating an original rock of Cambrian- Precambrian basement. Based on field geological and geochemical characteristics, the authors infer that the pluton formed in an island-arc environment or active epicontinental environment. In the late Devonian, the arc magmatism was well developed, and the ocean-continent subduction event basically came to an end in the northwestern part of western Junggar. These data indicate that the closing time of Paleo Asian ocean was not earlier than 364 Ma.
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Lile
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猴岩岩体位于佛冈复式岩体北东缘，总体呈南北向展布，出露面积约30 km2，岩性多为中细粒黑云母二长花岗岩、花岗闪长岩。本文对猴岩岩体花岗闪长岩样品进行LA-ICP-MS锆石U-Pb测年，获得的同位素年龄为(155.5 ± 4.2) Ma (MSWD = 2.0)，表明猴岩岩体侵位时代为晚侏罗世中期，是燕山第三幕岩浆活动之产物。通过对比，猴岩岩体与佛冈主体花岗岩的侵位时代相一致, 表明二者形成于同期构造–岩浆活动，猴岩岩体是佛冈主体花岗岩分异结晶之产物。猴岩岩体的花岗闪长岩是岩浆分异结晶时捕掳地层残留体，导致岩石成分产生差异而形成，为岩体的边缘相。佛冈复式岩体形成于古太平洋板块向欧亚大陆板块俯冲的构造背景下，其主体花岗岩的地球化学特征表明其物质主要来源于地壳，属陆壳改造型(即S型)花岗岩。 Located at the northeast of Fogang composite pluton, Houyan pluton, which is mainly composed of intermediate-fine grained biotite monzogranites and granodiorites, generally presents a north- south directional distribution and covers an area of 30 km2. In this paper, the LA-ICP-MS zircon U-Pb age of granodiorites of the Houyan pluton is (155.5 ± 4.2) Ma (MSWD = 2.0). The result shows that the emplacement age of Houyan pluton belonged to the middle stage of Late Jurassic, and it was the product of the third magma activity of Yanshan. As its age is the same as the main granite of Fogang composite pluton, they were in the same period of tectono-magmatic activity, and Houyan pluton was crystallized from magmas of main granite of Fogang composite pluton. As the crystallization differentiation of magmas captured the remained stratums, it caused differences in rock composition, and formed the marginal facies which are composed of granodiorites. Fogang composite pluton was formed in the process of subduction of the Pacific plate under Eurasian plate. The geochemical characteristics of its main granite indicate that its source mainly derived from the crust, which belongs to crustal transformation type (S-type) granite.
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Laoyaquan granitic pluton is the largest pluton containing tin deposit in the Beilekuduk tin metallogenic belt.It is mainly composed of biotite alkali-feldspar granites.LA-ICP-MS U-Pb dating for zircons from two samples yielded the 206Pb/238U ages of 301±2 Ma(2σ,MSWD=1.03) and 300±5 Ma(2σ,MSWD=5.90),suggesting that the emplacement of the pluton occurred at the end of Late Carboniferous.The Laoyaquan alkali-feldspar granite is enriched in silica,alkalis,REE,Rb,K,Th,U,Nd,Hf and depleted in Ba,Sr,P,and Ti,with a strong Eu negative anomaly,showing the features of A-type granites.Both the geochemical characteristics and the zircon U-Pb ages indicate that the formation of the pluton is related to the post-collision and the magmatic activity during Late Carboniferous in northern Xinjiang.
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The Bashierxi pluton is located in the western segment of the eastern Kunlun,between Baiganhu fault and Aerjin fault,this pluton mainly consists of monzonitic granite and K-feldspar granite,and the monzonitic granite is closely related with the ore-forming process of the Baiganhu tungsten-tin deposit.The internal structures,cathodeluminescence(CL) images and Th/U ratios of the zircon grains from the monzonitic granite reveal that these zircon grains have typical characteristics of magmatic zircon.The LA-ICP-MS analyses show that the zircon grains from the monzonitic granite have concordant U-Pb ages of(458.0±9.0)Ma,on the other hand,the zircon grains from the K-feldspar granite have U-Pb ages of(432.3±0.8)Ma,these data indicated that the Bashierxi pluton is a intrusion formed from Late Ordovician to Early Silurian.Major and trace element data of the monzonitic granite show that Bashierxi granite is weakly metaluminous or peraluminous A-type granite.These rocks were considered as melts derived from crustal source during back-arc basin extension in eastern Kunlun,and the early Baiganhu tungsten-tin deposit era is represented by the ages of monzonitic granite.
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Quartz monzonite
Pegmatite
Island arc
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