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Geochronology Study On Hongqiyingzi Complex In Chicheng, North Hebei Province, China

Posted on:2013-12-01Degree:MasterType:Thesis
Country:ChinaCandidate:X KongFull Text:PDF
GTID:2230330377950150Subject:Mineralogy, petrology, ore deposits
Abstract/Summary:PDF Full Text Request
The Hongqiyingzi Complex,which has EW-extending in general, locate in thenorth side of the Chongli-Chicheng fault belt and consisted of garnet biotite plagioclasegneiss as well as some tectonic blocks such as the retrograded eclogites, serpentinites(serpentinized harzburgites),(olivine) marble and so on.Geochemical study indicatesthat the original rock of garnet biotite plagioclase gneiss was formed in the island arcstructural setting and its protolith is sandstones and graywackes; the protoliths of theretrograded eclogite are basic rocks which have characteristics of mid-ocean ridgebasalt(MORB);the serpentinite(serpentinized harzburgite) contain more w(MgO),butless w(CaO), w(Al2O3, w(Fe2O3), and its total REE is less than the primitivemantle,those characteristics shows that the serpentinite comes from the depletedmantal which underwent high degree partial melting; the original rock of the (olivine)marble is the dolomite which has a sedimentary origin, and and its sedimentaryenvironment may be the closed, semi-closed forearc basin under the dry climateconditions.The zircon SHRIMP U-Pb dating of garnet biotite plagioclase gneiss indicates thatthe age of its detrital zircons is369~1855Ma and its protoliths formed in369Ma~349Ma; and the age of340.3Ma~340.5Ma and320.8Ma~321.4Ma mayrepresent the granulite facies and amphibolite facies metamorphic age of garnet biotiteplagioclase gneiss respectively. In addition, the Ar-Ar ages of biotites shows that thelate reformation age of garnet biotite plagioclase gneiss is238±Ma.The zircon SHRIMP U-Pb dating for retrograded eclogite shows that its originalrocks formed in438±Ma; the peak eclogite facies metamorphic occured in355±Ma; and the retrograded age of the granulite facies and the amphibolite facies is341±Maand322-326±Ma respectively.The retrograde granulite facies age (341±Ma) and amphibolite facies age(321-326Ma) of eclogite are similar to the granulite facies metamorphic age (340±Ma)and amphibolite facies metamorphis c age (321±Ma)of garnet biotite plagioclasegneiss, combined with the fact that the retrograded eclogites occur as separate tectoniclenses or lumps in the garnet biotite plagioclase gneiss and its major axes direction is inline with regional gneissosity, we come to believe that: the eclogite tectonic exhumationmake serpentinite (serpentinized harzburgite) and (olivine) marble emplace into thegarnet biotite plagioclase gneiss and thus cause the granulite facies metamorphism ofgarnet biotite plagioclase gneiss; the closure of the Paleo-Asian ocean results in theregional amphibolite facies metamorphism of Hongqiyingzi Complex.
Keywords/Search Tags:Zircon SHRIMP U-Pb dating, Geochronology, Hongqiyingzi ComplexChicheng, North Hebei Province
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