The Late Paleozoic Post Collision Intermediate-acid Instrusive Rocks In Sonidzuoqi Area Of Inner Mongolia

This paper is supported by The project“Inner Mongolia 1:50000 of Zhunheremuyin Sumu six pieces of regional geological and minerals survey”,the main research is the late Paleozoic post collision intermediate-acid instrusive rocks in Sonidzuoqi Area.The area is located in the Xing Meng Orogen of the eastern section of The Central Asian Orogenic Belt?CAOB?between the North China plate and Siberia plate.It belonged to the paleo Asian tectonic domain when in Paleozoic,When in Mesozoic,it belonged to West Pacific tectonic domain.Structural position of the study area belongs to Erlian-Hegenshan arc-ophiolite accretion zone,A large area of exposed late Paleozoic intrusive and volcanic rocks?Po gaomiao group?constitute magmatic belt NE trending,consistent with the regional tectonic line.Previous studies late Paleozoic intrusive rocks the area designated as the Permian,the regional survey project intrusions detail disintegration.Through detailed field geological survey and the basis for the newly acquired scientific LA-ICP-MS zircon U-Pb isotopic data,the establishment of intrusive geochronological framework,Redefinition of Carboniferous granodiorite-adamellite-syenogranite sequence,Carboniferous gabbro-diorite-quartz monzonite-fine-grained granodiorite sequence,Permian porphyry small rock body and massive dike swarm.This paper carried out by gabbro diorite-quartz monzonite-fine-grained granodiorite sequence petrology,geochronology and geochemical studies to determine the spatial distribution and formation time of intrusive rocks to explore the genetic types of intrusions,magma source characteristics,determined magmatic tectonic setting.The field investigation found gabbro diorite-quartz monzonite-fine-grained granodiorite sequence intrusive substantially Little Rock beads,Rock branches emplaced in Carboniferous continental margin arc granodiorite-granite syenite intrusions,located in the core of the arc granite belt.Zircon U-Pb isotopic dating results of this work show that the obtained gabbro diorite-quartz monzonite-fine-grained granodiorite sequence zircon age range is 304.3Ma-299.03Ma,and the region has an A-type granites geochemical affinity for alkali feldspar granite Age?303.1³04.3Ma?are identical,which is later than the arc sequence granodiorite emplacement age of?321.4³06.2Ma?,and field geological relations.Zircon ages result of the system shows two lava sequences present clear age intermittently,suggesting that they are the product of two stages of magma intrusion.Geochemical results showed that SiO₂ range gabbro diorite is 49.14⁵5.9wt%,MgO is2.91⁶.86 wt%,Mg#change to 64.3 to 44.They have high Al₂O₃?14.94¹8.88wt%? and CaO?6.38⁸.93wt%?,relatively low alkali content of the whole?K2O+Na2O=2.94⁵.26 wt%?and TiO₂ content?0.72¹.57wt%?.Compared with gabbro diorite,quartz monzonite has a relatively high content of SiO₂?61.79⁶9.1wt%?and total alkali content?K₂O+Na₂O=6.95⁷.44wt%?,relatively low TFe₂O₃?3.16⁵.97wt%?,MgO?1.12².17wt%?and CaO?2.21⁴.34wt%?.SiO₂ content range of fine-grained granodiorite is67.72⁷1.76wt%,low MgO?0.73¹.17wt%?and Mg#?37⁴7?,Al₂O₃ ranged from14.05¹5.17 wt%,CaO,0.69².68wt%,full-alkali content?K₂O+Na₂O? of 7.1⁷.86 wt%.Gabbro-diorite-granodiorite sequence having a calc-alkaline magma.In the TAS diagram,samples distributed in sub-alkaline region and presents its wholly alkali content positively correlated with SiO₂ content of samples from gabbro-diorite to granite zone continuous evolutionary trend.On K₂O-SiO₂ classification map,showing the sequence from K calc-alkaline to high-K calc-alkaline series continuous evolution of calc-alkaline magmatic evolution trend.The sequence is shown quasi aluminum magma geochemical affinity,showed significant A/CNK and A/NK negative trend in the evolution of the Al saturation index map.Gabbro-diorite-granodiorite sequence having LREE enrichment,HREE loss,weak rare earth\HREE fractionation and lack of obvious Eu anomaly,showing the light rare earth and the steep section to the right-heavy rare earth segment nearly flat REE distribution curves.The sequence intrusions enriched in LILE and water-activated elements Pb,relatively depleted in high field strength elements?Nb,Ta,Ti?,in the original mantle normalized incompatible element spider diagrams showed a significant peak Pb and Nb?-Ta?and Ti Valley,show a clear subduction zone magma geochemical characteristics.Gabbro-diorite rock with a smaller sequence(⁸⁷Sr/⁸⁶Sr)i ratios?0.7035-0.7043?and generally positive?Nd?t??+1.64⁺5.37?,Nd model ages(T_DM?t?)in the range of 670⁹47Ma.Their ²⁰⁶Pb/²⁰⁴Pb of 17.890¹8.257,²⁰⁷Pb/²⁰⁴Pb of 15.452¹5.505,²⁰⁸Pb/²⁰⁴Pb of 37.209³7.867,?and?values were 5.08¹4.43 and 1.26⁴.75.The rock sequence has loss ⁸⁷Sr/⁸⁶Sr and positive?Nd?t?and low radiogenic Pb isotopic composition,reflecting the loss of subduction zone asthenosphere mantle magma source isotopic composition.The above information indicates that the region granodiorite-syenogranite sequence intrusions and volcanic rocks Sec Prat gaomiao group formed at326.3³06.2Ma,Gabbro-diorite-granodiorite sequence intrusion,alkali feldspar granite rock and independent Prat gaomiao Group three sections volcanic rocks formed 305.3Ma-299.03Ma.These data suggest that the region there are two different magmatic phases.Most importantly,our findings show that more than two-stage magmatic nature obvious turning point,a profound reflection of the important deep process of change and geodynamics.It has been proved Carboniferous fire hillock diorite-syenite and granite intrusions sequence Po gaomiao group Sec volcanic rocks typical of the continental margin arc magmatic rocks,geochemistry and isotopic characteristics,but the gabbro-diorite-granodiorite intrusion sequence showing subduction zones of lithospheric mantle magma nature of its Sr-Nd-Pb isotopic data reflects the asthenosphere mantle magma source relative losses.Carboniferous exposed in the Carboniferous continental margin arc magmatic belt core part,the local development EW with rock dike swarm,and having A-granite geochemical affinity for alkali-feldspar granite magma intrusion doublet,indicating that formed in extensional tectonic environment,significantly different from the earlier continental margin arc intrusive rocks?Carboniferous granodiorite-syenogranite sequence?of compressional tectonic environment.District late Carboniferous tectonic environment change has also been a significant shift in the nature of volcanism support.Our latest research shows Po gaomiao Group Sec calc-alkaline volcanic rocks?326.3³07.3Ma?formed on the margin squeeze arc environment,Po gaomiao group three sections alkaline rhyolite?305.3Ma-303.04Ma?reflects the extensional environment.