摘要
内蒙古东部西拉木伦河以北双井子花岗岩侵入古生代晚期增生-碰撞杂岩,遭受了中生代强烈韧性构造变形的改造,在岩石学方面以含有白云母为特征,在岩石化学方面表现为富SiO_2、Al_2O_3和碱质,Na_2O/K_2O比值小于1,A/CNK比值为1.02～1.08,A/NK比值为1.20～1.35,轻稀土元素富集,Eu异常不明显,微量元素中Ti和Sc亏损、特别是Nb和Ta亏损、Th相对富集,^(143)Nd/^(144)Nd同位素比值介于0.512229～0.512286,^(143)Nd/^(144)Nd初始比值为0.512068～0.512199,其ε_(Nd)(t)均为负值,介于-2.71～-5.28,Nd模式年龄介于1000～1300Ma;^(87)Sr/^(86)Sr同位素比值介于0.713516～0.722096,^(87)Sr/^(86)Sr初始比值为0.705756～0.709187。这些特征揭示出该岩体是壳源的,可能主要来源于古生代增生-碰撞杂岩和相对古老的大陆边缘的重熔。从该岩体采集的两个样品选出的锆石SHRIMP U-Pb年龄分别为229.2±4.1Ma和237.5±2.7Ma,表明该岩体是在三叠纪中期侵位的。结合区域地质资料和前人相关研究成果。推测西伯利亚与中朝古板块之间沿西拉木伦缝合带的碰撞始于二叠纪中期(约270Ma),于三叠纪中期结束;从三叠纪岩浆岩的露头推测,这一碰撞事件形成了从北山向东通过内蒙古南部到吉林中部的近东西走向的巨型山脉;区域上晚三叠世岩浆活动形成于该山脉演化晚期的伸展构造背景,标志着该区地壳演化新阶段的开始。
The Shuangjingzi granite intruded the Late Paleozoic accretion-collisional complex, which is exposed in the north of Xar Moron River, eastern Inner Mongolia. This pluton underwent the intensively ductile deformation during the Mesozoic, and is characterized by occurrence of muscovite in mineral assemblage, high SiO2, Al2O3 and alkaline content, low Na2O/K2O ratio （ 〈 1 ）, higher A/CNK （ 1.02 - 1.08） and A/NK （ 1.20-1.35） ratios, light REE enrichment with weak Eu anomalies, depleted Ti and Sc, especially depleted Nb and Ta but enriched Th, higher ^143Nd/^144 Nd （0.512229 -0. 512286 ） and （^143 Nd/^144 Nd）;（0. 512068 0. 512199） ratios, lower εNd （t） （ -2.71 ～- 5. 28） values with younger Nd depleted mantle model ages （ 1000-1300Ma） , higher s7 Sr/S6 Sr （0.713516 - 0.722096 ） and （ ^87 Sr/^86 Sr） ; （ 0. 705756 - 0. 709187 ） ratios in petro-chemistry, indicating that this pluton is crust-derived, probably mainly come from the re-melting of Paleozoic accretion-collisional complexes and older continental margins. SHRIMP U-Pb dating of zircons from two samples of this granite yields apparent ages of 229.2± 4.1 Ma and 237.2±2.7 Ma, indicating the occurrence of this pluton in the Middle Triassic. Available geological data make us get conclusions that the collision along the Xar Moron suture between Siberian and Sino-Korean paleo-plates began at middle Permian （ about 270Ma）, and ended in the middle Triassic, which led to uplifting of a huge EW-extended mountain from Beishan eastwards through southern Inner Mongolia to central Jilin during the early to middle Triassic, and that the Late Triassic magmatic activities in the area occurred in the extensional setting in the late stage of tectonic evolution of the mountain, implying the beginning of a new stage of the crustal evolution of the area.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2007年第3期565-582,共18页
Acta Petrologica Sinica
基金
国家自然科学重点基金项目(编号40132020)资助
