The understanding of the subduction-related processes benefited by the studies of the high-pressure (HP) meta-morphic rocks from the western Alps. The most stimu-lating information was obtained from the inner part ...The understanding of the subduction-related processes benefited by the studies of the high-pressure (HP) meta-morphic rocks from the western Alps. The most stimu-lating information was obtained from the inner part of the western Alpine belt, where most tectonic units show an early Alpine eclogite-facies recrystallisation. This is especially true for the Austroalpine Sesia Zone and the Penninic Dora-Maira massif. From the Sesia zone,which consists of a wide spectrum of continental crust lithologies recrystallised to quartz-eclogite-facies min-eral assemblages, the first finding of a jadeite-bearingmeta-granitoid has been described, supporting evidencethat even continental crust may subduct into the mantle.From the Dora-Maira massif the first occurrence of regional metamorphic coesite has been reported, open-ing the new fertile field of the ultrahigh-pressure meta-morphism (UHPM), which is now becoming the rule in the collisional orogenic belts.展开更多
Some geologists reported their discovery of sandwiched low-grade metamorphic slabs within UHP metamorphic Complexes in Changpu, Yuexi County, Anhui Province. They also suggested that some coesite-bearing eclogites are...Some geologists reported their discovery of sandwiched low-grade metamorphic slabs within UHP metamorphic Complexes in Changpu, Yuexi County, Anhui Province. They also suggested that some coesite-bearing eclogites are igneous veins, which intruded low-grade metamorphic slabs and other related rocks. Moreover they further called in question to UHP matamorphic process and continental collision tectonism in the Dabieshan terrane. Based on our recent study so-called low-grade metamorphic slabs are strongly deformed fabric, fine-grained and tectonic recrystallized mylonites and tectonites. Their protolith rocks are garnet-bearing orthogneiss, eclogite and marble, as well as a few amounts of strongly deformed acid and basic veins. Their metamorphic, geochemical and geochronological characteristics are also identical with UHPM rocks and regional country orthogneisses. Therefore we conclude that there are not low-grade metamorphic slabs sand wiched with UHP metamorphic rocks in the Dabieshan terrane.展开更多
Zircon LA-ICP MS U-Pb dating of six metamorphic rocks and a metagranite (breccia) from southern basement of the Songliao Basin are reported in order to constrain the formation ages of basement. The basement metamorphi...Zircon LA-ICP MS U-Pb dating of six metamorphic rocks and a metagranite (breccia) from southern basement of the Songliao Basin are reported in order to constrain the formation ages of basement. The basement metamorphic rocks in the Songliao Basin mainly consist of metagabbro (L45-1), amphibolite (SN117), metarhyolitical tuff (G190), sericite (Ser) schist (N103), chlorite (Chl) schist (T5-1), biotite (Bi)-actinolite (Act)-quartz (Q) schist (Y205), and metagranite (L44-1). The cathodoluminesence (CL) images of the zircons from metagabbro (L45-1) and metagranite (L44-1) indicate that they have cores of magmatic origin and rims of metamorphic overgrowths. Their U-Pb isotopic ages are 1808±21 Ma and 1873±13 Ma, respectively. The zircons with oscillatory zoning from amphibolite (SN117) and Chl schist (T5-1), being similar to those of mafic igneous rocks, yield ages of 274 ± 3.4 Ma and 264 ± 3.2 Ma, re-spectively. The zircons from metarhyolitical tuff (G190) and Ser schist (N103) display typical magmatic growth zoning and yield ages of 424 ± 4.5 Ma and 287 ± 5.1Ma, respectively. Most of zircons from Bi-Act-Q schist (Y205) are round in shape and different in absorption degree in the CL images, implying their sedimentary detritals. U-Pb dating yield concordant ages of 427 ± 3.1Ma, 455 ± 12 Ma, 696 ± 13 Ma, 1384±62 Ma, 1649±36 Ma, 1778±18 Ma, 2450±9 Ma, 2579±10 Ma, 2793±4 Ma and 2953±14 Ma. The above-mentioned results indicate that the Precambrian crystalline basement (1808―1873 Ma) exists in the southern Songliao Basin and could be related to tectonic thrust, and that the Early Paleozoic (424―490 Ma) and Late Paleozoic magmatisms (264―292 Ma) also occur in the basin basement, which are consistent with the ages of the detrital zircons from Bi-Act-Q schist in the basement.展开更多
In this report, it is proven through stable iso-topic geochronological study that for the Jurassic sedimen-tary rocks in the Dushan area of Anhui Province, the source materials derived from high-pressure and ultrahigh...In this report, it is proven through stable iso-topic geochronological study that for the Jurassic sedimen-tary rocks in the Dushan area of Anhui Province, the source materials derived from high-pressure and ultrahigh-pressure metamorphic rocks are the products of subduction and ex-humation of the Yangtze plate under the North China plate during the Triassic period. The cobble of high-pressure or ultrahigh-pressure metamorphic rock in the Fenghuangtai Formation of Hefei Basin has Rb-Sr isotopic isochron age of phengite, apatite and whole rock, 232.1±2.1 Ma (MSWD = 0.59). Plateau ages of 40Ar/39Ar age spectra of detrital phengites in the Sanjianpu and Fenghuangtai formations are concordant, and they are 216.5±0.6 Ma and 217.4±1.3 Ma, respectively.展开更多
文摘The understanding of the subduction-related processes benefited by the studies of the high-pressure (HP) meta-morphic rocks from the western Alps. The most stimu-lating information was obtained from the inner part of the western Alpine belt, where most tectonic units show an early Alpine eclogite-facies recrystallisation. This is especially true for the Austroalpine Sesia Zone and the Penninic Dora-Maira massif. From the Sesia zone,which consists of a wide spectrum of continental crust lithologies recrystallised to quartz-eclogite-facies min-eral assemblages, the first finding of a jadeite-bearingmeta-granitoid has been described, supporting evidencethat even continental crust may subduct into the mantle.From the Dora-Maira massif the first occurrence of regional metamorphic coesite has been reported, open-ing the new fertile field of the ultrahigh-pressure meta-morphism (UHPM), which is now becoming the rule in the collisional orogenic belts.
文摘Some geologists reported their discovery of sandwiched low-grade metamorphic slabs within UHP metamorphic Complexes in Changpu, Yuexi County, Anhui Province. They also suggested that some coesite-bearing eclogites are igneous veins, which intruded low-grade metamorphic slabs and other related rocks. Moreover they further called in question to UHP matamorphic process and continental collision tectonism in the Dabieshan terrane. Based on our recent study so-called low-grade metamorphic slabs are strongly deformed fabric, fine-grained and tectonic recrystallized mylonites and tectonites. Their protolith rocks are garnet-bearing orthogneiss, eclogite and marble, as well as a few amounts of strongly deformed acid and basic veins. Their metamorphic, geochemical and geochronological characteristics are also identical with UHPM rocks and regional country orthogneisses. Therefore we conclude that there are not low-grade metamorphic slabs sand wiched with UHP metamorphic rocks in the Dabieshan terrane.
基金Supported by the National Oil-Gas Special Project (Grant No. XQ-2004-07)SinoPetrol & Chemical Corporation (Grant No. P04031)the Key Laboratory of Continental Dynamics, Northwest University
文摘Zircon LA-ICP MS U-Pb dating of six metamorphic rocks and a metagranite (breccia) from southern basement of the Songliao Basin are reported in order to constrain the formation ages of basement. The basement metamorphic rocks in the Songliao Basin mainly consist of metagabbro (L45-1), amphibolite (SN117), metarhyolitical tuff (G190), sericite (Ser) schist (N103), chlorite (Chl) schist (T5-1), biotite (Bi)-actinolite (Act)-quartz (Q) schist (Y205), and metagranite (L44-1). The cathodoluminesence (CL) images of the zircons from metagabbro (L45-1) and metagranite (L44-1) indicate that they have cores of magmatic origin and rims of metamorphic overgrowths. Their U-Pb isotopic ages are 1808±21 Ma and 1873±13 Ma, respectively. The zircons with oscillatory zoning from amphibolite (SN117) and Chl schist (T5-1), being similar to those of mafic igneous rocks, yield ages of 274 ± 3.4 Ma and 264 ± 3.2 Ma, re-spectively. The zircons from metarhyolitical tuff (G190) and Ser schist (N103) display typical magmatic growth zoning and yield ages of 424 ± 4.5 Ma and 287 ± 5.1Ma, respectively. Most of zircons from Bi-Act-Q schist (Y205) are round in shape and different in absorption degree in the CL images, implying their sedimentary detritals. U-Pb dating yield concordant ages of 427 ± 3.1Ma, 455 ± 12 Ma, 696 ± 13 Ma, 1384±62 Ma, 1649±36 Ma, 1778±18 Ma, 2450±9 Ma, 2579±10 Ma, 2793±4 Ma and 2953±14 Ma. The above-mentioned results indicate that the Precambrian crystalline basement (1808―1873 Ma) exists in the southern Songliao Basin and could be related to tectonic thrust, and that the Early Paleozoic (424―490 Ma) and Late Paleozoic magmatisms (264―292 Ma) also occur in the basin basement, which are consistent with the ages of the detrital zircons from Bi-Act-Q schist in the basement.
基金supported by the State Key Basic Research Development Program of China(Grant No.G1999075507)
文摘In this report, it is proven through stable iso-topic geochronological study that for the Jurassic sedimen-tary rocks in the Dushan area of Anhui Province, the source materials derived from high-pressure and ultrahigh-pressure metamorphic rocks are the products of subduction and ex-humation of the Yangtze plate under the North China plate during the Triassic period. The cobble of high-pressure or ultrahigh-pressure metamorphic rock in the Fenghuangtai Formation of Hefei Basin has Rb-Sr isotopic isochron age of phengite, apatite and whole rock, 232.1±2.1 Ma (MSWD = 0.59). Plateau ages of 40Ar/39Ar age spectra of detrital phengites in the Sanjianpu and Fenghuangtai formations are concordant, and they are 216.5±0.6 Ma and 217.4±1.3 Ma, respectively.
