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华北太古宙高压基性麻粒岩的两类PT轨迹及其构造意义:矿物化学和变质作用研究 总被引：5，自引：4，他引：1
在华北克拉通桑干构造带中,分布有许多太古宙高压基性麻粒岩,呈大小不等的岩块产于强烈变形的TTG片麻岩、二辉麻粒岩、混合岩和花岗岩中.高压麻粒岩富含石榴石斑晶,斑晶内部钙铝榴石含量明显高于边缘,一般可达25%～28%.许多石榴石含有单斜辉石包体,A12O3含量高达7.4%～11.2%,相应的契尔马克分子比例为12%～18%.这些成分特征指示了早期相对较高的变质压力.石榴石斑晶广泛发育后成合晶反应边,是Pl-Opx-Amp-Mt组合的放射状细粒交生体,邻接的单斜辉石和石榴石斑晶边缘与后成合晶组合近于反应平衡,单斜辉石Al2O3含量小于5%,石榴石边缘的钙铝榴石含量也大大低于核部.这些都显示了压力较低条件下石榴石和单斜辉石的分解.温度压力的计算结果揭示出高压麻粒岩的两类PT轨迹,它们早期的变质作用都表现出较高的压力(1.2～1.45GPa).一部分高压麻粒岩具有顺时针的PT轨迹,并显示升温减压和近等温减压过程.它们很可能形成于晚太古代某种型式的俯冲和碰撞构造过程.另一部分高压麻粒岩具有逆时针的PT轨迹,显示降温降压过程,并且早期变质温度高达1050C.它们很可能来自碰撞之前的岛弧下地壳底部.在碰撞阶段的后期,这些不同成因的高压麻粒岩都被卷入了与碰撞构造直接相关的桑干构造带,经历共同的构造抬升过程.桑干构造带可以认为是构造缝合带. 相似文献
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The granulites and granitoids around Rayagada in the north central part of the Eastern Ghats belt display structural and petrological
differences when compared to similar rocks from Chilka and Jenapore in the northern Eastern Ghats. The impress of F1 deformation is almost erased while that ofF
3 is muted. The metapelites have a restricted chemical range and are non-migmatitic. There are two varieties of leptynitic
granitoids, one of which is interlayered with yet another S-type granite containing cordierite. The maximum recorded temperature
from geothermometers is 780‡C, but the magnitude of pressure is comparatively low, the highest value being 6.3 kbar. Another
distinctive feature of the pressuretemperature record is the absence of evidence of decompression in the lower realms of pressure
and temperature. Metamorphic reactions that could be identified indicate cooling, a noteworthy reaction being the sillimanite
to andalusite transformation. Integration of data from pressure-temperature sensors suggest cooling at two pressures, 6 and
5 kbar. The generation of two types of granitoids from metapelites is interpreted to be due to intersection with solidus curves
for pelitic and graywacke-like compositions, constrained by recent experiments, at 6 and 5 kbar. The first melting occurred
on a prograde path while the second one was due to increase in temperature during exhumation at tectonic rates.
Thus inspite of a broad similarity in the geodynamic scenario across the northern part of the Eastern Ghat belt, differences
in exhumation rates and in style of melting were responsible for producing different signatures in the Rayagada granulite
terrane. 相似文献
3.
Within the metamorphic basement of the Coastal Cordillera of central Chile, the Western Series constitutes the high-pressure (HP)/low-temperature (LT) part (accretionary prism) of a fossil-paired metamorphic belt dominated by metagreywackes. In its eastern part, blocks derived from small lenses of garnet amphibolite with a blueschist facies overprint are locally intercalated and associated with serpentinite and garnet mica-schist. Continuously developed local equilibria were evaluated applying various independent geothermobarometric approaches. An overall anticlockwise PT path results. The prograde path evolved along a geothermal gradient of 15 °C/km, passing the high-pressure end of greenschist facies until a transient assemblage developed within albite-epidote amphibolite facies transitional to eclogite facies at peak metamorphic conditions (600–760 °C, 11–16.5 kbar; stage I). This peak assemblage was overprinted during an external fluid infiltration by an epidote blueschist facies assemblage at 350–500 °C, 10–14 kbar (stage II) indicating nearly isobaric cooling. The retrograde equilibration stage was dated with a Rb–Sr mineral isochron at 305.3±3.2 Ma, somewhat younger (296.6±4.7 Ma) in an adjacent garnet mica-schist. Localized retrograde equilibration continued during decompression down to 300 °C, 5 kbar. The retrograde evolution is identical in the garnet amphibolite and the garnet mica-schist.
The counterclockwise PT path contrasts the usual clockwise PT paths derived from rocks of the Western Series. In addition, their ages related to stage II are the oldest recorded within the fossil wedge at the given latitude. Its “exotic” occurrence is interpreted by the path of the earliest and deepest subducted material that was heated in contact with a still hot mantle. Later accreted and dehydrated material caused hydration and cooling of the earliest accreted material and the neighbouring mantle. After this change also related to rheological conditions, effective exhumation of the early subducted material followed at the base of the hydrated mantle wedge within a cooler environment (geothermal gradient around 10–15 °C/km) than during its burial. The exotic blocks thus provide important time markers for the onset of subduction mass circulation in the Coastal Cordillera accretionary prism during the Late Carboniferous. Continuous subduction mass flow lasted for nearly 100 Ma until the Late Triassic. 相似文献
4.
新疆阿勒泰地区发育了红柱石-矽线石型递增变质带,由绿泥石-黑云母带、黑云母-石榴石带、石榴石-十字石带、十字石-红柱石带和矽线石带组成,根据石榴石成分环带、变质与变形关系、矿物共生组合演化等特征,将变质作用分为峰前期、峰期和峰后期3个演化阶段。峰前期、峰期为连续的递增变质过程,形成典型的中-低压过渡型递增变质带,峰后期属于退变质过程。据石榴石一斜长石一黑云母-白云母-石英组合内部一致地质温压计估算出峰期温度-压力：T=580℃～670℃,P一0．4GPa～0．5GPa。变质作用演化具有顺时针的PTt轨迹,代表陆壳有一定程度的构造增厚,但幅度不大,没有大规模的陆壳俯冲或拆沉作用,这种增厚可能以陆壳的构造叠置机制为主。总体相当于地体间斜向走滑兼有一定垂直分量的拼合过程的地球动力学机制。 相似文献
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Phase Equilibria of Hornblende‐Bearing Eclogite in the Western Dabie Mountain,Central China 总被引：1，自引：0，他引：1
The high-pressure (HP) eclogite in the western Dabie Mountain encloses numerous hornblendes, mostly barroisite. Opinions on the peak metamorphic P-T condition, PT path and mineral paragenesis of it are still in dispute. Generally, HP eclogite involves garnet, omphacite, hornblendes and quartz, with or without glaucophane, zoisite and phengite. The garnet has compositional zoning with XMg increase, XCa and XMn decrease from core to rim, which indicates a progressive metamorphism. The phase equilibria of the HP eclogite modeled by the P-T pseudosection method developed recently showed the following: (1) the growth zonation of garnet records a progressive metamorphic PT path from pre-peak condition of 1.9–2.1 GPa at 508°C–514°C to a peak one of 2.3–2.5 GPa at 528°C–531°C for the HP eclogite; (2) the peak mineral assemblage is garnet+omphacite+glaucophane+quartz±phengite, likely paragenetic with lawsonite; (3) the extensive hornblendes derive mainly from glaucophane, partial omphacite and even a little garnet due to the decompression with some heating during the post-peak stage, mostly representing the conditions of about 1.4–1.6 GPa and 580°C–640°C, and their growth is favored by the dehydration of lawsonite into zoisite or epidote, but most of the garnet, omphacite or phengite in the HP eclogite still preserve their compositions at peak condition, and they are not obviously equilibrious with the hornblendes. 相似文献
9.
恒山西段广泛发育石榴石角闪岩和麻粒岩包体,石榴石斑晶的生长环带都完好地保留,甚至晚期的麻粒岩相变质条件也未使其破坏,显示了快速的构造过程和有限的热松弛。石榴石核心保存了早期高压角闪岩相的矿物组合和矿物化学特征,变质作用条件为６００—６５０℃和大约１１ ＧＰａ。随后,石榴石麻粒岩的变质温度和压力继续上升,达到高压麻粒岩相,大约为８１０℃和１２５ ＧＰａ。两类岩石变质作用的晚期都经历了特殊的减压升温过程,显示典型的顺时针ＰＴ 轨迹。因此可以推断,恒山西段在太古宙末或早元古代很可能经历了某种形式的大陆俯冲或碰撞过程,并且随后发育逆冲和一系列壳内变形剪切等。 相似文献
10.
MEI Hualin WU Changhua Tianjin Institute of Geology Mineral Resources CAGS Tianjin. JIN Wei Changchun University of Earth Sciences Changchun Jilin Hao Zhiguo Liu Xinzhu 《《地质学报》英文版》1998,72(1):14-28
Four distinct lithe-tectonic belts (zones) in the Yinshan area, North China, were identified by pressure-temperature contours and litho-tectonic features, such as the Sanggan granulite belt, Jining metasedimentary belt. Wulashan-Daqingshan front tectonic zone and Se' eratengshan belt. This area witnessed two important thermo-tectonic events. The older one is c. 2.5 Ga while the younger one c. 1.9 Ga. The Se' ertengshan Neoarchaean terrane features a clockwise PT path with the decompression ranging from > 1500 MPa to 800-1000 MPa in the Se' ertengshan belt, which implies an island arc setting. The Sanggan belt is a Mesoarchaean microcontinent reworked by Neoarchaean magma underplating, which shows an counterclockwise PT path. During the Palaeoproterozoic period, two Archaean continent (arc) collided. The Archaean basement of the Sanggan and Wulashan-Daqingshan belts overthrust northwards, the PTt paths of basement show a decompression from 1000-1200 MPa to 500-700 MPa. The PT paths of the Jining and Erda 相似文献