6第五章-動力變質(zhì)作用和接觸變質(zhì)作用概述

1、一一動力變質(zhì)巖動力變質(zhì)巖二二熱熱-接觸變質(zhì)巖接觸變質(zhì)巖未固結(jié)的固 結(jié) 的無面理的面理化的基質(zhì)的性質(zhì)構(gòu)造破碎強于重結(jié)晶構(gòu)造角礫構(gòu)造角礫巖碎裂巖系列初糜棱巖糜棱巖系列90重結(jié)晶為主變余糜棱巖 玻璃質(zhì)假玄武玻璃 碎裂巖系列碎裂巖系列(a) 構(gòu)造角礫巖構(gòu)造角礫巖; (b) 碎裂巖碎裂巖; (c) 假玄武玻璃假玄武玻璃. 糜棱巖系列糜棱巖系列 (a) 糜棱巖糜棱巖; (b) 千糜巖千糜巖; (c) 變余糜棱巖變余糜棱巖 縱向上：縱向上：一個深達下地殼的大型剪一個深達下地殼的大型剪切帶，從地表至地下不同切帶，從地表至地下不同深度深度P-TP-T條件不同，變形條件不同，變形機制不同，因而形成的動機制不同，因

2、而形成的動力變質(zhì)巖類型也不同力變質(zhì)巖類型也不同( (圖圖21-2)21-2)。 變形變強，脆性變形變強，脆性塑性塑性變形加強，脆性變形加強，脆性塑性塑性局限在侵人體與圍巖接觸帶附近圍巖之中圍繞侵入體分布局限在侵人體與圍巖接觸帶附近圍巖之中圍繞侵入體分布, 分分布寬度變化很大布寬度變化很大.由于變質(zhì)因素主要為由于變質(zhì)因素主要為T, 缺乏偏應(yīng)力缺乏偏應(yīng)力, 因而接觸因而接觸熱變質(zhì)巖一般熱變質(zhì)巖一般以具變晶結(jié)構(gòu)、無定向構(gòu)造為特征以具變晶結(jié)構(gòu)、無定向構(gòu)造為特征, 在接觸變質(zhì)暈外帶在接觸變質(zhì)暈外帶, 變余結(jié)變余結(jié)構(gòu)構(gòu)造發(fā)育構(gòu)構(gòu)造發(fā)育.但不排除繼承原巖定向性的繼承性定向構(gòu)造但不排除繼承原巖定向性的繼承性定

3、向構(gòu)造.接觸熱變質(zhì)屬于很低接觸熱變質(zhì)屬于很低PT變質(zhì)變質(zhì)(視地?zé)崽荻纫暤責(zé)崽荻?0km), 形形成深度淺成深度淺(通常通常P03GPa), 因而礦物成分上以紅柱石、堇青石因而礦物成分上以紅柱石、堇青石、硅灰石等低壓礦物為特征、硅灰石等低壓礦物為特征.由于導(dǎo)致接觸由于導(dǎo)致接觸-熱變質(zhì)的熱和流體來自侵入體熱變質(zhì)的熱和流體來自侵入體, 因而接觸變質(zhì)暈因而接觸變質(zhì)暈中出現(xiàn)自侵人體接觸帶向外變質(zhì)程度逐漸降低的變質(zhì)分帶中出現(xiàn)自侵人體接觸帶向外變質(zhì)程度逐漸降低的變質(zhì)分帶, 圍圍繞侵人體呈同心圈狀分布繞侵人體呈同心圈狀分布. 發(fā)育完整的接觸變質(zhì)帶發(fā)育完整的接觸變質(zhì)帶.因巖漿流體的作用因巖漿流體的作用, 接觸接

4、觸-熱變質(zhì)巖往往有夕卡巖等交代巖伴生熱變質(zhì)巖往往有夕卡巖等交代巖伴生.s大小大小s形狀形狀s方向方向s溫度溫度s組分組分高熱變質(zhì)作用高熱變質(zhì)作用例子例子變質(zhì)級別變質(zhì)級別增加增加Figure 21-14. Geologic Map and cross-section of the area around the Skiddaw granite, Lake District, UK. After Eastwood et al (1968). Geology of the Country around Cockermouth and Caldbeck. Explanation accompanyin

5、g the 1-inch Geological Sheet 23, New Series. Institute of Geological Sciences. London. Figure 21-15. Cordierite-andalusite slate from the middle zone of the Skiddaw aureole. From Mason (1978) Petrology of the Metamorphic Rocks. George Allen & Unwin. London. 1 mmFigure 21-16. Andalusite-cordieri

6、te schist from the inner zone of the Skiddaw aureole. Note the chiastolite cross in andalusite (see also Figure 22-49). From Mason (1978) Petrology of the Metamorphic Rocks. George Allen & Unwin. London. 1 mm 矽卡巖是瑞典文碎石或碎塊的意思矽卡巖是瑞典文碎石或碎塊的意思, 是瑞典的一個老礦山的術(shù)語是瑞典的一個老礦山的術(shù)語. 是指太古代的一些鐵礦和硫化物礦床是指太古代的一些鐵礦和硫化

7、物礦床, 交代石灰?guī)r形成交代石灰?guī)r形成 主要是由鈣、鎂硅酸鹽類礦物所組成主要是由鈣、鎂硅酸鹽類礦物所組成, 常為中粗粒粒狀變晶結(jié)構(gòu)常為中粗粒粒狀變晶結(jié)構(gòu), 塊狀構(gòu)造塊狀構(gòu)造. 常見的類型有常見的類型有: 鈣質(zhì)矽卡巖、鎂質(zhì)矽卡巖鈣質(zhì)矽卡巖、鎂質(zhì)矽卡巖. 巖性變化很大巖性變化很大. 常見造巖礦物有常見造巖礦物有: 鈣鋁鈣鐵榴石系的石榴子石鈣鋁鈣鐵榴石系的石榴子石;透輝石鈣鐵輝石系的單斜輝石透輝石鈣鐵輝石系的單斜輝石. 有時含硅灰石有時含硅灰石, 榍石榍石, 黑柱石等黑柱石等. 當(dāng)原巖為白云巖或其它鎂質(zhì)巖石時當(dāng)原巖為白云巖或其它鎂質(zhì)巖石時, 可以形成含硅鎂石族礦物可以形成含硅鎂石族礦物, 薔薇輝石薔

8、薇輝石, 鈣鎂橄欖石鈣鎂橄欖石, 鎂橄欖石鎂橄欖石, 金云母金云母, 尖晶石等礦物尖晶石等礦物. 原巖為原巖為凝灰?guī)r凝灰?guī)r, 侵入巖等硅酸鹽巖時侵入巖等硅酸鹽巖時, 還可以出現(xiàn)斜長石還可以出現(xiàn)斜長石, 普通角閃石普通角閃石, 符山石符山石, 斧石斧石, 方柱石等方柱石等. 巖石成因較復(fù)雜巖石成因較復(fù)雜, 目前通行的看法認(rèn)為目前通行的看法認(rèn)為: 鈣質(zhì)矽卡巖、鎂質(zhì)矽卡鈣質(zhì)矽卡巖、鎂質(zhì)矽卡巖主要是由中酸性侵入巖與鈣鎂碳酸鹽類巖石（石灰?guī)r、白云巖主要是由中酸性侵入巖與鈣鎂碳酸鹽類巖石（石灰?guī)r、白云質(zhì)灰?guī)r等）接觸時質(zhì)灰?guī)r等）接觸時, 由接觸交代作用所形成的一類巖石由接觸交代作用所形成的一類巖石. 矽卡巖

9、的外貌和顏色變化較大矽卡巖的外貌和顏色變化較大, 一般隨著礦物成分和粒一般隨著礦物成分和粒徑而變化徑而變化. 顏色常常為棕褐色、紅褐色、綠褐色、暗綠顏色常常為棕褐色、紅褐色、綠褐色、暗綠色、以及淺灰色等色、以及淺灰色等. 結(jié)構(gòu)多為主要為等?；虿坏攘Ａ钭兙ЫY(jié)構(gòu)結(jié)構(gòu)多為主要為等粒或不等粒粒狀變晶結(jié)構(gòu). 粒徑不等粒徑不等, 可以很細可以很細, 細到隱晶質(zhì)細到隱晶質(zhì), 也可以很粗粗到也可以很粗粗到500mm以上以上,一一般粒徑多在般粒徑多在120mm之間之間, 呈粒狀集合體呈粒狀集合體. 常含包含變晶結(jié)構(gòu)常含包含變晶結(jié)構(gòu), 環(huán)帶結(jié)構(gòu)環(huán)帶結(jié)構(gòu), 也可以出現(xiàn)各種交代變余也可以出現(xiàn)各種交代變余結(jié)構(gòu)、交代假

10、象結(jié)構(gòu)結(jié)構(gòu)、交代假象結(jié)構(gòu). 矽卡巖構(gòu)造多為塊狀、帶狀、條紋狀、斑塊狀、同心球矽卡巖構(gòu)造多為塊狀、帶狀、條紋狀、斑塊狀、同心球狀、角礫狀、晶簇狀狀、角礫狀、晶簇狀. 其還可以出現(xiàn)大量的空洞或空隙其還可以出現(xiàn)大量的空洞或空隙, 成為不規(guī)則的、被模狀、晶簇狀礦物充填或填滿成為不規(guī)則的、被模狀、晶簇狀礦物充填或填滿.Figure 29-2. A portion of the Alta aureole in Little Cottonwood Canyon, SE of Salt Lake City, UT, where talc, tremolite, forsterite, and periclas

11、e isograds were mapped in metacarbonates by Moore and Kerrick (1976) Amer. J. Sci., 276, 502-524. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.方鎂石方鎂石鎂橄欖石鎂橄欖石滑石滑石透閃石透閃石沖擊層沖擊層Figure 29-1. Chemographics in the CaO-MgO-SiO2 -CO2 -H2O system, projected from CO2 and H2

12、O. The green shaded areas represent the common composition range of limestones and dolostones. Due to the solvus between calcite and dolomite, both minerals can coexist in carbonate rocks. The dark red left half of the triangle is the area of interest for metacarbonates. Carbonated ultramafics occup

13、y the right half of the triangle. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Figure 29-3. T-XCO2 phase diagram for siliceous carbonates at P = 0.1 GPa. Calculated using the program TWQ of Berman (1988, 1990, 1991). The green area is the field in which tremolite

14、 is stable, the redish area is the field in which dolomite + diopside is stable, and the blue area is for dolomite + talc. Compatibility diagrams, similar to those in Figure 29-4, show the mineral assemblages in each field. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice

15、 Hall.Figure 29-6. T-XCO2 phase diagram for siliceous carbonates at P = 0.5 GPa, calculated using the program TWQ of Berman (1988, 1990, 1991). The light-shaded area is the field in which tremolite is stable, the darker shaded areas are the fields in which talc or diopside are stable. Winter (2001)

16、An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Figure 29-5. Metamorphic zones developed in regionally metamorphosed dolomitic rocks of the Lepontine Alps, along the Swiss-Italian border. After Trommsdorff (1966) Schweiz. Mineral. Petrogr. Mitt., 46, 431-460 and (1972) Schweiz. M

17、ineral. Petrogr. Mitt., 52, 567-571. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.F鎂橄欖石帶(Forsterite Zone):scalcite + brucite(氫氧鎂石氫氧鎂石) + clinohumite + spinelscalcite + monticellite + melilite + clintonite(綠脆云母綠脆云母)scalcite + monticellite + spurrite(灰硅鈣石灰硅鈣石) (or

18、tilleyite (粒硅鈣石粒硅鈣石) + clintonitesmonticellite + spurrite + merwinite + melilite(黃長石黃長石)F符閃石帶(Vesuvianite Zone):sVesuvianite (idocrase) + monticellite + spurrite + merwinite (默默硅鎂鈣石硅鎂鈣石) + melilitesvesuvianite + monticellite + diopside + wollastoniteF石榴石帶(Garnet Zone):sgrossular + diopside + wollastoniteFigure 21-17. Idealized N-S cross section (not to scale) through the quartz monzonite and the aureole at Crestm