Remind Igneous rocks ( 화성암류 ) : 마그마로부터 Lecture 3 Igneous Rocks: Their Structures and Texture 형성된결정질또는유리질암석 ( 냉각작 용및결정화작용 ) Magma : 화학적 / 물리학적으로복잡하고광물을만들수있는다양한분자들을포 함하고있는고온의용융체 Plate Tectonic - Igneous Genesis 1. Mid-ocean Ridges 2. Intracontinental Rifts 3. Island Arcs 4. Active Continental Margins 5. Back-arc Basins 6. Ocean Island Basalts 7. Miscellaneous Intra- Continental Activity kimberlites, carbonatites, anorthosites... Magma 맨틀또는하부지각에서형성됨. 주변과의밀도차이등으로인해서지표로상승이동 다양한환경에따라서여러가지암석이만들어짐 Volcanic rocks( 화산암 ) : 분출, 지표근처에서결정화 Plutonic rocks( 심성암 ) : 심부에서결정화작용됨. 화성암의인지및결정화과정 야외관찰 동시대의화산분출 화성암의구분및명명법 Texture ( 조직 ) Structure ( 구조 ) Composition ( 성분 ) 현존화성암류의특징 ( 구조 ) 실험적연구귀납적, 광물학적연구, 조직연구 ( 현미연역적추론경이용 ) 화학분석 용융체내에서화학반응과결 입자크기정도스케일에서암석의특징 ( 입자크기, 모양, 방향성, 분포, 상호간의관계등을관찰 ) 입자크기보다큰규모의스케일에서특징 ( 물리적인배열, 엽리, 구멍, 균열, 단층, 습곡등을관찰 ) 주원소 (Major element) 미량원소 (Trace element) 희토류원소 (Rare earth element; REE) 동위원소 (Isotope) 정화작용실험 물리적특징 화학적특징 1
화성암의인지과정 화성암의구조 (Structure) : 마그마분출로인하여형성된 구조 ( 대부분화산또는 ) Structure 대, 중, 소구조로구분 관입구조 : 지표의아래에서형성된구조 Texture Sampling Microscopic analysis Chemical analysis 화성암의구조 (Structure) Structures and Field Relationships 분출암 관입암 유리질 - 세립질, 냉각주변상은바닥에국한 세립 - 조립질 냉각주변상은암체의가장자리 ( 내부보다세립 ) 암체하부의산화토대와약한변성작용산화토대없고, 넓은접촉변성작용 표면이불규칙, 상위에퇴적물 ( 암 ) 하위암석의암편포함기공이나행인주변암석의변형유발없음 암체의표면이불규칙포획암기공과행인없음주변암석의변형유발 Volcanic landforms associated with a central vent (all at same scale). 대구조 : 용암대지 / 현무암평원, 화성쇄설암상 ( 혼합형 ), 순상화산, 혼합화산구 ( 층상화산 ) 대구조 : 용암대지 / 현무암평원, 화성쇄설암상 ( 혼합형 ), 순상화산, 혼합화산구 ( 층상화산 ) Basaltic plain pyroclastic sheet 2
대구조 : 용암대지 / 현무암평원, 화성쇄설암상 ( 혼합형 ), 순상화산, 혼합화산구 ( 층상화산 ) 대구조 : 용암대지 / 현무암평원, 화성쇄설암상 ( 혼합형 ), 순상화산, 혼합화산구 ( 층상화산 ) Mt. Fuji Shield volcano Strata volcano 분화구 / 칼데라 중구조 : 화성암설구 ( 분석구 ), 용암류, 도옴 Caldera & resurgent caldera (Cf. cauldron & resurgent cauldron, craters) The photo shows the eruption of Paricutin V olcano, Mexico, a classic example of a cinder cone. 중구조 : 화성암설구 ( 분석구 ), 도옴 (dome), 용암류 중구조 : 화성암설구 ( 분석구 ), dome, 용암류 Lava dome(volcanic dome) formed by the in-,ex-trusion or both of viscous siliceous magm a. Pahoehoe lava : smooth, vesicular, ropy surface. 3
용암류 Aa lava : rough, irregular flow tops, loose fragment 소구조 : 분화구, 리소피시 (Lithophysae), 화산압력구릉 (Pressure ridge), 용암동굴 (Lava tube), 주상절리 (Columnar joint), 유동띠 (Flow banding), 화산탄 (Bomb) Columnar joint : pencil-like cooling structure. 소구조 : 분화구, 리소피시 (Lithophysae), 화산압력구릉 (Pressure ridge), 용암동굴 (Lava tube), 주상절리 (Columnar joint), 유동띠 (Flow banding), 화산탄 (Bomb) Figure 4-13. a. Schematic drawing of columnar joints in a basalt flow, showing the four common subdivisions of a typical flow. The column widths in (a) are exaggerated about 4x. After Long and Wood (1986) Geol. Soc. Amer. Bull., 97, 1144-1155. b. Colonnade-entablature-colonnade in a basalt flow, Crooked River Gorge, OR. John Winter and Prentice Hall. Pillow lava : extruded under water 4
소구조 : 리소피시 (Lithophysae) Small Structure : Baked zone ( 산화토대 ) : weathering of a flow surface followed by extrusion of hot lava over the soil developed on the weathered surface will produce a brick-red zone of oxidized material Lithophsae : Hollow, bubble-like, or roselike spherulites, usually with a concentric structure, that occur in rhyolite, obsidian, and related rocks. (Cf: lithophysa.) Small Structure : Small Structure : 동원포획암 & 포획암 기공 & 행인 Small Structure : 소구조 : 화산쇄설물 쇄설물 화산회 화산력 화산탄, 암괴 직경 (mm) ~ 2 2 ~ 64 64 ~ Lapilli Bomb Flow banding ( 유동띠 ) Ash 5
Figure 4-18. Types of pyroclastic flow deposits. After MacDonald (1972), Volcanoes. Prentice-Hall, Inc., Fisher and Schminke (1984), Pyroclastic Rocks. Springer-Verlag. Berlin. a. collapse of a vertical explosive or plinian column that falls back to earth, and continues to travel along the ground surface. b. Lateral blast, such as occurred at Mt. St. Helens in 1980. c. Boilingover of a highly gas-charged magma from a vent. d. Gravitational collapse of a hot dome (Fig. 4-18d). Figure 4-16. Approximate aerial extent and thickness of Mt. Mazama (Crater Lake) ash fall, erupted 6950 years ago. After Young (1990), Unpubl. Ph. D. thesis, University of Lancaster. UK. 관입구조 (Table 2.3) 대구조저반 (batholith), 암주 (Stock), 분상암체 (Lopolith), 현수체 (Roof pendent) 중구조암주, 암맥 (dike), 원추형관입암상 (Cone Sheet), 암경 (Pipe, neck, vent), 깔때기형암체 (Funnel), 큐폴라 (Cupola), 관입암상 (Sill), 병반 (Laccolith), 패콜리스 (Phacolith), 현수체, 쉬리에렌도옴 (Schlieren dome)/ 아치 (arch) 소구조암맥, 돌기암맥 (Apophysis), 맥 (Vein), 관입암상, 엽리 (foliation), 쉬리에렌, 포획암, 동원포획암, 화성성층 (Layering), 선구조 (Lineation) 심성암체 (Pluton) : 심성암으로구성된암체를나타내는일반적인형식으로, 화강암질 (granitic) 조직을갖는다. 화강암질조직 : 화강암및이와관련된암석들의조직적특징을총칭하는말이다 ( 화강암을생각하면됨 ; 괴상, 등립질의중립질이상의암석 ). Intrusive structure (Table 2.3) : Major structure Batholith ( 저반 ) : plutonic bodies having map area of 100 km 2 and more. Cf) Stock ( 암주 ) : less than 100 km 2 mainly composed of granitic rocks Earlier idea(fig. 2.11c) : Steep-side, sylinderlike, great depth(bottomless) Ex. Sierran crust : elongated tabular or lensshaped batholith (<30 km thickness) 6
Intrusive structure 한반도의저반과암주 Red area : Daebo granite ( 저반 ) purple area : Bulkuksa granite ( 암주 ) Roof pendant( 현수체 ) : 관입암체위에놓인형상의고기변성암이나퇴적암 Schlieren(flow layer) domes and arches : tabular, diffuse, disk-like concentration of minerals within an igneous rock mass Cupolar : dome-shaped projection of igneous rock of a batholith Apophysis(offshoot; 돌기 ) : intrusion detached from its source a) Lopolith( 분상암체 ) : 대규모의접시모양의층상관입암체 (uncommon, economic) b) Sill( 관입암상 ) : 층의경계사이를관입한편판형의암체 c) Laccolith( 병반 ) : 층의경계사이를관입한위로볼록한렌즈모양의관입암체 d) Dike( 암맥 ) : 부조화적인평판형관입암체 The sill and dike with xenolith in the Precambrian basement rock. Yeoncheon, South Korea. a) Lopolith( 분상암체 ) : large, dishshape, layerd intrusion.(uncommon, economic) Dike( 암맥 ) : 복합적암맥 7
Virginia Dale ring dike d) 암전 (bysmalith): A roughly vertical cylindrical igneous intrusion, bounded by steep faults. It has been interpreted as a type of laccolith. Cf: bell-jar intrusion e) 패콜리스 (Phacolith) : lenticular intrusions, along fold axes f) Funnel : solid plutonic bodies in shich the layering dips inward, just as do the dikes of cone sheets. g) Cone sheet( 원추형관입암상 ) : downward-pointing cones in form Ring dike( 환상암맥 ) : verticlal, cylindrical in form 모두 cauldron collapse 와관련깊음 Figure 4-23. The formation of ring dikes and cone sheets. a. Cross section of a rising pluton causing fracture and stoping of roof blocks. b. Cylindrical blocks drop into less dense magma below, resulting in ring dikes. c. Hypothetical map view of a ring dike with N-S striking country rock strata as might result from erosion to a level approximating X-Y in (b). d. Upward pressure of a pluton lifts the roof as conical blocks in this cross section. Magma follows the fractures, producing cone sheets. Original horizontal bedding plane shows offsets in the conical blocks. (a), (b), and (d) after Billings (1972), Structural Geology. Prentice-Hall, Inc. (c) after Compton (1985), Geology in the Field. Wiley. New York. Figure 4-24. b. Cone sheets in the same area of Mull, after Ritchey (1961), British Regional Geology. Scotland, the Tertiary Volcanic Districts. Note that the yellow felsite ring dike in part (a) is shown as the red ring in the NW of part (b). British Geological Survey. Major structure vein : tabular bodies form fracture fillings(dike type). that consist of 1-2 minerals (quartz or calcite) Foliation( 엽리 ) Volcanic neck (pipe, vent; 암경 ) : residue of erosion at volcanic cone. Lineation( 선구조 ) layering( 화산성층 ) 8
Texture of Igneous Rocks Textures of Igneous Rocks Igneous rock = glass ± crystal ±fragment 조직 ( 미시적인특징 ) Fig. 2.19. Igneous rock texture plotted in terms of crystallinity and grain size. Arrows indicate a range of grain size within a single rock Photomicrograph of hypocrystalline texture crystal glass 현정질 (phaneritic) 과비현정질 (aphanitic) 현정질과비현정질암석의육안관찰 Photograph of holohyaline texture 현정질 (phaneritic) 과비현정질 (aphanitic) Pegmatitic( 페그마타이트질 ; 거정질 ) 현정질과비현정질암석의현미경사진 9
반상 (porphyritic) 조직 : 반정 + 석기 감람석반상현무암 : 감람석의반정과미립의감람석및사장석의석기로구성 Width = 6 mm. Maui, Hawaii. Aphyric( 무반정상 ) : 화산암류는반정이없음 (opp. phyric; 반정상 ) Microphyric ( 미반상 ): 반정 (phenocrysts) 과석기 (groundmass) 가비현정질 Cf) 비현정질반상조직, 현정질반상조직 구성광물의결정모양에따라... Idiomorphic-granular ( 자형입상 ) : 주로 euhedral Hypidiomorphic-granular ( 반자형입상 ): subhedral (Fig. 2.22) allotriomorphic-granular ( 타형입상 ) : anhedral crystal. 조직은확실한입자들의모양, 방향성, 상호관계등에의해특징을이루고있음. See Table 2.5 Figure 3-7. 초기에형성된자형의휘석과후기에간극을메운사장석 ( 평행쌍정 ). Stillwater complex, Montana. Field width 5 mm. John Winter and Prentice Hall. TAble 2.5. Names of Special Igneous Rock Texture Volcanic Plutonic Other Microlitic Spherulitic Vitrophyric Intersertal Intergranular Felty Pilotaxitic Trachytic Subophitic Ophitic Dictytaxitic Glomeroporphyritic Pyroclastic Seriate Spinifex Poikilitic Graphic Ophitic Subophitic Kiabasic Orthocumulate Mesocumulate Adcumulate Symplectic Myrmekitic Seriate Trachytoidal Granophyric Zoned Corona Kelphytic rim Rapikivi Epitaxial Poikilitic Microlitic( 미반상 ) : Kind of porphyritic. microlite( 작은침상결정 ) + glassy groundmass Spherulitic ( 구과상 ) 침상광물이방사상으로성장 10
Vitrophyric( 유리반정상 ) : Kind of porphyritic Small crystal phenocrysts + glassy groundmass Intersertal ( 인터서탈 ) 조직 : 주로직사각형의사장석과미립또는유리질의석기가있는것 Trachytic ( 조면암상 ) : Intersertal 조직에서장석류가배열된조직 Intergranular texture ( 입간조직 ) : 휘석과다른광물의입자가직사각형의사장석사이에끼어있는모습 Intersertal texture Trachytic texture 오피틱조직 (Ophitic texture) : ( 감람석반려암 ) 커다란단사휘석이사장석을둘러싼형태. ( 사장석이먼저생기고휘석이나중에생겼음 ) 휘석 > 장석 Vesicular ( 다공질 ) : the escape of gas leaves vesicles. Pumiceous ( 부석질 ) : vesicles become elongate into fine tabular hole (silica-rich, rhyolitic magmas) Poikilitic : 거정내부에불규칙한다른광물포유물존재 Graphic ( 문상 ) : 포이킬리틱조직과유사. 정장석내부에일정한광물배열 (Cf. Micrographic) Subophitic texture 포이킬리틱한휘석 (oikocrysts) 이커다란사장석결정들사이로성장하고상대적으로작은사장석들을에워싼형태 Base width = 17 mm. 휘석 = 장석, Myrmekitic : Irregular grains of quartz are intergrown within sodic plagioclase Granophyric ( 문상암질 ) : Irregular grains of quartz are intergrown within alkali feldspar. Symplectic : 벌래먹은모양의조직을총칭. 인접두광물의반응으로형성 Figure 3-14. Development of cumulate textures. a. Crystals accumulate by crystal settling or simply form in place near the margins of the magma chamber. In this case plagioclase crystals (white) accumulate in mutual contact, and an intercumulus liquid (pink) fills the interstices. b. Orthocumulate: intercumulus liquid crystallizes to form additional plagioclase rims plus other phases in the interstitial volume (colored). There is little or no exchange between the intercumulus liquid and the main chamber. After Wager and Brown (1967), Layered Igneous Rocks. Freeman. San Francisco. 11
Corona ( 외륜 ) or reaction rim ( 반응연 ) : 한광물을중심으로방사상으로자란광물 Figure 3-14. Development of cumulate textures. c. Adcumulates: open-system exchange between the intercumulus liquid and the main chamber (plus compaction of the cumulate pile) allows components that would otherwise create additional intercumulus minerals to escape, and plagioclase fills most of the available space. d. Heteradcumulate: intercumulus liquid crystallizes to additional plagioclase rims, plus other large minerals (hatched and shaded) that nucleate poorly and poikilitically envelop the plagioclases.. After Wager and Brown (1967), Layered Igneous Rocks. Freeman. San Francisco. Igneous Textures Figure 3-5. a. Compositionally zoned ( 성분적인누대구조 ) hornblende phenocryst with pronounced color variation visible in plane-polarized light. Field width 1 mm. b. Zoned plagioclase twinned on the carlsbad law. Andesite, Crater Lake, OR. Field width 0.3 mm. John Winter and Prentice Hall. Figure 3-6. Examples of plagioclase zoning profiles determined by microprobe point traverses. a. Repeated sharp reversals attributed to magma mixing, followed by normal cooling increments. b. Smaller and irregular oscillations caused by local disequilibrium crystallization. c. Complex oscillations due to combinations of magma mixing and local disequilibrium. From Shelley (1993). Igneous and Metamorphic Rocks Under the Microscope. Chapman and Hall. London. Igneous Textures Olivine melt reaction = pyroxene Figure 3-4. a. Skeletal olivine phenocryst with rapid growth at edges enveloping melt at ends. Taupo, N.Z. b. Swallow-tail plagioclase in trachyte, Remarkable Dike, N.Z. Length of both fields ca. 0.2 mm. From Shelley (1993). Igneous and Metamorphic Rocks Under the Microscope. Chapman and Hall. London. Figure 3-10. Olivine mantled by orthopyroxene in (a) plane-polarized light and (b) crossed nicols, in which olivine is extinct and the pyroxenes stand out clearly. Basaltic andesite, Mt. McLaughlin, Oregon. Width ~ 5 mm. John Winter and Prentice Hall. 12
Plagioclase melt reaction Figure 3-11. a. Sieve texture in a cumulophyric cluster of plagioclase phenocrysts. Note the later non-sieve rim on the cluster. Andesite, Mt. McLoughlin, OR. Width 1 mm. John Winter and Prentice Hall. Figure 3-11. b. Resorbed and embayed olivine phenocryst. Width 0.3 mm. John Winter and Prentice Hall. Figure 3-12. a. 조면암질조직 (Trachytic texture) : 사장석의미세한반정이마그마의흐름으로인해서배열되어있는조직. 반정주변의흐름관찰. Trachyte, Germany. Width 1 mm. From MacKenzie et al. (1982). Figure 3-11. c. Hornblende phenocryst dehydrating to Fe-oxides plus pyroxene due to pressure release upon eruption, andesite. Crater Lake, OR. Width 1 mm. John Winter and Prentice Hall. Figure 3-12. b. Felty or pilotaxitic texture : 은미정질의화성암에서미세한광물들 (microphenocrysts) 이불규칙하게배열되어있는것. 현무암질안산암. Mt. McLaughlin, OR. Width 7 mm. Figure 3-13. Flow banding in andesite. Mt. Rainier, WA. 화산재 Figure 3-15. 연정조직 (Intergranular texture) : 현무암. Columbia River Basalt Group, Washington. Width 1 mm. 응회암 (tuff or ignimbrite) Figure 3-16. a. 부석 (pumice; left) 에서공기방울사이의간극용암 (red) 가부서진부석질에포함된화산재에서세꼭지별모양의유리파편이됨. 만일이것들이화산재의퇴적이후또는부석의파쇄당시충분한열을가지고있다면, 이세꼭지별의단편들은일그러진모양으로구부러지고변형될것임 (as seen on the right and b. in the photomicrograph of the Rattlesnake ignimbrite, SE Oregon. Width 1 mm.) 13
Figure 3-18. a. Carlsbad twin in orthoclase. Wispy perthitic exsolution is also evident. Granite, St. Cloud MN. Field widths ~1 mm. John Winter and Prentice Hall. 칼스바드쌍정 : 알칼리장석 Figure 3-17. Ostwald ripening in a monomineralic material. Grain boundaries with significant negative curvature (concave inward) migrate toward their center of curvature, thus eliminating smaller grains and establishing a uniformly coarse-grained equilibrium texture with 120 o grain intersections (polygonal mosaic). John Winter and Prentice Hall Figure 3-18. b. Very straight multiple albite twins in plagioclase, set in felsitic groundmass. Rhyolite, Chaffee, CO. Field widths ~1 mm. John Winter and Prentice Hall. 알바이트쌍정 : 사장석 Figure 3-18. (c-d) Tartan twins in microcline. Field widths ~1 mm. John Winter and Prentice Hall. 격자 (tartan) 쌍정 : 미사장석 (K- 장석 ) Figure 3-19. Polysynthetic deformation twins in plagioclase. Note how they concentrate in areas of deformation, such as at the maximum curvature of the bent cleavages, and taper away toward undeformed areas. Gabbro, Wollaston, Ontario. Width 1 mm. 변형조직 ( 쌍정의구부러짐 ) Figure 3-20. a. Pyroxene largely replaced by hornblende. Some pyroxene remains as light areas (Pyx) in the hornblende core. Width 1 mm. b. Chlorite (green) replaces biotite (dark brown) at the rim and along cleavages. Tonalite. San Diego, CA. Width 0.3 mm. John Winter and Prentice Hall. Pyx Hbl Origin of Igneous Texture Igneous texture are controlled by crystallization from a melt (magma). Cooling process of magma (Ex. Plagioclase) All melt (liquid) 치환조직 Liquidus ( 액상선 ) Pyroxene : Ca(Mg,Fe)Si2O6 Hornblende : Ca2(Mg4AlFe)Si7AlO22(OH)2 Biotite : K2(Mg,Fe)6(SiAl)8O20(OH)4 Chlorite : (Mg,Fe,Al)12(SiAl)8O20(OH)16 Chl Bt Melt + Crystal (liquid + solid) Solidus ( 고상선 ) All solid (solid) NaAlSi3O8 CaAl2Si2O8 14
Nucleation ( 핵형성 ) : The formation of nuclei ( 결정핵 ) Homogeneous nucleation ( 균질핵형성 ) : 결정핵이형성, 결정이용융체내에서스스로성장함. Heterogeneo us nucleation ( 불균질핵형성 ) : 기존재하는결정표면에핵이발달함. 적은에너지필요. 핵형성의조건 용융체 (melt) 의온도, 구조, 성분및냉각속도 (cooling rate) 와관계깊음. 성분 : 초기정출되는광물의결정핵을만드는데중요한역할 Ex : Olivine (Fe, Mg 필요 ) 용액의구조 (structure of melt) : melt 의화학성분, 최대온도, 지속시간등과관련깊음. 용액내부에잔류물존재 : 불균질핵형성 여러이온존재 : OH -, Ca 2+, Mg + 높은온도유지 : 잔류물파괴 Fig. 2.24. Structure of silicate glasses and rocks. a) Pure SiO2 glass. b)sio2 + ion. c) Partially crystallized glass. d) Completely crystallized melt with crystals of mica The factors that influence growth 1. 용융체의성분 ( 화학적성분 ) 2. 결정핵의수 ( 밀도 ) 및종류 3. 결정화가시작될때용융체의온도 4. 냉각속도 5. 용융체를통한화학성분들의확산 6. 용융체-결정사이에서발생하는반응 7. 결정이성장하는지역에서열의흐름 Crystallinity ( 결정도 ) : 얼마나결정작용이발생했는가? ( 유리 질완정질, 반정질 ; factors 1, 3, 4) Hypocrystalline and Porphyritic texture ( factors 2, 4) ΔT1 : Nucleation density < growth rate ( 조립질 ) ΔT2 : Nucleation density = growth rate ( 세-중립질 ; 반자형입상조직 ) ΔT3 : Nucleation density > growth rate ( 세립질-비현정질 ) 등립질입자크기 : 핵형성속도, 밀도가매우중요. 시간적인요인도고려해야함. 입자크기의다양성 : 다양한냉각속도, 핵형성조밀도, 성장속도, 냉각과정반상조직 : 단일또는다단계정출과정 Fig. 2.25. Nucleation and crystal growth rate curves. (a) Hypothetical nucleation and growth rate curves. (b) Experimentally determined nucleation and growth rate curves for a synthetic granite with 3.5 wt.% H2O. T= temperature, ΔT = undercooling (T liquidus T crystal growth), Af = Alkali feldspar, Pl = Plagioclase feldspar, Q = Quartz 조립 세립 깊은곳서냉이일반적으로조립을형성 ( 결정속도느림 ) 성장속도가빠르고결정핵이적어도조립형성 즉, 결정크기는냉각속도의함수만으로는고려하지말아야함. Fig. 2.26. Rapid-growth crystal morphologies in pegmatite from the McKinney Mines, Spruce Pine District, North Carolina. (a) Diamond-shaped, hollow alkali-feldspar in Qtz. (b) Snowflake (dendritic) quartz in alkali feldspar. Plumose(dendritic) white mica nucleated on a large alkali feldspar crystal rimmed by fine-grained garnets. 15