Achala Batholith: Difference between revisions
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{{Short description|Group of plutons in central Argentina}} |
{{Short description|Group of plutons in central Argentina}} |
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The '''Achala Batholith''' ({{lang-es|batolito de Achala}}) is a group of [[pluton (geology)|plutons]] in the [[Sierras de Córdoba]] in central [[Argentina]]. With a mapped surface of over 2500 |
The '''Achala Batholith''' ({{lang-es|batolito de Achala}}) is a group of [[pluton (geology)|plutons]] in the [[Sierras de Córdoba]] in central [[Argentina]]. With a mapped surface of over {{convert|2500|km2}} it constitutes the largest group of [[intrusion (geology)|intrusion]]s exposed in the [[Sierras Pampeanas]].<ref name=LiraKirs1990/><ref name=Rapelaetal2008/> The oldest reference to the batholith dates to 1932.<ref name=LiraKirs1990>{{cite book |last1=Lira |first1=Raúl|last2=Kirschbaum |first2=Alicia M. |date=1990|chapter=Geochemical evolution of granites |title=Plutonism from Antarctica to Alaska|editor-last=Mahlburg Kay|editor-first=Suzanne|editor-last2=Rapela|editor-first2=Carlos W.|series=Geological Society of America Special Paper|volume=241 |pages=67–76 }}</ref> |
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==Host rock and structural setting== |
==Host rock and structural setting== |
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Plutons [[intrusion (geology)|intrude]] into older [[migmatite]]s, [[metamorphic rock]]s of [[sedimentary rock|sedimentary]] and [[volcanic rock|volcanic]] [[protolith]]s.<ref name=LiraKirs1990/><ref name=Patiños1987/> Some specific intruded rock types are: [[biotite]]-bearing [[tonalite|tonalitic]] [[gneiss]]es, [[amphibolite]], [[marble]] and [[quartzite]].<ref name=LiraKirs1990/> |
Plutons [[intrusion (geology)|intrude]] into older [[migmatite]]s, [[metamorphic rock]]s of [[sedimentary rock|sedimentary]] and [[volcanic rock|volcanic]] [[protolith]]s.<ref name=LiraKirs1990/><ref name=Patiños1987/> Some specific intruded rock types are: [[biotite]]-bearing [[tonalite|tonalitic]] [[gneiss]]es, [[amphibolite]], [[marble]] and [[quartzite]].<ref name=LiraKirs1990/> |
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In the large-scale the intrusion is parallel to the [[schistosity]] of the older rocks. However, at smaller scales the intrusion seems to disregard schistisity.<ref name=Patiños1987>{{cite journal |last1=de Patiño |first1=Marta G.|last2=Patiño Douce |first2=Alberto E. |date=1987 |title=Petrología y petrogénesis de batolito de Achala, provincia de Córdoba, a la luz de la evidencia de campo |journal=[[Revista de la Asociación Geológica Argentina]] |volume=XLII |issue=1–2 |pages=201–205 |language=es}}</ref> Host rocks are altered [[contact metamorphism]] and associated fluids. Alteration is seen in the occurrence of [[marble]] and minerals such as [[vesuvianite]] and [[humite]], both of which are high on [[fluorine]]. This alteration is thought to also have affected the batholith itself.<ref name=Deamngeetal1996/> |
In the large-scale the intrusion is parallel to the [[schistosity]] of the older rocks. However, at smaller scales, the intrusion seems to disregard schistisity.<ref name=Patiños1987>{{cite journal |last1=de Patiño |first1=Marta G.|last2=Patiño Douce |first2=Alberto E. |date=1987 |title=Petrología y petrogénesis de batolito de Achala, provincia de Córdoba, a la luz de la evidencia de campo |journal=[[Revista de la Asociación Geológica Argentina]] |volume=XLII |issue=1–2 |pages=201–205 |language=es}}</ref> Host rocks are altered [[contact metamorphism]] and associated fluids. Alteration is seen in the occurrence of [[marble]] and minerals such as [[vesuvianite]] and [[humite]], both of which are high on [[fluorine]]. This alteration is thought to also have affected the batholith itself.<ref name=Deamngeetal1996/> |
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==Lithology and alteration== |
==Lithology and alteration== |
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Most rocks of the batholith are [[monzogranite]]s<ref name=Rapelaetal2008/> but [[granodiorite]]s and [[tonalite]]s do also occur.<ref name=Deamngeetal1996/> The central parts of the batholith are fully granitic and include [[leucogranite]].<ref name=LiraKirs1990/> [[Grain size]] vary from coarse to fine and at places the rocks are [[porphyritic]]. [[Dyke (geology)|Dykes]] of [[lamprophyre]] and [[nephelinite]] that occur in the region are associated |
Most rocks of the batholith are [[monzogranite]]s<ref name=Rapelaetal2008/> but [[granodiorite]]s and [[tonalite]]s do also occur.<ref name=Deamngeetal1996/> The central parts of the batholith are fully granitic and include [[leucogranite]].<ref name=LiraKirs1990/> [[Grain size]] vary from coarse to fine and at places the rocks are [[porphyritic]]. [[Dyke (geology)|Dykes]] of [[lamprophyre]] and [[nephelinite]] that occur in the region are associated with the batholith.<ref name=LiraKirs1990/> |
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[[Pegmatite]]s and [[aplite]]s, albeit not voluminous, are recurrent in the batholith.<ref name=Deamngeetal1996/> The pegmatite of Las Tapias in the southwestern part of the batholith |
[[Pegmatite]]s and [[aplite]]s, albeit not voluminous, are recurrent in the batholith.<ref name=Deamngeetal1996/> The pegmatite of Las Tapias in the southwestern part of the batholith makes up Argentina's "most important" [[beryllium]] deposit. Other pegmatites of the batholith have been mined for quartz, feldspar and beryl plus lesser amounts of [[columbite]] and [[tantalite]].<ref name=LiraKirs1990/> More important deposits is the [[tungsten]] that can be obtained from [[skarn]]s with [[scheelite]] and [[wolframite]]-bearing quartz veins. Skarns are associated to marble and amphibolite host rock.<ref name=LiraKirs1990/> |
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The whole batholith has been subject to [[deuteric alteration]] that replaced rock's [[biotite]] with [[muscovite]] and in general depleted biotite in iron, [[magnesium]] and [[titanium]].<ref name=Deamngeetal1996/> [[Plagioclase]]s have been affected to a much lesser degree by alteration having have slight compositional changes along the crystal rims or limited transformation into muscovite. This alteration has also led to overall loss of alcalis ([[potassium]], [[sodium]]) from the rock.<ref name=Deamngeetal1996/> A number of fractures of the batholith show [[greisen]] alteration with quartz, [[sericite]], [[fluorite]] and [[tourmaline]]. No metallic deposits are known from these greisens.<ref>{{cite journal |last1=Lira |first1=Raul |last2=Ripley |first2=Edward M.|last3=Españón |first3=Adriana I.|date=1996 |title=Meteoric water induced selvage-style greisen alteration in the Achala Batholith, central Argentina |journal=[[Chemical Geology]] |volume=133 |issue=1–4 |pages=261–277 |doi=10.1016/S0009-2541(96)00077-0 |bibcode=1996ChGeo.133..261L }}</ref> |
The whole batholith has been subject to [[deuteric alteration]] that replaced rock's [[biotite]] with [[muscovite]] and in general depleted biotite in iron, [[magnesium]] and [[titanium]].<ref name=Deamngeetal1996/> [[Plagioclase]]s have been affected to a much lesser degree by alteration having have slight compositional changes along the crystal rims or limited transformation into muscovite. This alteration has also led to an overall loss of alcalis ([[potassium]], [[sodium]]) from the rock.<ref name=Deamngeetal1996/> A number of fractures of the batholith show [[greisen]] alteration with quartz, [[sericite]], [[fluorite]] and [[tourmaline]]. No metallic deposits are known from these greisens.<ref>{{cite journal |last1=Lira |first1=Raul |last2=Ripley |first2=Edward M.|last3=Españón |first3=Adriana I.|date=1996 |title=Meteoric water induced selvage-style greisen alteration in the Achala Batholith, central Argentina |journal=[[Chemical Geology]] |volume=133 |issue=1–4 |pages=261–277 |doi=10.1016/S0009-2541(96)00077-0 |bibcode=1996ChGeo.133..261L }}</ref> |
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The Achala Batholit contains unusual [[enclave (geology)|enclaves]] of biotite and [[apatite]] that form layers in the intrusion.<ref>{{cite journal |last1=Dorais |first1=Michel J. |last2=Lira |first2=Raul |last3=Chen |first3=Yadong|last4=Tingey |first4=David |date=1997 |title=Origin of biotite-apatite-rich enclaves, Achala batholith, Argentina |journal=[[Contributions to Mineralogy and Petrology]] |volume=140 |issue= 1|pages=31–46 |doi= 10.1007/s004100050347|bibcode=1997CoMP..130...31D |s2cid=129621632 }}</ref> |
The Achala Batholit contains unusual [[enclave (geology)|enclaves]] of biotite and [[apatite]] that form layers in the intrusion.<ref>{{cite journal |last1=Dorais |first1=Michel J. |last2=Lira |first2=Raul |last3=Chen |first3=Yadong|last4=Tingey |first4=David |date=1997 |title=Origin of biotite-apatite-rich enclaves, Achala batholith, Argentina |journal=[[Contributions to Mineralogy and Petrology]] |volume=140 |issue= 1|pages=31–46 |doi= 10.1007/s004100050347|bibcode=1997CoMP..130...31D |s2cid=129621632 }}</ref> |
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[[geochemistry|Geochemical]] characteristics indicate the granites are [[A-type granite]]s and peraluminous (aluminous A-type).<ref name=Rapelaetal2008/> These characteristics are interpreted to reflect a mixed origin for the magmas with sources both in the [[mantle (geology)|mantle]] and in the [[continental crust|crust]]. Crustal sources would have contributed to the magmas by [[partial melting|melting]] under anhydrous conditions, with such conditions being allowed by a large undetermined heat source.<ref name=Rapelaetal2008/> The magma formed and cooled in the aftermath of an orogeny and qualify thus the group of post-orogenic intrusions.<ref name=LiraKirs1990/> |
[[geochemistry|Geochemical]] characteristics indicate the granites are [[A-type granite]]s and peraluminous (aluminous A-type).<ref name=Rapelaetal2008/> These characteristics are interpreted to reflect a mixed origin for the magmas with sources both in the [[mantle (geology)|mantle]] and in the [[continental crust|crust]]. Crustal sources would have contributed to the magmas by [[partial melting|melting]] under anhydrous conditions, with such conditions being allowed by a large undetermined heat source.<ref name=Rapelaetal2008/> The magma formed and cooled in the aftermath of an orogeny and qualify thus the group of post-orogenic intrusions.<ref name=LiraKirs1990/> |
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Four igneous suites of rocks with geochemical affinities make up the batholith, these |
Four igneous suites of rocks with geochemical affinities make up the batholith, these are the Achala, El Condor, Champaqui, Characato and Cumbresita suites. The Achala suite has by far the largest extent making up ''c.'' 70% of the surface area of the batholith.<ref name=Deamngeetal1996>{{cite journal |last1=Demange |first1=Michel |last2=Alveres |first2=Juan O.|last3=Lopez |first3=Luiz|last4=Zarco |first4=Juan J. |date=1996 |title=The Achala Batholith (Cordoba, Argentina): a composite intrusion made of five independent magmatic suites. Magmatic evolution and deuteric alteration |journal=[[Journal of South American Earth Sciences]] |volume=9 |issue=1/2 |pages=11–25 |doi= 10.1016/0895-9811(96)00024-7|bibcode=1996JSAES...9...11D }}</ref> The five suites represents different magmatic episodes.<ref name=Deamngeetal1996/> Suites differ in associated metals as well as biotite chemistry.<ref name=Deamngeetal1996/> Chemical variations along each suite are concordant with the [[fractional crystallization (geology)|fractional crystallization]] model of [[igneous differentiation]].<ref name=Deamngeetal1996/> |
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==References== |
==References== |
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Latest revision as of 04:07, 1 July 2024
The Achala Batholith (Spanish: batolito de Achala) is a group of plutons in the Sierras de Córdoba in central Argentina. With a mapped surface of over 2,500 square kilometres (970 sq mi) it constitutes the largest group of intrusions exposed in the Sierras Pampeanas.[1][2] The oldest reference to the batholith dates to 1932.[1]
Host rock and structural setting
[edit]Plutons intrude into older migmatites, metamorphic rocks of sedimentary and volcanic protoliths.[1][3] Some specific intruded rock types are: biotite-bearing tonalitic gneisses, amphibolite, marble and quartzite.[1]
In the large-scale the intrusion is parallel to the schistosity of the older rocks. However, at smaller scales, the intrusion seems to disregard schistisity.[3] Host rocks are altered contact metamorphism and associated fluids. Alteration is seen in the occurrence of marble and minerals such as vesuvianite and humite, both of which are high on fluorine. This alteration is thought to also have affected the batholith itself.[4]
Lithology and alteration
[edit]Most rocks of the batholith are monzogranites[2] but granodiorites and tonalites do also occur.[4] The central parts of the batholith are fully granitic and include leucogranite.[1] Grain size vary from coarse to fine and at places the rocks are porphyritic. Dykes of lamprophyre and nephelinite that occur in the region are associated with the batholith.[1]
Pegmatites and aplites, albeit not voluminous, are recurrent in the batholith.[4] The pegmatite of Las Tapias in the southwestern part of the batholith makes up Argentina's "most important" beryllium deposit. Other pegmatites of the batholith have been mined for quartz, feldspar and beryl plus lesser amounts of columbite and tantalite.[1] More important deposits is the tungsten that can be obtained from skarns with scheelite and wolframite-bearing quartz veins. Skarns are associated to marble and amphibolite host rock.[1]
The whole batholith has been subject to deuteric alteration that replaced rock's biotite with muscovite and in general depleted biotite in iron, magnesium and titanium.[4] Plagioclases have been affected to a much lesser degree by alteration having have slight compositional changes along the crystal rims or limited transformation into muscovite. This alteration has also led to an overall loss of alcalis (potassium, sodium) from the rock.[4] A number of fractures of the batholith show greisen alteration with quartz, sericite, fluorite and tourmaline. No metallic deposits are known from these greisens.[5]
The Achala Batholit contains unusual enclaves of biotite and apatite that form layers in the intrusion.[6]
Origins of magmas
[edit]The batholith plutons intruded and cooled 370 million years ago in the Devonian Period.[7][2]
Geochemical characteristics indicate the granites are A-type granites and peraluminous (aluminous A-type).[2] These characteristics are interpreted to reflect a mixed origin for the magmas with sources both in the mantle and in the crust. Crustal sources would have contributed to the magmas by melting under anhydrous conditions, with such conditions being allowed by a large undetermined heat source.[2] The magma formed and cooled in the aftermath of an orogeny and qualify thus the group of post-orogenic intrusions.[1]
Four igneous suites of rocks with geochemical affinities make up the batholith, these are the Achala, El Condor, Champaqui, Characato and Cumbresita suites. The Achala suite has by far the largest extent making up c. 70% of the surface area of the batholith.[4] The five suites represents different magmatic episodes.[4] Suites differ in associated metals as well as biotite chemistry.[4] Chemical variations along each suite are concordant with the fractional crystallization model of igneous differentiation.[4]
References
[edit]- ^ a b c d e f g h i Lira, Raúl; Kirschbaum, Alicia M. (1990). "Geochemical evolution of granites". In Mahlburg Kay, Suzanne; Rapela, Carlos W. (eds.). Plutonism from Antarctica to Alaska. Geological Society of America Special Paper. Vol. 241. pp. 67–76.
- ^ a b c d e Rapela, C.W.; Baldo, E.G.; Pankhurst, R.J.; Fanning, C.M. (2008). The Devonian achala batholith of the Sierras Pampeanas: F-rich aluminous A-type granites. VI South American Symposium on Isotope Geology. San Carlos de Bariloche, Argentina.
- ^ a b de Patiño, Marta G.; Patiño Douce, Alberto E. (1987). "Petrología y petrogénesis de batolito de Achala, provincia de Córdoba, a la luz de la evidencia de campo". Revista de la Asociación Geológica Argentina (in Spanish). XLII (1–2): 201–205.
- ^ a b c d e f g h i Demange, Michel; Alveres, Juan O.; Lopez, Luiz; Zarco, Juan J. (1996). "The Achala Batholith (Cordoba, Argentina): a composite intrusion made of five independent magmatic suites. Magmatic evolution and deuteric alteration". Journal of South American Earth Sciences. 9 (1/2): 11–25. Bibcode:1996JSAES...9...11D. doi:10.1016/0895-9811(96)00024-7.
- ^ Lira, Raul; Ripley, Edward M.; Españón, Adriana I. (1996). "Meteoric water induced selvage-style greisen alteration in the Achala Batholith, central Argentina". Chemical Geology. 133 (1–4): 261–277. Bibcode:1996ChGeo.133..261L. doi:10.1016/S0009-2541(96)00077-0.
- ^ Dorais, Michel J.; Lira, Raul; Chen, Yadong; Tingey, David (1997). "Origin of biotite-apatite-rich enclaves, Achala batholith, Argentina". Contributions to Mineralogy and Petrology. 140 (1): 31–46. Bibcode:1997CoMP..130...31D. doi:10.1007/s004100050347. S2CID 129621632.
- ^ Dahlquist, Juan A.; Alasino, Pablo H.; Bello, Carina (2014). "Devonian F-rich peraluminous A-type magmatism in the proto-Andean foreland (Sierras Pampeanas, Argentina): geochemical constraints and petrogenesis from the western-central region of the Achala batholith". Mineralogy and Petrology. 108 (3): 391–417. Bibcode:2014MinPe.108..391D. doi:10.1007/s00710-013-0308-0. hdl:11336/12093. S2CID 128877732.