Grenville orogeny

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The Grenville orogeny was a prolonged mountain building process of Mesoproterozoikums which to form the supercontinent Rodinia led.

etymology

The Grenville Orogeny and the geological Grenville Province were named after the town of Grenville in Québec . The village bears the name of the British Prime Minister George Grenville .

Spatial expansion

Extension of the Grenville ore (in orange) in North America, according to Tollo et al. (2004) and Darabi (2004)

The Grenville Orogen Belt stretches from Labrador to Mexico and occupies a significant portion of the east side of North America . Crustal areas that were formed during the Grenville orogeny in the period 1250 to 980 million years BP ( Ectasium and Stenium ), however, have a worldwide distribution, they are also found in Scotland , for example . In a narrower sense, the term Grenville orogen only covers the areas of the southern and eastern edge of Laurentia .

In Africa , mountain formations during this period are referred to as Kibara orogeny and in Europe as Svekonorwegian orogeny , the latter being correlated with Grenville orogeny.

It is generally assumed that the eastern edge of Laurentia ultimately collided with the Rio-de-la-Plata craton , whereas the actual Grenville Province, Ireland / Scotland and Baltica collided with Amazonia . Evidence of the collision with Amazonia can be found in Scandinavia in the Svekonorwegian Orogen, in Ireland in the Annagh Gneiss Complex , in the Tyrone Central Inlier (and possibly in the metasediments of the Slishwood Division ) and in Scotland in the Glenelg basement break and in the Midland Valley , its Carboniferous volcanoes unearthed granulite-faced Grenville-age gneiss.

Timeframe

Temporal sequence of the Grenville orogeny, according to Rivers (2002)

The exact, chronological classification of the Grenville orogeny remains controversial to this day. The figure shown follows Rivers (2002), who in his detailed study differentiates between two cycles, an older Elzevir cycle with the Elzevirian orogeny (1250 to 1190 million years BP) and a more recent Grenville cycle with the Shawingian orogeny (1140 to 1080 million Years BP), the Ottawan Orogeny (1080 to 1020 million years BP) and the Rigolet Orogeny (1010 to 980 million years BP).

Rivers (2008) revised this scheme so that the Shawingian Orogeny now forms its own cycle, which is no longer counted as part of the actual Grenville cycle. Times have also changed a bit:

  • Elzevirian Orogeny - 1240 to 1220 million years BP
  • Shawingian Orogeny - 1190 to 1140 million years BP
  • Ottawan Orogeny - 1090 to 1020 million years BP
  • Rigolet Orogeny - 1010 to 980 million years BP

Geodynamic development

During the Grenville orogeny, the eastern and southern rims of Laurentia were active continental margins . The subduction of the B-type that took place accreted BP island arcs between 1300 and 1200 million years ago . In the period 1190 to 980 million years BP, two continental blocks finally collided with Laurentia.

Triggered by these converging thrusts and the accompanying metamorphosis but were not a continuous process, were replaced by periods of rest during which the so-called AMCG plutons were able to penetrate into the surrounding host rocks (AMGC is an acronym of anorthosite , mangerite , Charnockite and granite ) . The subduction polarity was not uniform within the orogen, but varied depending on the sector and time period.

The first major event in the Grenville Orogeny was the docking of an island arc during the Elzevirian Orogeny (1240 to 1220 million years BP). Around 1190 million years BP, the basin ( Backarc basin ) of the Elzevir cycle , located behind the arch of the island, closed .

In the time interval from 1180 to 1140 million years BP, extensive forces dominated, which can be attributed either to a cooling process of the lithosphere or to a reactivation of normal fault systems. At the same time, sedimentary basins were created, creating a relatively stable continental margin. Nevertheless, in some sections of the orogen between 1160 and 1130 million years BP, thrusts and terranic welding continued to take place parallel to the prevailing crustal expansion.

Generally westward thrust activity prevailed between 1120 and 1090 million years BP. Then stretch tectonics set in again, which was to last until 1050 million years BP. As a result, the Central Granulite Terrane , a terran made of granulite , was exhumed and at the same time intrusion space was created for Plutons. The reasons for the transition from compression to elongation cannot be clearly established, but are likely to be due to gravitational collapse, mantle delamination, penetration of a mantle diapir or a large-scale change in the stress field.

Lithological units

The Grenville Orogen is today characterized by northwest-vergente fold and thrust belts , high pressure metamorphosis and the characteristic AMCG magmatism. The medium to high grade metamorphosis generally reached the physical conditions of the amphibolite and granulite facies . Eclogitized metagabbros can be found in some places - mafic to ultramafic rocks that have been changed under very high pressure and indicate very high depths of subsidence or intense degrees of collision. Throughout the orogen, the high pressure rocks are intruded by AMCG plutons, which are commonly considered syn- to post-tectonic. This ACMG plutonism is mostly associated with a swelling of the asthenosphere beneath an expanding lithosphere. It is believed that the AMCG plutonism was triggered by olivintholeiites , which accumulated at the base of the sub-crust during a crustal expansion phase. The lithosphere can be thinned either by convection currents or by delamination. Delamination shears off the entire lower portion of the lithosphere. Both scenarios are being considered for the Grenville Orogen.

Based on its structure, lithology and thermochronology, the Grenville orogen can be divided into three areas ( terranes ), which are separated from one another by significant shear zones :

  • Gneiss belt (English. Gneiss belt )
  • Metasedimentgürtel ( metasedimentry belt )
  • Granulit-Terran ( granulite terranean )

The gneiss belt consists of silicon-rich gneisses and amphibolites that have reached the metamorphic degree of amphibolite and granulite facies. The thrusts occurred in this terran with a shallow angle of incidence and the deformations took place in the ductile state. The gneiss belt has had a long geological development that lasted from 1800 to 1180 million years BP. Around 1400 million years BP it was captured by a first regional metamorphosis. Between 1160 and 1120 million years BP, large-scale thrusts occurred in the course of the Shawingian Orogeny, at the same time the rocks were metamorphosed again.

The metasediment belt mainly contains metamorphosed sedimentary and volcanic rocks , the degree of metamorphosis of which ranges from green slate to granulite facies. It can be divided into the following sub-units:

  • Bancroft
  • Elzevir
  • Sharbot Lake
  • Frontenac
  • Adirondack Lowlands

Between 1420 and 1040 million years BP, Plutons invaded the metasediment belt. It was metamorphosed around 1160 million years ago, roughly at the same time as the gneiss belt.

The granulite terrane is built up by orthogneiss , including anorthosites . The anorthosites form plutonic massifs, which mainly consist of plagioclase . The earliest magmatism in the Granulite Terran can be dated to 1320 million years BP. The granulite facial metamorphosis began around 1150 million years BP and lasted around 150 million years. It could not be determined whether the metamorphosis was continuous.

Grenville Orogen Sectors

Proposed reconstruction of Rodinias around 750 million years BP. Orogenic belt from the Grenville period around 1100 million years old BP in green. Red dots mark anorogenic granites (A-type) from the time interval 1500 to 1300 million years BP.

For a better understanding, the total organic can be subdivided into the following sectors:

Mexico and Texas

Mexico and Texas formed what was then the southern edge of Laurentia, which very likely collided with a different continent than the eastern edge. The Zapotecan orogeny in Mexico took place at the same time as the later stages of the Grenville orogeny, the two orogenies are therefore regarded as belonging together. The igneous protoliths fall into two age groups in Mexico:

  • 1235 to 1115 million years old BP: the geochemical parameters indicate that these rocks were formed in island arches and in back-arc basins.
  • 1035 to 1010 million years old BP: AMCG magmatism.

An explanation of the AMCG rocks is problematic throughout the Grenville Orogen, as their place names were not preceded by any orogenic activity.

It is believed that subduction under the southern edge of Laurentia (which was then in Texas) ended 1230 million years ago BP with the accretion of the Mexico Terran. The direction of subduction has very likely changed polarity at this point in time to allow the colliding continent to advance northwards. In the area of ​​the Llano Uplift in Texas, there are no more signs of island arc magmatism after this point in time.

Appalachian Mountains

Small island-like deposits of the Grenville orogeny are found within the Appalachian Mountains . In terms of area, the Long Range Inlier with the Long Range Mountains in Newfoundland is the most important . Another important occurrence is the Blue Ridge Province of Virginia with the Shenandoah Massif and the French Broad Massif . The Blue Ridge Province is made up of various gneisses that reached the metamorphic grade of the upper amphibolite and granulite facies. The gneisses were intruded in three batches of massive to lightly foiled Charnockites and Granitoids:

  • 1160 to 1140 million years BP
  • around 1112 million years BP
  • 1080 to 1050 million years BP

Adirondacks

The Adirondacks , located on the Canadian-US-American border, are built up from a massive dome of Proterozoic rocks , in which both the orogen pulses of the Elzevirian (1250 to 1190 million years BP) and the Ottawan (1080 to 1020 million years BP) can be detected . These two pulses transformed the parent rocks into high-grade metamorphic rocks. The Adirondacks are divided into the Adirondacks Lowlands to the northwest and the Adirondacks Highlands to the southeast by a northeast-trending shear zone . It is believed that the high-displacement Carthage-Colton Shear Zone (CCSZ) acted as a transpressive shear zone during the Ottawan Orogeny, along which the Highlands were pushed onto the Lowlands. But it is also interpreted as a back thrust of the Shawingian, which was later converted to a deportation during the Ottawan.

Grenville Province

Grenville Province is the youngest crust segment of the Canadian shield . Since it has not experienced any further deformations or metamorphic overprints since the end of the Grenville orogeny, it represents an ideal study area for the tectonic movements during and before the mountain formation. Most of the knowledge about the Grenville orogeny come from it.

The approximately 400 kilometers wide, northeast-southwest-trending Grenville Province was thrust onto the Superior Craton along the Grenville Front . It can be divided into three tectonic units:

  • Parautochthonous belt (PB)
  • Allochthonous polycyclic belt (APB)
  • Allochthonous monocyclic belt (AMB)

The Parautochthonous Belt, which is a maximum of 200 kilometers wide, follows immediately behind the Grenville Front. In its northeast part it contains a discontinuous band of Gabbrointrusionen that about 1470 to 1460 million years ago Shabogamo Michael gabbros .

Behind the Parautochthonous Belt follows the Allochthonous Polycyclic Belt , which is up to 300 kilometers wide and crosses the Parautochthonous Belt along the Allochthonous Boundary Thrust . The belt, made up of several internal ceiling systems, contains numerous anorthosite intrusions such as the 1161 million year old Lac-Allard anorthosite , the 1155 million year old Lac-Saint-Jean anorthosite , the 1130 million year old atikonak anorthosite and the 1126 million year old Havre-Saint-Pierre-Anorthosite . The AMCG plutons were intruded primarily in three magmatic pulses, 1160 to 1140, 1082-1050, and 1020 to 1010 million years BP. At the northeast corner of the belt is the Pinware Terran . In the Long Range Mountains on Newfoundland it has a separate occurrence (English Outlier ).

The Allochthonous Monocyclic Belt , which begins southwest of Montreal , is separated from the Allochthonous Polycyclic Belt along the Central Metasedimentary Belt Boundary Zone (CMBBZ). It contains the Maberly Shear Zone (MSZ) and the Labelle Deformation Zone (LDZ) as internal movement paths. It is separated from the highlands of the Adirondacks by the Carthage-Colton Shear Zone (CCSZ) mentioned above. It contains AMCG plutons, including the 1153 million year old Morin anorthosite and the approximately 1150 million year old Marcy anorthosite in the Adirondacks. To the north of Natashquan it has a smaller occurrence ( Natashquan Domain ) separated from the main mass in the southwest .

Individual evidence

  1. ↑ a b Tollo, RP et al .: Proterozoic tectonic evolution of the Grenville orogen in North America: An introduction . In: Tollo, RP et al., Proterozoic tectonic evolution of the Grenville orogen in North America (Ed.): Geological Society of America Memoir . tape 197 . Boulder, Co. 2004, ISBN 978-0-8137-1197-3 , pp. 1-18 .
  2. ^ Rivers, T. and Corrigan, D .: Convergent margin on southeastern Laurentia during the Mesoproterozoic: tectonic implications . In: Canadian Journal of Earth Sciences . tape 37 , 2000, pp. 359-383 .
  3. ^ Nigel Woodcock and Rob Strachan: Geological History of Britain and Ireland . Blackwell Science Ltd, Oxford 2000, ISBN 0-632-03656-7 .
  4. ^ Rivers, T. et al.: The High Pressure belt in the Grenville Province: Architecture, timing, and exhumation . In: Canadian Journal of Earth Sciences . tape 39 (5) , 2002, pp. 867-893 , doi : 10.1139 / e02-025 .
  5. ↑ a b c Streepey, Margaret M. et al .: Exhumation of a collisional orogen: a perspective from the North American Grenville Province . In: Tollo, Richard P. et al., Proterozoic tectonic evolution of the Grenville orogen in North America (Ed.): Geological Society of America Memoir . tape 197 . Boulder, CO. 2004, ISBN 978-0-8137-1197-3 , pp. 391-410 .
  6. ↑ a b c d Corrigan, D. and Hanmer, S .: Anorthosites and related granitoids in the Grenville orogen: A product of convective thinning of the lithosphere? In: Geology . tape 25 , 1997, pp. 61-64 .
  7. ↑ Indares, Aphrodite; and Rivers, Toby: Fourth international eclogite conference, Morten . In: European Journal of Mineralogy . tape 7 (1) , 1995, pp. 43-56 .
  8. ↑ Emslie, RF: Anorthosite massifs, rapakivi granites, and Late Proterozoic rifting of North America . In: Precambrian Research . tape 7 , 1978, p. 61-98 , doi : 10.1016 / 0301-9268 (78) 90005-0 .
  9. ^ DeWolf, C. and Mezger, K .: Lead isotope analysis of leached feldspars: Constraints on the early crustal history of the Grenville Orogen . In: Geochimica et Cosmochimica Acta . tape 58 (24) , 1994, pp. 5537-5550 , doi : 10.1016 / 0016-7037 (94) 90248-8.hdl: 2027.42 / 31183 .
  10. ^ Mosher, Sharon et al .: Tectonic evolution of the eastern Llano Uplift, central Texas: A record of Grenville orogenesis along the southern Laurentian margin . In: Tollo, Richard P. et al., Proterozoic tectonic evolution of the Grenville orogen in North America (Ed.): Geological Society of America Memoir . tape 197 . Boulder, CO. 2004, ISBN 978-0-8137-1197-3 , pp. 783-798 .
  11. ↑ a b Cameron, Kenneth et al .: U-Pb geochronology and Pb isotopic compositions of leached feldspars: Constraints on the origin and evolution of Grenville rocks from eastern and southern Mexico . In: Tollo, Richard P. et al., Proterozoic tectonic evolution of the Grenville orogen in North America (Ed.): Geological Society of America Memoir . tape 197 . Boulder, CO. 2004, ISBN 978-0-8137-1197-3 , pp. 755-769 .
  12. ^ Mosher, S. et al .: Mesoproterozoic plate tectonics: A collisional model for the Grenville-aged orogenic belt in the Llano uplift, central Texas . In: Geology . tape 36 , 2008, p. 55-58 , doi : 10.1130 / G24049A.1 .
  13. ^ Johnson, Eric L. et al.: Proterozoic tectonic evolution of the Grenville orogen in North America . In: Tollo, Richard P. et al. (Eds.): Geological Society of America Memoir . tape 197. . Boulder, CO. 2004, ISBN 978-0-8137-1197-3 , pp. 357-378 .
  14. ↑ McLelland, JM and Selleck, BW: Late to post-tectonic setting of some major Proterozoic Anorthosite-Mangerite-Charnokite-Granite (AMCG) suites . In: The Canadian Mineralogist . tape 48 , 2010, p. 1025-1046 , doi : 10.3749 / canmin.48.4.729 .
  15. ↑ Morisset, C.-E. include: U-Pb and 40 Ar / 39 Ar geochronology of the Saint-Urbain and Lac Allard (Havre-Saint-Pierre) anorthosites and Their associated Fe-Ti oxide ores, Québéc: evidence for emplacement and slow cooling during the collisional Ottawan orogeny in the Grenville Province . In: Precambrian Research . tape 174 , 2009, p. 95-116 .
  16. ↑ Hervet, M. et al .: U-Pb crystallization ages of intrusive rocks near the southeast margin of the Lac-St-Jean anorthosite complex, Grenville Province, Quebec . In: Geol. Surv. Can. Rep. 1994-F, 1994, p. 115-124 .
  17. ^ A b Emslie, RF and Hunt, PA: Ages and petrogenetic significance of igneous mangerite-charnockite suites associated with massive anorthosites, Grenville Province . In: J. Geol. Volume 98 , 1990, pp. 213-231 .
  18. ^ Corrigan, D. and van Bremen, O .: U-Pb age constraints for the lithotectonic evolution of the Grenville Province along the Mauricie transect, Quebec . In: Canadian Journal of Earth Sciences . tape 34 , 1997, pp. 299-316 .
  19. ↑ Doig, R .: U-Pb zircon dates of the Morin anorthosite suite rocks, Grenville Province, Quebec . In: J. Geol. Volume 99 , 1991, pp. 729-738 .
  20. ↑ Hamilton, inter alia: SHRIMP U-Pb zircon geochronology of the anorthosite-mangerite-charnockite-granite suite, Adirondack Mountains, New York: ages of emplacement and metamorphism . In: Geol. Soc. At the. Mem. Band 197 , 2004, p. 337-355 .