Presentation on theme: "A multi-modal indirect approach Daniel P. Connelly 2009"— Presentation transcript:
1A multi-modal indirect approach Daniel P. Connelly 2009 Post presentation comments are in greenAge dating MAPCIS (Massive Australian Precambrian/Cambrian Impact Structure)A multi-modal indirect approachDaniel P. Connelly 2009You will find background at MAPCIS.netor at the GSA northeastern meeting March 2009 uploaded files, MAPCIS the Case for a Massive Australian Precambrian/Cambrian Impact Structure
2Original Ring Discovery 2007 Discoveries are tangible measurable and not up for debate. Theories are explanations based on discoveries and are very much debatable.Search moves from the general to specific, whether geographic area or age constraint.Discovery Vs TheoryThis discovery starts the search.The search leads to new discoveries.New discoveries propagate theories.
4Impact Constraints Acraman Gosse Bluff 590Ma 142Ma 800km & 200km from MAPCIS center Ejecta from Acraman does not cover MAPCISundisturbedGosse Bluff near the center is undisturbed and Acraman ejecta is not found over MAPCIS ejecta.Rain over Gosse Bluff 2/2008
5Alice Springs Orogeny Constraint ~450Ma Deposited during Petermann orogenyUplifted during Alice Springs OrogenyMt. Currie ConglomerateMutijulu Arkose,i Ayers RockDeposited during Petermann Orogeny mya. Uplifted during Alice Springs Orogeny 450mya
6Basement consistent with age? This map is used as an example of the many 1:250,000 Geology maps used to cross check basement ages by examining exposed outcrops.Although this 1954 map conforms with the 2008 GA Mafic Ultramafic map, there is considerable debate on the accuracy of these maps in this region.Neoproterozoic ridges Kangaroo Island
7MAFIC Events and MAPCIS Dating Basic plate tectonics: When multiple events are divided, look for the youngest event to estimate the date of division.13291110MGr Moorilyanna Graben ~550MaME29 Skipworth Event ~575ME 26 Gairdner Event ~825A26 Amata dyke swarmG26 Gairdner dyke swarmME16 Curramulka Event ~1590ME13 Woman in White Event ~1680ME 11 Lunch Creek Event ~1750ME10 Hart Event ~1780ME 9 Mount Hay Event ~1810Ma9Tasman Gap26MGr169A26101129261316G26Derived from
8Musgrave = Grenville age zircons Zircon age diagram of suspected post impact proximal ejecta depositsWorldwide Cambrian SS EnigmaAreniteDistalGrenville Age zirconsFeldspar localA. Camacho et AlMusgrave Provence = Impact CenterOver 120,000 Sq. KmThe enigma is solved, if one has a huge impact in the center of a Grenville Aged province. This is what appears to have happened.ArkoseConglomerateP/C Boundary
9Seven smaller impacts possibly coeval with MAPCIS A cross check of impact age databases found this grouping of possibly coeval impacts, that appears to be associated with the predicted impact trajectory noted in dark blue .All have evidence of a younger age constraint ~ at P/C boundary
10Foelsche ~545Ma and Bukalara SS Bukalara SS with shocked clasts blends into extensive regional unit.Antrim Plateau Volcanics (Kalkarindji LIP) ~ MaCover unlithifiedBukalara SSAfter impact rapid burialInfers a rapid sequence of impact, fill, and coverage by basalt.NowP.W. Haines &D.J. Rawlings 2001
11MAPCIS Center Overview Trajectory Northeast to SouthwestRadial Transpression Ridges ? Visible on 1:250, 000 Geology mapsPT Arcuate & Radial light blueFrom Ayers Rock 1:250,000 Geology Map 2002Largest known Pseudotachylite deposits, similar to Vredefort and Sudbury impacts.1. Understand the locations shown on the next slideNeoproterozoic Winnall, Inindia & Pinyinna beds of Mt. Conner appear to be missing from MAPCIS Center.
12Mt. Frazer Radial Pseudotachylite Edgoose CJ, Scrimgeour IR, Close DF 2003 Geology of the Musgrave Block, NT, NT Geological Survey Report 15An example of PT not associated with a major fault.
13Sampling Data from NT Geological Survey There appears to be no attempt to date the pseudotachylite itself
14Sample sites plotted on Google Earth Sample B549Derived fromEdgoose CJ, Scrimgeour IR, Close DF 2003 Geology of the Musgrave Block, NT, NT Geological Survey Report 15Mt. Frazer
15Sample B549 30km North of Mann Range pseudotachylite Notable that these zircons have a metamorphic peak at 561ma , and zircon 13 exhibits a mosaic pattern.Mosaic patterns in zircons has been associated with shock metamorphism.
16Cumulative probability diagram of biotite ages for entire Musgrave Provence Camacho et al., 2002Inferred that all faultsystems in the MusgraveProvence were activatedduring thethe Petermann Orogeny.120,000 square Km moved here and portions were exhumed from 40km deep.Camacho All faults and shear zones were activatedCamacho et al., 2002
17Conclusions1. Precambrian Basement underlies all visible parts within the outer ring.2. No known Precambrian impacts within 600km radius.3. Ejecta from Acraman 590Ma does not overlay MAPCIS ejecta.4. Gosse Bluff 142Ma and Alice Springs Orogeny structures are undisturbed.5. Lower Cambrian layers, proximal and distal exhibit a Musgrave fingerprint.6. Neoproterozoic beds appear to be missing from impact center.7 . Moorilyanna Graben forms and the Tasman Gap opens syn-orgenic with Petermann Orogeny8. Cambrian Bukalara SS fills and preserves Foelsche impact ~545mya.9. Mass extinction of Ediacarans in Australia occurs at the end of Precambrian.10. Dating of monazite and zircons nearest to pseudotachylite gives dates close to 545mya.MAPCIS probably occurred just before the Precambrian/ Cambrian Boundary. Further research is needed to refine this dating.