Age dating MAPCIS (Massive Australian Precambrian/Cambrian Impact Structure) A multi-modal indirect...
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Transcript of Age dating MAPCIS (Massive Australian Precambrian/Cambrian Impact Structure) A multi-modal indirect...
Age dating MAPCIS (Massive Australian
Precambrian/Cambrian Impact Structure)
A multi-modal indirect approach
Daniel P. Connelly 2009You will find background at MAPCIS.net
or at the GSA northeastern meeting March 2009 uploaded files, MAPCIS the Case for a Massive Australian Precambrian/Cambrian Impact Structure
Post presentation comments are in green
Original Ring Discovery 2007
This discovery starts the search.The search leads to new discoveries.New discoveries propagate theories.
Discovery Vs Theory
D. P. Connelly 2009
~545 Ma
Impact ConstraintsAcraman Gosse Bluff 590Ma 142Ma 800km & 200km
from MAPCIS center
Rain over Gosse Bluff 2/2008
undisturbed
Ejecta from Acraman does not cover MAPCIS
Alice Springs Orogeny Constraint ~450Ma
Mutijulu Arkose,i Ayers RockMt. Currie Conglomerate
Deposited during Petermann orogeny
Uplifted during Alice Springs Orogeny
Basement consistent with age?
Neoproterozoic ridges Kangaroo IslandNeoproterozoic ridges Kangaroo Island
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.
MAFIC Events and MAPCIS Dating
29
29
MGr
1311
109
13
10
11
9
2626
16
16
A26G26
MGr 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 ~1810Ma
Tasman Gap
Derived from
Basic plate tectonics: When multiple events are divided, look for the youngest event to estimate the date of division.
Musgrave = Grenville age zircons
Arenite
Feldspar local
ArkoseConglomerate
Grenville Age zircons
Worldwide Cambrian SS Enigma
P/C Boundary
Distal
Zircon age diagram of suspected post impact proximal ejecta deposits
Musgrave Provence = Impact CenterOver 120,000 Sq. Km
A. Camacho et Al. 2002
The enigma is solved, if one has a huge impact in the center of a Grenville Aged province. This is what appears to have happened.
Seven smaller impacts possibly
coeval withMAPCIS
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 .
Foelsche ~545Ma and Bukalara SS
P.W. Haines &D.J. Rawlings 2001
After impact rapid burial
Now
Bukalara SS with shocked clasts blends into extensive regional unit.
Antrim Plateau Volcanics (Kalkarindji LIP) ~510-545MaCover unlithifiedBukalara SS
Infers a rapid sequence of impact, fill, and coverage by basalt.
MAPCIS Center Overview1. Trajectory Northeast to
Southwest2. Radial Transpression Ridges ?
Visible on 1:250, 000 Geology maps
3. PT Arcuate & Radial light blue
Neoproterozoic Winnall, Inindia & Pinyinna beds of Mt. Conner appear to be missing from MAPCIS Center.
From Ayers Rock 1:250,000 Geology Map 2002
Largest known Pseudotachylite deposits, similar to Vredefort and Sudbury impacts.
Mt. Frazer Radial Pseudotachylite
Edgoose CJ, Scrimgeour IR, Close DF 2003 Geology of the Musgrave Block, NT, NT Geological Survey Report 15 An example of PT not associated with a major fault.
Sampling Data from NT Geological Survey
There appears to be no attempt to date the pseudotachylite itself
Sample sites plotted on Google Earth
Mt. Frazer
Sample B549
Edgoose CJ, Scrimgeour IR, Close DF 2003 Geology of the Musgrave Block, NT, NT Geological Survey Report 15
Derived from
Sample B54930km North of Mann Range pseudotachylite
Notable that these zircons have a metamorphic peak at 561ma +- 11, and zircon 13 exhibits a mosaic pattern.
Mosaic patterns in zircons has been associated with shock metamorphism.
Cumulative probability diagram of biotite ages for entire Musgrave Provence
Camacho et al., 2002Inferred that all fault systems in the Musgrave Provence were activated during thethe Petermann Orogeny.
120,000 square Km moved here and portions were exhumed from 40km deep.
Camacho et al., 2002
Conclusions• 1. 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 Orogeny• 8. 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.