To the south, continuous, linear, well-defined anomalies outline the open, upright folds of the KNSZ against a quiet magnetic background. Anomalies in the KRSZ. Colin Gatehouse and Wolfgang Preiss of SADME for critical comments on geology and for revising parts of the thesis.
CONVBN"IONS AND ABBREVIA?IONS
SOUTH AUSTRALIA
STUDY AREA
AUSTRALIA
INTRODUCTION
Aeromagnetic and aeroradiometric interpretation
PACIFIC EXPL
Aims of this thesis
The basic purpose of this thesis was to provide new facts and ideas, thereby improving and expanding the geological model of the area. Regional and detailed magnetic maps and available gravity and seismic data were used to reassess the geological setting of the Kanmantoo Group and to test the new models developed by current researchers.
Guide to maPs
Part I
CURNA CRATONIC
SHELF
GAWLER CRATON
FLINDE GES
OLARY
MU RRAY BASIN
CHAPTER 1. THE GEOLOGY OF THE KANMANTOO GROUP
Chapter 1
- Regional geology
CHAPTER 1.. THE GEOLOGY OF THE KANMANTOO GROUP
MAJOR HIATUS
MAJOR HIATUS BASBMtrNT: BAROSSA COMPLBX
CHAPTER 1. THE GEOLOGY OF THE I(A]VMANTOO GROUP
- Detailed geology
- L Stratigraphy and lithologY
The Ulupa Siltstone lies near the base of the Wilpena Group and is overlain by the ABC Range quartzite and the Bunyeroo Formation. Chemistry of the well-differentiated gray aluminous rocks that make up the Ulupa Siltstone.
KRSZ
KNSZ
The type section of the Kanmantoo Group is located along the south coast between Tunkalilla Beach and Rosetta Head (Sprigg and Campana, 1953). In the new classification the Carrickalinga Head Formation represents the basal unit of the I (anmantoo Group and the Middleton sandstone the Much of the Kanmantoo Group outcrop in the main study area is dominated by rocks of the Backstairs Passage Formation, Talisker Calc siltstone and Tapanappa Formation.' The Carrickalinga Head Formation has been subdivided by Daily and Milnes (1972a) into three members: the Madigan Inlet Member, the Blowhole Creek Siltstone and the Campana Creek Member.
CHAPTER 1, THE GEOLOGY OF THE I{ANMANTOO GROUP
Tectonics
The structural history of the Kanmantoo Group is complex and multi-phased and difficult to unravel. After the development of the macroscopic folds was the development of folds on smaller scales.
CHAPTER 1, THE GEOLOGY OF THE KA¡TMANTOO GROUP 11
OF THE
MT. LOFTY RANGES
- CHAPTER 1. THE GEOLOGY OF THE ITANMA¡ÙTOO GROUP T2
- Metamorphism
- Igneous intrusives
- CHAPTER 1. THE GEOLOGY OF THE KANMANTOO GROUP t4
- Discussion
- Chapter 2
- CHAPTER 2. ROCK MAGNETISM AND RADIOACTIVITY T7
- Magnetic mineral petrogenesis
- CHAPTER 2. ROCK MAGNETISM AND RADIOACTIVITY 18
- L Sediments
- Haematite and other oxides
- Pyrrhotite
The depositional environments of the various units in the Kanmantoo sequence are not resolved. Backstairs Passage Formation, Middleton Sandstone, (Mancktelow, 1979; Boord, 1985), and the Madigan Bay Member of the Carrickalinga Head Formation at Sedan.
Thus, there is a general tendency of iron-bearing rocks to become more magnetic with increasing metamorphic grade. The two most important controls on the production of secondary iron oxides are total iron content and oxidation state.
BIOTITE
CHAPTER 2. ROCK MAGNETISM AND RADIOACTIVITY 22 Total iron content lron-rich rocks have a greater magnetite producing potential
- Granitoids
The magnetite-series granitoids probably developed at higher temperatures and under higher oxidizing conditions than the ilmenite-series granitoids. Their conclusion was that all magnetite-series granitoids are indeed I-type, but that ilmenite-series may include both S-types.
CHAPTER 2. ROCK MAGNETISM AND RADIOACTIVITY 23
- Rock magnetism and opaque mineralogy of rocks in the studY area
As a result, the measured directions of slope and deflection of the residual field are not reliable, although the intensity measurements are reliable. During fieldwork, we searched for surface expressions of anomalous sources and performed sensitivity measurements on outcrops in their vicinity.
CHAPTER 2, ROCI{ MAGNETISM AND RADIOACTIVITY 25
CHAPTER 2. ROCK MAGNETISM AND RADIOACTIVITY 2ß Nairne pyrite facies, Ulupa Siltstone and magnetic Backstairs Passage Formation can possess
- Opaque mineralogy and petrogenesis
The dominant opaque in the metasediments is either magnetite or pyrrhotite or hemoilmenite * ilmeno-hematite. In the Andalusian shales of the Ulupa Siltstone, this combination of opaque materials is common.
CHAPTER 2. ROCK MAGNETISM AND RADIOACTIVITY 28
Although there are insufficient data, the available data seem to indicate that the metaarenites of the Backstairs Passage Formation and Middleton Sandstone have higher oxidation ratios than the pelitic rocks of the Ulupa Siltstone and Tapanappa Formation. Euhedral, MD magnetite grains (as large as 2-4 mm) have been observed in samples of the Palmer Granite and the Rathjen Gneiss.
CTIAPTER 2, ROCI{ MAGNETISM AND RADIOACTIVITY 29
The radiornetric rnethod
L Radio-element abundances in crustal rocks
Part II
CHAPTÐR 3. EFFECTIVE DISPLAY OF DATA 32
Chapter 3
- Systematic approach to displaying geophysical data
CHAPTER 3. EFFECTIVE DISPLAY OF DATA 33
- Display formats
CHAPTER 3, EFFECTIVE DISPLAY OF DATA 34
- Design of good displays
The contours are irregularly spaced and the value increases from blue to black to red contours. As in the figure above, red contours represent the highest values, blue the lowest values, and black the intermediate values.
TOTAL FIELD CONTOURS
VERTICAL GRADIENT CONTOURS
CHAPTER 3. EFFECTIVE DISPLAY OF DATA 35
The total magnetic field can be continued upwards or filtered using a low-pass filter to remove the effects of shallow souls (e.g. to remove the effects of the tilt of the Earth's magnetic field, it is customary, especially at low magnetic latitudes, to reduce the field to the pole Gradient data that is free of diurnal variations is generally used to constrain and consequently improve the grid of the total field.
CHAPTER 3. EFFECTIVE DISPLAY OF DATA 36
- Interpretation stages
- Stacked Profiles
Data for the lower right part of the study area were not available at the time the image was produced. Stacked profiles of the vertical magnetic gradient. or another derivative) can be used for trend analysis and mapping of magnetic horizons. Modeling of anomalies is usually done on graphs of profiles of the total magnetic field and these can be displayed on paper or on a graphics terminal connected to a computer.
CHAPTER 3, EFFECTIVE DISPLAY OF DATA 38
CHAPTER 3. DFFECTIVE DISPLAY OT DATA
Noise and noise anomalies are usually prominent in the output, making them easier to identify as such. Comparing the VG contour map of the tires (Figure 3.3) and the stacked profiles (Figure 3.2), it is easy to see that much more information is retained in the stacked plo files and that the representation is much better than the VG contour map. The stacked profiles exhibit better resolution than the total magnetic intensity contour map and better representation of information than the VG contour map, and interpolation between flight lines is in the hands of the interpreter.
VERTICAL GRADIENT
AMPLIFIED PROFILES
- CHAPTER 3. EFFECTIVE DISPLAY OF DATA 40
- Digital images
- cm 14.50 cm M (TOTAL MAGNETIC FIELD)
- CHAPTER 3. EFFECTIVE DISPLAY OF DATA 42
- CHAPTER 3. EFFECTIVE DISPLAY OF DATA 43
- Chapter 4
The variables in a shadow relief map are the azimuth and elevation of the light source. Quantitative analysis of magnetic anomalies includes determination of parameters (depth, thickness, dip, depth extent, strike extent, magnetic susceptibility contrast and magnetization). The main profile is taken to be perpendicular to the strike of the magnetic source.
CHAPTER 4, VERTICAL MAGNETIC GRADIENT ANALYSIS 46
- Interpretation of thin dyke anomalies
- Ecluation 4.4 gives the total rnagnetic field due to a thin sheet at any point P(y) along a
- CHAPTER 4. VERTICAL MAGNETIC GRADIENT ANAIYSIS 48 The method assumes that the proflle is perpendicular to the strike of the dyke and Ihat B,
- Experimental results
- CHAPTER 4. VERIIICAL MAGNETIC GRADIENT ANAIYS/S 49
- Error analysis
- Interpretation of thick dyke anomalies
- CHAPTER 4. VERTICAL MAGNETIC GRADIENT ANATYSIS 51
- Interpretation of edge anomalies
- Conclusion
As a first approximation, the vertical gradient anomaly amputation should give a score of (-Itlh2). Once d is known, the depth to the top can be determined using the appropriate value of Lolh. The two main sources of error in estimating depth and d arise from inaccuracies in approximating the vertical gradient and in estimating the width-to-depth ratio. Getting the width-to-depth ratio right is critical to success.
Part III
Chapter 5
- Introduction
Rocks that show little variation in lithology may show small but significant variation in the amount and shape of magnetic minerals. The most recent data in the same area (Figure 5.2) show the wealth of geological information that is part of the magnetic data. As Table 4.1 and Figure L2 show, the high-resolution data covers the Kanmantoo Group in the region of Mt.
CHAPTER 5. REGIONAL GEOPHYSICAL OVERVIEW 55
- Forrnat of Part III
- Regional interpretation
- L Magnetic data
In the western part of the region there are anomalies due to the outcrops and the magnetic base of d.eeper. In the southern and western part of the C[ZrKanmantoo Group the rocks are folded into the Kanmantoo Synclinorium, which consists of a series of high-grade south-dipping synclines. Otherwise, the basement of the Kanmantoo Group is nonmagnetic and may be within a few hundred meters of the surface.
CHAPTER 5. REGIONAL GEOPHYSICAL OVERVIEW 58
MURRAY BASIN WESTERN MARGIN
MURRAY BASIN: WESTERN MARGIN
- Gravity data
- CHAPTER 5. REGIONAL GEOPHYSICAL OVERVIEW 60
- A gravity high runs parallel to and partly coincides with the Murray Magnetic High. It
- CHAPTER 5. NEGIONAL GEOPHYSICAL OVERVIEW 61
- Seismic data
- CHAPTER 6. GEOPHYSICAL RESPONSES OF KNOW¡ü NOCK TYPES 62
- Metasediments .1 Kanmantoo GrouP
- CHAPTER 6. GEOPHYSICAL RBSPONSES OF I(NOWN ROCI( TYPES 64
The Morgan fault has also been linked to the right angle change in the course of the Murray River. However, after subsequent erosion, isostatic compensation would have resulted in the disappearance of the mountain root. The resulting mining activity in the region makes it difficult to isolate the magnetic effect of mineralization.
CHAPTER 6, GEOPHYSICAL RESPONSES OF I(NOWN ROCI( TYPES 66
CHAPTER 6. GEOPHYSICAL RESPONSES OF KNOWN ROCI( TYPES 67
Here a triangular outcrop pattern of greywackes (lVymond, 1g50) has been identified by Mancktelow (1979) as a channel at the base of the Backstairs Passage Formation. As the width of the channels changes, so does the width of the BP-SA anomaly. Magnetic susceptibility measurements on samples by Toteff (1977) indicate that the basal member of the Passage Pass Formation is the most magnetic.
CHAPTER 6. GEOPHYSICAL RBSPONSES OF I(NOWN ROCK TYPES 68
CHAPTER 6. GEOPHYSICAL RESPONSES OF KNOWIÙ ROCK TYPES 69
Stolz (1gg5) measured the NRM of the Ulupa siltstone near Delamere and his results showed that the magnetic unit has a weak remanence (8 - 0.5) close to the direction of the present freld. The residual magnetism of the Ulupa siltstone is clearly related to its degree of rneta-. In the Australian Lowlands area, Drummond (lg12) mapped the Ulupa silt on both arms of the Karinya syncline.
CHAPTER 6. GEOPHYSICAL RESPONSES OF KNOWN ROCK TYPES 7I
- Barossa ComPlex
CHAPTER 6. GEOPHYSICAL RESPONSES OF KNOWN ROCK TYPES 72
- Igneous rocks
- L Granites and granitic gneisses
The northern part of the granite is dominated by the coarse-graio"ã typ" and is more magnetic and radiometric than the southern part, which is The "tail" of the gneiss is a thin near-vertical sheet that protrudes between the migmatites and the palmer granite. This magnetic source has an arcuate outline and may represent a subsurface extension of the Rathjen Gneiss (Plate 5).
CHAPTER 6. GEOPHYSICAI RESPONSES OT KNOWN NOCK TYPES 75
- Gabbros, amphibolites and dolerites
- Radiometric response
The expansion phase that led to the intrusion of the granites is an important event in the history of the region. There are several such anomalies in the vicinity of the original Black Hill Norite that have been interpreted as caused by similar gabbros. Color integration of aeromagnetic and radiometric data assisted in the mapping of faults, contacts, and.
CHAPTEN 6. GEOPHYSICAL RESPONSES OF KNOWN ROCK TYPES 78
CHAPTER 6. GEOPHYSICAL RESPONSES OF K]VOWN NOCK TYPES 79
Chapter 7
CHAPTER 7. MACROSCOPrc STRUCTURES 81
- L Scope of aeromagnetic interpretation in structural analysis
- Structural patterns in the Kanmantoo Synclinal Subzone
Depending on the curvature of the magnetic source, the accuracy of the drop estimation varies. In diagram A of this figure, the contours of the vertical magnetic gradient mark the Macclesfield syncline. Different weathering profiles of rocks on either side of a fault can cause a.
TP-EB rtt r-l
CHAPTER 7. MACROSCOPrc STRUCTURES 85
- L Macclesffeld Syncline-strathalbyn Anticline
In the south and southwest the syncline opens southwards and the southern boundary of the KNSZ has not been traced. South of the Encounter Fault (Firman, 1974) and north of MS3 and MS4, weak linear anomalies (< 20nT in amplitude) trend subparallel to the flight paths. The units of the Adelaide Supergroup below the Ulupa Siltstone vary widely in their lithology.
CHAPTER 7. MACROSCOPrc STNUCTURES 86
A rift has been proposed between the Normanville Group and the Kanmantoo Group in the region of the Macclesfielã Syncline. The western band was assigned by Thomson to the Talisker Calc siltstone and the eastern to the Tapanappa Formation (1g6gb), although Kleeman and Skinner (1959) interpreted both pyrite bands as part of the Nairne pyritã Formation (the old name for what Mancktelow (1979) identifies as the Nairne pyrite facies of the Talisker Calc siltstone.' The NNW trend anomalies between the northern end of TC-MS and the southern end of TC-\MKS may be due to dikes parallel and similar are with the dike swarm along the Mt.
CHAPTER 7. MACROSCOPIC STRUCTARES 88
- Kanmantoo Syncline
In this thesis, the main folds are interpreted as part of F^oin, the main stage of macroscopic folding. Magnetic markers include magnetic horizons defining the eastern limb of the Strathalbyn Anticline, as well as TP-DM (Dawesley Magnetic Anomaly) and BP-WKS. Figure 7'9: Formation magnetic marker of the Bp-NKS Passage outlining the closure of the Kanmantoo syncline shown superimposed on the total magnetic field contours.
CHAPTER 7. MACROSCOPrc STRUCTURES 90
CHAPTER 7. MACROSCOPrc STRUCTURES 91
- Monarto Syncline
- Harriet Hill Folds
- KNSZ: Conclusions
- Structural patterns in the Karinya Synclinal Subzone
- The KarinYa SYnclinorium
Macroscopic folds initiated during the F^oin control the outcrop of the Kanmantoo Group in the KNSZ. East of the Bremer Fault, younger rocks of the Kanmantoo Group have been folded into the Harriet. The northern closure of the main syncline is best defined by the US-T magnetic marker in the Ulupa siltstone.
CHAPTER 7. MACROSCOPrc STRUCTURES 95
- Truro Anticlinal structure
- Structural patterns in the Intermediate subzone
Because the Adelaide Supergroup rocks on the western limb of the Karinya syncline form the east. As in the NTA, rocks of the Adelaide Supergroup are found in the core of the anticline. The western branch of the Karinjska syncline does not form the eastern branch of the STA.
CHAPTER 7. MACROSCOPrc STRUCTURES 99
- L Subareas in the ISZ
Lawrence (1980) mapped the arkoses as belonging to the middle member of the Backstairs Passage Formation. Despite the ptygmatic fold associated with the migmatite zone, the overall trend of the magnetic units is dominantly NNW. Closures from contour maps indicate the presence of isoclinal folds folded by F^o¿n. The limbs of the fold are parallel and trend NN\M.
CHAPTER 7. MACROSCOPrc STRUCTURES
- Fold generations
These granites are not part of the Murray Bridge Suite and are syntectonic (section 6.2.1). Their spatial dimensions are much larger than the Palmer Granite and Rathjen Gneiss (Section 6.2.1). The relationship between structures in ISZ and F^o¿n folds in KNSZ and KRSZ is unclear, and this is attributed to overprinting of F^o¿n folds by Flot"r.
CHAPTER 7. MACROSCOPrc STRUCTURES 103
- Structural historY
Chapter 8
- The development of the Kanmantoo Group
- Deposition Age of sediments
This places the age of deposition of the òarrickalinga head formation in the Early Paleozoic. There is no difference between the arkoses found in the Backstairs Passage Formation and the Tapanappa Formation. The Kanmantoo Group has been described by Daily and Milnes (7972a) as a conformal series of units as described in the type section along the south coast of the Fleurieu Peninsula.
CHAPTER 8. DISCUSilON AND CONCLUDING REMARKS 108 Thickness
CHAPTER 8, DISCUSSION AND CONCLUDING REMARI{S 109
Concluding remarks
It was thus possible to present a unified interpretation of the rock types based on the difference in their magnetic properties. The transformation of the interpretation into a geologically comprehensible model requires the study of the relationship between the magnetic properties of the rocks and their geological evolution. Anomalous areas have been targeted where detailed geological investigations may reveal evidence crucial to an understanding of the early history of the Kanmantoo Group.
APPENDIX A 113
BMR data
The various d.ata sets were digitized, integrated into a color image and also printed separately as grayscale images. The digital dataset (BMR) was gridded and contoured in color and also presented as small grayscale images. The complex magnetic pattern characteristic of the EMZ could be more easily interpreted using colored rather than black-and-white contour maps.
