For a geoscientist Pakistan is a wonderful country. With an active subduction zone on its souther... more For a geoscientist Pakistan is a wonderful country. With an active subduction zone on its southern margin along the Makran coast, Palaeocene ophiolites preserved along its western border, on-going continental collision between India and Asia in the northern part of the collision, with a fossil island arc sandwiched between the two continents, and the fastest uplifting piece of continental crust on Earth within the Nanga Parbat syntaxis, the country is an open air laboratory for testing plate tectonic theory. Surprisingly, remarkably little was known about the geology of Pakistan 30 years ago. Prior to partition of India, the geology of Pakistan came under the remit of the Indian Geological Survey and this far flung region to the northwest, with little obvious mineral wealth, was not a key area for survey. Two factors spawned the explosive growth in our knowledge of the geology of Pakistan within the last 30 years. First, was the acceptance of the Plate Tectonic paradigm which, by itself, should have stimulated interest in the geology of the region. Second, was the …
For many metamorphic petrologists, the study of low-grade metamorphic rocks is something of a bla... more For many metamorphic petrologists, the study of low-grade metamorphic rocks is something of a black art. Because low-grade rocks are frequently fine-grained, contain a wide variety of low-temperature minerals with limited stability fields, and have high porosities and fluid contents they are not as readily understood as higher grade metamorphic rocks. For these rocks, few, if any, of the standard thermobarometers or thermobarometric datasets are applicable and the derivation of fluid evolution histories is complicated by the high concentration of, frequently reduced, fluids. Low-grade metamorphism, at T <400°C and P <4–5 kbar, spans the P – T interval between what may be erroneously termed ‘proper’ metamorphism and the field of diagenesis, although in reality there is no clear or sharp break between the diagenetic and metamorphic fields. As such, techniques relevant to the study of low-grade metamorphism span those of both the sedimentary and metamorphic fields. This …
For a geoscientist Pakistan is a wonderful country. With an active subduction zone on its souther... more For a geoscientist Pakistan is a wonderful country. With an active subduction zone on its southern margin along the Makran coast, Palaeocene ophiolites preserved along its western border, on-going continental collision between India and Asia in the northern part of the collision, with a fossil island arc sandwiched between the two continents, and the fastest uplifting piece of continental crust on Earth within the Nanga Parbat syntaxis, the country is an open air laboratory for testing plate tectonic theory. Surprisingly, remarkably little was known about the geology of Pakistan 30 years ago. Prior to partition of India, the geology of Pakistan came under the remit of the Indian Geological Survey and this far flung region to the northwest, with little obvious mineral wealth, was not a key area for survey. Two factors spawned the explosive growth in our knowledge of the geology of Pakistan within the last 30 years. First, was the acceptance of the Plate Tectonic paradigm which, by it...
The thematic set of papers on the topic of Environmental Mineralogy published in this issue of th... more The thematic set of papers on the topic of Environmental Mineralogy published in this issue of the Mineralogical Magazine represents part of a collaborative effort with the Mineralogical Society of America (MSA). A parallel issue of the American Mineralogist (2003, volume 88 part 11–12) includes a separate thematic set of papers on the same topic. A request for papers following the Environmental Mineralogy sessions at IMA 2002, held in Edinburgh, has led to these two thematic issues. The papers appearing in these two ‘green’ issues are the result of an effort jointly conceived by officers of the Mineralogical Societies of Great Britain and Ireland (MSGBI) and of America (MSA). Both Societies have separately come to realize that they are currently not the natural home …
For many metamorphic petrologists, the study of low-grade metamorphic rocks is something of a bla... more For many metamorphic petrologists, the study of low-grade metamorphic rocks is something of a black art. Because low-grade rocks are frequently fine-grained, contain a wide variety of low-temperature minerals with limited stability fields, and have high porosities and fluid contents they are not as readily understood as higher grade metamorphic rocks. For these rocks, few, if any, of the standard thermobarometers or thermobarometric datasets are applicable and the derivation of fluid evolution histories is complicated by the high concentration of, frequently reduced, fluids. Low-grade metamorphism, at T <400°C and P <4–5 kbar, spans the P – T interval between what may be erroneously termed ‘proper’ metamorphism and the field of diagenesis, although in reality there is no clear or sharp break between the diagenetic and metamorphic fields. As such, techniques relevant to the study of low-grade metamorphism span those of both the sedimentary and metamorphic fields. This …
Geological Society, London, Special Publications, 2000
ABSTRACT New amphibole, muscovite and biotite Ar-Ar and K-Ar data and zircon and apatite fission ... more ABSTRACT New amphibole, muscovite and biotite Ar-Ar and K-Ar data and zircon and apatite fission track data are presented from the western margin of the Nanga Parbat syntaxis as well as from the Indus and Astor valley sections which cross the syntaxis. Amphibole data date a regional cooling through 500 degrees C at 25 +/- 5 Ma and are inconsistent with earlier suggestions that the peak of regional metamorphism was Neogene in age, although there is no doubt that some rocks were still at upper amphibolite facies temperatures as recently as 5 Ma. The data can be used to constrain structural models for syntaxial uplift. After an initial phase of crustal-scale buckling, bodily uplift of the syntaxis was along subvertical shear zones developed along its margins, although with a significantly higher time-averaged strain rate for shears developed along the western margin than along the eastern margin. The latter may be antithetic to the former. These shears were operative from 10 to &lt;1 Ma. In the southwestern part of the syntaxis, this subvertical uplift was superseded, since 6 Ma, by uplift along moderately SE-dipping NW-vergent shears on the hanging wall of which are located Neogene-aged migmatites.
The Kamila Shear Zone is a deep to mid crustal structure developed within the Kohistan island arc... more The Kamila Shear Zone is a deep to mid crustal structure developed within the Kohistan island arc complex of North Pakistan prior to Himalayan collision between Kohistan and India. Meta-gabbros of the Chilas complex were transported southwards across the shear zone onto a stack of high pressure rocks that had been assembled in the hanging wall of the Tethyan subduetion zone. The shear zone is constituted by an anastomosing array of amphibolite facies ductile high strain zones within which fabric intensity varies although mylonitic zones are common. Shear criteria and kinematic indicators have a consistent SW-vergence. Little microstructural evidence for the high temperature ductile shearing is preserved, fabrics having been over-printed by post-deformational processes of recrystallisation, annealing and grain growth. A subsequent history of exhumation during decreasing temperature is documented by a progressive sequence of down temperature retrogression and deformation in superimposed shear zones which predominantly affected coarse grained rocks unaffected by the earlier crystal plastic deformation. The shearing involved dominantly cataclastic amphibolite to greenschist facies deformation culminating in lower greenschist facies shearing and mylonitisation, and the development of a distributed network of minor cataclastic and gouge-filled fault rocks.
The Kola alkaline province of NW Russia is the type example of the occurrence of abiogenic hydroc... more The Kola alkaline province of NW Russia is the type example of the occurrence of abiogenic hydrocarbons (HCs) in crystalline rocks. Methane and higher hydrocarbons, up to C5H12, are contained primarily within abundant fluid inclusions in rock-forming minerals or as free gas contained in sealed microfractures or along grain boundaries. Such occurrences are not unique to Kola. High-temperature, hydrocarbon-rich fluid inclusions are present in alkaline rocks from Ilimaussaq, Greenland, and in recent years they have been described in other silica-undersaturated igneous rocks as well as in hydrothermal systems associated with basic igneous rocks. Two main models (Potter and Konnerup-Madsen, 2003) have been proposed for the genesis of these abiogenic HCs: (1) a late-magmatic model whereby the HCs are equilibrium products of volatiles exsolved directly from magmas, and; (2) a post-magmatic, disequilibrium model whereby HCs are generated via Fischer-Tropsch type reactions at ca. 350°C invol...
For a geoscientist Pakistan is a wonderful country. With an active subduction zone on its souther... more For a geoscientist Pakistan is a wonderful country. With an active subduction zone on its southern margin along the Makran coast, Palaeocene ophiolites preserved along its western border, on-going continental collision between India and Asia in the northern part of the collision, with a fossil island arc sandwiched between the two continents, and the fastest uplifting piece of continental crust on Earth within the Nanga Parbat syntaxis, the country is an open air laboratory for testing plate tectonic theory. Surprisingly, remarkably little was known about the geology of Pakistan 30 years ago. Prior to partition of India, the geology of Pakistan came under the remit of the Indian Geological Survey and this far flung region to the northwest, with little obvious mineral wealth, was not a key area for survey. Two factors spawned the explosive growth in our knowledge of the geology of Pakistan within the last 30 years. First, was the acceptance of the Plate Tectonic paradigm which, by itself, should have stimulated interest in the geology of the region. Second, was the …
For many metamorphic petrologists, the study of low-grade metamorphic rocks is something of a bla... more For many metamorphic petrologists, the study of low-grade metamorphic rocks is something of a black art. Because low-grade rocks are frequently fine-grained, contain a wide variety of low-temperature minerals with limited stability fields, and have high porosities and fluid contents they are not as readily understood as higher grade metamorphic rocks. For these rocks, few, if any, of the standard thermobarometers or thermobarometric datasets are applicable and the derivation of fluid evolution histories is complicated by the high concentration of, frequently reduced, fluids. Low-grade metamorphism, at T <400°C and P <4–5 kbar, spans the P – T interval between what may be erroneously termed ‘proper’ metamorphism and the field of diagenesis, although in reality there is no clear or sharp break between the diagenetic and metamorphic fields. As such, techniques relevant to the study of low-grade metamorphism span those of both the sedimentary and metamorphic fields. This …
For a geoscientist Pakistan is a wonderful country. With an active subduction zone on its souther... more For a geoscientist Pakistan is a wonderful country. With an active subduction zone on its southern margin along the Makran coast, Palaeocene ophiolites preserved along its western border, on-going continental collision between India and Asia in the northern part of the collision, with a fossil island arc sandwiched between the two continents, and the fastest uplifting piece of continental crust on Earth within the Nanga Parbat syntaxis, the country is an open air laboratory for testing plate tectonic theory. Surprisingly, remarkably little was known about the geology of Pakistan 30 years ago. Prior to partition of India, the geology of Pakistan came under the remit of the Indian Geological Survey and this far flung region to the northwest, with little obvious mineral wealth, was not a key area for survey. Two factors spawned the explosive growth in our knowledge of the geology of Pakistan within the last 30 years. First, was the acceptance of the Plate Tectonic paradigm which, by it...
The thematic set of papers on the topic of Environmental Mineralogy published in this issue of th... more The thematic set of papers on the topic of Environmental Mineralogy published in this issue of the Mineralogical Magazine represents part of a collaborative effort with the Mineralogical Society of America (MSA). A parallel issue of the American Mineralogist (2003, volume 88 part 11–12) includes a separate thematic set of papers on the same topic. A request for papers following the Environmental Mineralogy sessions at IMA 2002, held in Edinburgh, has led to these two thematic issues. The papers appearing in these two ‘green’ issues are the result of an effort jointly conceived by officers of the Mineralogical Societies of Great Britain and Ireland (MSGBI) and of America (MSA). Both Societies have separately come to realize that they are currently not the natural home …
For many metamorphic petrologists, the study of low-grade metamorphic rocks is something of a bla... more For many metamorphic petrologists, the study of low-grade metamorphic rocks is something of a black art. Because low-grade rocks are frequently fine-grained, contain a wide variety of low-temperature minerals with limited stability fields, and have high porosities and fluid contents they are not as readily understood as higher grade metamorphic rocks. For these rocks, few, if any, of the standard thermobarometers or thermobarometric datasets are applicable and the derivation of fluid evolution histories is complicated by the high concentration of, frequently reduced, fluids. Low-grade metamorphism, at T <400°C and P <4–5 kbar, spans the P – T interval between what may be erroneously termed ‘proper’ metamorphism and the field of diagenesis, although in reality there is no clear or sharp break between the diagenetic and metamorphic fields. As such, techniques relevant to the study of low-grade metamorphism span those of both the sedimentary and metamorphic fields. This …
Geological Society, London, Special Publications, 2000
ABSTRACT New amphibole, muscovite and biotite Ar-Ar and K-Ar data and zircon and apatite fission ... more ABSTRACT New amphibole, muscovite and biotite Ar-Ar and K-Ar data and zircon and apatite fission track data are presented from the western margin of the Nanga Parbat syntaxis as well as from the Indus and Astor valley sections which cross the syntaxis. Amphibole data date a regional cooling through 500 degrees C at 25 +/- 5 Ma and are inconsistent with earlier suggestions that the peak of regional metamorphism was Neogene in age, although there is no doubt that some rocks were still at upper amphibolite facies temperatures as recently as 5 Ma. The data can be used to constrain structural models for syntaxial uplift. After an initial phase of crustal-scale buckling, bodily uplift of the syntaxis was along subvertical shear zones developed along its margins, although with a significantly higher time-averaged strain rate for shears developed along the western margin than along the eastern margin. The latter may be antithetic to the former. These shears were operative from 10 to &lt;1 Ma. In the southwestern part of the syntaxis, this subvertical uplift was superseded, since 6 Ma, by uplift along moderately SE-dipping NW-vergent shears on the hanging wall of which are located Neogene-aged migmatites.
The Kamila Shear Zone is a deep to mid crustal structure developed within the Kohistan island arc... more The Kamila Shear Zone is a deep to mid crustal structure developed within the Kohistan island arc complex of North Pakistan prior to Himalayan collision between Kohistan and India. Meta-gabbros of the Chilas complex were transported southwards across the shear zone onto a stack of high pressure rocks that had been assembled in the hanging wall of the Tethyan subduetion zone. The shear zone is constituted by an anastomosing array of amphibolite facies ductile high strain zones within which fabric intensity varies although mylonitic zones are common. Shear criteria and kinematic indicators have a consistent SW-vergence. Little microstructural evidence for the high temperature ductile shearing is preserved, fabrics having been over-printed by post-deformational processes of recrystallisation, annealing and grain growth. A subsequent history of exhumation during decreasing temperature is documented by a progressive sequence of down temperature retrogression and deformation in superimposed shear zones which predominantly affected coarse grained rocks unaffected by the earlier crystal plastic deformation. The shearing involved dominantly cataclastic amphibolite to greenschist facies deformation culminating in lower greenschist facies shearing and mylonitisation, and the development of a distributed network of minor cataclastic and gouge-filled fault rocks.
The Kola alkaline province of NW Russia is the type example of the occurrence of abiogenic hydroc... more The Kola alkaline province of NW Russia is the type example of the occurrence of abiogenic hydrocarbons (HCs) in crystalline rocks. Methane and higher hydrocarbons, up to C5H12, are contained primarily within abundant fluid inclusions in rock-forming minerals or as free gas contained in sealed microfractures or along grain boundaries. Such occurrences are not unique to Kola. High-temperature, hydrocarbon-rich fluid inclusions are present in alkaline rocks from Ilimaussaq, Greenland, and in recent years they have been described in other silica-undersaturated igneous rocks as well as in hydrothermal systems associated with basic igneous rocks. Two main models (Potter and Konnerup-Madsen, 2003) have been proposed for the genesis of these abiogenic HCs: (1) a late-magmatic model whereby the HCs are equilibrium products of volatiles exsolved directly from magmas, and; (2) a post-magmatic, disequilibrium model whereby HCs are generated via Fischer-Tropsch type reactions at ca. 350°C invol...
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Papers by Peter Treloar