Terénní výzkum a jeho vliv na interpretaci analytických dat Nejdůležitější, nejkomplikovanější a nejrizikovější část studia magmatických hornin 1) Vztahy k okolí - kontaktní metamorfóza, chlazené okraje, pillow lávy, sheeted dikes, migmatity, tektonikcké okraje 2) Dvoufázové struktury - vývoj magmatu 3) Enklávy - zdroj magmatu, granity vs. basalty 4) Míšení magmatu - zdroje magmatu, pt podmínky 5) Alterace a deformace - post-solidus vývoj, barva, sekundární minerály, vztah krystalizace a deformace Fig. 10. Hypidiomorphic granular texture in photomicrograph of the Santa Rosa Tonalite, Rio Lurin, Peru L__J 1 cm Coarse-grained allotriomorphic texture Coarse-two phase texture with abundant granitic megacrysts and lithic clasts in a relatively sparse fine-grained matrix Advanced two-phase texture with a smaller proportion of granitic relics set in a finegrained matrix Two-phase texture with: xenocrysts and granite ■ Bf lis §■1 mm mm ^^^^^^^^^^^La - ■■■ ■■■■.................................-............... A very advanced stage with fine grained groundmass 1 cm 1 cm Fig. 14. Tuffisite, Cruz de Laya, Rio Lurin Peru. Photomicrograph showing megacrysts of quartz and plagioclase set in a heterogeneous quartzo-feldspathic base 1 cm Fig. 15. Porphyry stock. Acos Upper, Rio Chancay, Peru. Photomicrograph showing two-phase texture with crystals and lithic fragments set in a fine-grained quartzo-feldspathic matrix I_I 1 cm Fig. 17. Schlieren with enclaves, whirlpool structure, Mt Givens granodiorite Sierra Nevada Batholith. Hammer 30 cm Fig. 18. Schlieren and enclaves within the Mt Givens granodiorite, Sierra Nevada. Hammer 40 cm Fig. 23. Coarse K-feldspar megacrystic granite intruding earlier gabbro. The granite exploited a joint in the gabbro. However the entrance to the fissure was blocked by a large megacryst. Residual fluids percolated around the obstruction into the crack where they crystallised as fine-grained granite. Note also the development of quartz ocelli in the gabbro. Lisa Aragabo pluton Kola Peninsula, Russia. Lens cap 4 cm Fig. 24. Mafic enclaves with dark margins. Jerong pluton, Eastern Province Peninsular Malaysia. Pen 12 cm Fig, 37. Deformed anatexitic S-type granite with folded relic of metasedimentary material. St Cast Plage, Brittany. Hammer 30 cm Fig. 38. Foliated anatexitic S-type granite with quartz lumps derived from metasedimentary source rock. St Cast Plage, Brittany. Coin 2 cm Fig. 39. Relatively undeformed S-type granite with enclaves of predominantly pelitic source material. Beach 2 km west of St Cast, Brittany. Hammer 30 cm Sample No Locality Rock Type Granite Unit Distinguishing features Texture and grain size Primary Modified Catadastic Incipient 2-phase Micragrartite V coarse Coarse Medium Fine Porphvritic Equigranular Inequigranutar MARC MINERALS % Size (mm) Mode of occurrence to ä Outline Shape Colour/Relationships Range Av. singles dusters I-min clots Hornblende Needles Prisms Stubby Equant Biotite Barrels Books Rakes Sheets Muscovite Cooks Rakes Sheets FELSIC MINERALS MEGACRYSTS % Size Tim) Colour > n Outline Ind. Shape/Relationships Range Av. K-feldspar Plagioclase Quartz GROUNDMASS K-feldspar Plagioclase -singles Quartz - -clusters Accessories Tourmaline Sphene Foliation/alignment Yes No Weak Moderate Strong ; Dip Strike Magnetic Susceptibility j Ratemeter Count Xenoliths Enclaves % Size range Mafic Yts No Cognate Accidental Megacrysts ' Yes No Uthology Shape: Angular Round Oval .enticular Rattened Dykes & veins Uthology Width Dip Strike REMARKS: Fig. 40. Field description sheet for granites The various types of enclaves: ihesr nature and main petrographic features Terra Nature | Shape Features. Xenollth Piece of country rocks (homfcls) Sharp Angular Contact-metam. texture & minerals Xenocryst Isolated foreign crystal Sharp Globular Corrosion Reactional aureole Surmicaceous enclave Residue of melting (restite) Sharp with biotitic crust Lenticular Metamorphic texture Micas & Al-rich minerals Schlieren Disrupted enclave Gradual Oblate Planar orientation Fehle microgranular enclave Disrupted fine-grained margin Sharp or gradual Ovoid Fine-grained Igneous texture Mafic microgranular enclave Blob of coeval magma Mostly sharp Ovoid Fine-grained Igneous texture Cumulate enclave (Autoilth) Disrupted cumulate Mostly gradual Ovoid Large-grained Cumulate texture Fig. 1. Synplutonic mafic dykes exposed on the southern shore of Cortes Island, opposite George Harbour, Queen Charlotte Strait, British Columbia, Canada, (a) Oblique view on edge of cliff of two members of the swarm (shown in black) within a granodioritic host (white). The one in the foreground cuts across a fluxioned zone of more dioritic composition (stippled) replete with half digested mafic enclaves, (b) View on the cliff face of a less disrupted member cutting a more disrupted, earlier member of the swarm—apparently along a healed zone of displacement. Pig, 2. Comparison of the detail of synplutonic dyke relationships, (a) Microdiorite dyke disrupted within a monzogranitc host, Quebrada Huamilache, south of Sayan, Peru, (b) Two examples of disrupted microdiorite dykes in monzogranite host, (c) Disrupted and strongly deformed microdiorite dykes within a monzogranite host. Both (b) and (c) from Quebrada El Carmen, WNW of Sayan, Peru, (d) Disrupted microdiorite dykes in undeformed granodioritic host, Cortes Island, opposite George Harbour, British Columbia: note variation in degree of alteration in adjacent fragments. Dykes (black), granitic host (white), dioritic hybrid (stippled), foliated dykes (lined), pegmatite (zig-zag). KINETIC PATH Principal fabric attribute Grain orientation VISCOUS MAGMA FLOW CRYSTALLIZATION: CRYSTAL NUCLEATION AND GROWTH TEXTURAL EQUILIBRATION FRAGMENTATION VOLATILE FLUID NUCLEATION AND CAVITY GROWTH Fluid cavities -reralized kinetic paths involved in the creation of magmatic iz~c as a metastable melt transforms to a solid magmatic Most fabric attributes evolve along multiple paths. For : imple, layering can develop by magma flow or by crystal-ixv.on processes.